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Lately Published, Price 6s. 6d., 
 
 THE MASTER BUILDER'S PLAN; 
 
 S OF ORGANIC AKCHITECTURE 
 rVTiTP\TFn T^^ THE TYPTriAL 
 iOlvxMfc) Oi? AJSTIMA 
 
 By GEORGE OGILVIE, M.D., 
 
 Institutes of Medicine in the University c 
 Aberdeen. 
 
 The author has- fultilled his task well. We cornmeud the work to the 
 "to have a lou^ ' and popular \ievi of tbi- 
 ' -^ "^^ itLij-'ldcal Jovr '^ 
 
 : uu^ri jiiiJL A'jlumc, the purpuse ui wuil-ji i 
 
 '"m a j...^ form, the viek^.-: now generally held )> 
 
 ts ir rr j-urd to a coinmon plan of constructi- 
 . divisions of the animal Hngdoii. 
 >\y writt-ei',. and extremely well illustrated. 
 
 aid recommend Dr. Ogilvie's little book as a convenient ii 
 ...tor in this subject. It is at once elegant in expression, ajid, so i. 
 
 It also abounds in well-draAv 
 
 y'.iituL'i^ .■> 1/ uc I /( (.'. 
 
 the thing wantc 
 
 
 •' Wo have here a mobt intei 
 . \. i-v student of Katnral H 
 
 bvlent to be provided vri\h so poucI -nsc 
 ii the sub; 
 .1' rough and raodestj scientific and 
 
 ;ind much wanted volume, whi 
 study." — Medical Times a 
 
 \ice hub been Uv 
 ;raiaiiy welcome." — Al 
 
 Lhe publication of this work, 
 
 i.oyrniA 
 
 \TTF'R'nT'F\ 
 
 ;:-RnT\'\ 
 

 
 
Zbt i. H. lltll ICtbrarg 
 
 Nnrtb (taroltna ^latF (EolUg^ 
 
 035 
 
 &-'■?•«> 
 
GENETIC 
 
 This book IS due on the date indicated below 
 and IS subject to a fine of FIVE CENTS a 
 day thereafter. 
 
 I 
 
X 
 
 GENETIC CYCLE IN ORGANIC^ 
 
 NATURE; 
 
 OR, THE SUCCESSION OP FORMS IN THE 
 PROPAGATION OF PLANTS AND ANIMALS. 
 
 BY GEORGE OGILVIE, M.D., 
 
 REGIUS PROFESSOR OF THE INSTITUTES OF MEDICINE IN THE UNIVERSITY OF 
 
 ABERDEEN ; AUTHOR OF THE *' MASTER BUILDER'S PLAN 
 
 IN THE TYPICAL FORMS OF ANIMALS." 
 
 ABERDEEN : A. BROT 
 
 EDINBURGH: JOHN MENZIES. 
 LONDON : LONGMHr^N & CO. 
 
 MDCCCLXI. 
 
ABEKDEEN : 
 PRINTED BV D. CHALMERS AND COMPANY, 
 ADELPHI COURT, UNION STREET. 
 
PREFACE. 
 
 The objects of the present work are, firstly, to determine the 
 mutual relations of those diversified forms Avhich the recent 
 researches of i^aturalists have sho^Ti to be propagated from 
 each other, in many different species among the lower orders 
 of both kingdoms of I^ature ; and, secondly, to consider 
 what analogy can be traced between the successive forms in 
 these species, and the phenomena which occur in the repro- 
 duction of those higher in the scale of organization, where, 
 to all appearance, like always produces like. 
 
 The Author is well aware that a much abler pen than his 
 would have but little chance of enlisting the interest of any 
 large circle of readers in such a work as the present ; for, 
 though it would not be easy to point to any subject in the 
 whole range of Biological Science more calculated to excite 
 feelings of wonder and enquiry, yet the obscurity of some 
 of the questions iuA'-olved, while it has stimulated the 
 zeal of many earnest investigators, has no doubt kept back 
 others from giving the same attention to this, as to other 
 branches of Physiology ; besides which, it is not to be denied 
 
vi PREFACE. 
 
 that the Xatui-al Sciences — ^rapid as has been their advance 
 of late in popular ftivour — are still far from occupying their 
 ftiir place in public estimation. A conviction of this would 
 probably have prevented his ever setting of his o^vn accord to 
 -vvTite for publication on the subject. But this work was 
 Avritten, in the first instance, for a different purpose, having 
 been undertaken originally in response to a call made with 
 reference to the late Meeting of the British Association at 
 Aberdeen, though, as it came to be too unmeldy for this, 
 an abstract was afterwards substituted, which was subse- 
 quently printed in the Edinburgh Philosojjhieal Journal for 
 January of last year. 
 
 Tlie primary object of bringing forw^ard the communication 
 was to elicit discussion on views for the systematizing of one 
 of the most perplexed questions in Physiology, and the re- 
 marks to which it gave rise, though necessarily restricted, 
 went to invite their fuller examination. For this end, the 
 Author is now led to publish the Treatise itself, in all essen- 
 tial points as it originally stood, though he has submitted it 
 to a careful revision in matters of detail, and has re-written a 
 large part, for greater clearness of expression. 
 
 At the same time, he must admit, that when his work 
 had taken shape, he felt — as in the case of a former one on 
 the Unity of Organization — that it went, in so far, whether 
 fitly or not, to occupy a void in biological literature. As the 
 nature of the subject, however, precludes its consideration, 
 except by bona fide students of Natural Science, he has made 
 no attempt, in the present work, to treat it in a popular way? 
 
PREFACE. Vll 
 
 his object having been simply to make use of such expres- 
 sions as seemed best fitted to convey his meaning. If, as he 
 has some reason to fear, his anxiety for this, and his wish to 
 present the subject in different points of view, have led him 
 into needless repetitions, he can only now express his regret 
 that circumstances latterly have not allowed him leisure to 
 determine what might be retrenched with advantage. 
 
 In explanation of the absence in the text of any reference 
 to the accompanying Plates, it is but fair to mention that 
 their introduction was an after- thought. The difficulties in 
 the way of publication interfered with the illustration of the 
 text by w^ood-cuts, as is now commonly done in treatises of 
 this kind, and it was not till after the work was in print 
 that the use of outline figures w^as suggested. Much selec- 
 tion was then impossible, but the Author hopes that those 
 which have been introduced will be found an advantage, from 
 the acknowledged importance of illustrative figures of some 
 kind, when frequent reference has to be made to peculiarities 
 of structure and conformation. 
 
 To personal researches on the subject in hand the Author 
 cannot make much pretension ; he can claim little more than 
 to have taken for many years a lively interest in the observa- 
 tions of others. He must, therefore, readily admit his liability 
 to fallacies and misconception in making his statements at 
 second hand, though there may be some compensation for 
 this in a comparative freedom from influences which are apt 
 to bias the views of original observers. He may at least, in all 
 honesty, claim to have entered on the consideration of the 
 question without any conscious prepossession one way or 
 
Vlll PREFACE. 
 
 other ; and, although the conclusions here brought forward 
 have for some time back fully approved themselves to his 
 judgment, he is free to admit that his views had j^re^dously 
 undergone many and imj^ortant modifications smce this de- 
 partment of Physiology first became the subject of his par- 
 ticular attention. But in the present state of the Science, 
 indeed, no conclusions can well claim more than a provisional 
 acceptance. 
 
 It only remains to acknowledge the kind assistance received, 
 in various ways, from several friends, and particularly from 
 Professors Sharpey, Simpson, and Allen Thomson, and to ex- 
 press the hope that the work may contribute something, at 
 least by placing facts in a new point of view, to the elucida- 
 tion of a much -perplexed department of ISTatural Science. 
 
CONTENTS. 
 
 I. — Derivation of Organic Beings. 
 
 1. — Parental Derivation a distinctive character of Or- 
 ganic Bodies, ..... 
 
 2. — Grounds for disallowing the theory of a Physical 
 Derivation or Spontaneous Generation of Living 
 Beings, ...... 
 
 3. — Derivation from one, or from two Parents, 
 
 4. — Tendency of these modes of i)i"opagation to Alter- 
 nate, or recur periodically, when they co-exist in 
 the same species, ..... 
 
 5. — Distinction of Cases of Alternation into livotortwr- 
 phic, orthomorphic, and gamomorphic, according 
 to their relations in the Genetic Cycle, 
 
 6. — Indications of Representative Phenomena in the 
 Higher Species, ..... 
 
 II. — Survey of the Reproductive Process in the 
 Vegetable Kingdom. 
 
 Page. 
 1 
 
 2 
 9 
 
 10 
 
 12 
 15 
 
 1. — Introductory Remarks, 
 
 2. — General character of the process in the Vegetable 
 Kingdom, 
 
 3. — Reproduction in the Protophyta, 
 
 4. — In Alg?e generally, and Characese, 
 
 5. — In Fungi and Lichens, 
 
 6. — In Hepaticae and Mosses, 
 
 7. — In Ferns and Equisetacese, 
 
 8. — In Lycopodiacese and Rhizocarpess, 
 
 9. — In Gymnospermous Phanerogamia, 
 10. — In Angiospermous Phanerogamia, 
 11. — Concluding Remarks, 
 
 17 
 
 20 
 22 
 32 
 40 
 49 
 52 
 55 
 57 
 61 
 66 
 
Xll 
 
 co:ntents. 
 
 III. — Survey of the Reproductive Process in the 
 
 Animal Kingdom. 
 
 Page. 
 
 1. — General Character of the Process, . . 68 
 
 2. — Reproduction in the Protozoa, ... 74 
 
 3. — In the Coeleuterata, .... 81 
 
 4. — In the Echinodermata, .... 84 
 
 5. — In the Polyzoa, ..... 87 
 
 6. — In the Tiinicata, ..... 89 
 
 7. — In the higher MoUusca, .... 91 
 
 8. — In the Hehnintha, .... 94 
 
 9. — In the AnneHda, .... 99 
 
 10. — In the higher Articnlata, . . . 102 
 
 11. — In the Vertebrata, .... 106 
 
 12. — Concluding Remarks, .... 107 
 
 IV. — Nature and Varieties of Alternation of Gene- 
 rations. 
 
 1. — Points of Agreement and Diversity in cases of Al- 
 ternation, ..... 109 
 
 2. — Protomorphic Alternation, as in the Trematoda, 
 from Gemmation in the Early Stage of Develop- 
 ment, ...... 112 
 
 3. — Gamomorphic Alternation, as in the Poly^Difera, 
 
 from a later Gemmation, in the evolution of Sex, 117 
 
 4. — Relations of these two forms of Alternation, . 128 
 
 5. — Their Co-existence in the case of the Cestoid Worms, 131 
 
 6. — Ortlwmorphic Alternation, as in the Aphides, from 
 Gemmation in the evolution of the Typical Or- 
 ganization, ..... 133 
 
 7. — Reference of the best known cases of Alternation, 
 
 to one or other of the foregoing heads, . 136 
 
 8. — Co-existence of all the three forms in the case of 
 
 some Annelida, ..... 137 
 
 9. — Alternation in the Salpce, .... 140 
 
 10. — Protomorphic and Gamomorpliic Alternation in 
 
 Mosses and Ferns among Plants, . . 142 
 
 V. — PULLULATION. 
 
 1. — Notice of a Series of Successive Gemmations, inter- 
 polated at certain points. 
 
 146 
 
CONTENTS. Xlll 
 
 Page. 
 
 2. — Most frequent in the Middle Stage of Development, 147 
 
 3. — Ramified disposition of Plants and Zoophytes from 
 
 Adhesion of the Genimse, . . . 149 
 
 4, — Such adhesion a point of minor importance in the 
 
 present enquiry, .... 160 
 
 5. — Pullulation itseK of secondary importance to Alter- 
 nation, ...... 153 
 
 VI. — Embryogeny, as representing one Form of 
 
 Alternation. 
 
 1. — Representative Phenomena in the Higher Species, 156 
 
 2. — Representation in Embryonic Develoj^ment, . 167 
 
 3. — Illustration from Dujjlex Monstrosity, . . 157 
 
 4. — From the Development of the Polyzoa, . . 160 
 
 5. — From that of Cestoid Worms, . . . 161 
 
 6. — From that of the Echinodermata, . . 162 
 
 7. — Essential Community of Nature, . . 164 
 
 VII. — Representation of the other Forms. 
 
 1. — Representation of Orthomorphic Gemmation in the 
 
 Higher Species, .... 166 
 
 2. — Representation of Gamomorphic Alternation in the 
 
 Maturation of Sex, .... 167 
 3. — Illustration from the Periodic and Late Develop- 
 ment of the Organs, .... 167 
 4, — From the case of the Polyzoa, . . . 170 
 5. — From some aberrant Crustacea, . . . 172 
 6. — From the later phases of the Cestoid Entozoa, . 173 
 7. — From the reproduction of the Polypifera, . 173 
 8. — Points of distinction between Organs aud Zooids, 174 
 9. — Illustration from the reproduction of Phanero- 
 gamic and Crjrptogamic Plants, . . . 180 
 10. — Correspondence inferred between the process of 
 
 Maturation and Gamomorphic Alternation, . 188 
 
 VIII, — Relations of Ova and Gemm^. 
 
 1. — Points of distinction between Ova and Gemmae, 
 
 with notice of transitional forms, . . 190 
 
XIV 
 
 CONTEXTS. 
 
 2. — Nature of the Germs in the Viviparous Aphides and 
 allied Insects, ..... 
 
 3. — Nature of the Ei:)hii3pial and Common Eggs in En- 
 tomostraca and Rotifera, 
 
 4. — Development of Unimpregnated Ova in certain In- 
 
 5. — Occasional development of Unimpregnated Ovules 
 
 in Plants, ..... 
 
 G. — Nature of the Viviparous Flowers of Plants, 
 7. — Indications of a tendency to development in the 
 
 Sexual Elements singly, 
 8. — Essential community of nature between Ova and 
 
 Gemmae, ...... 
 
 0. — Question of the necessary recurrence of Sexual 
 
 Generation, ..... 
 
 10. — Bearing on the theory of Alternation of Generations, 
 
 IX. — Summary of Conclu signs. 
 
 1. — Recapitulation of Results, - 
 
 2. — Formula of the Genetic Cycle, 
 
 3. — Modification for the higher Animals, 
 4. — Extension for Pullulation, 
 
 5. — Concluding Remarks, 
 
 Page, 
 101 
 
 193 
 
 195 
 
 199 
 
 2( 
 
 200 
 
 202 
 204 
 
 206 
 
 208 
 
 212 
 216 
 216 
 218 
 219 
 
 X. — CAisES Simulating Alternation of Generations. 
 
 1. — Casual Alternation of Gemmation and Generation, 221 
 
 2. — Alternation of Diverse Gemmations, , . 221 
 
 3. — Atavism, ..... 222 
 
 4. — Metamorphosis, ..... 223 
 
 5. — Sperm atop hores and Sporophores, . . . 225 
 
 XI. — Homological Relations of the Structures concerned 
 
 IN the Genetic Cycle. 
 
 1. — Nature of the ultimate Sexual Elements, . 229 
 2, — Homological Relations of the Germinal and Sjjer- 
 
 matic Elements, .... 234 
 3, — Links of the Genetic Cycle in the several Groups of 
 
 Organized Beings, ^ - . . 237 
 
COj^TENTS. XV 
 
 Page. 
 4. — ^Relations of the Sex to the Individual, . . 241 
 
 5. — Concluding Remarks, .... 248 
 
 APPENDIX. 
 
 Table I. — Of the Genetic Cycle in Plants, . . 254 
 
 II. — The Genetic Cycle in Animals, . . 255 
 
 III, — Periods of Interpolation of Gemmation in 
 
 diiferent groups of Organized Beings, . 256 
 
 IV. — Resting periods in the Genetic Cycle, . 257 
 
 V. — Abstract of Dr. Sanderson's Table of Ana- 
 logies in the Development of different 
 Classes of Plants, . . . 258 
 
 VI. — ) Analogies in the Genetic Cycle of Plants, 
 VIII. — I as indicated in this Work, . . 2^1 
 
 IX. — ( Tabular Views of the Genetic Cycle in 
 XVIII. ~ / the different Classes of Animals, . 266 
 
ON THE GENETIC CYCLE. 
 
 I. 
 
 DERIVATION OF ORGANIC BEINGS. 
 
 Although there is no distinction in Nature more clear or 
 more universally recognized than that between Organic and 
 Inorganic Bodies, yet, when we descend to the lowest forms 
 of the former, we find the marks which characterize them 
 as a class become at last so little appreciable, that there is 
 perhaps only one among those generally brought forward as 
 diagnostic, which may be looked for as universally present 
 — their derivation, by a process more or less direct, fi'om 
 previously existing individuals of a like kind. 
 
 In a certain sense, indeed, derivation from like forms 
 may have place also in the origination of various substances 
 simply physical in their nature, but — to pass over other 
 difterences — there is this obvious distinction, that it is not 
 essential to their formation. When it has place, it may 
 facilitate their production more or less, as we find the 
 crystallization of a saline solution accelerated by the pre- 
 sence in it of crystals of the salt, already formed, which 
 serve as nuclei for additional deposits of the like kind ; but 
 such production will occur whenever the requisite chemical, 
 mechanical, and other physical agencies come to operate 
 upon matter in which the ultimate elements of the sub- 
 stances in question are present. 
 
 B 
 
2 DERIVATION OF ORGANIC BEINGS. 
 
 But mth Organic Bodies it is different ; for in their case 
 not only must their ultimate chemical elements be present 
 in some shape or other, but they must be present as com- 
 bined by the prior operation of the Hving powers of indi- 
 viduals of a like kind into fertilized germs or other repro- 
 ductive bodies. If such a germ or reproductive body has 
 been normally constituted, then, and then only, mil the 
 application of certain appropriate influences of the nature of 
 light, heat, chemical action, &c., become the means of its 
 being developed into a body eventually resembling that 
 from which it was itself derived. 
 
 § 2. On the validity of this point of distinction between 
 organic and inorganic forms, naturalists and physiologists, 
 after some vacillation, are probably now pretty well agreed ; 
 the most recent researches affording as strong evidence 
 against the origination of organic beings de novo, as any of 
 a negative kind can well be. It is well known that organic 
 matter in the state of decomposition into which it passes so 
 readily when exposed to air and moisture at a suitable tem- 
 perature, is found to swarm with minute forms of animal 
 and vegetable life. But it has been shown by repeated, and 
 apparently conclusive experiments, that no such develop- 
 ment of living beings will occur if all the materials concerned 
 in the experiment — that is, both the air and the organic 
 matter, with water and other adjuncts — be subjected to 
 processes which effectually destroy all particles they may 
 contain of the nature of eggs or seeds, endued with a latent 
 capacity of vital action ; and this, though care be taken not 
 to alter their nature so as to unfit them in any way for the 
 support of life once developed. 
 
 The experiments of Professor Schultze, of Berlin, are 
 among the first of the kind which were performed \vith 
 the precision necessaiy in operations of this nature. They 
 consisted in passing the air which was allowed to come in 
 contact with the decomposing matter through a fluid (oil 
 
DERIVATION OF ORGANIC BEINGS. 3 
 
 of vitriol), capable of destroying organic matter by actual 
 contact, without emitting any noxious fumes. Though the 
 air was constantly renewed, no production of living forms 
 took place in the substances under observation, so long as 
 the current of air was subjected to this filtration ; while 
 in comparative experiments, in which the decomposing 
 matter was freely exposed to the atmosphere, without the 
 employment of any such sifting process, the usual develop- 
 ment occurred of the lower forms both of animal and 
 vegetable life.* Without being at all aware of these ex- 
 periments, I made some myself, of a similar nature, and 
 with the same result, by passing the air through red-hot 
 capillary tubes. These I reported in a communication to 
 the Parisian Medical Society, in 184?3. Some years after, 
 on the reports cuiTcnt of the discoveries of the late Mr. 
 Crosse, the electrician, I repeated the experiments of Pro- 
 fessor Schultze, with some modifications, — as by passing a 
 continuous electrical current of low intensity through the 
 organic matter, -^but I have obtained always the same 
 negative result. M. Milne Edwards also refers to experi- 
 ments of his own, of the same general nature, and, like 
 Schultze's, entirely opposed to the spontaneous development 
 of organic forms."!* 
 
 Quite lately, however, we have the report of experiments 
 by two independent observers, affording a different result. 
 I refer to those of M. Pouchet, communicated last year to 
 the French Academy ; and those of Dr. Daubeny, which 
 were brought under the notice of the British Association at 
 its late meeting at Oxford. M. Pouchet's experiments 
 consisted in macerating in distilled water a portion of the 
 contents of a flask of hay Avhich had been exposed (dry) to 
 a high temperature in an oven for half-an-hour. The ap- 
 
 * For a detailed notice of these experiments, see the Edinburgh Philo- 
 sophical Journal for July, 1837 ; also, Owen's Compar. Anat. I., 32. 
 f Edinburgh Philosophical Journal, Oct., 1859. 
 
 B 2 
 
4 DEPJVATION OF ORG.VNIC BEI^^GS. 
 
 paratus was immediately sealed hermetically ; but, notwith- 
 standing these precautions, Infusoria were soon developed 
 in the contained fluid. To the cogency of these experi- 
 ments, Milne Edwards takes objection on the following 
 grounds : — 
 
 1. The inadequacy of the means employed to ensure the 
 heating of the whole mass of hay to the boiling point, or to 
 any temperature inconsistent with the retention of vitality. 
 
 2. The capacity of animals, such as the Rotifera — much 
 higher in the scale than the simpler Infusoria — of recovering 
 their vitality on being moistened after desiccation, and even 
 after exposure in the dry state, to a degree of heat which 
 would be fatal in the natural condition.* 
 
 Dr. Daubeny's experiments were of the same general 
 nature as those of Schultze. No development of animal 
 life took place ; but, notwithstanding all the precautions 
 employed, mouldy vegetations made their appearance in 
 the fluid. In the discussion which ensued on the reading 
 of Dr. Daubeny's paper, tv>^o possible sources of fallacy were 
 suggested — the employment of lint-seed meal luting, and 
 the passage of the air through the oil of vitriol in bubbles 
 of too laro'e a size to ensure the full action of the caustic 
 on all the suspended particles of an organic nature. But, 
 as far as concerns the mucedinous Fungi, which give origin 
 to these vegetations, it would appear that sulphuric acid, 
 however employed, is no real barrier ; for M. Pasteur has 
 found that they will bear even the prolonged contact of the 
 concentrated acid without losing their power of germination.-f* 
 
 The experiments of M. Pasteur, in some other points 
 «'onnected with this subject, are so satisfactory in their 
 results, both positive and negative, that a short reference 
 to them is essential to complete our notice of the question. 
 M. Pasteur first satisfied himself of the actual existence of 
 
 * Edinburgh PhilosopLical Journal, Oct., 1859. 
 t Annalee des Sciences Naturelles. Ser. lY., torn. XII. (zool), p. 8G. 
 
DERIVATION OF ORGANIC BEINGS. 5 
 
 organic particles in the air, by drawing it through a small 
 dossil of gun-cotton, which was then dissolved in a mixture 
 of alcohol and ether, and the residuary matters, after wash- 
 ing, examined by the microscope. Some of the particles 
 thus obtained were evidently of an organic nature, as indi- 
 cated by their form and structure. A good many appeared 
 to be minute grains of starch, and were at once dissolved by 
 concentrated sulphuric acid ; but some corresponded with 
 the spores of the mucedinous Fungi in their powers of 
 resistance to that reao-ent. M. Pasteur then made various 
 experiments to test the possibility of spontaneous genera- 
 tion, of the same general nature as those already noticed. 
 In one of these a fermentible saccharine fluid was placed in 
 a large glass flask, with the neck drawTi out into a capillaiy 
 tube. After prolonged boiling, the flask was allowed to fill 
 itself with air in cooling, the capillary neck through which 
 the air entered being made red hot, and afterguards herme- 
 tically sealed, when refrigeration was complete. No de- 
 velopment of life took place so long as the flask was intact, 
 though kept at a warm temperature for a month or even 
 six weeks ; but when a small plug of gun-cotton was intro- 
 duced — charged in the way described mth atmospheric 
 dust — though precautions were taken which appeared 
 abundantly sufiicient to prevent the entrance of any other 
 extraneous matters, a turbidity soon became apparent in 
 the fluid, which was quite limpid before, and vegetations 
 began to develop themselves in about the same time that 
 they appeared in comparative experiments on liquids freely 
 exposed to the atmosphere, gradually spreading from the 
 vicinity of the ball of cotton through the whole contents of 
 the flask. 
 
 These and other experiments of M. Pasteur's, bearing on 
 the same subject, appear fully to justify his conclusion, 
 that there is nothing in the air, save these dust-like germs, 
 which can be the cause of the development of animal and 
 
6 DERIVATION OF ORG.VNIC BEINGS. 
 
 vegetable life, follo\nng on its free access. Even the oxygen 
 comes into play only as a supporter of the life of the forms 
 originating from these genns. Neither gas nor liquid, 
 neither electricity nor magnetism, nor ozone, nor anything 
 else, known or unkno^^^l, which may be present in the air, 
 save only the germs which it carries, are the essential con- 
 dition of the development of life.* 
 
 The general result of experiments of this kind, taken in 
 conjunction with arguments from the general analogy of 
 plants and animals, have now led to the abandonment, by 
 common consent, of the theories, once so prevalent among 
 physiologists, of spontaneous generation ; for the clear in- 
 ference from these experiments is, that there exist con- 
 stantly, either in the organic matter, or, more probably, in 
 the natural air or water, multitudes of germs of many 
 different organisms, and that the speciality of the forms 
 that appear in particidar cases depends, either on the nidus 
 variously modifying the development of germs originally 
 identical, or on its so favouring the growth of some, that 
 the others are stifled, as it were, and so prove abortive. 
 
 We have many other indications of the existence of 
 multitudes of such germs floating in the air. It is mainly 
 by the conveyance of pollen in this way that we account 
 for the fertilization of the seeds of dioecious plants ; and 
 that the spires of various species of ferns must be simi- 
 larly wafted about in their vicinity, appears from the diffi- 
 culty of obtaining pure seed to be depended on for the 
 multiplication of any particular species, many of the plants 
 raised turning out of quite a different kind from that from 
 which the spores were collected. "I* 
 
 It is true that there are still many cases in which Natu- 
 ralists are much perplexed to account for the formation of 
 organized beings, if the idea of their origination indepen- 
 
 * Op. Cit. pp. 85-89. 
 t Dr. Balfour, in Edin. N. Phil. Jouru. VIII., 278. 
 
DERIVATION OF ORGANIC BEINGS. 7 
 
 dently of parents — or their spontaneous generation^ as it has 
 been called — is to be held inadmissible. This is especially 
 the case in regard to the development of parasitic beings ; 
 but so much has been done of late years in the investiga- 
 tion of these obscure cases, as to render it highly probable 
 that those as yet unexplained are no real exception to the 
 general law of parental derivation. The facts which have 
 come to light in the pursuit of such enquiries are of a kind 
 equally surprising and interesting, but it would be out of 
 place to refer to them more in detail here, as many of the 
 phenomena will again come under notice in the farther 
 treatment of the subject proposed for discussion in this 
 work — the laws regulating the derivation of living beings 
 from each other. It may suffice, therefore, to close this 
 allusion with the following summary of the subject, in the 
 words of Prof. Owen : — "The ' thread-worms ' ( Filar iw) of 
 certain insects, which present no trace of sexual organs, 
 were supposed to be spontaneously developed in those in- 
 sects. The little worms were, however, by special and 
 due research seen to wind their way out of the caterpillars 
 they infested. Von Siebold placed these free Filariw in damp 
 earth, into which they soon bored : in a few weeks he found 
 that the sexual organs were developed in them, and that 
 they laid hundreds of eggs. Early in spring the young 
 worms were hatched, and began to creep about. Von Sie- 
 bold took some young caterpillars of the moth ( Iponomeuta 
 evonymella) in which were no parasites : he placed them in 
 the soft earth in which the young Filariw had been hatched, 
 and, in twenty-four hours, most of the caterpillars were in- 
 fested by the young thread-worms, which had bored their 
 way through the soft skin, into the interior of the young 
 caterpillars. The long hair-worm of fresh waters (Gordius 
 aquaticus), vulgarly conceived to be the result of a meta- 
 morphosis of the hair of a horses' tail, passes its early life 
 as a parasite in the body of an insect. But many Entozoa 
 
8 DERIVATION OF ORGANIC BEINGS. 
 
 acquire their full or sexual development, not as free worms, 
 but within the body of another animal, and of a species 
 distinct from that in which they had passed the early stage 
 of their existence.* 
 
 In illustration, Professor Owen gives a summary of the 
 reproduction of the Distomata, which we shall presently 
 have occasion to consider more at length. 
 
 He proceeds : — " The sum of the recent researches on 
 the generation of the Entozoa, teaches that, to the success 
 in life of the majority of these internal parasites, two diffe- 
 rent species of much higher organized animals are subser- 
 vient ; and that these two species stand in the relation of 
 prey and devourer. The habits of the prey favour the ac- 
 cidental introduction — as when a slug crawls over the 
 droppings of a thrush — of the eggs of the bird's intestinal 
 parasite. These are hatched in the slug. The slug, in its 
 turn, is devoured by the thrush, but the parasitic passen- 
 gers are not digested — only the coach is dissolved, and the 
 larvae, thus set free, find in the warm intestines of the bird 
 the appropriate conditions for their metamorphosis and full 
 development. In like manner, the Rhynchobothria of a 
 cuttle fish are the larvae of the Tetrarhynchus or four-ten- 
 tacled tape worm of a dog-fish. The encysted sexless 
 Tricenophorus of the liver of the char becomes the free and 
 perfect Trioenophorus of the gut of the pike. Tlie Ligula 
 of a herring becomes a Tcenia only when introduced into 
 the interior of a cormorant. The bladder-worm (Cysticercus 
 fasciolaris) of the mouse's liver becomes the tape-worm 
 (Twnia crassicollis ) of the cat. The Cysticercus pUlf or mis 
 of the liver of the hare becomes the Tcenia serrata of the 
 dog and fox. Dr. Kuchenmeister of Zittau first proved, ex- 
 perimentally, by feeding animals with Cysticerci (Hydatids 
 of the flesh and glands of herbivorous animals) that they 
 
 * Address to Brit. Assoc, at Leeds, 1858. P. 23. 
 
DERIVATION OF ORGANIC BEINGS. 9 
 
 became Twnice (intestinal tape-worms) in carnivorous 
 animals.'' * 
 
 § 3. But, although it would appear that we may safely 
 enough admit the universal derivation of living beings more 
 or less directly from others of the same kind, which stand 
 to them in the relation of parents, it is by no means so 
 clear that we are entitled to assume any absolute unifor- 
 mity in the way in which this law is carried into operation. 
 In fact, even a superficial survey of nature must make us 
 aware of one notable point of difference ; for, while in all 
 the higher forms, we find two parents (or their representa- 
 tives) concerned in the act of reproduction, w'e meet with 
 many cases among those lower in the scale of organization 
 in which a single individual appears capable of procreation 
 by its own unaided powers. It will suffice at present to cite 
 in illustration the case of the Aphides among insects. 
 
 The existence of these two diff'erent modes of origin — by 
 single and double derivation — is now so universally 
 admitted that special terms are in use for their designation 
 — such as homogenesis or monogenesis for the former, and 
 heterogenesis or digenesis for the latter. i" The term gemma- 
 tion (budding) is also used by many authors to denote pro- 
 pagation by single derivation, as distinguished from that 
 higher form of generation which involves the combination 
 of two original elements. In the former mode of origin a 
 portion of the body of the parent becomes the seat of a 
 
 * Address to Brit. Assoc, 1858. P. 31.. 
 t This is the sense in which the terms monogenesis and digenesis are 
 proposed by Prof. A. Thomson (Cyclop. Anat. and Physical, Art. Ovum, 
 Suppl. p. 42), and the sense in which they will be employed in the fol- 
 lowing pages ; but it is necessary to observe that Prof. Van Beneden, in 
 his extensive works on the reproduction of the Entozoa, uses them with 
 a very different meaning ; by tnonogcnesis he understands direct develop- 
 ment ; and by digenesis the interpolation of intermediate forms, in the 
 way of alternation — i.e. not as here, genesis from two origins, but genesis 
 in two stages. 
 
 B 3 
 
10 DERIVATION OF ORGANIC BEINGS. 
 
 certain independent manifestation of vitality, and a focus of 
 such intensity of the plastic processes, that, in the course 
 of time, the part is converted into a distinct organism, 
 capable of detachment from the parent, and fitted to main- 
 tain a separate existence. Such a detached gemma may be 
 termed 2^ free zooid ox phytoid. 
 
 In the ordinary form of reproduction again — that by the 
 co-operation of the sexes — a fusion seems to take place of 
 two highly vitalized portions of the same or kindred organ- 
 isms, which results in the formation of a fecundated germ, 
 possessed henceforth of an independent vitality, endowed 
 mth a capacity for ultimately acquiring the structure 
 characteristic of the species, and destined to be thrown on 
 its own resources, by its extrusion from the protecting 
 envelopes, as soon as its organization is sufficiently ad- 
 vanced for this condition. In all but the very lowest forms 
 of life — the conjugating Algse — a difference is observable 
 between the two factors of the embryonic product, which 
 are recognized respectively as male and female, or as the 
 spermatic and germinal elements. 
 
 § 4. It has long been known that these two modes of 
 propagation may co-exist in the same species — ^the plant or 
 animal multiplying now in one way, now in the other ; but 
 the general relations of the two modes of increase to each 
 other, throughout series of organised beings as a whole, has 
 only recently engaged the attention of naturalists. Till 
 lately, the general opinion seemed to be that the latter 
 form of reproduction was the normal one in the higher 
 species both of plants and animals, while derivation from a 
 single parent prevailed in the lower grades of both king- 
 doms, there being some in an intermediate position, which 
 furnished examples of the co-existence of the two forms. 
 This arrangement was considered to be quite exceptional 
 among animals, though of common occurrence, under some 
 modifications, in the vegetable kingdom ; but no farther 
 
DERIVATION OF ORGANIC BEINGS. 11 
 
 relation was indicated between the two processes in such 
 cases, than that a high development of the one was usually 
 accompanied by a proportionate abeyance of the other. 
 
 Now, in so far there can be no doubt that it is only 
 in the lower forms that gemmation is met with as an ob- 
 vious phenomenon ; but the idea can no longer be enter- 
 tained that sexual reproduction is confined in the same 
 way to the higher species, the tendency of recent investiga- 
 tions being rather in favour of greatly extending the limits 
 of both forms. In particular, an origin from two parents is 
 now known to have place in many species, in which it had 
 long been overlooked on account of its recurring only at 
 intervals, the ordinary mode of propagation being by offsets 
 from a single stock. Thus, in some of the lower Algse, the 
 ordinary mode of increase is by the formation of new cells, 
 which, becoming detached from the parent frond, may form 
 each the nucleus of a new and independent plant. This 
 goes on with more or less vigour during the whole season ; 
 but when such a change of external circumstances super- 
 venes, as to interfere with continuous growth, a new mode 
 of propagation is brought into play in the process termed 
 conjugation, or the coalescence of two cells in separate 
 fronds, so as to form a seed-like body, which, after lying 
 dormant till the return of conditions favourable to veo-eta- 
 tion, gives origin to a new frond, like one of those previously 
 produced by detached cells. Here the process of digenesis 
 — represented by the fusion of two cells — comes in only at 
 intervals, to supplement, as it were, what is in this case the 
 more usual one of monogenesis — represented by the detach- 
 ment and o;ermination of single cells. 
 
 In those of the lower species, in which both modes of 
 propagation are well marked features, we find that they 
 have a tendency to succeed each other in a regular order. 
 with corresponding differences in the immediate progeny, 
 to which the term alternation of generations has been 
 
12 DERIVATION OF OllGAXIC BEINGS. 
 
 applied — an expression which, though open to some ob- 
 jections, has now come into very general use. 
 
 The recurrence of sexual reproduction, in some form or 
 other, has now been ascertained in so many species, ordi- 
 narily propagated in the way of gemmation, as strongly to 
 suggest the probability of the occasional interposition of the 
 other form being eventually detected, by close and long 
 continued observation, even in those cases in which deriva- 
 tion from a single source is the only mode of increase yet 
 known ; and the impression is gaining ground among 
 naturalists that the two are co-existent, and alternate with 
 more or less regularity and distinctness in many of the 
 lower Invertebrata, and probably still more universally in 
 the vegetable kingdom. It is unnecessary at present to go 
 into any argument on the point, as the sketch which will 
 presently be given of the modifications of the function of 
 reproduction in both kingdoms of nature will serve to show 
 the grounds on which this view is founded. 
 
 § 5, I believe, indeed, that it falls short of the truth, 
 and that there are processes co-extensive with organic 
 nature which represent, in some degree, the gemmation of 
 the lower species, and alternate in the same way with the 
 sexual act. 
 
 I must premise, however, that, even in cases where the 
 phenomena of alternation come out most clearly, I cannot 
 legard the processes as all of a parallel kind. They ap- 
 pear to me to fall into groups whose characteristic features 
 depend principally on the period of the life-history of the 
 species at which a process of gemmation is interpolated in 
 the genetic cycle. 
 
 The gemmation sometimes occurs just before, and is, as it 
 were, ancillary to sexual reproduction ; sometimes it occurs 
 after it, when it is subservient rather to the progress of 
 development. In the former case, what may on the whole 
 be considered as the most typical of the diverse forms be - 
 
DERIVATION OF ORGANIC BEINGS. 13 
 
 longing to the species, is still defective in having no proper 
 organs of reproduction — a function which is vicariously 
 performed by a set of gemmae detached from it. The 
 original stock is really neuter ; but true sexes appear in 
 these buds, after they have been transformed by a process 
 of development into isolated zooids or phytoids. They 
 may then be considered as a highly individualized form of 
 those organs which were wanting in the parent stock. Such 
 organs constitute, at least, the essential part of their 
 economy ; and although, along with them, there may be 
 present also others, more or less fully developed, for dis- 
 charging functions, such as alimentation and locomotion, 
 required by their status as free zooids, yet their gTeat office 
 is reproduction, and this end effected, their life speedily 
 comes to a close. In this they contrast strikingly with the 
 stock from which they were derived ; for it is endowed with 
 a much gxeater permanence of life, frequently detaching, 
 during its period of vigour, many successive swarms of 
 sexual zooids ; just as among the higher animals, the same 
 parent may develope many successive broods of young. 
 
 On the other hand, when the budding process occurs in 
 the course of development, the gemmae are detached from 
 the immediate product of impregnation while it is still in a 
 rudimentary condition, comparable to the first stage in the 
 evolution of the ovum of the higher animals. The germ- 
 parent itself never attains to the full development of the 
 species, but remains the whole term of its brief existence in 
 a rudimentary state ; but the progeny, which it buds off, 
 acquire, in due course, the typical form, or at least give 
 origin, mediately or immediately, to others which do so. 
 
 For the better distinction of these varieties of alternation, 
 and for the purpose of bringing out more clearly what I 
 ctjnceive to be their points of correspondence ^vith pheno- 
 mena occurring in the higher animals, I have found it con- 
 venient to divide the life history of an organic being into 
 
14 DERIVATION OF ORGANIC BEINGS. 
 
 three stages, all of wliicli come out prominently in one form 
 or other of alternation, while, as I shall endeavour to show, 
 they are covertly represented even in those species in which 
 no phenomena of alternation are recognised. The first, or 
 what I term the protomorphic stage, is that which intervenes 
 between the fecundation of the germ and the first appearance 
 of the characteristic or typical organization of the species ; 
 the second, or ortkomorphic, that which corresponds to the 
 development and full perfection of this organization ; while 
 the third, or gamomorpJdc, is that of the formation or matu- 
 ration of those structures in w^hich the spermatic and germi- 
 nal elements are generated, in preparation for another act of 
 fecundation, as the commencement of a new genetic cycle. 
 
 In one of the forms of alternation just noticed, the inter- 
 polation of gemmation takes place in the protomorphic 
 stage, — that is, prior to that development by which the 
 features most characteristic of the species are gTadually 
 evolved. The other form of alternation, just contrasted 
 with it, is that in which the process of gemmation is inter- 
 polated in the gamomorphic stage — ^that is, after the general 
 acquisition of the typical conformation of the species, and 
 in connection v/ith the development of the organs which 
 form the sexual elements. 
 
 In the intermediate period of the life history of the 
 species — that here termed ortliomorpliic — which intervenes 
 between the appearance of the general typical character of 
 the family and the maturation of sexual organs, gemma- 
 tion, though, perhaps, a more frequent character than either 
 in the incipient or terminal stages, rarely comes before us 
 as a case of alternation of generations, in consequence of 
 the gemmae commonly remaining in adhesion to each other, 
 so that their separate individuaUty is never clearly mani- 
 fested, and the whole aggregation passes as a single plant or 
 animal. This is especially the characteristic an'angement 
 in the vegetable kingdom, and in the zooph}i:ic forms of 
 
DERIVATION OF ORGANIC BEINGS. 15 
 
 animal life. Where the gemmae do become detached, how- 
 ever, the case may assume the aspect of a form of alternation, 
 one of the most striking examples — that occun-ing in the 
 propagation of the Aphides — being, as I believe, referable to 
 this head. 
 
 In cases, therefore, where alternation is an obvious and 
 well recognized occurrence, I would distinguish these three 
 varieties : — 
 
 1. That in which the gemmation occurs in the proto- 
 morphic or germinal stage, prior to the appearance of the 
 typical organization ; 
 
 2. That in which it occurs in the gamomorphic or later 
 stage of the life history — that is, the connection with the 
 maturation of the reproductive organs ; and 
 
 3. That in which it occurs in the orthomorphic or inter- 
 mediate stage — -that is, during the manifestation of a more 
 fully developed condition of the typical organization, but 
 prior to the maturation of the sexual organs. 
 
 § 6. But, even in the higher forms of life, where we no longer 
 find any obvious alternation, I believe that phenomena occur 
 which are in some degree representative, and which admit 
 of the same sort of classification. Thus, though the well- 
 marked cases of alternation, due to the evolution of proto- 
 morphic zooids, are confined to a few of the lower orders, a 
 certain nisus, or tendency in this direction, — a fresh start, 
 as it were, in the course of germinal development — may be 
 traced with more or less distinctness in all cases of 
 embryogeny, as in all instances there is formed first a 
 cellular germ-mass, from one point of which there is subse- 
 quently developed a new axis of embryonic gro^Hh. And 
 as the appearance of the new centre of organization in the 
 early germ may stand as representative of protomorphic 
 alternation, so to the contrasted form marked by the produc- 
 tion of sexual or gamomorphic zooids, we may trace a certain 
 correspondence in the maturation of the reproductive organs. 
 
16 DERIVATION OF ORGANIC BEINGS. 
 
 The subject of these relations I propose to examine with 
 more detail after the survey, just refen*ed to, of the repro- 
 ductive process in organic nature, but it seemed necessary 
 to premise so much here, as I have made use, in its course, 
 of forms of expression, to avoid circumlocution, which 
 would hardly be intelligible without such explanation. 
 
SURVEY OF THE REPRODUCTIVE PROC^'^;^ 17 
 
 II. 
 
 SURVEY OF THE REPRODUCTIVE PROCESS IN 
 THE VEGETABLE KINGDOM. 
 
 What is true in a degree of all physical science, applies with 
 especial force to Biology — namely, that the so-called 
 " General Laws," being really nothing else than general 
 expressions of facts, can only be determined when the in- 
 dividual facts have first been clearly ascertained in a great 
 variety of instances, and then carefully and minutely com- 
 pared for the discovery of their mutual relations. A 
 partial selection of facts can serve only as the basis of con- 
 jecture, and nothing, probably, does more to damage the 
 progress of science than the abuse of hypotheses, to give a 
 false show of symmetry and completeness to empty systems, 
 which are the product merely of the speculator's fancy, and 
 have no real counterpart in nature. Our dislike to confess 
 ignorance, and go through investigations which promise no 
 immediate result, predispose us but too much to adopt such 
 ready-made systems, which must fall to pieces, indeed, 
 at last from their own rottenness, but which, for a time, do 
 much mischief by stifling the ardour of research, or giving 
 it such a false bias as to cause facts and relations to be 
 overlooked in a manner which seems almost incredible 
 after the delusion has once passed away. 
 
 Yet it is admitted that there is a use of hypothesis in 
 science which is perfectly legitimate, and which, when em- 
 ployed with due tact and caution, has proved of most signal 
 service in the hands of many of the most gifted students of 
 nature in unlocking her secret recesses. 
 
 What is it but such a guarded use of hypothesis that 
 gives modern chemistry a claim to rank as a philosopliical 
 
18 SURVEY OF THE REPrtODUCTIVE PROCESS 
 
 pursuit, which could never be awarded to the laborious but 
 desultory researches of the old alchymists. In the main, 
 chemistry still is, and must long remain, an empirical 
 science : the very fluctuations of its nomenclature show that 
 its so-called theories are no more than hypotheses, still they 
 have the important use of giving system to what would 
 otherwdse be a chaos of unconnected facts ; and there is 
 undoubtedly a certain amount of truth in the relations thus 
 indicated, though in any fully developed system this is as 
 obviously eked out by conjectures. To those who have the 
 acuteness to distinguish between them, the former furnishes 
 important indications for the course of farther investigations; 
 and these, when completed, serve to determine the truth of 
 the conjectural superstructure. 
 
 But, in fact, the natural tendency of the human mind to 
 generalize makes it impossible to prevent the introduction 
 of hypothesis. Few persons can address themselves to the 
 consideration of any extensive series of phenomena without 
 attempting to trace certain relations of this kind among 
 them, and the validity of their conclusions is entirely a 
 question of degree. In proportion as the facts are numerous 
 and accurately known, and as they are carefully and 
 judiciously comj)ared, the results arrived at will be entitled 
 to rank as weU ascertained general law^s ; but far short of 
 this conclusions will be drawn. With the averao^e constitu- 
 tion of minds, it is impossible it should be otherwise ; and 
 there is, therefore, probably more good likely to be done by 
 insisting on the necessity of distinguishing the well-founded 
 from the merely conjectural, than by entirely excluding the 
 latter. 
 
 Though w^e may admit, therefore, as is the opinion of some 
 well qualified to judge, that we have not yet in most 
 branches of biological science a sufficient knowledge of 
 actual facts to admit of our conclusions from them ranking 
 much above the level of hypothesis, we still reasonably ex- 
 
IN THE VEGETABLE KINGDOM. 19 
 
 pect to derive some advantage from their guarded use, 
 especially in methodizing the more intricate departments ; 
 and none, surely, stands more in need of being systematized 
 than that involving the consideration of all those diversified 
 and seemingly anomalous phenomena, which have <jf late 
 been so abundantly accumulated in connection witli the 
 function of reproduction. Only we must see that no 
 hypothesis be admitted which is not in consistency with 
 known facts, and jealously resist all attempts to bend facts 
 into conformity with hypothesis. 
 
 It is with this view that I now propose, before proceed- 
 ing to theorize on the nature and relations of the reproduc- 
 tive function, to give a summary of what I believe to be the 
 main facts of the process in the principal groups of both 
 kingdoms of nature. But I may observe at the same time 
 that the conclusions which were indicated at the close of 
 the last chapter are only partly of the nature of hypotheses 
 — partly I consider them as matters of fact. Thus I believe 
 it to be a matter of fact that there is a very essential dis- 
 crepancy in the so-called cases of alternation of generations, 
 and that of a kind to divide them naturally into groups as 
 above indicated. It is, on the other hand, a matter of 
 theory — and it may be of mere conjecture — that one class 
 is represented by the process of embryogeny, and the other 
 by that of the maturation of the sexual organs in the higher 
 species. It is at least a question that requires to be argued, 
 and this cannot be done till the facts have been brought 
 forward ; but that the difference referred to does exist in 
 cases of alternation, is only, I think, what will appear in 
 the course of the summary from the very facts of the 
 case. 
 
 It is no part of my intention to discuss here the whole 
 history of Reproduction. I propose to confine myself to 
 such points as have some distinct bearing on alternation, 
 but these I will endeavour to state, as distinctly as I can. 
 
20 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 and as fully as is consistent Tsitli the brief limits to which 
 I feel that I should confine myself in such a summary. 
 
 As Reproduction, like other functions, is performed in a 
 less complex way in the more rudimentary forms of organi- 
 zation, I propose proceeding from the lower to the higher 
 species, and for similar reasons, I commence with the Vege- 
 table kingdom. 
 
 § 2. A few remarks may be made, by way of introduc- 
 tion, concerning the general characters of the process in 
 this division of oroanized nature. 
 
 Indications of sexual relations in the function of repro- 
 duction, have now been so generally ascertained, as to make 
 it highly probable that they are always present. Three 
 principal modifications have been recognized in cases where 
 their existence has been positively ascertained. 
 
 The most rudimentary manifestation of sexual action 
 occurs in the conjugation of. the lower Algae. In these 
 simple forms of hving matter there is at first no differentia- 
 tion of organs for the work of reproduction, more than for 
 any other vital function. The plant consists simply of a 
 repetition of cells, which — whether isolated or aggregated 
 into fronds, (tumid, membranous, or filamentous) — are in- 
 distinguishable from each other, being all nucleated and 
 filled with a green granular mass, termed endochrome. In 
 the farther development of the cells, we find that in those 
 which are to take part in the reproductive process, the en- 
 dochrome becomes condensed into a spheroidal mass ; after 
 this, a communication is established between two neigh- 
 bouring cells by a perforation of their walls, and a fusion 
 of their contents takes place, resulting in the formation of 
 an embryonic corpuscule, which eventually becomes a true 
 cell, by the formation of a proper wall on its exterior. 
 Along with a general sameness in the essential features of 
 this process, in all the simpler Algae or Protophyta, there are 
 certain specific differences, mainly dependent on variations 
 
IN THE VEGETABLE KINGDOM. 21 
 
 in the mode of perforation of the cell-wall, and the invest- 
 ment of the embryonic corpuscule. 
 
 In the higher Cryptogamia another modification of the 
 reproductive process prevails, in which the sexual elements 
 are represented by phytozoa and archegonial corpuscules. 
 LinngBus was led to apply to the class in which he placed 
 these species, the name of Cryptogamia, from his not being 
 able to extend to it those principles of sexual relation which 
 he recognised in the higher plants. But since his time, 
 after much groping on wrong tracks, relations of this na- 
 ture have at last been detected, more closely analogous in 
 some respects to the reproductive phenomena of animals, 
 than even those with which we were previously acquainted 
 in phanerogamic plants. The analogy lies mainly between 
 the spermatic or fertilizing elements in the two kingdoms, 
 the vegetable phytozoa, being like the spermatozoa of ani- 
 mals, minute rounded or filiform bodies, endowed in general 
 with motile powers by the action of ciliary appendages. 
 The germinal element, which is lodged in the centre of a 
 flask-shaped group of cells, termed the archegonium, appears 
 to be at first a homogeneous mass of protoplasm, but after 
 fertilization by the phytozoa, it becomes a true cell by the 
 development of a distinct wall on its exterior. There is a 
 great similarity throughout the gToup, in the general cha- 
 racter of both kinds of corpuscules, and in their immediate 
 investments, but very great diversity in their relations to 
 the parent stock. Sometimes, as in mosses, they are de- 
 veloped at once on the leafy axis ; in other cases, as in ferns, 
 they are formed in detached phytoids, resembling distinct 
 plants of a lower type — peculiarities which will come again 
 to be noticed, in reference to the contrast between these 
 two families, as representing opposite forms of alternation 
 of generations. 
 
 The remaining modification of the reproductive process 
 ^— that by pollen grains and ovules — characterises all the 
 
22 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 liigher or plianerogamic plants, which constitute the vast 
 majority of the present flora of the world. The ovule is a 
 cellular body containing the germ, and developed from a 
 peculiarly modified leaf or carpel, which in the Coniferse 
 leaves it quite exposed, but in by far the greater number 
 of plants is ^vrapped round it to form the germen or ovary. 
 Tlie pollen grains are secondary cells developed in an 
 anther or terminal appendage of a stamen — representing 
 the lamina of a peculiarly modified leaf — and are set free 
 by the dehiscence of its exterior envelope. They have the 
 property, when brought in contact with the ovule or the 
 stigmatic surface of the ovary, of emitting, through valvular 
 openings in their outer coat, long tubes produced by the 
 outgTowi:h of the contents and inner wall. The pollen tube 
 passing through the tissue of the style or neck of the ovary 
 to the ovule — or, when this exposed, entering its micropyle 
 directly — comes into that relation with the included ger- 
 minal corpuscule, which is necesssry to its fertilization. 
 
 With these preliminary remarks on the general relations 
 of the reproductive process in the vegetable kingdom, we 
 may now proceed to a summary of the most important mo- 
 difications of its details in the principal groups, commencing 
 with the simpler cellular forms. 
 
 REPRODUCTION IN THE PROTOPHYTA. 
 
 Under this head I propose to consider the process in 
 some of the simpler Alg^, which I take by themselves simply 
 for convenience sake, and without hazarding any opinion on 
 the value or limits of the group. The tenn, I think, is 
 generally employed in this indefinite way, and it is, there- 
 fore, to be regretted that its etymology should suggest a 
 parallelism to that of Protozoa, a very natural primary 
 division of the animal kinodom. 
 
 I confine myself, then, in this section to Algie of those 
 
IN THE VEGETABLE KINGDOM. 2o 
 
 rudimentaiy forms in which the process of conjugation pre- 
 vails. All these species may be considered as unicellular ; 
 for though the cells are not in every case isolated, they have 
 always the capacity of maintaining an independent life, 
 when by any means they are separated from each other. 
 
 When in connection with each other, the cells are ar- 
 ranged in various fashions ; in some Palmellese they are 
 embedded in a gelatinous matrix, in other cases they co- 
 here sidemse to form flat or bullate fronds, but in the ma- 
 jority they are connected in single file, in filaments simple 
 or branched according to the species. Except in Palmellese, 
 the cell wall becomes eventually a well-defined structure, 
 and consists of a layer of cellulose, lined by a film of an 
 albuminous nature, which is probably nothing more than 
 the outer pellicle of the protoplasmic contents. This in- 
 ternal protoplasm is generally coloured green — occasionally 
 red — by an accumulation of granules, termed endochrome. 
 
 These Algae multiply in various ways. The smplest is by 
 a process of fission follo\^'ing on gemmation or cell-formation 
 — the points at w^hich the new cells are developed, and their 
 continued adhesion or otherwise, giving rise to the varied 
 forms of differently shaped fronds, or isolated cells. But 
 the most characteristic form of reproduction is by conjuga- 
 tion, already noticed as representing in a rudimentary way 
 that by the co-operation of the sexes. 
 
 Conjugation has been observed in the confervoid genus 
 Zygnema and its allies, in most of the Desmidiese, and in 
 some species of Palmellese and Diatomacese.* The first step 
 in the process appears to be the rupture of the cell wall by 
 the groAvth of the contents, which then protrude as a se- 
 tt condary or pseudo-cell, surrounded by a pellicle formed 
 within the wall of the original cell. On coming in contact 
 
 * For a notice of the recorded observations on the conjugation of the 
 Diatomacese, see the Notes to the Translation of Hoffineister's Papers in 
 the Annals of Nat. Hist., 3d ser. I. p. 7. 
 
24 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 with the endochrome, which escapes in a similar way from 
 a neighbouring cell, the two plastic masses unite by the 
 deliquescence at the meeeting point of their imperfect walls 
 and become fused into a single spore, the investment of 
 which subsequently acquires the character of a true cellulose 
 membrane.* 
 
 The variations of the process in different cases appear to 
 depend very much on the mode of dehiscence of the original 
 cells. In Desmidie?e, in which the cells — generally isolated 
 — are marked by a median constriction, each of the pairs 
 of cells concurring in the process of reproduction splits into 
 two, and the effused contents comingling in the void space 
 surrounded by the four empty valves, are there developed 
 into a germ mass, whose investing layer acquires subse- 
 quently a cellulose character, and usually betjomes covered 
 also with siliceous spines. 
 
 In Diatomacea3 the pair of conjugating fnistules first be- 
 come embedded in a mass of gelatine, and then the valves of 
 each separate as if hinged at one side, so as to form fissures 
 along their contiguous margins, through wdiich the contents 
 escape, and become amalgamated in the gelatinous matrix. 
 Two sporoid bodies are generally produced, "f* owing, there 
 is reason to believe, to a sub-division of the original germ- 
 mass. They appear as a pair of new frustules lying cross- 
 wise to the original ones, and of much larger dimensions. ^ 
 
 In Meloseira a somewhat analogous kind of action seems 
 to take place between the ends of a single cell — the cell 
 being an elongated cavity, apparently foraied by the fusion 
 of two or three into one. § 
 
 In the confervoid filamentous Algfe, Dr. Carpenter gives 
 
 * HofEmeister — Annals of Nat. Hist., 3d eer. I. 1. 
 t TLwaites in Ann. Nat. Hist., XX. pp. 9 and 343. In Fragillaria 
 however, there is but a single spore. 
 
 + Thwaites in Ann. Nat. Hist. 2d Ser., I. 166. 
 § J. H. Carter in Ann., 2d Ser., XYll. 1. 
 
IX THE VEGETABLE KINGDOM. 25 
 
 the following account of the process : — " The conjugation 
 ordinarily takes place between the cells of distinct filaments ; 
 these approximate to each other, and put forth little pro- 
 tuberances that coalesce, and establish a free passage 
 between the cavities of the cells, whose contents then inter- 
 mingle."* In reality, how^ever, the outer walls of the con- 
 juga,ting cells are probably as passive in this as in the 
 former cases, the papilla being protruded, and eventually 
 ruptured at the point of contact by the force of growth of 
 the contained endochrome or portions of the wall already 
 beginning to soften. The united contents on their fusi(jii 
 appear to undergo condensation, and the common mass is 
 generally retracted wholly into one of the original cells."f" 
 
 In the geiiiis Zygnema, and in most other species of the 
 gi'oup, the conjugation takes place solely or chiefly between 
 the cells of two filaments which lie parallel to each other, 
 so as to present with their connecting passages a ladder-like 
 appearance ; but in some it takes place promiscuously on 
 all sides, interw^eaving the whole mass of filaments into an 
 inextricable network. There are also species in which the 
 conjugation takes place between the adjacent cells of the 
 same filament : in this case a channel of connnunication is 
 fonned through a protuberance just over the septum, the 
 contents of one cell thus escaping into the other, and then 
 form.ing the spore ; so that after the process is completed 
 the alternate cells contain spores, the intermediate ones 
 being empty. In all these cases the recipient cell, as the 
 matrix of the spore, may, with a certain propriety, be con- 
 sidered to have a female character ; and when, as in the 
 geilus Spirogyra, all the cells of one filament thus empty 
 themselves into those of another, the sexual distinction 
 
 * Principles of Compar. Physiol., p. 190. 
 t This is the case also in a species of Didi/moprium, one of tb.e filamon- 
 tous Desmidiese. Ralf s Monograph, pp. 58 — 62. 
 
 C 
 
26 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 may, of course, be extended to the whole frond. But in 
 the Desmidiese and Diatomaceae, in which the spore is formed 
 outside the cells, and in Mesocarpus among the Conjugatse, 
 in which it is lodged in a dilatation of the connecting pas- 
 sage, we can only in a general way allege indications of 
 sexuality, having no guide to determine which is male and 
 which female.* 
 
 The modifications of conjugation just noticed may be 
 arranged as follows : — 
 
 I. In isolated cells : 
 
 1. Fusion of two pseudo-cells into one — Palmoglea.'f 
 
 2. Dehiscence of two cells, and fusion of their contents 
 
 into a single spore — Desmidiese. 
 
 3. Effusion of the contents of two cells, and formation 
 
 from thence of two new frustules, larger than 
 those in conjugation — Diatomaceae. 
 
 II. In cells aggregated into filaments — Conjugatse. 
 
 4. Contents of two cells in different filaments effused 
 
 into a dilatation of the connecting tube, and 
 there formed into a spore — Mesocarpus. 
 
 5. Contents of the cells of one filament passing pro- 
 
 miscuously into those of others, through com- 
 municating tubes, the recipient cells maturing 
 the spores — Mougeottia. 
 
 6. Conjugation of the same kind between adjoining 
 
 cells of the same filament — Rhynchonema. 
 
 7. Conjugation of the same kind, one filament evacu- 
 
 ating the contents of aU its cells into those of 
 a connected filament — Spirogyra. 
 
 * Carter remarks tLat in Spirogyra the recipient cell is generally tlie 
 larger of the two, and hence suggests that the inequality in the size of 
 the conjugating frustules which is occasionally observed in Diatomacese 
 may also possibly have a sexual import. Ann. Nat. Hist., 3d Ser., I. 35. 
 
 f Braun, Rejuvenescence in Nature, pp. 136 and 327. 
 
IX THE VEGETABLE KINGDOM. 27 
 
 8. Conjugation between the contents of opposite ends 
 of the same cell* — Me lose ir a. 
 
 The co7ijiiqate-spore has been seen, in the case of iSpi- 
 7'opi/ra, to split its coat in germination in two halves, and 
 emit a fusiform cell, from which others are budded off, so 
 as to form a confervoid filament like that in which the 
 spores were originally formed."]* But the development is 
 not always so direct. Recent observations indicate that in 
 various Desmidiese the contents of the conjugate-spore are 
 transformed by repeated binary sub-division into numerous 
 derivative celLs, which finally assume tlie form of the origi- 
 nal cells concerned in the act of conjugation, and are set 
 free by the dissolution of the outer wall of the spore. The 
 existence of such a process was rendered probable by the 
 observations of Focke, Jenner, and Ealfs on Closterium, and 
 has since been satisfactorily followed out in Cosmarium by 
 Hoffmeister.J A similar multiplication of the spore-contents 
 has been noticed in one of the Palmellese ( Palmoglea), and 
 in Thwaitesia and Mesocarpus among the Conjugat9e.§ 
 
 There are other cases again in which the primary product 
 of the spore appears to be a cluster of zoospores, probably 
 reproducing the original form by a second process of germi- 
 nation. This is asserted by Pringsheim of Chlamydococcus 
 
 * This subject is treated at some length, by Braun (Rejuvenescence, 
 &c. Ray. Soc. Transl., pp. 284, et seq.) 
 
 t This is the account given by Vaucher, Meyen, Smith, and Prings- 
 heim. Agardh, however, maintains that its contents become resolved 
 into Zoospores. The probability of an actual diversity in this respect is 
 confirmed by the observations of Pringsheim and Henfrey, that zoospores 
 are sometimes formed, instead of one large resting spore, as the primary 
 result of conjugation. See Ann. Nat. Hist., 2d Ser, XI., 210-297. 
 
 X Ralf s British Desmideae, p. 11 and PI. XXVII. Annals of Natural 
 Hist., 3d Ser., I. 16. 
 
 § Micrographic Dictionary. See also Berkeley's Introduction to Cryp- 
 togamic Botany, p. 152, and Prof. Braun's Rejuvenescence in Nature. 
 Ray. Soc. Transl., p. 136. 
 
 c 2 
 
28 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 and some Palmelleee * In Pahnella itself Mr Thwaites 
 figures a branched filament proceeding from a spinulose 
 cell — very like a conjugate spore — and bearing ordinary 
 palmella-cells at its free extremities. -[• And so in Diato- 
 mace?e, from the frustules developed in conjugation being 
 much larger than their parents, it is probable that they also 
 split up into smaller pieces or frustules. t 
 
 The conjugate spore, whatever be its mode of develop- 
 ment, is always very retentive of vitality, and is commonly 
 several months of germinating. Hence it is fitted to perpe- 
 tuate the race from year to year, and is frequently spoken 
 of as the resting or winter-spore. Bodies of a similar kind 
 are found even in tribes in which as yet no conjugation 
 has been observed, but in these cases we have no satisfac- 
 tory information concerning their mode of origin. The dis- 
 semination of the species under circumstances which admit of 
 continuous vegetation, is effected by zoosjjores or motile 
 gemmae, very similar of those of the higher Algae. 
 
 Remarkable as the process of conjugation undoubtedly is, 
 and quite ditferent from all other modifications of the re- 
 productive process in the vegetable kingdom, it is very 
 doubtful if the species in which it occurs can be definitively 
 marked off from others, as constituting a natural gi'oup of 
 themselves, for in many, which certainly seem to be closely 
 allied to those now under consideration, fertilization ap- 
 pears to be effected, as in the higher algae, by phytozoa. 
 Corpuscules of this nature are described by Carter in the 
 remarkable unicellular alga Vohox, which ranked so long as 
 an infusory animalcule. § In other cases again, as in Cijlin- 
 drosperinum, among Nostochineae, the filaments are termi- 
 
 * Quar. Journ. Micros. Science, IV., 313. 
 t Ann. Nat. Hist., 2d Ser., II. 313. 
 X Tlnvai+es' Ann. Nat. Hist., XX. (1847). Griffith Ann. 3d Ser. XYI- 
 92, 1855. 
 
 § Annals of Nat. Hist., 3d Ser., II., 237, III. 1. 
 
IN THE VEGETABLE KIXGDnM. 2^) 
 
 nated by a pair of cells, of wliicli the proximal forms a spore 
 in its interior, while the distal, which goes under the name 
 of heterocyst, has been considered to contain spermatic 
 matter, though no motile particles have been seen to issue 
 from it, nor anything of the nature of fusion or conjugation 
 been observed to take place between it and the spore-cell. 
 Clear cells, to which the name of heterocysts has also been 
 applied, occur in most other Nostochinese, but without tlie 
 accompanying sporangia, so far as has yet been observed.* 
 There are besides other species in which neither conjugation, 
 nor indeed any form of digenesis, has yet been detected. 
 This is the case, for instance, with the Oscillatoriea3, and 
 Ulvacese, which are not known to multiply but by the de- 
 tachment of cells or frustules, and in the case of the latter 
 also by the emission of zoospores. It is asserted, however, 
 by Itzigsohn that Oscillatoria is only a particular phase of 
 Chlamydococcus, a unicellular alga allied to Palmella — the 
 filaments of the former arising from minute spiral corpus- 
 cules, generated within gTeen gonidia discharged from the 
 latter ; while the frustules of the Oscillatoria are stated to 
 be again developed into the globules of clilami)dococcxis.'\ 
 The subject at least invites farther investigation, for there 
 is a prevailing impression among botanists that the Oscilla- 
 torieaj are merely barren phases of plants which may fruc- 
 tify in some other form. Among the Ulvaceae it is to be 
 noticed that in some species motile corpuscules occur of two 
 kinds, borne on different plants, one quadriciliate, the other 
 biciliate. The former are regarded by Robin as phytozoa, 
 but Thuret alleges that both kinds germinate. If phytozcta 
 exist we should expect to meet also with corresponding- 
 bodies of the nature of resting-spores, but such have not 
 yet been detected, at least in the majority of the group. 
 
 * M. G. Thuret— Ann. Nat. Hist., 3d Ser., II. 1. 
 t Quarterly Journal of Micros. Science, II., 188 (Botanisclie Zeihing). 
 
30 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 There is reason to believe that future researches will 
 show that conjugation, or some cognate process, is of very- 
 general occurrence among these low forms of organization, 
 for if any modification of digenesis may be held to extend 
 to the most rudimentary forms of living matter, it is most 
 likely to be that in which there is little or no differentiation 
 of sex. Alternation of form, too, must prevail to some ex- 
 tent, if the suspicions of naturalists be correct as to many 
 of the reputed species being merely transitory phases of 
 others. At present, however, all is conjecture on the sub- 
 ject, and the only well-ascertained phenomena of the kind 
 are those just noticed as occurring as a preliminary (or pro- 
 tomorphic) stage in the germination of certain spores. 
 
 A tabular view is here subjoined of some points in the 
 development and reproduction of the orders of algae just 
 referred to : — 
 
IN THE VEGETABLE KINGDOM. 
 
 31 
 
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o'2 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 4. § REPRODUCTION IN THE ALGiE GENERALLY AND CHARACE^. 
 
 Of the three current divisions of Algae — Confervoide?e or 
 green-spored, Floridese or red-spored, and Fucoideae or olive- 
 spored — the first is generally considered as including those 
 simpler forms already noticed in which conjugation occurs, 
 as well as others of higher organization, in which, as in the 
 order generally, a distinction of sexual elements seems to 
 prevail. 
 
 The spermatic particles of Algse go under the name of 
 antherozoids or phytozoa, but, with one or two doubtful ex- 
 ceptions, they are not filiform hke the bodies so called in 
 the higher Ciyptogamia, but ordinarily of an ovoid form, 
 wth two long cilia attached at one end, whose play im- 
 presses upon the corpuscule a rapid jerking motion. The 
 particles supposed to play the part of antheriozoids in the 
 Floridese appear to be destitute of cilia and of all motile 
 power. The germinal bodies are small globular masses of 
 protoplasm occupying the interior of cells termed sporangia. 
 No conjugation or direct union of cells takes place in this 
 group, but the concourse of the elements is effected by the 
 fonnation of pores in the cell-walls, through which the sper- 
 matic particles escape from their proper cells and gain access 
 to the interior of the sporangia ; the perforations in the 
 latter are termed micropyles. 
 
 Zoospores — a sort of motile cihated gemmules found in 
 connection with the conjugating Algse which have no anthe- 
 rozoids — occur also throughout the present group, except 
 among the Floridese. Though liable to be confounded together, 
 the two kinds of corpuscules present generally certain struc- 
 tural diversities, and have totally different functions. The 
 zoospores are generally larger, their cilia are more numerous, 
 and their motion through the water more uniform. They 
 appear to be formed by the breaking up of the endochrome 
 of some of the component cells of the filament or frond, and 
 
IN TUB VEGETABLE KINGDOM. 33 
 
 escape by perforations in the walls ; the autherozoids again 
 originate in special cells of the nature of antheridla. Tlu'v 
 are both indeed concerned in propagation, bnt while tin- 
 peculiar office of the latter is to impregnate the germs, the 
 zoospores appear to be merely a kind of gemmae capable of 
 spontaneous development, for it is observed that after a 
 time their motion ceases from the loss of the ciha, and they 
 begin to o-enninate into new fronds. 
 
 Only such particulars of the reproductive process in the 
 minor divisions of the order will be noticed here as are 
 illustrative of the main points now under consideration. 
 To beoin with the Confervoideaj — as limited to the ffreen- 
 coloured Algte, both fresh water and marine, which do not 
 conjugate — w^e may take for illustration of the filamentous 
 species, formed by the coherence of cells in linear series, 
 those contained in the genera Sphceroplea, Bulbochwte and 
 CEdogonium, as having been the subjects of the most satisfac- 
 tory observations. Zoospores have been detected only in some 
 of the species, but the occurrence of autherozoids appears to 
 be general. They are developed from special cells, either 
 directly as in Bplia^roplea, or through the medium of a pro- 
 thallial frond or androspore, as in various species of the 
 other two genera. In the latter, according to the observa- 
 tions of Pringsheim, small bodies like zoospores (micro- 
 ponidia) are formed singly in cells, which are smaller than 
 the rest, and present certain other peculiarities. These 
 corpuscules, after their period of activity is over, attach 
 themselves to the neighbourhood of the sporangia, and ger- 
 minate into minute fronds of three cells, one of which serves 
 as a pedicle of attachment, while the other two become 
 antheridia, each maturing an antherozoid of some size. By 
 a peculiar fissuring of the anthericUum, and the formation 
 of a pore or micropyle in the sporangium, the antherozoi<l 
 passes from its own cell to that containing the globular 
 mass of o^erminal matter, in the substance of which it seems 
 
 c 3 
 
34 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 to be absorbed. The mass then acquires a membrane of 
 cellulose on its exterior, and becomes a true spore.* 
 
 In CEdogoniiim, Btdhochocte, and Coleochwte a process has 
 also been observed during the germination of the spore, 
 which might be termed one of protomorphic gemmation. "I* 
 In these, and perhaps also in some other genera, the spore 
 does not germinate at once into a new frond, as in other 
 Algae (Aclilya, Vaucheria, (&(;.j but becomes converted into 
 a sort of capsule containing four bodies, precisely resembling 
 the ordinary zoospores of the plant in their appearance, 
 their motion, and their power of germinating into new 
 fronds. 
 
 The genus Vaucheria may be taken as the type of an- 
 other family ofconfervoid Algse — the Siphoneae — which are 
 sometimes described as unicellular, the filaments having no 
 tranverse septa. The sporangia commence as lateral 
 diverticula, but are afterwards shut off as separate cells. 
 The antheridium originates as a papilla, in close proximity 
 to the sporangial dilatation, and generally precedes it a 
 little in its first development. It ultimately acquires the 
 form of a hooked process, or abortive tendril (" hornlet"), 
 curving over the sporangium. The point of the hornlet is 
 soon converted into a separate cell, and its contents, which 
 had previously become colourless, are then resolved into 
 antherozoids. Perforations taking place subsequently, both 
 at the point of the hornlet, and at the most prominent part 
 of the sporangium, the antherozoids come in contact with 
 
 * Pringslieim's Report to tlie Berlin Academy. See Quarterly Journal 
 of Microse. Science, IV., 131, andEdinb. PLilosopliical Journal, N.S. V., 
 376 (1857). In the species of CEdogonium observed by Mr Carter the 
 antherozoids were not formed in free androspores, but were emitted di- 
 rectly by peculiar short cells, grouped in pairs or clusters of three, and 
 giving a ringed appearance to certain parts of the filament. Ann. Nat. 
 Hist., 2d Ser., XVIII., 81, and 3d Ser., I., 19. 
 
 t Edinburgh Philosoph. Journal, V., 376 (1857). Quarterly Journal of 
 'Microscopic Science, IV., 133. 
 
IN THE VEGETABLE KINGDOM. 85 
 
 the unwalled contents of the latter, which are then converted 
 into a spore, the soft mucous investment being transformed 
 into a consistent cell-wall. 
 
 The latest observations on Vaucheria we owe to Prings- 
 heim,* who has also directed much attention to the corres- 
 ponding processes in AcJilya ( Saproleqnia Kutz.^, a genus 
 really closely allied, though of very different external ap- 
 pearance, the filaments being colourless and much more 
 minute, and growing like a tuft of mouldiness on dead flies 
 and other animal matter macerating in water. The sporan- 
 gium has here the same general relations as in Vaucheria, 
 but their walls are perforated by a great number of pores, 
 and they contain eventually numerous spores. Although 
 no antherozoids have yet been detected, the antheridia 
 appear to be represented by slender vermiform branchlets 
 which arise between the sporangia, and sometimes twine 
 round them in irregular coils. These, according to Pring- 
 sheim, throw out lateral papilla), v;hich protrude into the 
 pores of the sporangia.")* 
 
 Both these genera propagate usually by gemmae de- 
 veloped in the dilated extremities of the branches, which 
 are converted into cells by the formation of transverse septa 
 in the filaments. In Vaucheria the whole contents, when 
 mature, are thrown out through a perforation in the apex 
 of the cell, as one large ciliated spore; mAchlya they break 
 up into a swarm of motile corpuscules like the zoospores of 
 other Algae. It is not ascertained whether the co-existence 
 of these two kinds of reproductive bodies is connected witli 
 any form of alternation of generation ; no phenomena of 
 the kind have yet been observed in this group. 
 
 * Quart. Journ. Micr. Sc, lY., 63, 130. 
 t Braun, Nsegeli, and Karsten supposed that a real conjugation of 
 cells took place in Siphonea; ; but the view founded on the late observa- 
 tions of Pringsheim is now generally received. Achhja, however, is sf ill 
 considered by some as merely the early phase of a true mould or fungns< 
 
86 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 Among the Floridese or rose-coloured algae — a group ex- 
 clusively marine — we find commonly three different kinds 
 of fructification, situated mostly on separate fronds : — 
 
 1. Tetraspores, considered as gemmse by Thwaites, 
 Harvey, Berkeley, and Pringsheim, and consisting of qua- 
 ternary aggTegations contained in receptacles, which are in 
 some cases simply imbedded in the frond. 
 
 2. Antheridia, containing, in special receptacles, par- 
 ticles which have been taken for antherozoids, though desti- 
 tute of cilia, and perhaps also of motile, power. 
 
 8. Conceptacles, containing clusters of sporoid bodies, 
 which are generally regarded as the germs or true spores. 
 
 Pringsheim, however, is inclined to think that the last- 
 - mentioned bodies — at least in some species of Cermnium — 
 are rather gemmse, which develope prothallia for the pro- 
 duction of the real ^'erms, as he has seen them begin to 
 germinate while still in the conceptacle, before any perfora- 
 tion had taken place for the entrance of antherozoids, and 
 observed that the result was an irregular cellular growth, 
 quite different from the ordinary frond. In this view the 
 prothallium, though unisexual like that of (Edogonimn, 
 would differ in representing the opposite sex, bearing not 
 spermatic but germinal particles, whose impregnation would 
 be effected by the rod-shaped antherozoids formed directly 
 on the male frond. 
 
 The constancy of the occurrence of three forms of repro- 
 ductive organs, just noticed on different plants, gives a 
 certain probability to the idea of an alternation of forms, 
 like that occurring in some species of animals — the fronds 
 originating from fertilized germs bearing only gemmse (tet- 
 raspores), which, in turn, would develope other fronds 
 maturing true sexual organs. 
 
 In most of the littoral gToup of fucoids or olive-coloured 
 seaweeds, antherozoids and proper germs have now been 
 detected, generally in separate receptacles on the same 
 
IN THE VEGETABLI^ KINGDOM. 37 
 
 frond. According to the observations of Tliuret on dif- 
 ferent species of Fiicus, impregnation is effected by the 
 simultaneous evacuation of both elements from their re- 
 spective envelopes. During the recess of the tide, -when 
 the tissues contract somewhat by desiccation in the air, the 
 antheridial cells are expelled, as well as the contents of the 
 so-called spores, consisting of eight protoplasndc bodies 
 enveloped in a gelatinous mucus. On being again sub- 
 merged, the antheridia rupture by imbibition, and the 
 antherozoids come in contact with the srerminal bodies. 
 In about twenty-four hours after this, the gelatinous layer, 
 which surrounds each o-erm mass, is converted into a toutrh 
 membrane, in which Pringsheim mentions observing certain 
 red corpuscules, which he considers to be the nuclei of the 
 antherozoids.* Then follows germination — a simple process 
 of cell-formation, resulting in the production of a new 
 frond. In some fucoids, however, the cells first formed in 
 this process separate from one another, being set free by the 
 rupture of the common investing membrane of the spore ; 
 and each of them may give origin to a distinct plant or 
 phytoid. 
 
 Zoospores are now kno^\'n to occur in this group also, but 
 no obvious alternation of forms has ever been observed. 
 
 It would seem, therefore, that the only general conclu- 
 sion in regard to the reproduction of the Algse which, in our 
 present defective state of information, we are warranted in 
 drawing is this : that a sexual act probably occurs normally 
 from time to time in the life-history of all the species, 
 though impregnation has been actually observed only in a 
 few. We know, indeed, that non-sexual propagation prevails 
 to a great extent and in great variety of forms. Not only 
 is there the usual pullulation of new shoots, characteristic 
 of vegetables generally, which is here represented by the 
 
 * Joum. of Micros. Science, IV., 125 (An. Jes Sciences Nut.) 
 
38 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 continued growth and occasional branching out of the frond 
 by the addition of new component cells, but independent 
 fronds are also sometimes produced by detachment of 
 bulbils or other portions of the substance of a pre-existing 
 one ; and, besides this, almost all the species bear more 
 than one kind of sporoid bodies. We are not, however, in 
 a position to say whether, or in what way, spore-gemmation 
 alternates with sexual generation generally throughout the 
 group. We only know that in a few species a gamomorphic 
 porthallium is budded off from the spore for the develop- 
 ment of the reproductive organs of one of the sexes, and 
 that some of the same species (GEdogonimn and its allies) 
 are also the subjects of a sort of gemmation in the proto- 
 morphic stage, as well as certain fucoids — the spores which 
 actually germinate into new fronds being only a secondary- 
 product of impregnation ; while in other cases (some Floridese 
 as Ceramiimi) there are certain theoretical gTounds for sup- 
 posing that the sexual fronds may originate from the tetras- 
 pores of the gemmiparous fronds. 
 
 A few words may be added in reference to the order 
 Characege, on the systematic position of which botanists are 
 not quite agreed. These plants are described by Berkeley 
 as consisting '' of confervoid articulated threads, simple as 
 in Cladophora, or compound as in Folysiphoniar^ In their 
 vegetative axis, therefore, they have quite the organization 
 of the true Algas, and though their reproductive organs are 
 certainly very peculiar, they are perhaps reducible to a mo- 
 dified form of the same general type. Two kinds of fructi- 
 fication are met with in Chara, the nucule and the globule, 
 which are supposed to contain respectively the germinal and 
 spermatic elements. This opinion rests mainly on the de- 
 velopment in the latter of articulated filaments, containing 
 motile ciliated bodies, having a great general resemblance 
 
 * Ciyptogamic Botany, 425. 
 
IN THE VEGETABLE KINGDOM. 30 
 
 to the antherozoicls of the higher Ciyptogamia, for impreg- 
 nation has never been actually observed. The globules of 
 Chara are round red bodies, whose outer Avail consists of 
 eight pieces, each having the form of an equilateral right 
 angled spherical triangle, and consisting of a whorl of cells, 
 radiating from the outer extremity of a perpendicular 
 column. The supporting columns of all these parietal 
 segments arise in the centre of the globule, from an inward 
 prolongation of the footstalk of the organ, and at the same 
 point there are also attached numerous jointed threads, 
 each of the articulations of which produces a spiral anthe- 
 rozoid, with two cilia at its dilated extremity. Mr. Berkeley 
 ingeniously explains the morphosis of the globule as a 
 fascicle of branchlets given oif from the tip of the axis, 
 radiating in eight different directions, and each producing 
 in turn another whorl of branchlets, which, by the co- 
 aptation of their extremities, form the wall of the globule.* 
 
 In connection with this the antheridial threads may be 
 considered as a secondary order of filaments, arising in the 
 axils of the first, and bearing, in their individual cells, the 
 spermatic particles — a view which helps to approximate the 
 fructification to the type of antheridial development among 
 the Algae. 
 
 The co-related organ — the nucide — consists of a central 
 sac filled with starch, and coated by a layer of five elongated 
 cells, wound spirally round it, attached at their bases to the 
 insertion of the footstalk, and free at their tips, where there 
 is an aperture leading into the interior. Morphologically, 
 therefore, the nucule may be looked upon as a whorl of 
 unicellular branchlets, cohering by their edges, but Anthout 
 the secondary fascicles, and the axillary antheridial fila- 
 ments, which give such a complex character to the globule. 
 
 The nucules germinate by the formation of a cell at the 
 
 * Cryptogamic Botany, 127. 
 
40 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 top of the central sac, which developes do^\aiwards into 
 rootlets and upwards into stem.* 
 
 The Characese multiply also by deciduous leaf-buds ; but 
 we are very deficient in observations regarding the develop- 
 ment of this singular group of plants. 
 
 5. § REPRODUCTION IN FUNGI AND LICHENS. 
 
 The Fungi are a large order of aerial cellular plants of 
 low development, intermediate between Algee and Lichens, 
 and passing into both orders by the closest possible affini- 
 ties. In their structure there is generally a very marked 
 distinction between the vegetative tissue and the reproduc- 
 tive organs ; the former, termed the mycelium, is always 
 the most inconspicuous, and frequently escapes observation 
 altogether, being embedded in the soil or basis on which 
 the fungus grows. It consists of a mass of branched con- 
 fervoid filaments, inextricably entangled, and frequently 
 even anastomosing together. 
 
 The vitality and vegetative power of these filaments is so 
 great that even fragments of them will suffice to reproduce 
 the mycelium. Such fragmentary portions are indeed pro-r 
 fusely detached as gemmae in the normal development of 
 the tissue ; and as the particular form and connections 
 of these reproductive bodies vary at different periods of the 
 life-history of the plant, we meet with a great variety of 
 fructification even on the same species ; as many as five 
 different forms are stated, on the authority of Mr Berkeley, 
 to occur in the same species of Erysiphe.^ As the specific 
 identity of these forms, depending on their connection with 
 the same mycelium, may readily escape observation, it is 
 not wonderful that many of them figure as distinct plants 
 
 * Berkeley, Op. Cit., p. 428. Carter in Ann. Nat. Hist., 2d Ser., 
 XVIII., 107. 
 
 t Cryptogamic Botany, p. 78. Quarterly Journal of Microscophic 
 Science, Jan., 1857, p. 51. 
 
IN THE VEGETABLP; KINGDOM. 41 
 
 in scientific works. The conseqnence has been the esta- 
 blishment of a great number of spurious genera and species, 
 and the inextricable confusion of a subiect, involved from 
 its very nature in much perplexity. Thus the numerous 
 species assigned to Sderotium are in reality perhaps none of 
 them proper or autonomous, but only transitory conditions 
 of Fungi already known by other names, such as Peziza, 
 Sphwria, Agaricus, &c., which in maturity differ as widely 
 as can well be conceived.* 
 
 Great progress, however, has lately been made by the 
 researches of MM. Tulasne and others in tracino; out the 
 reproductive process in this group ; and, though we are 
 still far from being in a position to draw positive conclu- 
 sions, there appear to be good gTOunds for the opinion that 
 organs of sexual import are very generally present. There 
 is, indeed, a general agreement as to the male element being 
 represented by the spermatia, minute staff-like bodies, 
 somewhat resembling the supposed antherozoids of the red- 
 spored algae. These particles have no cilia nor any motile 
 powers beyond what may be accounted for on physical 
 principles, and the received views as to their functional 
 import rest less on any positive evidence than on analogy, 
 and on their not possessing any power of germination. 
 They have not been met with, save exceptionally, in the 
 higher Fungi, but have now been very generally detected in 
 other divisions of the order. They are usually attached to 
 filaments which are either associated with the organs 
 bearing the fertile spores, or occupy distinct receptacles."!" 
 
 The true spores, which have been seen to germinate, are 
 developed in the interior of cells, or are attached to their 
 exterior. External or naked spores are met with both in 
 the Hyphomycetes or moulds, and in the higher divisions of 
 
 * Berkeley's Cryptogamic Botany, p. 268. 
 t Tulasne, Comptes Rendus. March 31, 1851. See also AuuaLa of 
 Nat. Hist., 2d Ser., VIII., 117. 
 
42 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 Gasteromycetes and Hymenomycetes. In the first they 
 occur in beaded chains clustered at the ends of filaments ; 
 in the latter they are attached in groups of four to the 
 apices of elongated cells, termed hasidia. When the 
 spores are developed in the interior of cells, the latter — 
 which are termed asci or thecce — have generally the form of 
 elongated pods. They come to maturity at a later period 
 than the spermatia, and then contain a variable number of 
 spores — usually some power of two — arranged in linear 
 series. The presence of spores of this kind (ascospores, or 
 thecaspores) has long been recognized in one large tribe of 
 Fungi, hence called Ascomycetes ; but the researches of 
 Tulasne go to shew that they occur also in other divisions 
 of the order. In the large group of Coniomycetes, including 
 the smuts, and other such like epiphytic parasites, it has 
 been shown that many of those Fungi which produce naked 
 spores are but preliminary stages of species, which, in 
 another phase of development, form spermatia, and spores 
 contained in asci, or at least reducible to that type. Thus 
 the epiphytes, which go under the name of Uredo, are the 
 protomorphic or rudimentary forms of others, hitherto re- 
 ferred to distinct genera, as JEcidium, Phragmidium, Puc- 
 ci7iia, &c. Stilbospora in the same way appears to be a pre- 
 cursor of a form of Sphceria* Mr. Berkeley observes that 
 " it is quite certain that a large portion of the so-called species 
 of Plioma, Leptostroma, Diplodla, Hendersonia, Cytispora, 
 Septoria, &c. are mere cases of dualism ; and the same may, 
 without much chance of error, be predicated of those cases 
 
 * Tulasne, Ann. Nat. Hist., 2d Ser., YIII., 114. Comptes Eend., Mar., 
 1851. Currey in PHlos. Transac. for 1857, p. 548. M. L. R. Tulasne, 
 along with many others, identifies also the following : — Ncemaspora 
 Rihis with Bpliceria Ehrenhergii, Micropera Drupacearuni with 8. Leo- 
 eillei, Asteroma Uhni with Dodithea Ulmi; and he remarks that in 
 Rhytisina every species may be said to have a precursor in a Melasmia 
 (a fungus with acrogenous spores), which play the same part here that 
 Cytispora and its analogues do in regard to the Sphcerias. 
 
IN THE VEGETABLE KINGDOM. 43 
 
 as Dilophosfjorium, Neotkosporium, and Pestalozzia, where 
 the objects are of some interest on account of their curious 
 appendages. All, indeed, are interesting so far as ascertained 
 dualism is concerned, or as far as there may be a prospect 
 of shewing that they are the spermagonia or pycnidia of 
 ascophorous species."* 
 
 This relation of associated fonns may be illustrated by 
 the development of jEcidium. The spores of this fungus 
 produce a mycelium, the filaments of which bear the naked 
 spores of the Uredo, and these, when they come to germinate, 
 originate a second mycelium, in connection with which are 
 developed spermatia and the thecaspores of the JEcidium.^ 
 
 It is possible that in some species without spemiatic 
 fruit particles of a similar kind may be developed from 
 certain of the spores, by an arrangement like that described 
 by Pringsheim in the androspores of (Edogonium, for in the 
 o;ermination of certain funoi it has been observed that 
 while some of the spore-like bodies emit mycelial threads, 
 others give origin to minute corpuscules, which undergo no 
 farther development. These have been conjectured to be of 
 a spermatic nature. J In some species of Peziza, according 
 to Kadlkofer, a process of this kind occurs, w^hile in others 
 the corresponding bodies originate the spermatic particles 
 less directly by the intermediate development of a special 
 spermatiferous mycelium. § 
 
 This may be considered as a sort of alternation of genera- 
 tions ; and it is to be observed that it occurs in the ganio- 
 morphic stage of development, that is, in the maturation of 
 
 * Introd. to Cryptogamic Botany, p. 331. 
 t Tulasne, as quoted before. Sometimes the succession is complicated 
 by other intermediate forms ; thus in the germination of some species of 
 'Erysiplie a succession of mycelial forms are produced from sporoid Iwdies 
 of different kinds, and the series is closed by the development of the 
 sporifcrous theese. 
 
 X Cun-eyin Journal of Micros. Science (April, 1857), pp. 124-12G. 
 § Radlkofer— Ann. Nat. Hist., 2d Ser., XX., p. 217. 
 
44 SURVEY OF THE REPIIODUCTIVE PROCESS 
 
 the sexual elements, in which respect it contrasts with a 
 process of multiplication occurring in some other cases in 
 the protomorphic stage — viz., the binary division and sub- 
 division of the contents of the spore into so many reproduc- 
 tive cells, that the original spore becomes itself a sort of 
 secondary theca. All these derivative cells may germinate, 
 and in some cases they do so simultaneously, sending out 
 their mycelial filaments through the outer or common wall, 
 so as to give the composite spore somewhat the appearance 
 of an insect with its legs extended on each side of its body.* 
 As might be expected, an isolated fragment of such a com- 
 pound spore still retains the power of germinating. 
 
 In illustration of these statements the development of 
 the ergot-fungus may be referred to, as explained by 
 Tulasne and others, though some points still remain to be 
 cleared up, for the completion of its history, and the har- 
 monizing of the accounts of different observers. The fungus 
 originates as a mycelial gro'wth in the ovary of the rye or 
 other grass which it attacks, and soon matures its conklia 
 or naked spores, on the ends of filaments. These have 
 been observed by Tulasne to germinate and become elon- 
 gated into new filaments, which appear to be concerned in 
 the formation of the dense fibro-cellular stroma of the 
 proper ergot-growth (sclerotium). This gradually acquires 
 the form and dimensions which have led to the grain 
 affected receiving the name of " spurred rye." The ergot- 
 growth, when shed and exposed to moisture, gives origin to 
 a small club-shaped fungus, to which the name of Claviceps'f 
 has been given, and which is identical with a species known 
 to botanists as Sphceria purpurea. This developes on the 
 surface of its globular heads numerous small cavities or 
 conceptacles, with thecse in their interior, which bear spores 
 
 * Currey in Quar. Jour. Micr. Sc, IV., 200 ; also April, 1857, p. 122. 
 t Cordycejys or Cordyliceps of Fries. 
 
IN THE VEGETABLE KINGDOM. 45 
 
 in the usual way. The sporoid bodies, when they gain 
 access to the flower of the rye, develope the fungus- 
 gTowth, from which the ergot originates in the way de- 
 scribed.* 
 
 The point of greatest difficulty is the determination of 
 spermatic organs. Spermatia do not seem as yet to have 
 been detected in connection with the sphieria-growtli. 
 Leveille and others appear to regard the conidia as " fer- 
 tilizing organs ;" but besides that this is not consistent with 
 Tulasne's observations of their germination, the wide inter- 
 val between them and the spores is of itself opposed to 
 such a view. 
 
 The highest group of Fungi is the one in which our know- 
 ledge of the reproductive process is as yet the least satis- 
 factory. Spermatia have been met with only exceptionally 
 — as in Tremelline^e"!* — and proper thec?e, as it would seem, 
 not at all. The characteristic fructification consists of naked 
 spores borne in clusters of four, as described already, on 
 elongated cells termed basidia, which in the Hymenomycetes 
 occupy some part of the exterior surface of the proliferous 
 receptacle — as we see in the gills of the common mushroom 
 — while in the Gasteromycetes they are developed from the 
 lining membrane of an internal cavity of which we have an 
 example in Bomsta or the puff ball. In this case the spores 
 
 *' Comptes Rendus. Dec, 1851, and Seq. Ann. des Sciences Nat., 
 3d Ser. XX., p. 553. Annals of Nat. History, 2d Ser. IX. 494. Com- 
 pare the account in the Micrographical Dictionary. 
 
 + lu some of this group, according to Radlkofer, the hymeni'um or 
 fructifying surface bears spermatia, and basidia crowned with spores like 
 those of agarics. This occurs in Tremellamesenterica. In others, as 
 Dacrymyces deZ-igatescenSjwehaveinthe same position multilocular spores, 
 all of like aspect, but some acting as aijdrospores, and originating in ger- 
 mination spermatiferous pedicels ; while others, representing apparently 
 the opposite sex, emit mycelial filaments. Annals of Natural HietorTk-, 
 2d Ser., XX., 247. See also Berkeley's Introduction to Cryptogamic 
 Botany, p. 350. 
 
46 SURVEY OF THE REPEODUCTIVE PROCESS 
 
 when ripe escape by special apertures, or by the general 
 breaking up of the cyst. The basidia wdth their quaternate 
 spores have certainly much more the character of a gemmi- 
 parous fructification, such as the stylospores of the lower 
 Fungi or the tetraspores of the Floridese, than of impregnated 
 germs, such as the spores produced in thecse are presumed 
 to be ; so that in these plants — though they seem to stand 
 at the head of their own type of vegetation — the only 
 obvious reproduction is of a non-sexual kind. It remains for 
 future investi2;ation to decide whether sexual oroans exist 
 at all, or what may be their relations ; whether the spores, 
 like those of the ferns, originate androgynous prothallia, or 
 whether the stool of the mushroom, like the capsule of the 
 moss, is itself the result of a process of impregnation, 
 effected by organs standing in some more immediate rela- 
 tion to the mycelium, which have not yet been detected. 
 That an *' alternation" of some kind prevails the analogy of 
 other Fungi would lead us to anticipate. 
 
 In the group of Hyphomycetes also, which presents one 
 of the lowest types of fungoid growth, containing the various 
 forms of mould and mildew, spermatia, and spores fecun- 
 dated by them have not yet been generally recognized. But 
 there are grounds for believing that many of these vegeta- 
 tions are not true or autonomous species, but, like the 
 forms of Coniomycetes before noticed, merely states of the 
 mycelium of other species, bearing a secondary kind of 
 fructification. Thus Aspergillus has been observed by Bary to 
 yield a form of Eurotium ; Fusarium is known to develope 
 a species of Peziza ; the genera Tuber cularia and Myrioce- 
 phalum appear to be mere precursors of species of Sphceria ; 
 and Oidium is admitted generally to be only an early con- 
 dition of ErysipJie* Others of these rudimentary forms of 
 organization, it is possible, ought rather to be referred — 
 
 * Berkeley Op. Cit., pp. 248, 292, 300, 330. 
 
IN THE VEGETABLE KINGDOM. 47 
 
 along mth the lower algoid forms, with which they have 
 close affinities — to the group of Protophyta. When the 
 mycelium originates, as is frequently the case, in a watery 
 fluid, it so precisely resembles the filamentous gTowth of 
 some of the algoid Protophyta, that we find many of them 
 described as such in botanical works. Thus the white- 
 felted mass, which is apt to form in ink, is described as an 
 Alga under the name of Hygrocrocis atramentl, but if its 
 progress be watched, it is clearly seen to be only the sub- 
 merged mycelium of some common form of mould, and it is 
 the same with the so-called " vinegar plant." The charac- 
 teristic fructification appears only on those branches which 
 emerge fi'om the fluid, and generally consists of naked 
 sporules attached in various fashions to the ends of elon- 
 gated filaments. Even the genus AcJilya, commonly re- 
 garded as a well-established alga, and having certainly 
 many points of analogy with Vaucheria, as already noticed,* 
 is regarded by Berkeley as only a fluid-born mycelium of 
 Miicor, a well-kno-vvn variety of mould. "f* This view is 
 hardly reconcilable with the presence of sexual organs in 
 Achlya, which the researches of Pringsheim seems to indi- 
 cate. It is to be remarked, however, that these observa- 
 tions do not actually demonstrate the existence of sper- 
 matic particles in the organs, which, from their analogy 
 with those of Vaucheria, he was inclined to consider as 
 antheridia. 
 
 If any of the group of Fungi now referred to are rightly to 
 be considered as allied to the Protophyta, we should look for 
 some modification of conjugation, either in the submerged 
 or the aerial filaments ; and it is so far in support of such a 
 
 * V. Infra., p. 108. 
 t Berkeley's Cryptogamic Botany, pp. 132, 145, 295. The authors of 
 the Micrographic Dictionary mention (Art. Mucor) that their experi- 
 ments have hitherto afforded only negative results. 
 
4:8 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 ^ 
 
 iew, that a process of this kind is kno\\Ti to occur in the 
 genus Syzycfites, a mould common on decaying agarics.* 
 
 The order of the Lichens may be noticed here on account 
 of their close analogy to the ascophorous Fungi in their 
 organs of fructification. The reproductive organs, known 
 under the name of apothecia, have long been recognised ; 
 they have generally the appearance of shield-like discs of a 
 different colour from the rest of the frond or thallus, and 
 contain sporiferous thecse, intermingled with filiform or 
 clavate processes (abortive thecse), termed poraphyses, both 
 placed in a perpendicular position, and forming the coloured 
 layer of the apothecium. The co-related organs are of later 
 discovery, and are termed spermagonia. They consist of 
 small cavities in the thallus, indicated externally by puncti- 
 form apertures, serving for the emission of the spermatia, 
 which exactly resemble those of Fungi, and are produced 
 like them on the ends of filaments projecting from the walls 
 of the cavities.*!* 
 
 Besides these two forms of fructification many Lichens 
 possess other minute organs, called pycnidia, outwardly 
 resembling spermagonia, but containing corpuscules termed 
 stylospores, which differ from spermatia in being usually 
 oval or pyriform, hollow, and of large size — that is, alto- 
 gether more like spores. In some species (as Scutula and 
 AhrotJialliis) these pycnidia seem to replace the spermagonia, 
 on v/hich account, and from the existence of certain inter- 
 mediate forms, Dr Lindsay is inclined to consider them as 
 modifications of these organs. J But as organs kno-vvn as 
 pycnidia co-exist in certain Lichens with spermagonia of the 
 ordinary character, and in some cases yield corpuscules 
 
 * Griffitli & Henfrey's Micrograph. Diet., p. 626. Berkeley's Crv-pto- 
 gamic Botany, p. 295. 
 
 t Tulasne Comptes Eendus. March 24', 1851. Ann. Nat. Hist. N.S., 
 YIII., 114, XXXII., 427. 
 
 X Quarterly Joum. of Micros. Science (Jany., 1857) p. 53. 
 
IN THE VEGETABLE KINGDOM. 49 
 
 capable of germinating, the stylospores, in these cases at least, 
 appear rather to be — like the bodies of the same name among 
 fungi — a secondary form of spores.* They seem to occur 
 with greatest frequency in species most allied to the Fungi. 
 
 In many Lichens we find yet another form of organs, which 
 are undoubtedly of a gemmiparous kind ; these are the sore- 
 dia, little pulverulent masses of the green cells termed goni- 
 dia, of which, generally throughout the order, a stratum is 
 interposed between the medullary and the upper cortical 
 layer of the thallus. The beaded filaments formed by these 
 gonidia are probably the only organic pecuUarity which se- 
 parates the order of Lichens from certain tribes of Fungi, for 
 between these two orders we find a great general similarity, 
 both in the parts of fructification, as now noticed, and in the 
 structure and disposition of the tissues. In both we have a 
 primordial structure or substratum of confervoid filaments, 
 kno^^^l as the mycelium of the fungTis, and the hypothallus 
 of the lichen ; in both also we have generally, but by no 
 means universally, a more compact tissue — the hymenium or 
 crust — developed subsequently to the other, and in more 
 immediate connection mth the organs of reproduction. 
 
 No phenomena of the nature of alternation are as yet 
 known to occur among Lichens. 
 
 § 6. REPRODUCTION IN HEPATIC^ AND MOSSES. 
 
 These orders introduce us to that hidier division of the 
 Cryptogamia, which is characterized by the formation of a 
 leafy axis. Such an axis first appears in the section of the 
 Hepaticse represented by Jungermannia ; it is universal in 
 mosses, and attains its maximum development in ferns, 
 where it is constituted in part of fibrovascular tissue, while 
 it is entirely cellular in the lower forms. 
 
 * Dr. Lindsay in Edin. Plulos. Joum. (July, 1859), p. 124. 
 
 D 
 
50 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 As reproductive organs, both Hepaticse and mosses bear, 
 on the same or on different plants, certain correlated struc- 
 tures, termed antheridia and pistilUdia, and performing the 
 same sexual functions as the anthers and pistils of the 
 higher plants. They are frequently surrounded by a leafy 
 sheath, or a circle of leaf-scales, termed \\\q perichwtium, and 
 are either immersed in the cellular tissue of the receptacle, 
 or attached to its surface, or raised on a peduncle. 
 
 The antheridium is a small club-shaped process, which 
 contains in its distended extremity minute cellules, each 
 enclosing an actively moving filament or antherozoid. The 
 pistillidium, or archegoriium again, consists of cells built up 
 into a flask-shaped structure somewhat resembling the pistil 
 of a flower, with a dilatation like an ovaiy at its base, con- 
 taining a peculiar central corpuscule. Through the canal 
 in the apparent style some of the antherozoids seem to gain 
 access to the corpuscule, and the latter on fecundation de- 
 velopes, by endogenous formation, a whole mass of cells 
 which eventually assume, by a process of transformation, 
 in the course of growth, the form of the theca or capsule. 
 In mosses this organ, with its seta, calyptra, operculum, 
 and columella, has rather a complicated structure ; in 
 Hepatic?e it is simpler, but in all cases alike its internal 
 cellular tissue developes a mass of dust-like spores. In the 
 frondose Hepaticae the spores germinate at once into the 
 lobed expansion of gTeen parenchpna, constituting the 
 typical form of these plants, but in those species which have 
 a true axis, and in mosses, the germination first gives origin 
 to confervoid threads, which, after ramifying into a mass of 
 tangled filaments, termed the protonema,^ send up here and 
 there a leafy axis, bearing eventually like the original one 
 antheridia and archegonia. 
 
 This development of the fecundated germ into the organ 
 
 * Once ranked as an alga under the name of Bysms. 
 
IN THE VEGETABLE KINGDOM, 51 
 
 known as the " fruit" — which, whether more or less compli- 
 cated, has always this remarkable peculiarity, that it is an 
 apparatus for the multiplication of gemiinating particles or 
 vspores — has been compared by some authors with altematioTi 
 of generation. The analogy may at first appear far fetched, 
 as there is no actual separation of parts, the new structure 
 seeming as much an appendage of the original leafy axis, 
 as the fruit is of any phaenogamous plant, yet closer inves- 
 tigation will certainly show a real community of nature 
 between the two processes. As this point, however, will 
 again come under consideration, no farther reference need 
 be made to it at present than to remark that in this case 
 two of the stages of development, which were distinguished 
 in the last chapter, are very distinctly marked : — 
 
 1. That termed protomorphic, immediately following the 
 fertilization of the genu, by which are fonned the " fi'uit" 
 and the derivative spores. 
 
 2. That termed orthomorphic, which consists in the de- 
 velopment from the latter of the typical plant, bearing in 
 turn new reproductive organs. 
 
 The point mainly to be observed is this, that the fecun- 
 dated germ is not at once developed into the typical plant, 
 but into an intermediate form known as " the fruit," in 
 which numerous spores are formed. These spores, in ger- 
 mination, give rise to the typical form, either directly or 
 through the intervention of a filamentous protonema, and 
 the typical frond or axis bears the reproductive organs, witli 
 the sexes, sometimes united, sometimes separated. In 
 general the orthomorphic form is much more conspicuous 
 than the protomorphic. Buxbaumia is perhaps an excep- 
 tion, as the axis which supports the archegonium and after- 
 wards the capsule is here represented only by a tuft of 
 minute scales. The protonema is perhaps best regarded as 
 a second link in the series of forms marking the proto- 
 morphic stage. 
 
 D 2 
 
52 SURVEY OE THE REPRODUCTIVE PROCESS 
 
 For the normal fructification of mosses a certain dryness 
 and insolation are required. In a moist and gloomy 
 atmosphere the stems, instead of bearing fruit, are con- 
 verted into leafy shoots, from which other like shoots may 
 be budded oif, the pullulation being continued indefinitely, 
 and the development of fructification postponed, till some 
 chano:e occurs in external circumstances. For a time the 
 pullulations continue in adhesion to the parent stock, 
 forming a ramose vegetation, but the common axis being of 
 a perishable nature they are eventually set free by its 
 decay. In this way even mosses which rarely fructify 
 may extend themselves very widely, rivalling, as has been 
 remarked, the largest forest trees, both in the space covered 
 by their derivative phytoids, which physiologically are 
 parts of themselves, and in their aggregate longevity. 
 Free gemmee, also, which are detached at once to form 
 new plants, are not uncommon, both among mosses and 
 Hepaticse. 
 
 § 7. REPRODUCTION IN FILICES AND EQUISETACE^. 
 
 In these orders we have antheridia and archegonia, 
 bearing a general resemblance to those of mosses ; they 
 are not formed, however, in connection with the leafy axis, 
 which bears only the gemmae known as spores, but in 
 minute detached parenchymatous phytoids, termed pro- 
 thallia, into which the spores germinate, and from which 
 the embryo emerges as the result of impregnation. 
 
 Two views may be taken of the homologies subsisting 
 between these plants and the mosses. A physiological 
 correspondence being admitted by all between the gemmi- 
 parous production of spores in both cases on the one hand, 
 and the formation of antheridia and archegonia on the 
 other, some eminent cryptogamists — as Hofmeister and 
 
IN THE VEGETABLE KINGDOM. 53 
 
 Sanderson* — would argue from this a homology between 
 the structures standing in the most direct relation to these 
 processes — that is, between the foliaceous axis of the moss 
 and the prothallium of the fern, as the parts which bear 
 the sexual elements ; and again, between the leaf-bearing 
 stem of the fern and the thcca of the moss, as immediately 
 derived from the impregnated germ, and as originating the 
 succeeding phase by a gemmiparous process (the formation 
 of spores). Without at present entering into any argu- 
 ments of a general nature on the correctness of this view, 
 it may be simply remarked that the prima facie aspect 
 suggests rather a homology between the leaf-bearing stems 
 in the two orders, in which case we should ascribe the 
 different relations between them and the reproductive 
 organs to the interposition of a process of gemmation at 
 different periods of the genetic cycle — that is, just before 
 impregnation in the fern, and immediately after it in the 
 moss. Not that the resemblance is merely of a prima facie 
 kind. In some respects it grows upon us the more we con- 
 template it, for the persistent character of the leafy axis of 
 the moss, and its frequently yielding many successive sets 
 of sporiferous capsules, assimilate it, independently of struc- 
 tural features, rather to the stem of the fern than to its 
 prothallium, which is an organ even more evanescent than 
 the capsule of the moss, its existence terminating when tlie 
 embryo formed in it has begun to germinate.'f In this 
 view the gamomorphic stage, which is not represented in 
 mosses farther than by the formation of antheridia and 
 archegonia as mere appendages of the typical axis, embraces 
 in ferns and Equiseta the development and dispersion of 
 spores, and their germination into prothallia bearing the 
 sexual organs, either in different phytoids, as is generally 
 
 * Veget. Ovum, in Cyc. Anat. and Pliys., Vol. IV. 
 t Jenner in Edin."Pliilos. Journal, N.S. III. 2G9, Radlkofer, Annals 
 Nat. Hist. 2d Ser. XX. pp. 211, 314, 439. 
 
54 SURVEY OF THE REPRODUCTI\^ PROCESS 
 
 the case in the latter order, or in the same one, as is the 
 common rule in ferns. On the other hand, the proto- 
 morphic stage, which is so much protracted in Hepaticae, 
 and still more in mosses, is represented in ferns only by the 
 confervoid chain of cells, termed the suspensor, which is the 
 first result of the development of the impregnated germ, 
 and at the farther end of which the embryo is formed. 
 
 In both groups the impregnated archegonial cell germi- 
 nates while still within its receptacle, so that the resulting^ 
 growth has the appearance of being simply an expansion of 
 the structure immediately preceding ; thus the theca^ of the 
 moss simulates a mere out-gTOwth from the parent axis, 
 while the prothallium, which is also really the parent of the 
 fern-stem, has been described as its primordial leaf or 
 cotyledon, from its resemblance to that organ in the higher 
 plants ;* for as the embryonic structure advances, it sends 
 downwards rootlets into the earth, and upwards a fern 
 stem — the centre of growth still remaining in the prothallial 
 frond. 
 
 The continuity of the organization is not broken in upon 
 by any act of the nature of " seeding," till the dispersion of 
 the spores. These particles, though physiologically equi- 
 valent in the two groups — inasmuch as in both they are 
 a*g^exual gemmae, and not the direct products of impregna- 
 tion — thus come to have very different homologies ; for 
 they belong in one case to the protomorphic stage, and 
 germinate more or less directly into the leafy axis, while in 
 the other they are gamomorphic gemmse from that axis, 
 and develope the prothallium or sexual phj^oid. 
 
 On the assumption of the line of homology now indicated, 
 we may establish a parallel between the separate fern-fronds 
 and the leafy shoots of the moss — observing that in both 
 orders alike, free gemmae are occasionally detached for the 
 
 * Carpenter Compar. Phys. 4tli Ed., p. 507, Note. 
 
IN Till] VEGETABLE KINGDOM. 55 
 
 multiplication of the plant — and we may farther compare 
 the sporangia of the former to the perichsetial involucre of 
 the latter, both being modifications of the prevailing type 
 of leaf-development. This is obvious in the moss, and it 
 is indicated also in ferns by the circinate development both 
 of fronds and sporangia, as well as by the occun'ence of 
 certain transitional forms, like those through which the 
 ordinary leaves of Blechnum and Osmunda are depauperated 
 into the spikes of fructification, or like the leaf-shoots which 
 in some of the " viviparous" species take the place of the 
 sporangia themselves.* In Equisetum, too, we can trace in 
 the concentric arrangement both of the sporangia and their 
 peltate receptacles, a marked relation to the general type of 
 the whorls of primary and secondary branches, which repre- 
 sent the leaves — a relation of the same general character as 
 that already noticed in the organs of Char a. 
 
 § 8. LYCOPODIACE^ AND RHIZOCARPEtE. 
 
 The Lycopodiaceae of the present epoch are a group of 
 plants intermediate in habit between mosses and fenis. 
 They resemble the former in their prostrate and ramose 
 growth, and their minute scale-like leaves, while their 
 affinity to ferns is indicated by the fibro-vascular system 
 of the stem, and by the spores of the cauline fructifica- 
 tion not being the result of any prior act of impregna- 
 tion. In their process of reproduction they depart ^videly 
 from mosses, and occupy a position in some respects inter- 
 mediate between ferns and phanerogamic plants. But the 
 process has not been satisfactorily traced out, except in 
 Selaginella and Isoetes, which differ from the rest of the 
 order in having two kinds of spores, a lesser and greater, 
 termed respectively mic7'ospores and macrospores. The 
 
 * Lindley Veget. Kingdom, p. 75. 
 
5G SURVEY OF THE REPRODUCTIVE PROCESS 
 
 former are antheridia, containing cellules in the usual way, 
 each with an antherozoid in its interior ; but these are not 
 developed for a considerable time after the shedding of the 
 spore. In about the same time the macrospore developes 
 in its interior a prothalhal layer, containing archegonia, in 
 one of which the central corpuscule becomes converted into 
 an embryo, the access of the antherozoids for impregnation 
 being effected by the rupture of the spore-coats. In its 
 small dimensions and internal position this prothallial layer 
 presents an evident approximation to a structure presently 
 to be noticed in certain phanerogamic ovules. 
 
 The first development of the impregnated germ is into 
 the cellular suspensor. This grows downwards through the 
 substance of the prothallium into the general cellular con- 
 tents of the spore, and at its farther end the proper embryo 
 is formed. By a change in the direction of gro^vth the 
 latter emerges from the spore, sending upwards a leafy 
 axis, and emitting radicles from below, much in the manner 
 of the embryo of a true seed. The axis increases by lateral 
 pullulations, all assuming a prostrate position, and emitting 
 rootlets as they creep along. Eventually they become inde- 
 pendent phytoids by the decay of the first formed portion 
 of the stem. The fructification is generally in distinct 
 shoots, w^hich assume the form of vertical spikes, with the 
 leaves more closely imbricated, and bearing the sporangia 
 in their axils. 
 
 In the small order of Marsileacese or Rhizocarpeae, con- 
 taining a few aquatic plants, the general character of the 
 reproductive process is much the same as in Lycopodiaceae. 
 The two kinds of spores are contained in separate capsules 
 within the same multilocular receptacle, termed a sporocarp. 
 The process of germination comes still nearer to that of 
 Phanerogamia than in the case just described, for provision 
 is made for the entrance of the antherozoids, and the exit 
 of the embryonic axis, not by the simple rupture of the 
 
IN THE VEGETABLE KINGDOM. ■ 57 
 
 spore-coats, but by a regular aperture or micropyle, evi- 
 dently corresponding with the perforation so named in tlie 
 coats of the ovule. No such aperture is required in the 
 lower orders, where the archegonia are either naked as in 
 mosses, or merely sunk in the surface of an exposed pro- 
 thallium as in ferns. The pore going by this name in the 
 sporangial cell of an Alga corresponds rather to the arche- 
 gonial canal, than to the micropyle of these spores, or of 
 true seeds.* 
 
 § 9. REPRODUCTION IN THE GYMNOSPERMOUS PHANEROGAMIA. 
 
 The group of plants now known as Gymnospermete, in- 
 cluding the Coniferse and their allies, agree with the other 
 Phanerogamia in the general character of the reproductive 
 process — that is to say, the ovules which contain the germi- 
 nal bodies are formed and matured in connection with the 
 parent plant, and are fertilized by the action of pollen 
 grains produced in anthers, which grow on the same or on 
 different individuals, according as the monoecious or dicecious 
 aiTangement prevails in the species. At the same time 
 they present some interesting peculiarities, which indicate 
 an approximation to the process as performed in the higher 
 Cryptogamia. The characteristic feature of the fructifica- 
 tion is that the carpels which bear the ovules are not folded 
 so as to enclose them, but merely bear them on their mar- 
 
 * The first discoverers of the prothallial structures of the higher Cr\']'>- 
 togamia were Nageli, Munter, and Suminski. A notice of the lat( r 
 writers is given by Professor Heufrey in the Annals of Natural History, 
 2d Ser., Vol. IX., p. 441. Hofmeister is the best known. An English 
 edition of his works was announced some years ago, but has not yet ap- 
 peared ; it is understood, however, that the Ray Society has it in con- 
 templation. A general survey of the reproduction both of Cryptogamic 
 and Phanerogamic plants is given by Dr. Sanderson in the C3'clopf d a of 
 Anatomy and Physiology, Art. " Vegetable Ovum.," Vol. IV., p. 211. 
 (Part XLV. March, 1855.) 
 
 D 3 
 
58 SURVEY or THE REPRODUCTIVE PROCESS 
 
 gins, so as to leave them exposed, and allow impregnation 
 to be effected by the direct contact of the pollen grain with 
 the aperture of the coats at the apex of the nucleus, known 
 as the micropyle. 
 
 The two coats and the nucleus of the ovule evidently 
 correspond to the double-wall and cellular contents of the 
 spore of the Rhizocarps, but it is in the development of a 
 peculiar intra-ovular structure — the Albuminous body — 
 that the principal interest of the comparison lies. It ori- 
 ginates as a simple cell, but as it enlarges it generates in 
 its interior a cellular mass, which may be held to repre- 
 sent the prothallium of the Cryptogamic spore. In its 
 substance are subsequently developed two or three minute 
 capsular bodies — the Corpuscula of Brown — each sur- 
 mounted by a crown of four cells, like those forming the 
 neck of the archegonium of the spore. The Corpuscula 
 contain minute cell-like bodies, the one at the base corres- 
 ponding to the germ cell of the archegonium, as well as to 
 the " germinal" or " embryonal" vesicles of other ovules. 
 Concomitant with this are the changes affecting the pollen 
 grains, which, though they present certain peculiarities in 
 Gymnospermeae, are formed, as in other Phanerogamia, 
 ^vithin a modified leaf or anther, by the quaternary division 
 of the contents of the central cells of the parenchyma. 
 From the exposed condition of the ovule in the Coniferge, 
 the grain finds direct axis to the micropyle, but it lies 
 there for some time before it protrudes the pollen tube. 
 
 Schacht has observed that this outgrowth is connected 
 with a process of cell-development in the interior of the 
 grain, though he is not inclined on this account to allow 
 any analogy with the antheridial cellules of the Crypto- 
 gamia. In the pollen tube he admits only the presence of 
 free protoplasmic particles and starch grains.* Other 
 
 * Vegetable Auat. Pliys. (Currey), p. 172-180. 
 
IN THE VEGETABLi: KINGDOM. 59 
 
 authors, however, assert tlie existence of free cells in this 
 situation, at least in certain families, as the CupressinccX'.* 
 Hofmeistet in particular mentions the formation of cells in 
 the dilated extremity of the pollen tube, by a process of en- 
 dogenous multiplication. The last formed cells contain 
 granules, along wth minute vesicles, which may be the ulti- 
 mate stage of the granules, and fusiform particles, which 
 are perhaps originally the nuclei of the vesicles, and which 
 somewhat resemble the spermatia of Lichens and Fungi. "f* 
 
 The Pollen-tube, after insinuating itself into the tissue 
 of the nucleus, has its growth arrested in some species 
 for a w^hole season, and only recommences its progress when 
 the " Corpuscula" are fully matured. It then penetrates 
 through the overlying stratum of the nucleus, and through 
 the wall and upper stratum of the albuminous body. Im- 
 pinging finally on the summit of one of the Corpuscula, it 
 displaces the rosette of cells here situated, and either sends 
 down a process into the Corpusculum by invaginating its 
 wall, or becomes merely flattened out over its summit, no 
 aperture being formed either in the wall of the cavity or in 
 that of the pollen tube. After this the germ cell at the 
 base of the Corpusculum resolves itself, by a process of di- 
 vision and sub-division, into a group of eight cells, the four 
 lower being the rudimentary embryos — of which, however, 
 all but one abort — while tlie four upper become elongated, 
 by a continuance of the sub-division, into so many cellular 
 filaments or suspensors, whose grow^th pushes down the 
 embryos — as in the spore of the Rhizocarps — into the un- 
 derlying stratum of the nucleus. 
 
 This development in the ovule, the whole of which takes 
 place while it is still attached to the tree, occupies a very 
 long time, many Conifers not ripening their seeds till the 
 next year after flowering. The fall of the seed arrests the 
 
 * Micrograpbic Dictionary, p. 518. 
 t Annals of Nat. Historj-, 2a Ser., XIV., 427. 
 
60 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 development, but it is renewed in germination by the up- 
 ward gro\\i;h of one of tbe embryos, and tlie consequent 
 emergence of the plumule and radicle of the young plant, as 
 in the case of other seeds. 
 
 This sketch of the reproductive process in the Coniferae 
 will suffice to show its leading relations, both to the other 
 Phanerogamic orders and to the Cr^^togamia. 
 
 The main points of agreement mth the latter are : — 
 
 1. The nakedness of the ovule at the time of im- 
 
 pregnation. 
 
 2. The develoj)ment in its interior of the albumi- 
 
 nous body and corpuscula, representing the 
 prothallium and archegonia. 
 
 3. A certain amount of cellular development inside 
 
 the pollen grain. 
 
 4. The arrest in the development of the pollen 
 
 tube, which divides it into two stages, admit- 
 ting of comparison with the maturation and 
 emission of the microspore, and the subsequent 
 evolution and discharge of antherozoids from it. 
 
 The points again in which the Coniferse depai't from all 
 Cryptogamic, and agree ^ith other Phanerogamic plants, are 
 principally the following : — 
 
 1. The adhesion of the ovule to the parent plant 
 
 till after impregnation and the formation of 
 the embryo. 
 
 2. The lapse of time between the formation of the 
 
 embryo and its evolution in germination ; this 
 is the period of the latent life of the seeds, 
 during which their fall and dispersion take 
 place. 
 8. The substitution of fo villa in a pollen tube, in 
 
IN THE VEGETABLE KINGDOM. 61 
 
 the place of free antlierozoids, as the medium of 
 impregnation. 
 
 The first of these points of difference is that which gives 
 its most obvious cha,racter to the reproductive process — ^just 
 as among Cryptogamia the feature most obviously distin- 
 guishing the Ehizocarps is the absence of an external pro- 
 thallium, which is tantamount to the suppression of one ()f 
 the two germinations (prothallial and embryonic) under- 
 gone by the fern spore. This maturation of the embryo in 
 situ, of course, affects the position of the breach of con- 
 tinuity of organization, or the dissemination of the plant — 
 the severance of the new generation from the old. It 
 transfers it from the place occupied in the higher Crypto- 
 gamic orders — the early part of the gamomorphic stage — 
 to the interval between the protomorphic and orthomorphic 
 stao;es ; or rather to the commencement of the latter, for 
 the embryo is already fashioned in most species before the 
 seed is shed. But in the Coniferse, besides this, which may 
 be called the great breach of continuity, there is a lesser 
 one — the shedding of the pollen, which affects only the 
 male element. Here, as elsewhere, this, of course, occurs 
 prior to impregnation. 
 
 § 10. REPRODUCTION IN THE ANGIOSPERMOUS PHANEROGAMIA. 
 
 The vast majority of the plants of the present epoch be- 
 long to this gTOup, and principally to its higher or dicotyle- 
 donous division. The reproduction is throughout by pollen 
 grains and ovules, but both, and particularly the latter, differ 
 considerably from those of the Gymnosperms. 
 
 The carpellary leaf, instead of merely supporting the 
 ovule, is wrapped round it to form a germen, generally of 
 a more or less flask-shaped figure, with a neck or style re- 
 sulting from the rolling up of its distal portion, and termi- 
 
62 SURVEY OF THE REPrtODUCTlVE PROCESS 
 
 nating in a stigmatic point denuded of cuticle. All direct 
 contact of the ovule and pollen gTain is thus prevented, and 
 impregnation is effected by the grains adhering to the 
 stigma, and from that sending do\vn their tubes, through 
 the lax tissue of the canal of the style, into the micropyles 
 of the ovules in the germen below. No process of cell- 
 formation has been observed in the interior of the pollen 
 grain, and it is probable that its first protrusion is due 
 simply to an endosmotic action, causing the contents — en- 
 sheathed in the extensible inner wall — to be protruded in 
 finger-like processes through perforations at points where 
 the outer cellulose coat has given way. But the farther 
 advance of the tube must be effected by a proper growth, 
 for its extension soon comes many times to exceed the size of 
 the grain from which it was emitted. The ovule consists 
 at first of a cellular nucleus, round which a double coat 
 grows up, leaving only at the apex the pore termed the 
 micropyle, and within which a cell cavity or embryo-sac is 
 afterwards formed. This sac acquires much greater size in 
 some cases than in others, and occasionally protrudes from 
 the micropyle in the form of an " ovule-tube.* It contains 
 only a semifluid granular matter, or at most a mass of very 
 delicate cells. Among the contents, however, are generally 
 seen two or three particles more conspicuous than the 
 others, which have received the name of " germinal vesicles," 
 but which some observers consider to be mere unwalled 
 masses of protoplasm. "f* Unlike the germ cell of the Coni- 
 ferae, which lies at the bottom of the " Corpusculum," they 
 occupy the space near the apex of the embryo-sac. The 
 precise relations between the point of the pollen-tube and 
 the embryo-sac were for some time the subjects of much dis- 
 cussion. Schleiden, Geleznoff, De Bary, Wydler, Schacht, 
 and Tulasne, maintaining either an introversion or perfora- 
 
 * Dr. Dickie, Ann. Nat. Hist., N.S., I., 260. 
 f Giiffith & Henfrey, Micr. Diet., p. 482. 
 
IN THE VEGETABLE KINGDOM. 63 
 
 « 
 
 tion of the sac, and the formation of the embryo from a 
 process of cell-formation in the extremity of the pollen 
 tube, while other botanists of note did not admit more than 
 an intimate contact between the extremity of the tube and 
 that of the embryo-sac. 
 
 The controversy may be said to be now mere matter of 
 history, the former view having latterly been abandoned by 
 its most distinguished supporters — Tulasne, Schleiden, and 
 Schacht.* It seems to have arisen from the suspensor of 
 the embryo having been mistaken for, or confounded with, 
 the extremity of the pollen-tube. As it would appear, 
 therefore, that there is no perforation either of the embryo- 
 sac or of the pollen-tube, such commixture of their con- 
 tents, as may be necessary for impregnation, must be held 
 to depend on the transudation of the fo villa through the 
 interposed membranes into the sac, in which it is now ge- 
 nerally admitted that the embryo is developed, out of one of 
 the contained "germinal vesicles." Impregnation through 
 interposed membranes is certainly not according to the ge- 
 neral analogy of the reproductive process, but it were prema- 
 ture to assert that it does not occur in other divisions of 
 organic nature."!* The " germinal vesicle" which has under- 
 gone impregnation becomes resolved, as in the Coniferne, 
 into two cells, the upper forming the confervoid suspensor, 
 the lower the embryo. ^ The latter is at first a globular 
 mass of cells, but generally, while the seed is ripening, cer- 
 
 * Henfrey— Annals Nat. Hist., 2d Ser., XVII., 3-1.3. 
 
 t In Dr. Cai*ter's Observations on (Edogonium,hc£oTe noticed, (eh. II., 
 § 4), no bodily penetration of the antherozoids was visible. They 
 seemed to degenerate into drops of reddish mucilage on the mucus-layer 
 of the sporangium, and to be absorbed by a sort of endosmose. Annals 
 of Nat. Hist., 2d Ser., XVIIL, 81. 
 
 J In the phanerogamic ovule, the suspensor is generally formed after 
 the development has commenced of the proper embryo ; its prior forma- 
 tion in the Coniferae is one of the points in which tliis group presents a 
 transition to the characters of the Cryjjtogamia. 
 
64 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 tajn rudimentary organs are formed — the plumule, radicle, 
 and cotyledons, representing the axis, root, and leaves of 
 the future plant — and it is on differences in this respect 
 that the great division into Monocotyledons and Dicotyle- 
 dons is based.* 
 
 The whole process of development is more rapid than in 
 the Coniferae, there being no arrest in the grorfi of the 
 pollen-tube, and the flowering and seeding of the plant 
 being generally accomplished in the same season ; but there 
 is an entire agreement in the main feature — the adhesion 
 of the ovule to the parent plant till the maturation of the 
 embryo. In some exceptional cases the connection is not 
 entirely broken off even then ; the inextricable thickets of 
 Mangrove, with which swampy tropical shores are fringed, 
 are said to be due to the property which the seeds of this 
 tree have of Q-erminatino; while still attached to the branch.i* 
 
 From this sketch of the reproductive process, it appears 
 that the Angiospennous Phanerogamia differ both from 
 Coniferse and from the higher Cryptogamia (Rhizocarps, 
 Ferns, &c) — firstly, in the absence of any accessory cells at 
 the summit of the embryo-sac, like those which form the 
 crown of the corpusculum and the styloid neck of the arche- 
 gonium ; secondly, in the non-development of any distinct 
 tissue in the ovule, like the albuminous body or the 
 prothalhum ; in compensation for which, as it were, Ave 
 have, thirdly, an additional outer envelope — the germen or 
 ovary. From the Cryptogamic orders they differ farther in 
 the separation, as it would seem, of the two elements by 
 the continuous membranes of the pollen-tube and embryo- 
 sac. In Phanerogamia we have two distinct genital canals, 
 but neither of them corresponds to the archegonial canal 
 
 * In^the Orobranchese and OrcMdacese, tlie embryo reaches no higlier 
 development, in the ripening of the seed, than a globular mass of cells. 
 
 t In apples, &c.j the seeds are sometimes seen in a state of germina- 
 tion. 
 
IN THE VEGETABLE KINGDOM. 65 
 
 of the fern ; one of them — the micropyle — leading through 
 the coats of the ovule, appears first when the prothallium 
 becomes internal, as in the Rhizocarp ; the other, that of the 
 style, being entirely extra-ovular, can, of course, have no 
 existence v/hen the spores are deciduous, as in the Cryptoga- 
 mia, nor even when the ovule is uncovered, as in the Coniferaj. 
 The true homology of the relation in which the various 
 intra-ovular structures of the Gymnospermese stand to those 
 of other Phanerogamia, is a point on which authors are 
 either not agreed, or else are so loose in their terminology 
 as to obscure their real meaning,* but the bearing of the 
 several envelopes to each other, and to the germ which 
 they enfold, may be represented to a certain extent, as fol- 
 lows, both in these groups and in the higher Cryptogamia, 
 without entering into the discussion : — 
 
 Angiosperms have three germ-envelopes — viz., 
 Germen — pervious through the style ; 
 Ovule-coats — pervious by the micropyle ; 
 Embryo-sac — imperforate. 
 
 Gymnosperms have also three germ-envelopes, though 
 not all homologous with the foregoing, viz. : — 
 
 Ovule-coats — pervious by the micropyle ; 
 Albuminous body (prothallium) — perforated by the 
 pollen-tube ; 
 
 * Thus the term endosperm is applied both to the tissue of the albunii- 
 nous body of the Coniferse, and to the cellular growth which takes place 
 within the embryo-sac in the course of development in many plants, and 
 which remains as a permanent constituent of the seed in llanunculacete 
 and Nympheacese ; but, of course, the identification of these structures is 
 incompatible with a homology between the embr^'O-sac and the corpus- 
 culum or archegonium — as much so, indeed, as the notion implied in the 
 old name of PistilUdiii/tn applied to the last mentioned organ. See the 
 article on Vegetable Reproduction in the Cyclopaedia of Anatomy and 
 Physiology. 
 
66 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 Corpusculiim (arcliegonium) — imperforate ; 
 
 Rliizocarps have also three germ-envelopes ; 
 
 Spore-coats — pervious by the micropyle ; 
 
 Prothallium ) . i .i ^ c ^\ i ±j. 
 
 .1 • > pervious bv the canal oi the latter. 
 
 Arcliegonium J 
 
 In Ferns, from the spore being merely a provisional 
 structure, and from the prothallium being exposed, and not 
 enclosing, but only supporting the archegonium, the latter 
 is the only germ-envelope, and its canal the only passage of 
 access. 
 
 In mosses, as has been shown, there is no body corres- 
 ponding to the spore of the ferns ; both it and the deriva- 
 tive prothallium, which in that group had already ceased to 
 be germ-envelopes, have now no longer any existence, the 
 archegonia being attached directly to the leafy axis of the 
 plant. 
 
 § 11. The general conclusion to be drawn from the fore- 
 going survey of the leading modifications of the reproduc- 
 tive process in plants, appears to be that the difference be- 
 tween the higher and lower species consists mainly in the 
 constructive energy of the former being as it were concen- 
 trated on that embryogenetic development, whereby a higher 
 degTee of organization is attained in the typical or ortho- 
 morphic condition ; the other two stages in the cycle of 
 propagation being represented only by the maturation of 
 the floral organs, and the formation of the cellular mass 
 which is the earliest condition of the embryo. The latter 
 process, though really the beginning of a new cycle, is so 
 blended with the concluding or gamomorphic stage of the 
 preceding, and both are so merged in the following ortho- 
 morphic phase of development, that their individuality is 
 quite lost, and they appear as mere subsidiary processes, 
 affecting only certain organs of the typical plant, Avhose 
 term of life is popularly supposed to commence from the 
 
IN THE VEGETABLE KINGDOM. 67 
 
 germination of the seed, though this is really nothing 
 more than the evolutioii of an embryo already elaljorated^ 
 As we descend to lower forms, we find one or other of these 
 subsidiary stages becoming more prominent by the diffusion 
 over them, as it were, of plastic energy, abstracted from the 
 elaboration of the typical form, which declines proportion- 
 ally in complexity of organization. In the Gymnospermeai 
 and the higher Cryptogamia it is the gamomorphic stage 
 which gTaduaUy acquires importance, the protomorphic not 
 being conspicuously brought out till we reach the mosses 
 and lower orders. 
 
 In the following chapter a similar survey Avill be taken 
 of the modifications of the process in the animal kingdom. 
 
68 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 III. 
 
 SURVEY OF THE REPRODUCTIVE PROCESS IN 
 THE ANIMAL KINGDOM. 
 
 § 1 . The function of reproduction in the Animal Kingdom, 
 while it embraces wide variations in accessory points, pre- 
 sents a great, if not an absolute, uniformity in the produc- 
 tion and conformation of the sexual elements. The sper- 
 matic particles, or spermatozoa, are developed as the solitary- 
 nuclei of secondary cells — the vesicles of evolution — which 
 are in turn generated in variable numbers within the cells 
 occupying the cavities of the spermatic gland. When 
 liberated by the rupture of their envelopes, the particles 
 float freely in the fluid secreted by the gland — singly or in 
 bundles as the case may be. Their normal form is that of 
 a minute rounded body, with a long filiform appendage or 
 cilium, by the vibration of which an onward motion is given 
 to the whole corpuscule. Both parts are sufiiciently ap- 
 parent in the higher animals, but among the lower tribes, 
 as, for instance, in insects, we find the body sometimes so 
 much attenuated as to be undistinguishable from the 
 cilium, while in other cases the latter appendage disappears, 
 and with it the motile power. This modification obtains 
 in some Crustacea and Entozoa.* 
 
 The germinal corpuscula, on the other hand, appears in 
 the form of a minute nucleated body, and is known as 
 the germinal vesicle. Like the spermatozoon it seems to 
 be developed as the nucleus of a secondary cell (the ovum), 
 which is generated in the interior of another (the ovisac), 
 
 * Siebold's Compar. Anat., § 348, 290, 117. 
 
IN THE ANIMAL KINGDOM. G9 
 
 lying in the substance of the ovarian gland — such at least 
 is the case in the higher animals ; but it is very doubtful if 
 these relations can be satisfactorily made out in all the lower 
 orders, though the ovum has very constantly the character 
 of a nucleated cell. It is commonly only the outer enve- 
 lope that dehisces, the ovum itself being merely penetrated 
 by the spermatic secretion, for the accomplishment of the 
 act of fecundation. It is not yet absolutely certain that 
 the spermatozoa always penetrate into the ovum in form ; 
 possibly in some cases there may be nothing more than a 
 transudation of their liquified substance. Their bodily 
 presence within the ovum, however, has now been so fre- 
 quently detected as to afford gTound for believing a formal 
 penetration to be the usual rule.* We find, indeed, what 
 may be considered as a special provision for their intro- 
 duction, in the micropyle, which is found in many eggs, and 
 consists of one or more apertures at one of the extremities. 
 The functional import of the micropyle, as a passage of 
 access for the spermatozoa, is rather confirmed by the cir- 
 cumstance, that its homological relations are not the same 
 in all ova. In such as have been originally attached by a 
 
 * The first distinct observations of spermatozoa in the ovum appear to 
 be those of Dr. Martin Barry on the rabbit (Philos. Transact. 1840, 
 1841, 1843, March and June. Edin. Philosoph. Journal, Vol. LY., 326, 
 LVI., 36). They have also been observed by Dr. Farre in the earth- 
 worm, by Dr. Nelson and Meissner inAscaHs (Philos. Transac. II., 1852), 
 and by Dr. Newport in the frog (Philosoph. Transactions, 1853, p. 266- 
 281). In the following year Bischoff, who had before discredited the 
 penetration of the spermatic particles, himself observed it, and since then 
 Siebold has detected it in the ova of the bee (True Parthenogenesis, p. 
 85), and Gengenbauer in those of Hydrozoa (Huxley, Oceanic Hydrozoa, 
 p. 22). Claims have also been advanced for Prevost and Dumas, Wagner 
 and Keber. Keber's statements have not received much consideration 
 from naturalists generally, except as regards the discovery of a micropyle 
 in the ova of 177210 and Anodonta. A notice of the successive discoveries 
 in this department is given by M. Claparede — Annals of Nat. Hist., 2d 
 Ser., Vol. XVTI., 298. 
 
70 SURVEY OY THE REPRODUCTIVE PROCESS 
 
 stalk — as in those of Ecliinodermata and Helmintha — the 
 portion of the hollow pedicle which remains in connec- 
 tion with the ovum becomes the micropyle, but in 
 other cases a special aperture appears to be formed for the 
 purpose, in the previously continuous wall of the ovum. A 
 micropyle has now been observed in the ova of all insects, 
 and in those of Acephalous Mollusca, and of Osseous Fishes, 
 as well as in those of some Crustacea, Annelida, Echinoder- 
 mata, and Nematoid Entozoa. In the case of the Cepha- 
 lopoda and Batrachia the evidence is less satisfactory, and 
 no trace of it has yet been detected in the Mammalian 
 ovum, though the preseiice of spermatozoa in its interior 
 has now been verified by more than one observer. Here, 
 therefore, we can only conjecture that they may gain access 
 by a sort of boring action, or by the formation of extempo- 
 raneous apertures.* The micropyle is certainly not the 
 only provision for the purpose. In some cases the proper 
 wail of the ovum disappears before it comes into connection 
 with the Spermatozoa, which then penetrate into it over its 
 whole extent, their filamentous extremities giving the sur- 
 face a ciliated appearance. This has been observed by 
 Meisner in the Lumbricus, and may perhaps occur also in 
 some Hirudinei and Mollusca. In the Helmintha ao-ain, 
 the spermatozoa are frequently brought in contact with the 
 ova while the latter are yet in process of formation, as will 
 be more fully mentioned in the notice of that class. In the 
 Hydrozoa, too, impregnation seems to be effected in the 
 nascent condition, as it were, of the ova, for these bodies 
 do not appear to have any proper investing membrane, 
 
 * In tlie ovum of the rabbit Dr. M. Barry describes (Op. Cit.) the for- 
 mation of a cbiak for the entrance of the Spermatozoa. In that of the 
 frog, according to Mr Newport, there is no perforation, aperture, or 
 fissure of any kind visible to the eye, but he has distinctly observed the 
 penetration of the Spermatozoa in considerable numbers and with great 
 rapidity (in less than a minute). Philos. Transactions. 1853. 
 
IX THE ANIMAL KINGDOM. 71 
 
 when they are detached from their capsules and broiifi^ht in 
 contact with the spermatozoa.* 
 
 * About the time of impregnation the germinal vesicle 
 is generally stated to disappear. In the Batrachia Mr. 
 Newport is inclined to think that it is ruptured by the 
 pressure of a brood of minute cells formed in its in- 
 terior, and its contents dispersed in the form of clear 
 spherules through the yolk or mass of oleo-albuminous 
 particles with w^iich the ovum is filled. This may serve in 
 some way as a preparation for fecundation ; at all events he 
 is positive that in the ova of the newi; and frog the disap- 
 pearance of the vesicle takes place before impregnation, and 
 not in consequence of it.*f* The first obvious result of this 
 act is the repeated cleavage or segmentation of the original 
 contents of the ovum, and the formation thereby of a mass 
 of cells or plastic spherules, out of w^hich the embryo is de- 
 veloped either immediately, or with the intervention of some 
 of those diverse forms which occur in cases of so-called 
 Alternation of Generations. 
 
 After impregnation, and when the process of segmenta- 
 tion is about to begin, a clear nucleated cell — the " embryo 
 cell" — is generally observed in the interior of the yolk. In 
 
 * Gegenbaiir, quoted by Huxley, Oceanic Hydozoa (Ray Soc), p, 22. 
 These diversities in tlie mode of access of the Spermatozoa may be tabu- 
 larly represented as follows : — 
 
 By a micropyle, in Echinodermata, Worms, Insects, Crustacea, 
 and Osseous Fishes (possibly also in some Reptiles (HylaJ ; 
 By fissure of the wall of the OArum, in Mammalia ; (?) 
 By penetration through its substance, in Batrachia ; 
 By commixture before the ovum is coated over, in some Treraa- 
 
 toda and Nematoidea, and in Hydrozoa; 
 By dissolution of the investing membrane, in Lumhricvs, and 
 perhaps in some Hirudinei and MoUusea. 
 The subject is noticed with some detail in Professor A. Thomson's article 
 (Ovum) in the supplementary volume of the Cyclopajdia of Anatomy and 
 Physiology. Also in the paper by M. Claparede, quoted above. 
 f Philosoph. Transactions (1851), p. 169. 
 
72 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 Entochoncha mirabilis, a molluscous animal, this, ac- 
 cording to J. MuUer, is identical with the germinal vesicle, 
 which in that species never disappears. In other cases, as 
 Ascaris, it has been supposed to arise from the nucleus of 
 the vesicle. Some such connection has been assumed, in- 
 deed, even when the vesicle seems to disappear entirely, as 
 it does in most ova. It has been thought that the deli- 
 quescence may not extend to its whole contents, and that 
 the " embryo-cell" may originate from some residuary por- 
 tions, as from some of the clear spherules, before referred 
 to, in the ova of Birds and Batrachia. In the Hydrozoa, 
 according to Gegenbauer, at least in the Corynidae, Calyco- 
 phoridse, and Physophoridse, " the germinal vesicle" does 
 not disappear, but its division immediately precedes that of 
 the yolk, so that its progeny must eventually become the 
 " embryo-cells" of the division masses.* The observations 
 of the same naturalist on Sagitta, and of Professor Huxley 
 on Pyrosoma, also tend to show that the '' embryo-cells" 
 are the lineal descendants of the germinal vesicle. 
 
 The division of the " embryo-cell" immediately precedes 
 that of the yolk. The segmentation is commonly effected 
 by each division of the '' embryo -cell" becoming coated over 
 with a corresponding portion of the gTanular matter of the 
 yolk, so that every one of the multitude of minute sphe- 
 rules, into which the latter is ultimately resolved, contains, 
 as its nucleus, a derivative of the "embryo-cell." But in a 
 few cases, confined, so far as is yet known, to some Nema- 
 toid and Cestoid worms, the progeny of the original " em- 
 bryo-cell" do not coat themselves in this way, but seem 
 rather to absorb the granular and fluid matter, growing, 
 as it were, at its expense, so that the yolk entirely dis- 
 appears by the time the segmentation is complete. Pro- 
 fessor Huxley considers that a somewhat analogous pro- 
 
 * Huxley's Oceanic Hydrozoa, p. 22 
 
IN THE ANIMAL KINGDOM. 73 
 
 cess of cell-formation occurs in tlie ova of Pyrosoma and 
 Salpa.* 
 
 The embryo — whether the direct or indirect product of 
 impregnation — differs in the majority of cases from tlie 
 adult form, not only in size, but in many points also of 
 structure and configuration, and the progressive changes 
 which it undergoes before acquiring perfect conformity to 
 the organization of the parent go under the name of meta- 
 morphosis. Sometimes they occur within the embryonic 
 envelopes, but at other times the young is extruded while 
 still in an imperfectly developed state. Such naked em- 
 bryos are termed larva? — masks, as it were, disguising 
 what is ultimately found to be the true aspect of the species. 
 
 In some Invertebrata, Fishes, and Reptiles, and still more 
 strikingly in Birds, the segmentation appears not to extend 
 to the whole contents of the ovum, but the exception is 
 more apparent than real, for the yolk of the fertilized egg- 
 in such cases contains part of the granular matter within 
 the ovisac, over and above the proper substance of the 
 
 * Annals of Nat. History, 3d Ser. (Jany., 1860), p. 35. There is per- 
 haps more force in Mr. Huxley's other suggestion of an analog}' with the 
 Bird's ovum, though in this view the part wanting would not he the true 
 cleaving yolk, hut the wall of the proper germinal vesicle, and the true 
 ovum would he represented hy what he calls the germinal vesicle, not by 
 the unwalled contents of the ovisac, which would coiTespond rather to the 
 adventitious or yolk-food of the Bird. The homologies would stand as 
 follows : — 
 
 Vitelline memhrane wanting . 
 
 Food yolk liquifying yolk of Huxley. 
 
 m n-Ar ^ ^ (wall of "germinal ve- 
 
 ^- i emporary zona of Meckel j • n ,, otj -> 
 
 True or primitive central ") ri i. x r v i 
 
 T ^ n } Contents oi above, 
 
 granular yolk ) 
 
 "Wall of germinal vesicle wanting. 
 
 Macula of do germinal spot. 
 
 Eeasons will be given afterwards for regarding the ivall of the germinal 
 vesicle as a non-essential structure, though one certainly of great con- 
 stancy in the animal kingdom. 
 
 E 
 
 •f^ 
 
74? SURVEY OF THE REPRODUCTIVE PROCESS 
 
 original ovum, owing to the obliteration of tlie primordial 
 wall of the latter, and the subsequent formation of a new 
 limiting membrane — the vitelline — nearer the w^all of the 
 ovisac* The supplementary material does not undergo 
 segmentation, and goes under the name of food-yolk ; it is 
 evidently provided to secure a larger supply of nutriment 
 within the e<>;oi:, in cases where none is to be obtained from 
 without during the development of the embryo. It is not 
 present in the Mammalia, where the fsetus is nourished 
 through the placenta, nor in cases among the lower orders 
 in which the embryo is speedily set free as a larva. 
 
 It is to diversities in such secondary points as those last 
 alluded to, that the infinite variety is due, which the 
 Animal Kingdom presents in the details of the process of 
 reproduction. In the points more essentially connected 
 with the formation and fertilization of the germ, there is, 
 as has been mentioned, an essential sameness throughout, 
 for the phenomena which at first sight appear most eccentric 
 — those connected with the alternation of generations — do 
 not arise from anomalies in the sexual process itself, but 
 from the interpolation of an independent process of Mono- 
 genesis, at different periods in the life history of the species. 
 
 It is the relation between these two associated processes 
 Avhich will form the principal subject of attention in this 
 summary of the modifications of reproduction in the more 
 important groups of animals ; the other peculiarities of the 
 function will be alluded to only in so far as they help to 
 illustrate this point. 
 
 § 2. REPRODUCTION IN THE PROTOZOA. 
 
 Following the same ascending order as in the last 
 chapter, we are met at once on the threshold of the Animal 
 Kingdom with a form of life to which we are not yet in a 
 
 ^ Thomson in Cyc. Anat. and Pliys., Part LIV., p. 77. 
 
IN THE ANIMAL KINGDOM. 75 
 
 position to apply unreservedly any of the general principles 
 above stated, as hitherto no indications of sex have been 
 discovered in the majority of the species. Such points, 
 however, will be stated as seem to have any distinct bear- 
 ing on the subject before us. 
 
 Under the name of Protozoa are comprehended certain 
 unicellular animals having more or less affinity \nth the 
 infusorial animalcules, in the restricted sense in which this 
 term is now used, after the elimination of the embryos of 
 the higher species, of unicellular plants, such as have been 
 already considered, and of other extraneous forms. But 
 there can be little doubt that names still occur in the list 
 of Protozoa, which do not represent real species, but only 
 the embryonic condition of such as are referable in their 
 adult state to far higher types of organization, for a trans- 
 formation which has now been satisfactorily traced in so 
 many instances, may fairly be suspected to occur in not a 
 few others still referred to the lower group. The detection 
 of such cases must be left to patient observation, with the 
 conviction that, though this is a slow process, it will even- 
 tually yield results which may confidently be relied on. 
 
 But even in cases where long continued observation 
 shows that the unicellular organisms in question never at- 
 tain any liigher type of structure, there still remains be- 
 hind another difficulty — namely, to determine whether they 
 are of an animal or vegetable nature, and the grounds on 
 which this is to be decided, or the points of distinction be- 
 tween the Protophyta and the Protozoa, form a question 
 about wliich naturalists are not yet quite in agreement, 
 though sensibly approaching to it. The following are the 
 points now generally admitted as distinguishing the unicel- 
 lular animal from the vegetable : — 
 
 1. Contractility of the substance or of the bounding 
 wall of the organism, which is a main agent in its locomo- 
 tion, though ciliary action is also employed, and to a much 
 
 E 2 
 
76 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 greater extent than in the vegetable cell, whose motile 
 powers are consequently less marked and less constant. 
 
 2. The predominance of albuminous compounds over 
 those ternary principles, such as cellulose, starch, and chlo- 
 rophyll, which form the bulk of the vegetable cell and its 
 contents, and the absence of the green colour which the 
 action of light on these vegetable principles evolves. 
 
 The Protozoa, on the elimination of these spurious or 
 intruded species, constitute a truly natural group, but one, 
 at the same time, hardly admitting of any good general 
 definition, applicable to the several forms it includes, being 
 distinguished from those referable to the other primary 
 divisions of the Animal Kingdom chiefly by negative cha- 
 racters, such as the absence of a nervous system and of 
 organs of sense, and in many even of a distinct alimentary 
 apparatus. They are sometimes described as unicellular, 
 ■svith a nucleus or minute solid particle, and certain clear 
 sj)aces or vacuoles in their interior,* but it is to be observed 
 that no true cell-wall is developed in the lowest forms — the 
 body consisting of a mere mass of plastic jelly, without any 
 distinct membrane bounding its exterior. 
 
 In the greater number of the Protozoa, reproduction is 
 only as yet known to take place in the way of monogenesis. 
 Two leading modifications of this are admitted, though they 
 are not alw^ays to be distinguished from each other — -Jissioti 
 and ciem7nation.'\ Fission, or the spontaneous separation 
 of the body into two or more segments, prevails mostly in 
 the higher group known as Infusorial Animalcules — gem- 
 
 * Greene's Manual of the Protozoa, p. 2. 
 f Fission, as Professor Owen remarks (Parthenogenesis, p. 10), though 
 it presents a wide prima facie diversity from ordinary gemmation, in half 
 of the body of the parent, instead of only a small portion of it, going to 
 form that of the offspring, is after all only a modification of the other 
 process, the difference depending on the very small size in gemmation of 
 the portion of parenchjnna w4iich takes on the new development, in rela- 
 tion to the whole body, and on its superficial position. 
 
IN THE ANIMAL KINGDOM. 77 
 
 mation, or the development of external buds, in the Ptizopods 
 and Sponges. In the latter case there is a tendency — thouuh 
 not so general as in the vegetable kingdom — for the 
 gemmae to remain in adhesion with the basis from which 
 they have been budded off, so as to give rise to composite 
 multicellular organisms, whose configuration depends on 
 corresponding variations in the mode of gemmation. 
 
 Of these ao-greo-ated Protozoan structures, the Foramini- 
 fera, and especially the Sponges, are the forms that attain 
 the largest dimensions. 
 
 Indications, however, are not wanting of the occurrence 
 of sexual reproduction, though as yet they have been recog- 
 nized only in a few isolated cases. In Tethya, an animal 
 of this division, ova and spermatozoa have been detected by 
 Mr. Huxley.* 3^hey do not appear to be formed in special 
 organs, but occur in mixed masses within the spicular invest- 
 ment of the common organism. The other cases are those 
 observed by Balbiani among the Infusoria, as described in a 
 late communication to the Academy of Sciences of Paris. 
 This author has met with indications of the process in six 
 or seven species representing different groups, but confines 
 himself in this paper to a description of it as it occurs in 
 Faramcecium Bursaria, the species in which he has been 
 able to trace it most completely.'!* For several generations 
 the Paramcecia multiply by spontaneous fission, each of 
 the two new individuals obtaining half the primitive nucleus, 
 but under the influence of conditions, of which w^e are still 
 ignorant, the species propagates itself by sexual concourse. 
 When the period for this arrives, the individuals are found 
 coupled together in pairs, adherent laterally, and, as it were, 
 locked together, with the similar extremities turned in the 
 
 * Annals of Nat. Hist., 2d Ser., YII., 370. Also by Lieberkiilin in 
 SponcjiUa, Op. Cit., XVII., 4.12. 
 
 t Annals of Natural History, 3d Ser., I., 435. (Comptes Eendns, 
 March 27, 1858, p. 628). Greene— Manual of Protozoa, p. 72. 
 
78 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 same direction, and the two mouths closely applied to each 
 other. In this state the two conjugated individuals con- 
 tinue moving mth agility in the liquid, and turning con- 
 stantly round their axis.* There is notliing before copula- 
 tion to announce the evolution of the sexual elements ; it 
 is during the act itself, of which the duration is prolonged 
 for five or six days, or even longer, that their development 
 takes place, at the expense of the nucleus and nucleolus of 
 each animalcule. The nucleolus undergoes a considerable 
 increase in size, and becomes converted by sub-division into 
 two or more capsules, which contain ultimately minute 
 fusiform bodies wLih fine filamentous extremities, regarded 
 by Balbiani as spermatozoa. The corpuscules, wliich he 
 considers as of a genninal nature, are certain spheroidal 
 bodies, with indistinct central spots, formed in the sub- 
 stance of the nucleus with or without its previous segmen- 
 tation. Fecundation seems to be effected by a transference 
 of one or more of the spermatic capsules, through the closely 
 adpressed mouths, from the body of one animalcule into 
 that of the other. They continue to increase in size after 
 their transference has taken place, one only arriving at ma- 
 turity at a time. Five or six days after copidation, minute 
 rounded germs make their appearance, and in the com-se of 
 development are extruded from the body of the parent 
 animal, but for some time aft«r tliis they remain adherent 
 to its exterior by means of the knobbed tentacles or suckers 
 with wliich they are provided. At length they detach 
 themselves, lose their suckers, acquire a mouth in their 
 stead, and, becoming furnished mth vibratile cilia, take on 
 the aspect of adult Paramcvcia.'\' 
 
 * In a second commnnication Mr. Balbiani generalizes his eonclnsions, 
 and extends them to several other Infusoria, as Euplotes, Cliilodon 
 Spirostomnm, and Oxytricliina. Annals of Nat. Hist., 3d Ser., II., 4-iO, 
 
 t Dr. A. Thomson in Cyclop. Anat. and Physiol., Art. Ovum, p. 7. 
 Greene's Protozoa, p. 51-71. 
 
IN THE ANIMAL KINGDOM:. 79 
 
 A sort of conjugation lias been observed in some Infuso- 
 rians, and particularly in the allied order of Gregarinidfe, 
 consisting mostly of parasites infesting the intestines of 
 insects ; but that attempts to assimilate it to the conjuga- 
 tion of the Protophyta are at least premature, is sho^vn by 
 the diversity of the two processes in some important points. 
 For, firstly, the fusion which has been observed in Vorti- 
 cella and Gregarina by Stein and others, is not always con- 
 fined to a pair, but occasionally three have been seen to 
 coalesce in this way ; and, secondly, the union does not 
 seem to be of the same nature, for after coalescing in this 
 manner, the animals have been seen to separate again in all 
 their integrity. Where it really is preliminary to the for- 
 mation of embryos, we may, therefore, more reasonably 
 consider it as a kind of intimate copulation, like that w^hich 
 has just been described from Balbiani.* 
 
 In connection with the reproduction of the Infusoria, two 
 other points seem to call for a short notice — encystment, 
 and the transformations which have been described by some 
 authors. 
 
 The encysting process has been most accurately observed 
 in Vorticella, but it probably occurs in all animals of the 
 class. A Vorticella about to become encysted contracts 
 slightly, closes the peristome or ciliated depression in which 
 the mouth is situated, and envelopes itself mth a mucous 
 
 * In some of the species observed by Balbiani, the union amounted to 
 an actual fusion of the individuals for more than two-thirds of their an- 
 terior part, and in all probability many supposed cases of incipient fission 
 have really been of this nature. Among the Entozoa, still more striking 
 cases of so-called conjugation have been observed. In Syiigamns there 
 appears to occur a real fusion of tissue, and in Biporpcib even a coalescence 
 of certain viscera between the two individuals, which, indeed, were first de- 
 scribed as one duplicated animal ; yet, in its bearing on reproduction, the 
 act seems more allied to ordinary copulation than to conjugation as it 
 occurs in the Protoph^^a, as both the individuals concerned have proper 
 generative organs of the ordinaiy type of the class. See Annals of Nat. 
 Hist., 2d Ser., VII., 428. 
 
80 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 secretion which gTadually consolidates into a hard shell. 
 In some cases the encystment seems to depend on exposure 
 to cold or drought, and is then probably simply a means of 
 protection from these influences — a sort of hybernation — 
 for the animal may remain unchanged in the cyst, and, 
 when humidity and warmth are restored, it may burst its 
 envelope and resume its former life. But in other instances 
 it appears to have a physiological import, and to be preli- 
 minary to certain transformations of the animalcule itself. 
 Stein mentions several metamorphosis undergone by the 
 Vorticella in the interior of the cyst, especially its breaking 
 up into a number of minute corpuscules, which, on reaching 
 maturity, are shed by the dehiscence of the shell, and serve 
 as free gemmae for the multiplication of the species. He 
 describes^' also the {conversion of the cyst itself .into an 
 'Acineta, by the protrusion from its exterior of the charac- 
 teristic knobbed tentacles. The convertibility of these two 
 forms, and many others of Stein's conclusions, are rejected 
 by Lachmann on the ground that suf&cient care was not 
 taken in the isolation of the specimens observed. More 
 lately, however, M. d'Udekem has reasserted the derivation 
 of acineta forms from the encysted Vorticella, though he 
 differs from M. Stein in his account of the metamorphosis. 
 He describes the transformation of the Vorticella within 
 the cyst into a simple ciliated Infusorian (Opalina), by its 
 dissolution into granules, the exterior layers of which coa- 
 lesce to form an integument, by a process somcAvhat resem- 
 blino- the formation of the blastodermic membrane of the 
 ovum. Tlie ciliated body after escaping from the cyst, 
 which is ruptured by its groA\i;h, is transformed into an 
 Acineta. By careful isolation, and the observation of in- 
 termediate forms, M. d'Udekem has satisfied himself of the 
 reality of this change. Ciliated embryos, formed from the 
 nucleus, have been seen by many observers to be discharged 
 from the Acineta. Stein observed these, though he was 
 
IN THE ANIMAL KINGDOM. 81 
 
 never able to trace their farther progress, but he conjectured 
 that they -might give origin to Vorticella forms, to complete 
 the genetic cycle. It is possible this may be the destiny of 
 those acineta-embryos which M. d'Udekem has seen to be- 
 come encysted, but it is now clearly ascertained, both by 
 this observer and by J. Miiiler and Lachmann, that they 
 may also be directly developed again into fresh Acinetw* 
 
 § 3. REPRODUCTION IN THE COELENTERATA. 
 
 Until of late the lowest of the four primary divisions of 
 the Animal Kingdom admitted by Cuvier — the Radiata — 
 remained much in the condition in which that illustrious 
 naturalist found the whole invertebrate series — a sort of 
 lumber store, in which all forms not readily reducible 
 under the three higher divisions were conveniently stowed 
 away. Even after the labours of later authors had extri- 
 cated from the confused assemblage various aberrant forms 
 of the Molluscous and Articulate types — as by associating 
 the Polyzoa with the Tunicata, the Lernseadaj with the 
 Crustacea, and the Entozoa with other vermiform tribes — 
 it still remained as impossible as ever to establish any com- 
 munity of organization among the residuary species. Later 
 researches have shown, however, that the restricted Radiata 
 fall into three groups, all equally natural, though of very 
 different relative value — namely, the Protozoa, which have 
 just been noticed, the Caelenterata and the Echinodermata. 
 Of these the two former are now ranked as primary divi- 
 sions, while the position of the last, which is evidently of a 
 subordinate character, still continues to be one of the great 
 puzzles of systematic zoology. 
 
 The Coelenterata, as established by Leuckart and Frey, 
 coincide with the group termed NematojjJiora by Professor 
 
 * Annals of Nat. Hist., 2d Ser., IX., 171, 3d Ser., IV., I. 
 
 E 3 
 
82 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 Huxley, and undoubtedly from a very natural assemblage, 
 for in essentials a very complete unity of organization is to 
 be traced tlirougli all the species. Along with this, how- 
 ever, there is so much variety in many adventitious points, 
 aifecting both the development of particular organs, and 
 their mode of arrangement, that the general appearance is 
 often strikingly unlike in the different sections of the gToup. 
 The reproductive process seems to present a corresponding 
 diversity, some species furnishing the most remarkable 
 examples of alternation, while in others no phenomena of 
 the kind have yet been noted. How far these variations 
 may be brought within the scope of a common law will 
 afterwards be considered ; at present it may be sufficient to 
 remark that in the protomorphic or early development of 
 the Coelenterata, the principal point of interest is that the 
 germinal mass becomes covered with a membrane bearing 
 cilia, by whose play it moves freely through the water like 
 an infusory animalcule, ^^^len the action of the cilia ceases, 
 a mouth is formed on one side, and the embryo, assuming a 
 cup-shaped form, becomes transformed into a polype. 
 
 Gemmation is generally a very conspicuous feature of the 
 polypiform phase. It is by repeated pullulation of gemmae, 
 and their continued adhesion to the parent stock, that those 
 composite structures are formed, so characteristic of the 
 group, which have received the name of zoophytes or plant- 
 animals, from their resemblance to ramose gro\\i:hs of a 
 vegetable nature. 
 
 The polypiform condition is the most permanent stage of 
 development, and for this and other reasons, which will 
 afterwards be given, it is here considered as the orthomor- 
 phic or typical phase in the genetic cycle or life history of 
 the species. In many cases, however, it is not that which 
 matures the sexual organs. In the higher division, indeed, 
 of the group (Actinozoa of Huxley) containing the Asteroid 
 and Helianthoid polypes, and also in the common Hydra, 
 
IN THE ANIMAL KINGDOM. 88 
 
 the ova and spermatozoa are borne directly by the polypi- 
 form zoophytes into which the germ passes, by a continuous 
 course of development,* but in the compound polypes allied 
 to Coryne and Sertularia, and in the Calycophoridse and the 
 Physophoridae of Huxley — all referable to his lower section 
 of Hydrozoa — we have, as a very common arrangement, an 
 alternation of forms, occurring in what has been distin- 
 guished as the Gamomorphic stage, i.e., in connection with 
 the evolution of the proper reproductive organs — the sexual 
 elements being developed, not in organic union with what 
 may be considered as the typical form, but in peculiar zooids 
 detached from it. These go under the name of Medusoids, 
 and though there are great diversities of detail, which \\'\\\ 
 afterwards be adverted to, in their mode of origin from the 
 polypiform zoophytes, and in their size and completeness of 
 organization, there is a certain uniformity in their general 
 structure, which consists of a natatory organ, developed 
 round the spermatic or ovarian sac, and assuming the cam- 
 panulate form, so prone to repeat itself at all points in this 
 type of organization. 
 
 The sexual zooids of the compound polypes are of very 
 minute size and rudimentary organization, while those of 
 the Lucernarian section acquire a much larger size and more 
 elaborate structure ; so that although the two forms were 
 associated in one order — as the naked and hood-eyed Me- 
 dusae — long before their true derivation was known, yet the 
 idea of their being both alike the homologues of detached 
 ovaries was long of making its way to the general accept- 
 ance it has now obtained, on account of the chsparity be- 
 tween the structures themselves, and still more on account 
 of the disproportion of their development to that of their 
 
 * The reproductive process seems to be direct also in the Ctenophora, 
 from tlie few observations we have on the subject. See a notice of the 
 development of Cydippe, in Edinb. New Philos. Journal, N.S., IV., p. 89, 
 by Dr. T, S. Wright. 
 
S4 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 respective parent stocks ; for wliile in the Hydroid and 
 Sertularian Polypifera the zoophytic stem is a far more con- 
 spicuous object than the Medusoid, the polypoid stock, or 
 larva, as it has been incorrectly termed, of the other form 
 is quite . an insignificant organism, in comparison of the 
 colossal hood-eyed Medusae which originate from it. 
 
 The Medusa-zooids seem to be almost universally of 
 separate sexes, and most commonly it would appear that all 
 those from one polype or polypidom are of the same sex — 
 an arrangement comparable to that termed dioecious in 
 botany.* 
 
 As the reproduction of the Hydrozoa will again come 
 under review, in considering the nature and relations of the 
 phenomena of alternation, it seems unnecessary at present 
 to go into farther details on the subject. 
 
 § 4. ECHINODERMATA. 
 
 This division of animals, so natural in itself, but so 
 puzzling in its relations to other leading gToups, presents 
 us with phenomena in the protomorphic stage of develop- 
 ment, not inferior in interest to the gamomorphic zooids of 
 the class last under consideration. From the obsei-vations 
 of various naturalists, and particularly of Prof J. MUller, 
 who has been the principal labourer in this field, it appears 
 that the germ of an Echinoderm has at first the character 
 of a ciliated Infusorian, with a tendency to a bilateral form. 
 In some species of Stamsh (Eckinaster, Asteracanthion) the 
 development of the typical Echinoderm takes place by a 
 nearly direct process. The ciliated body soon manifests a 
 distinction of parts, a four-lobed portion appearing at one 
 extremity, by which the nascent animal adlieres to any sup- 
 port ; but this appendage is more than a mere pedicle of 
 
 * Dr. Wright in Edin. Philos. Journal, N.S., IV., 88. 
 
IN THE ANIMAL KINGDOM. 85 
 
 attachment, as it has a mouth and gastric cavity of its own. 
 The back of the ciliated body assumes a polygonal form, and 
 is directly transformed into the starfish, which developes a 
 new mouth in the centre of the ventral surface, a little to 
 one side of the pedicle, the latter appendage gradually dis- 
 appearing by a process of absorption. 
 
 But in the great majority of the class there is in the 
 course of development a marked change, of the nature of 
 alternation. In all these cases, a decided breach occurs in 
 the continuity of the process, by the establishment of a new 
 focus of organization ; and in not a few there is a breach 
 of structure also, in the mechanical separation of the later 
 from the pre-existing growth. The first steps of develop- 
 ment — those which directly affect the germ — consist in the 
 formation of an alimentary canal, with oral and anal open- 
 ings, and in the disappearance of the cilia on the extemal 
 surface, except in particular spots, especially along a circle 
 surrounding the oral region. These are follow^ed by certain 
 alterations of external form and configuration, differing in 
 the different sections of the class, and distinguished by par- 
 ticular names. That characteristic of the Holothuridce has 
 been termed Auricular ia, and is of a cylindrical or barrel 
 shape, girt with numerous ciliated rings, and not unlike the 
 larva of some Annelida. That of the Asteridse, known 
 under the name of Bipinnaria, attains a considerable size — 
 an inch or more in length — and assumes a very extraordi- 
 nary form, from the development of the ciliated region in 
 front of the mouth, wdiich throws out several long processes 
 on each side, and at the anterior extremity two fin-like ex- 
 pansions, placed one above the other. But the most ela- 
 borate specimen of such provisional organization is presented 
 to us in the Pluteus — the form from which the Echinida? 
 and Ophiuridae are derived. The general form of the 
 Pluteus is that of a quadrilateral pyramid, dome-shaped 
 above and slightly excavated at the base, the corners oi 
 
86 SURVEY OF THE REPEODUCTIVE PROCESS 
 
 which are prolonged into straight slender legs, strengthened 
 by filiform rods of calcareous matter reaching to the summit 
 of the dome. The mouth projects as a proboscis from the 
 middle of the concave base, and the circle of cilia surround- 
 ing it fringes the circumference of the base of the pyramid, 
 and the four projecting processes, which in swimming are 
 directed forwards. 
 
 The new process of organization always originates in a 
 diverticulum of the dorsal integument of the germ, which 
 grows inward and lays the foundation of the future water- 
 vascular system, on which the other organs of the Echino- 
 derm are subsequently modelled. 
 
 In Holothuria, the new formation amalgamates to a great 
 extent with the germ structures, and no part is absolutely 
 cast off, though the original mouth is obliterated, and a 
 new one formed on what was the dorsal aspect of the Auri- 
 cularia. In the Echinidae and Ophiuridse, and also in the 
 Asteridse, a new mouth is formed much in the same way ; 
 but the only organ of the original appropriated by the 
 Echinoderm is the alimentary canal. As development ad- 
 vances, a difference appears in the two cases, for while the 
 unappropriated part of the Pluteus vanishes, the Bipinnaria 
 retains its original form more persistently, and gTadually 
 becomes detached from the Starfish. The latter then sinks 
 to the bottom, and creeps by its newly developed sucking 
 feet, while the protomorphic zooid — eviscerated as it is by 
 the process — still swims about for some time as before, but 
 eventually perishes.* 
 
 No alternation of forms is known to occur in this class, 
 after the acquisition of the typical organization, nor any 
 phenomena at all of the nature of gemmation, except we 
 are to consider the development of the sexual organs, or 
 the regeneration of lost parts, as rudimentary manifestations 
 
 * An. Nat. Hist., 2d Ser., Till., p. 4. 
 
IN THE ANIMAL KINGDOM. 87 
 
 of a process of this kind.* Nor have we any remarkable 
 structural metamorphosis in this stage, except in the pe- 
 dunculated species, some of which at least are known after- 
 wards to become free by separating from the calcareous 
 stem. In this way the so-called Pentacrinus Europeus is 
 converted into the Comatula rosacea, as was first discovered 
 by Mr. J. V. Tliompson."f" From the later observations of 
 Prof. Wyville Thomson it appears that the young Echino- 
 derm — formed from a barrel-shaped zooid, like that of a 
 Holothuria — is at first a free egg-shaped body ; by the 
 elongation of the narrow end it then becomes club-shaped, 
 and the pointed extremity attaches itself by a disc of 
 cement matter to some foreign body. The consolidation of 
 the pedicle by the deposit of calcareous matter in its tissue 
 at intervals gives it subsequently a jointed character. The 
 rays or arms are of later growth, and do not acquire their 
 full development till close on the period of the detachment 
 of the body. I 
 
 § 5 REPRODUCTION IN THE POLYZOA. 
 
 The class of Polyzoa (Bryozoa or Bryozoaria of Foreign 
 Zoologists) consists of minute Polype-like animals, having 
 a great prhnd facie resemblance to some of the Co^lenterate 
 type, and having also, like them, a great tendency to the 
 development of zoophytic or composite forms. Popularly 
 they both go under the name of polypes, and even by zoolo- 
 gists they were confounded till a recent period. The 
 Polyzoa, however, have a much higher organization than the 
 
 * The Holot]iuriaa, according to Siebold, may form an exception. He 
 quotes Dalzell for their power of spontaneous division into two or moi-e 
 parts, each of which may become a complete animal, and Quatrefages for 
 a similar multiplication oy fissuration occurring in Synapta Duve^rnea. 
 Compai-ative Anatomy (EchinodermataJ , § 95, note 1. 
 
 t Edin. Philosoph. Journal, for April, 1836, p. 296. 
 
 X Transactions of Royal Society, Jany., 1857, and Jany., 1859. 
 
88 SLTtVEY OF THE REPRODUCTIVE PROCESS 
 
 Coelenterate or Hydraform polypes, and one which distinctly 
 presents the rudiments of the MoUuscan type. In parti- 
 cular there are always distinct muscular fibres, a well- 
 defined alimentary canal with two openings and proper 
 walls, and traces even of a nervous system, in a single 
 ganglion situated on one side of the oral aperture. 
 
 Their reproduction presents some interesting peculiarities, 
 both in the protomorphic and gamomorphic stages. The 
 early development of the germ has been followed out by 
 Professor Allman, particularly in some of the freshwater 
 species. By his account we have first, as the immediate 
 result of the development of the ovum, " a ciliated sac-like 
 embryo [germ], resembling in form and habit an infusorial 
 animalcule. As development proceeds, we find the ciliated 
 embryo, while still confined within the coverings of the egg, 
 presenting in some part of its surface an opening which 
 leads into the central cavity; and through this opening an 
 unciliated hernia-like sac is protruded by a process of eva- 
 gination. In the interior of the protrusible portion . 
 
 . a polypide [polype] is developed. The gemmation 
 of the first polypide is immediately followed by that of 
 another close beside it, so that the young polyzoon has now 
 the appearance of a transparent closed sac, filled with fluid, 
 the posterior part ciliated, the anterior part destitute of 
 cilia, and partially or entirely pushed back into the posterior 
 by a process of invagination, while the sac carries mthin it 
 two young polypides, which are suspended from the inner 
 surface of the unciliated portion."* 
 
 The prominent peculiarity here is the formation from the 
 original germ of two gemmae, which are really the embryos 
 of the first pair of polypes. 
 
 The polypiform, which is also the orthomorphic or typical 
 phase of development, once acquired, the tendency to gem- 
 
 * Allman's Freshwater Polyzoa (Ray Soc), p. 41, 33, and 34. 
 
IN THE ANIMAL KINGDOM. 89 
 
 mation becomes still more marked, and gives rise, by the 
 continued pullulation of new zooids, to the formation of the 
 variously branched polypidoms, which are so characteristic 
 a feature of the class, as is indicated by the names which 
 different naturalists have applied to it. The species are 
 perhaps never solitary, but in a few cases they occur in 
 pairs, the gemmation stopping short at the initial stage of 
 the production of a double embryo. 
 
 The peculiarity referred to in the gamomorphic stage of 
 the life history is that the structures elaborating the sexual 
 elements are developed at so late a period, and in a manner 
 so similar to the pullulation characteristic of the class, as to 
 give them less the appearance of mere organs, than of dis- 
 tinct gemmae or attached zooids like the polypes themselves. 
 The fuller discussion of this point, however, must be re- 
 served till the general relations of the organs of reproduc- 
 •tion come under consideration. 
 
 § 6. REPRODUCTION IN THE TUNICATA. 
 
 The Tunicata, which, along vdth. the Polyzoa, constitute 
 the inferior division of the MoUuscan sub-kingdom, have 
 long been kno^\^l to propagate both by impregnated ova and 
 by gemmae. The latter are generally formed on long 
 tubular processes emitted from the parent stock, which are 
 equivalent to, and sometimes closely resemble, the hollow 
 polypidoms of the Polyzoa. As in that class, too, the gem- 
 mae frequently give rise by their cohesion to compound 
 structures, quite distinguishable, however, by characteristic 
 differences in the connection and disposition of the com- 
 ponent zooids. This arrangement prevails especially in 
 certain families, while solitary forms are more characteristic 
 of others. 
 
 But a difference in this respect is not always to be re- 
 garded as a specific character, for it is well ascertained that 
 
90 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 in Salpa (and possibly in other genera) there is an alterna- 
 tion of two forms, from the sexual organs making their ap- 
 pearance only in those zooids which are derived from the 
 original form by gemmation. It was the discovery of the 
 connection between the two forms of Salj^oe that first led 
 Chamisso to introduce the expression of '' Alternation of 
 Generations ;" a term since extended by Steenstrup and 
 others to a variety of cases — some of them of very doubtful 
 relationship. The chains which the aggTegated Salpss 
 form by the cohesion of processes of their gelatinous integu- 
 ment, are modelled within the respiratory sac of the parent, 
 on a j)eculiar tube, which may be compared to an introver- 
 sion of the external stolon of other Tunicata. The tube, 
 being an outgrowth from the vascular system, serves to 
 establish a continuity between the circulation of the parent 
 and that developed in each of the gemmae on its exterior. 
 The tube appears to be in a state of continuous growth 
 from its attached extremity, for the gemmae are most ad- 
 vanced at its free end. As they attain maturity, a portion 
 of the tube breaks off from time to time with its encrusta- 
 tion of gemmae, and escapes with the expiratory current, as 
 a freely floating Salpa-chain. The aggregated Salpce are 
 bisexual, though, as the ova are much in advance of the 
 spermatozoa, they cannot be self-impregnating, but must 
 depend for fecundation on the entrance of the spermatic 
 particles of other chains with the water of the respiratory 
 current, for the development of the contained ova is well 
 advanced before the catenated gemmae are themselves throT\^i 
 off. Each one of the Salpa? composing a chain matures, by 
 the ordinary process of development, a single embryo, which 
 eventually becomes a Salpa of the solitary kind, and in turn 
 buds off in its OAvn interior other chains of zooids like its 
 o^\Ti progenitors. From the great transparency of these 
 animals, both forms may readily be seen at once — one 
 within the other — and even the rudimentary beginning of a 
 
IN THE ANIMAL KINGDOM. 91 
 
 new alternation. In the living state, the different modes of 
 connection to the parental system of the embryo and the 
 gemmse are at once indicated by the continuity of the cir- 
 culation in the latter, and its participation in all the oscil- 
 lations and irrea^ularities of that of the adult, while the 
 embryonic current is quite distinct, notwithstanding the 
 vessels are curiously interlaced with those of the parent in 
 the medium of attachment, which has very much the struc- 
 ture of the placenta of a Mammalian. 
 
 Changes of form also of the nature of metamorphosis 
 occur in the development of some Tunicata. Thus the 
 young of Ascidia quit the egg in the form of a Cercaria or 
 microscopic tadpole (Spinula of Dalzell), which is afterwards 
 transformed into that of the adult by the loss of the tail, 
 and the evolution of the characteristic organs from the sub- 
 stance of the head portion. 
 
 § 7. REPRODUCTION OF THE HIGHER MOLLUSCA. 
 
 Among the Mollusca proper, gemmation is a very excep- 
 tional phenomenon. Not only is alternation unknown at 
 any stage of the life history, but even the implantation of 
 the embryonic structure* on the primitive germinal mass — 
 which is so characteristic a feature in the development of 
 segmented animals — is here replaced by a process of trans- 
 formation of the entire yolk into the substance of the em- 
 bryo, and the origination of all the organs of the latter in 
 the cells that are formed by the sub-division of the former. 
 
 The most remarkable phenomena in Molluscan embryo- 
 geny appear indeed at first sight to indicate a process of 
 exactly the opposite kind — the fusion of numerous germinal 
 masses into a single embryo, Koren and Danielssen have 
 
 * Dr. Carpenter, Principles of Compar. Physiol., 4th Ed,, p. 579. In 
 the highest class — the Cephalopoda — the embryonic structures originate 
 from one point of the vitellus, as in most other ova. 
 
92 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 observed that the multitude of bodies with the characters 
 of ova, which originally fill the egg-capsules of the Pectini- 
 branchiate Molluscs, coalesce after a time into a compara- 
 tively small number of embryonic masses, but Dr. Carpenter 
 shows very satisfactorily that the majority of the egg-like 
 bodies, in the nidimentary envelopes of these animals, are 
 not true ova, but mere masses of vitelline matter, or pos- 
 sibly, as all undergo cleavage, though with perceptible dif- 
 ference? they may be unimpregnated ova, and this their last 
 act of expiring vitality. These \dtelline spheres become 
 fused together to form a store of food-yolk, for the nutri- 
 ment of the comparatively small number of embryos which 
 are actually developed.* 
 
 In the development of Mollusca a shell is always fonned, 
 even in those species which are afterwards naked. We find 
 also certain other organs of a provisional and temporary 
 nature, such as a contractile caudal vesicle, and anteriorly 
 two ciliated lobes, which serve as organs of locomotion, 
 when the young is discharged from the egg in an immature 
 or larva state.-|- 
 
 Here we can hardly avoid noticing what Dr. Burnett well 
 calls " that most remarkable episode in the embryology of 
 the Mollusca — the development of certain Mollusks in 
 Holothurioidea."J The facts of the case rest on the au- 
 thority of Prof. Miiller, and are mainly these. § In certain 
 individuals of Spiapta dlgitata, one of the Holothuridse, 
 there are found from one to three sac-like bodies in the 
 general cavity of the animal, attached by their superior ex- 
 tremities to the head, and by their lower ends to the in- 
 
 * Transac. Microse. Society, III., 17. 
 
 t Siebold, Comp. Anat., § 229. 
 
 X Concluding note to tlie Anatomy of the CepliaIopliora,in the transla- 
 tion of Siebold' s Compar. Anatomy. 
 
 § For a translation of liis paper, and some judicious comments on it, 
 see An. Nat. Hist., 2d Ser., IX., pp. 22-103. 
 
IN THE ANIMAL KINGDOM. 08 
 
 testinal blood-vessel. At the point of connection the 
 vessel is perforated, and the lower part of the sac so intro- 
 verted on itself, that the blood can penetrate freely into the 
 intus-suscepted portion. In the upper part of the sac are 
 found spermatic and ovarian cysts, which discharge their 
 contents when mature into the main sac. After fecundation 
 from fifteen to twenty ova become invested with a common 
 capsule. The embryos have not yet been traced to full ma- 
 turity, but the course of development indicates a relation- 
 ship to the Pectinibranchiata, and, as Miiller thinks, to the 
 genus Natica. 
 
 These facts do not seem explicable by any process of 
 alternation on the part of the Synapta — even were we pre- 
 pared to admit the existence of such a relation between an 
 Echinoderm and a Mollusc — for this is not a case of gem- 
 mation but of sexual generation ; and yet it is not the true 
 sexual generation of the Synapta, for this animal has the 
 proper reproductive organs and embryogeny of its own class, 
 and such organs have been found even in the same indivi- 
 dual with the Molluscan brood. Parasitism affords a more 
 plausible explanation than either "alternation" or the notion 
 of " heterogony," which at one time suggested itself to the 
 discoverer ; but even this view involves some startling ad- 
 missions, for we must regard the sac either as a retrogres- 
 sive development of a normal Mollusc, resulting in a degree 
 of degradation — " a vermiform metamorphosis," to use 
 Miiller's own expression — unparalleled even among the 
 Ctrrhipedes or Lerneans — or else as an alternating form, 
 budded off from a normal mollusc, for which we have as 
 yet no precedent among the Mollusca proper. We have 
 besides the difficulty of explaining the access of the para- 
 site, and still more the very intimate nature of its connec- 
 tion with the vascular system of its host, though these are 
 points which we can quite as little account for in some 
 other well-known cases, unquestionably of a parasitic nature. 
 
94 SUEVEY OF THE REPRODUCTIVE PROCESS 
 
 Mollusca, it may be remarked, do some times, though 
 rarely, occur of parasitic habits, as, for instance, Stylifer 
 astericola. 
 
 Of the gamomorphic phase of the life history of Mol- 
 lusca, little need here be said. Alternation, as has been 
 remarked, is unknown, except the presumed parasite of the 
 Sy7iapta may furnish an example. Hermaphroditism is not 
 uncommon among the Mollusca, but self-impregnation must 
 be rare, if it occurs at all. In some cases, indeed, it is evi- 
 dently made impossible by the conformation of the parts, 
 and in others by the sexual elements not ripening simul- 
 taneously in the same individual. ♦ 
 
 § 8. REPRODUCTION IN THE HELMINTHA. 
 
 Among the lower vermiform tribes, the Helmintha are of 
 especial interest for characteristic examples of the leading 
 modifications of alternation, and for the peculiar relations 
 of the sexes, which are here more closely associated than 
 perhaps anywhere else in the animal kingdom. The species 
 are frequently not only bisexual, but self-impregnating, and 
 in some the eggs may be said to be impregnated in the very 
 act of formation, the germinal vesicles, vitelline matter, and 
 spermatozoa being first commingled, before they become in- 
 vested with a vitelline membrane to form the ovum.* 
 
 * It is perhaps more correct to regard tlie so-called germinal vesicles with 
 their granular investments as ova which have not acquired a proper wall, 
 or in which, as in those of the bird, the original ovum-wall has had but a 
 temporary existence, and to consider the matter from the so-called "vitel- 
 ligenous organ," added in conjunction with the spermatozoa, as a sort of 
 adventitious or food-yolk. See Siebold's Compar. Anat., I., § 115. 
 Huxley in Medical Times, XIII., 133-134. Claparede (Ann. of Nat. 
 Hist., 2d Ser., XVIII., 298 N.) Thomson in Cyclopaedia of Anat. and 
 Physiol. Supp. [120] (Ovum). In Pelodytes hermaphroditus, according 
 to Schneider, in the same generative tube spermatozoids first make their 
 appearance, and then eggs, and fecundation is effected at once. Annals 
 Nat. Hist., 3d Ser., Y., 506. 
 
IN THE ANIMAL KINGDOM. 95 
 
 As the reproduction of the Trematoda Avill be afterwards 
 noticed more in detail, in illustration of alternation in the 
 protomorphic stage, it will suffice at present to observe that 
 the recent researches of Van Beneden* go to show that 
 these parasites fall into two very natural groups, distin- 
 guished alike by differences in structure, habit, and develop- 
 ment. Some are ectozoic, that is, parasitic on the exterior 
 of other animals ; they live nearly all on the gills of fishes, 
 and attach themselves by one or even many sucking discs 
 situated at the back part of the body. These species are 
 viviparous, and the young, hatched from the large ova, 
 within the body of the parent, have a development as di- 
 rect as in any other animal. The second group, of which 
 the genus Dlstoma may stand as an example, live in the 
 interior of the body, and attach themselves by a sucker in 
 the fore or middle part of their body. These are all ovi- 
 parous. The eggs are small and very numerous, and a 
 succession of diverse forms is very constantly interposed in 
 the course of their development. The germ which escapes 
 from the ovum, in the form of a ciliated animalcule, under- 
 goes itself no farther development, but matures in its in- 
 terior, and discharges a tubular sac, furnished occasionally 
 with some rudimentary organs. Gemmse are formed in its 
 interior, and these, when set free by its rupture, are either 
 converted themselves into the typical form, or give origin 
 to others which are so. In the genus Distoma this trans- 
 formation is generally effected by a gradual metamorphosis, 
 the form first assumed being that of a Cercaria or micro- 
 scopic tadpole, which, losing its tail, is eventually trans- 
 formed into the perfect Distoma, during an encysting pro- 
 cess which the parasite undergoes, immediately on penetrat- 
 ino* into the tissues of livino- animals. Sexual oro-ans are 
 
 o o o 
 
 * See Translation of Van der Hoeven's Abstract, in Annals of Nat. Hist., 
 3d Ser., III., p. 344. 
 
96 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 not developed till some time after the distoma form has 
 been fully acquired. 
 
 The series of changes is still more complicated in the 
 case of many of the Cestoid worms,* and the study of their 
 development has led to the discovery that the Cystic worms, 
 once supposed to be a distinct order of Entozoa, are merely 
 provisional forms, belonging to the early progress of species 
 of the Cestoid division. The egg of a Tape-w^orm, or other 
 Cestoid Entozoon, gives origin to a minute contractile vesicle, 
 armed with six hooks, by which it is enabled to bore its way 
 into the tissues of animals. Allien it is once established in 
 suitable quarters, the primary cyst buds off what must be 
 regarded as the typical form of the order — the Twnia-head 
 — characterized by its four suckers and apical circlet of 
 hooked teeth. By a continuation of the budding process, 
 the Taenia head may be raised on the extremity of a hollow 
 jointed pedicle forming a flexible neck, but no development 
 of proper reproductive organs takes place, so long as the 
 parasite continues in the same locality. On its being 
 transferred, however, to the alimentary canal of a warm- 
 blooded animal, the original caudal vesicle is cast off, and 
 a series of new segments are budded off from the hinder 
 part of the Taenia head. As the gemmation is continuous, 
 and the segments first generated remain adherent to those 
 of subsequent formation, by whose outgrowth they are 
 pushed off from their point of origin, a long jointed ap- 
 pendage is developed, extending backwards from the head. 
 This new formation constitutes the " body" of the Tape- 
 worm, and it is in its segments that the reproductive organs 
 eventually make their appearance. But the ultimate seg- 
 ments are not all directli/ derived from the head, as a pro- 
 cess of transverse sub-division comes in to supplement the 
 
 * AccordiBg to Van Beneden, direct development, without alternation, 
 occurs only in Caryophylleus, a genus inhabiting the intestinal canal of 
 certain fishes. Annals Nat. Hist., 3d Ser., III., 346. 
 
IN THE ANIMAL KINGDOM. 97 
 
 original gemmation. The joint next the head is soon 
 divided by a transverse fissure into two, each of which re- 
 peats the process as soon as it is somewhat grown. Whilst 
 the joints multiply in this way they increase in size in the 
 same proportion, and so, of course, remove the joints from 
 the head.* But at a certain distance from the head, the 
 whole nutritive power is applied to the development of the 
 organs of generation, and this mode of sub-division ceases, 
 though the budding on of new segments from the head con- 
 tinues. The segments are at first very minute, but as their 
 growth now becomes rapid, they soon come greatly to ex- 
 ceed the size of the head from which they were originally 
 derived. It is this enlargement of the segments, when they 
 have been thrust to some distance from the head, that gives 
 rise to the peculiar form of the neck of the tapeworm — 
 attenuated to a mere filament where it joins the head, but 
 thickening behind, as it passes insensibly into the body. 
 Organs of both sexes occur in the same segment, but they 
 do not begin to make their appearance till the joints have 
 acquired considerable dimensions, and are always found 
 more mature as we pass towards the hindmost — ^that is, the 
 first-formed segments of the body. When impregnation 
 has taken place, and the ova are ready for evacuation, the 
 segments break off, and are discharged with the foeces, still 
 retaining a certain degree of contractile vitality, which aids 
 in the dispersion of the contained ova. 
 
 In no species probably of either kingdom are all the three 
 stages before distinguished as protomorphic, orthomorphic, 
 and gamomorphic, more clearly marked than in the Cestoid 
 Entozoa. To the first belongs the contractile six-hooked 
 vesicle discharged from the egg, to the second the Ttenia- 
 head, and to the third the jointed body of the Tapeworm. 
 Of these tliree successive phases, each of the later is derived 
 
 * Eschriclit on the Generation of Intestinal Worms. Ediuburgh 
 Philosophical Journal (Oct., 184'1), p. 340. 
 
98 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 from the preceding by a distinct gemmation ; yet, from the 
 gemmae remaining adherent to the stock, the process has so 
 much the character of a continuous growth, that only two 
 alternating forms are generally recognised — the Cystic and 
 the Cestoid — and even these owe their distinction as much 
 to the disappearance of the caudal vesicle of the former as 
 to any formative act. Hence the Tapeworm is often de- 
 scribed as a tsenioid entozoon which has lost its original 
 cystic appendage, and developed a long cestoid one in its 
 stead. But in no proper sense can the caudal cyst be 
 termed an appendage of the Tsenia-head — the head is 
 rather an appendage of the cyst, as developed from it. The 
 T^enia-head is indeed the one common feature that unites 
 the two forms, but it stands in a very different relation to 
 the one and to the other ; it is the offspring of the cyst — 
 the parent of the cestoid body. A sort of inversion occurs 
 in the direction of the gemmation during the course of the 
 genetic cycle. It is forwards till the head is formed, when 
 it is reversed, and goes on subsequently in a backward di- 
 rection, so that, had the cyst not been thrown off in the 
 meantime, w^e should expect to find the whole length of the 
 jointed body interposed between it and the head. Some- 
 thing of this kind would seem actually to occur in certain 
 species,* and such is the normal arrangement in the class of 
 Annelida, i" 
 
 In the third order of these Entozoa, the Nematoid worms, 
 alternation is certainly not the general rule, though there 
 are grounds for admitting its occurrence in some species. 
 Thus of late reasons of weight have been brought forward 
 to induce us to look for the progenitor of the formidable 
 Guinea worm in a microscopical inhabitant of tropical pools 
 — the Tankworm — of such tenuity as to be capable of 
 
 * Especially iu Tetrarhynclms, according to Van Beneden. 
 t Carter, Annals of Nat, Hist., 3d Ser., I., 299 ; IV., 33-99. 
 
IN THE ANIMAL KINGDOM. 99 
 
 effecting an entrance into the sudoriparous ducts of the 
 skin. Other Filai'ice which do not develope sexual organs 
 may probably have a like origin. In the same way Kuchen- 
 meister and other writers are inclined to identify the Tri- 
 china spiralis with the Trichocephalus dispar ; but in re- 
 gard to this there is gTeater dubiety, as there is a certain 
 amount of evidence in favour of the Trichina developing 
 sexual organs of its own.* 
 
 § 9. REPRODUCTION IN THE ANNELIDA. 
 
 Though egg-like bodies with more than one embryo have 
 been met mth in some Annelida, the probability is that 
 they are only nidimentary envelopes, such as are common 
 among the Gasteropoda, for we have no evidence of any 
 fissiparous or gemmiparous multiplication in this class, in 
 the protomorphic stage of development.*!" With the first 
 
 * For a list of references on fhe development of Trichina, see Burnett's 
 note in his Transl. of Siebold's Compar. Anat., p. 31. 
 
 The most recent researches are those of Leuckart, communicated in the 
 present year to the Royal Academy of Sciences of Gottingen. The re- 
 sults are as follows : — 
 
 The Trichina is the young state of a small Nematoid worm hitherto 
 unknown, but occurring in large numbers in the intestines of many Mam- 
 malia and Birds. It is introduced by the ingestion and digestion of the 
 flesh of the prey affected with the parasite, and very soon when set free 
 acquires fuU sexual maturity. The young are developed in about six 
 days, and immediately begin to make their way to the muscular tissues, 
 by penetrating through the wall of the intestine, and the peritoneal cover- 
 ing of the abdominal cavity. They make their way finally into the in- 
 terior of the ultimate muscular fibres, and there attain within fourteen 
 days the size and organization of the Trichina spiralis, as commonly met 
 with. The penetration of these embiyos in large quantity sometimes gives 
 rise to dangerous peritonitis. Annals of Nat. Hist., 3d Ser., V., 50-1. 
 
 f In some Nemertini, according to Desor and Schulze, the early develop- 
 ment somewhat resembles that of the Trematode Entozoa, for the first 
 formation from the egg is a ciliated infasorian, vnth a mouth-Uke cleft on 
 one side. Within this is generated an active vermiform body, which 
 eventually escapes from the matrix, carr^^ng away the cleft mentioned, 
 
 f2 
 
100 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 appearance, however, of the embryonic structures, gemma- 
 tion comes into play, manifesting itself primarily and most 
 extensively in the multiplication of the segments of the 
 body. The species vnth external branchia quit the egg as 
 short ciliated larva-like Infusoria, and only acquire the ver- 
 miform character by the successive gemmation of segments 
 from behind, much as the joints forming the " body" of the 
 Tapeworm are developed from the back of the Tsenia-head. 
 Only there is this difference, that, with the exception of the 
 caudal appendage, the segments are budded off from each 
 other, not all from the head, so that the penultimate is 
 always the most recent, while in the Cestoids the posterior 
 segments are the oldest. 
 
 In both cases it is only in these derivative segments that 
 generative organs are developed, and the parallel is carried 
 still farther, when, as in Syllis, they are thrown off as sexual 
 zooids, the main difference being that in the Annelida the 
 offsets have more the character of distinct animals. The 
 joints are not only thrown off in sets, like the catenated 
 zooids of the Salpw, but such an organic unity is established 
 among the connected segments as to give each set quite the 
 character of a complete animal. In these cases one or more 
 of the later segments become secondary foci of a budding 
 process, which proceeds exactly in the same way as in the 
 young annelidan first formed from the ovum ; that is, the 
 ring which is to develop e the new zooid sub-divides into 
 two parts, which acquire the organization respectively of 
 head and tail segments, but it presents at first no farther 
 division, the other joints being gradually formed afterwards, 
 between the cephalic and caudal extremities, and always in 
 succession from the posterior of the segments previously 
 produced. Phenomena of this kind were first observed by 
 
 as its own mouth. From this body the annelidan is probably developed, 
 after the plan which prevails generally in the class. Huxley in Medical 
 Times, XIII., 281. 
 
IN THE ANIMAL KINGDOM. 101 
 
 Otto Mliller in Nais pf^oboscidea, and by Gruithuisen in a 
 species of Nereis. More recently M. Quatrefages lias made 
 similar observations on the Si/llis jjroU/era. This species 
 forms ordinarily but a single zooid at a time, but Mr. 
 Milne Edwards in another annelidan — Myrianida fasciata 
 — has seen as many as six in process of formation at the 
 same time from the terminal segments of the parent. The 
 first formed and most complete was situated furthest back, 
 and each newer zooid presented a less developed structure 
 than the preceding one. The anterior or youngest ha<l 
 only ten rings, the second had fourteen, the third sixteeTi, 
 the fourth eighteen, the fifth twenty -three, and the last or 
 caudal one thirty rings. In some of the species named, the 
 fissiparous multiplication has very markedly the character 
 of a process ancillary to sexual reproduction, for the zooid.s 
 when thrown off speedily develope the appropriate organs, 
 but retain life only long enough to impregnate or mature 
 the resulting broods of ova.* In other cases, perhaps, 
 multiplication may go on indefinitely, by the detached 
 zooids repeating the same fissiparous process — the forma- 
 tion of sexual organs appearing to depend in some degree 
 on external circumstances. Midtiplication may also be 
 effected by artificial division, in some cases in which the 
 fissiparous process does not seem to come into play as a 
 spontaneous mode of increase. *[* 
 
 In the sexual relations of the Annelida there is consider- 
 able variety, hemaphroditism beinj^ a common character 
 among the Terricolse and Suctoria, while the sexes are 
 generally separate in the other orders. There is no evi- 
 dence of self-impregnation in any. 
 
 * Quatrefages Ann. Des. Sci. Nat. (1814) T. I., p. 22. Edwards, Oi:.. 
 Cit. (18i5),T. III., p. 170. Dr. A. Thomson, Cyclop. Anat. and Physiol., 
 Art. Ovum., p. 32-33. 
 
 t Siebold, Compar. Anat. I., § 163. 
 
102 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 § 10. ARTICULATA. 
 
 Among the higher Articulata, it is only in a few aberrant 
 species that we have any obvious manifestation of gemma- 
 tion ; consequently, though in these exceptional cases, we 
 meet wth some well marked examples of " alternation," 
 such phenomena are not in accordance ^\dth the general 
 course of development in this type of organization. 
 
 It may be necessary in some degree to qualify this state- 
 ment, as applicable to the Myriapoda, for as these approach 
 the Annelida in configuration, so they do also in multiply- 
 ing their segments up to a certain point, by a process of 
 gemmation from the penultimate segments, subsequent to 
 the emission of the embryo from the egg, though no in- 
 stances are known of spontaneous fission of the body.* 
 
 A striking feature in the reproductive process among 
 Articulata is what is called metamorphosis. In Insects par- 
 ticularly, and also in many Crustacea, the embryonic form 
 first assumed often differs very widely from that of the 
 adult, in the conformation of its parts both external and in- 
 ternal, and this not merely in its organization being rudi- 
 mentary, but in a total dissimilarity of particular organs or 
 members, and even in the existence of structures which 
 afterwards waste or entirely disappear by absorption, or are 
 throAVTi off from the body. Metamorphosis, indeed, is not 
 confined to this division of the Animal Kingdom ; allusion 
 has before been made to its occurrence in some of the other 
 groups, and, as a general rule, it may be said to be more 
 marked in proportion as the typical organization becomes 
 more elaborate. It is nowhere, however, more observable 
 
 * According to Fabre, tlie larva of Scutigera lias at first only the seven 
 anterior segments, containing the organs of sense and the digestive ap- 
 paratus ; the posterior segments — those behind the large plates or elytra 
 — are of later formation. It is in this region, as in the case of the Anne- 
 lida, that the reproductive organs are situated. Annals of Nat. Hist., 2d 
 Ser., XIX., 165. 
 
o 
 
 IN THE ANIMAL KINGDOM. 10.' 
 
 than in the case of Insects, owing partly to the real magni- 
 tude of the changes which take place, and partly also to the 
 prominence with which they are brought under the eye of 
 the observer. The embryo even of Mammalia undergoes 
 in the course of its development a series of remarkable 
 changes, very parallel to the metamorphosis of an insect ; 
 the conformation of its vascular system, for instance, is 
 changed more than once, and certain provisional organs, 
 such as the wolffian bodies, the umbilical vesicle, and the 
 allantois, appear, which are afterwards absorbed or cast oif. 
 But these transformations have only been traced by labo- 
 rious anatomical investigations, as they are all gone through 
 in the interior of the uterine cavity — in those hidden re- 
 cesses w^here the new being is " made secretly, and fashioned 
 beneath in the earth," as it were — w^hile in the Insects and 
 some others of the lower animals, the embryo being ex- 
 truded, not only from the body of the parent, but also from 
 its own eo:o;-coverinQ!:s, while still in an unformed or larva 
 state, the whole subsequent course of metamorphosis takes 
 place in the outer w^orld, and is in great measure presented 
 naked to our view. Larv?e are not unknown in other 
 forms of animal life — even among Vertebrata they occur in 
 the case of the Batrachia and Marsupialia, and also in some 
 Fishes* — but in Insects they are not the exception but the 
 rule — the guise under which the young are normally 
 brought forth. 
 
 Entomologists distinguish three stages in the develop- 
 ment of Insects, by the terms lar'ca, pupa, and imago. 
 But these expressions do not always indicate homologous 
 conditions, for the point of development at which the young 
 quits the egg varies considerably in different orders of the 
 class. "In all cases the germinal mass, while still within the 
 
 * The metamorphosis is very marked in the Lamprey. Miiller's 
 Archives Anat. Physiol. (1856), p. 323. 
 
10-1'' SURVEY OF THE REPRODUCTIVE PROCESS 
 
 egg, is first converted into a footless worm, resembling the 
 higher Entozoa, or the inferior Annelida, in its general or- 
 ganization, but possessing the number of segments — thirteen 
 — which is typical of the class of Insects."* It is at this 
 stage of its progress that the embryo of the Diptera, Hy- 
 menoptera, and of some of the Coleoptera or Beetle-tribe, 
 comes forth as a larva, such as is commonly kno\\Ti as a 
 " Maggot." In Butterflies, again, and in the greater num- 
 ber of Beetles, the organization of the larva is rather more 
 advanced, as it is furnished with the rudiments of the 
 thoracic legs, besides certain provisional organs of the same 
 nature on the posterior segments of the body — the abdomi- 
 nal tubercles or pro -legs. Such larvae are termed " Cater- 
 pillars." In the Orthoptera, Hemiptera, and a portion 
 of the Coleoptera, there cannot be said to be any pro- 
 per larvse, as the young do not emerge from the egg 
 till they have attained the conformation of the adult in 
 almost all respects, except the evolution of the wings. The 
 true or vermiform larva feeds voraciously, and continues 
 for some time without any other obvious change than a 
 rapid increase in size, attended generally with several cast- 
 ings of its skin. As the period of its transformation ap- 
 proaches, it passes into the pupa condition — a state of inac- 
 tivity, during which it undergoes its change into the imago, 
 or perfect insect, with six jointed legs, four wings, and other 
 peculiarities of that type of organization. " The pupa is 
 enclosed in the last skin exuviated by the larva, which, in- 
 stead of being thrown off, dries up, and remains to encase 
 the proper skin of the pupa that is formed beneath it ; and, 
 in addition to this, it is frequently protected by a silken 
 ' cocoon,' the construction of which was the last act of 
 larval life.""f* To this association of external inactivity, 
 with great internal constructive energy — that is, to the 
 
 * Carpenter, Compar. Physiol., 4tli Ed., p. 599. 
 f Carpenter, Op. Cit., p. 601. 
 
IN THE ANIMAL KINGDOM. 105 
 
 pupa state in a physiological sense — that which corresponds 
 in the case of the Orthoptera and Hemiptera, is the later 
 period of development within the egg. In other words, 
 these embryos pass through stages, corresponding both to 
 larva and pupa within the egg, or at least are only dis- 
 charged while still undergoing some of the concluding 
 changes of the latter state. Mr. Andrew Murray brings for- 
 ward evidence to show that in some cases even a sort of 
 cocoon is formed within the egg, and that the young insect, 
 after certain changes, emerges from it, before it is finally 
 discharged from the egg.* 
 
 In the lower orders of Insects, the development is more 
 or less arrested ; in the Anoplura, and Thysanura, which 
 come out of the egg as active pupae, there is no farther 
 metamorphosis, and in the Homoptera, it is so far imperfect 
 that but two wings are formed ; in the flea tribe also, 
 though the larva and pupa states are regularly gone 
 through, the development of the imago form is imperfect, 
 the abdomen not being marked off from the thorax, and the 
 wings being represented only by rudimentary appendages 
 attached to the second and third segments of the body ; in 
 Diptera the posterior wings are in like manner rudimentary. 
 In other cases it is only one of the sexes, or it may be only 
 certain individuals of the sex, whose development is so ar- 
 rested. Thus the females of Coccus and Lamj^yris never 
 develope wings, and in the ant tribe neither these organs 
 nor those of reproduction are evolved in the majority of the 
 sex, full development being attained by a few individuals 
 only, which breed for the whole community. Among the 
 Termites, or white ants, the '' soldiers" appear to be pupiie 
 arrested in their development, while the " workers" have 
 the characters of permanent larvae. The working females 
 of the bee, on the other hand, acquire the external charac- 
 
 * Ed. Phil. Journal. 1S58. 
 
 F 3 
 
106 SURVEY OF THE REPRODUCTIVE PROCESS 
 
 ters of the perfect insect, only their sexual development 
 being arrested. In this they contrast with those cases in 
 which the males are the subiects of arrest, as amono- the 
 Cin'hipedes and Lerneans ; for then it is the general organi- 
 zation that is defective, the sexual parts being developed 
 out of all proportion to the rest of the body. 
 
 The whole development, however, of these last-mentioned 
 orders is exceedingly anomalous. The first change, induced 
 on the germ-mass of the ovum, assimilates it to the gene- 
 ral character of Entomostraceous Crustaceans, but a sub- 
 sequent transformation, of what is called a retrograde 
 character, results in the loss of vision and of the power of 
 locomotion, and so masks the articulate character that the 
 forms ultimately assumed were long referred to wholly 
 different types of organization. There is, however, another 
 possible view of such cases, which will be considered after- 
 wards. 
 
 Throughout the articulate series, the sexes are normally 
 separate, except in some aberrant forms of the Crustacean 
 class, and perhaps also some of the lower Arachnida. 
 
 The cases of well-marked alternation, such as occurs 
 among the Aphides, will be taken into consideration when 
 that subject comes to be discussed. 
 
 § 11. VERTEBRATA. 
 
 The remarks just made in regard to the abeyance of 
 gemmation, the absence of phenomena of alternation, and 
 the constancy of the separation of the sexes in Articulata, 
 all apply with still greater force to the Vertebrate division 
 of the Animal Kingdom ; but no farther remarks seem to be 
 called for here on the reproductive process in this gTOup, as 
 the relation to it of various modes of propagation occurring 
 among the lower organisms has been throughout a primary 
 object of attention in this summary. 
 
IN THE ANIMAL KINGDOM. 107 
 
 § 12. An observation that suggests itself in comparin*-'- 
 the reproductive process in the several groups of Animals, 
 as represented in the preceding summary, with the modifi- 
 cations of the same functions ,of Veo-etables, is the sino-ular 
 difference of the general result in the two kingdoms, aris- 
 ing from the same general law of the interpolation of gem- 
 mation at certain points in the genetic cycle. Its effect in 
 the case of plants is to establish a wide apparent diversity 
 between the reproductive process of the higher and the 
 lower cryptogamic plants ; while in animals it is rather 
 to bring forward, in the case of particular families or 
 species, a series of forms, which, however apparently dis- 
 similar, are really only successive phases of one individual, 
 or detached offshoots or members of the same orioinal stock. 
 
 Very much of the general character of the reproductive 
 process in any family depends on the mutual relations of 
 certain epochal acts, as they may be called — such as access 
 of the spermatic element (Insemination=I) ; discharge of 
 the ovum or its contents (Extrusion=E) ; escape of the 
 young from the egg coverings (Birth=B) ; and the full 
 acquisition of the typical characters (Development^D). 
 The follomng tabular statement, therefore, in which these 
 acts are denoted by the letters above indicated, may be of 
 interest, as showing some of the more usual variations, in 
 their order of succession, in the different tribes of animals. 
 When two letters follow each other immediately, it denotes 
 that the acts are simultaneous ; the interposition of a 
 greater or less number of points indicates a corresponding 
 interval of time in the succession : — 
 
 Mammalia I DEB 
 
 Marsupialia I...EB D 
 
 Birds I.E DB 
 
 Batrachia EI...B D 
 
 Fishes E.I...B D 
 
 Insects LE...B D 
 
108 SURVEY OF THE REPRODUCTIVE PROCESS, &C. 
 
 There would be considerable difficulty in extending such 
 a table to the Invertebrata generally, from the want of 
 uniformity in many of the orders, in the points refeiTed 
 to. 
 
THE NATURE AND VARIETIES, &C. 100 
 
 IV. 
 
 THE NATURE AND VARIETIES OF ALTERNATION 
 
 OF GENERATIONS. 
 
 § 1 . The two modes of propagation — by gemmai capable of 
 spontaneous evolution, and by germs dependent on impreg- 
 nation — as has been already observed, are frequently asso- 
 ciated with no less remarkable diversities in the immediate 
 result of the development, leading in cases of periodic recur- 
 rence or alternation of the former, to a corresponding mu- 
 tation or alternation of dissimilar forms in the same species. 
 It is only, however, quite recently that this has been ad- 
 mitted generally by zoologists, who were not unnaturally in- 
 disposed to it, by observing the constant succession of like 
 to like in the higher animals. But since the time that 
 Chamisso called the attention of naturalists to the recur- 
 rence of two forms in Salpa, as a case of " Alternation of 
 Generations," analogous phenomena have been abundantly 
 brought forward in other tribes of organised beings. Steen- 
 strup was the first to group together these cases, applying 
 to them the same term as was used by the former naturalist, 
 for which some later writers would substitute that of Me- 
 tageiiesis, proposed originally by Professor Owen. 
 
 In all these cases we may admit so much as this in 
 common — that an act of digenesis recurs with greater regu- 
 larity in the interval of the acts of monogenesis ; and that 
 the products of the former differ more or less in their con- 
 formation from the organisms budded off in the latter. 
 
 Hence, as both forms must be taken into account to 
 complete our idea of the perfection of the species, it has 
 been proposed to term them zooids in the case of animals, 
 
no THE NATURE AND VARIETIES OF 
 
 and phytoids in that of plants, as indicating that any one 
 of them is not so much a complete animal or plant in 
 itself, as a fragment or fractional part of one — the whole 
 series, considered as specific unit, rather than any one 
 among the successive links of which it is made up, answer- 
 ing to our idea of individual completeness, as this is dra^\^l 
 from the higher animals, in which like seems always to 
 produce like. 
 
 In confirmation of such a view, it is noticed that in not 
 a few cases these fractional phytoids and zooids really re- 
 main in organic union for life — making up an arborescent 
 form — like what we call a polypidom in animals, which is 
 readily recognized as being in its entireness the individual 
 representative of the species. ' 
 
 In this view zoological individuality becomes a very dif- 
 ferent thing from metaphysical individuality,* for orofans, 
 which in one species are integrally united into a whole 
 which is indivisible without mutilation, are found in others 
 more or less broken up into separate and independent 
 structures. Hence if we would avoid the solecism of speak- 
 ino; of the indi'ciduaL as in some cases beino- divided into a 
 number of parts, having all a general character of com- 
 pleteness, and use the word, as propriety seems to require, 
 in its loocical sense of that which is individualized, we must 
 be prepared to admit as a consequence, that the individuals 
 of one species are not always homologous with those of 
 another."!* 
 
 But though we may allow so much in common in 
 these cases of " alternation," as is involved in the occur- 
 rence in all of a periodic diversity of derived forms, there 
 are yet — as was pointed out in the introductory chapter — 
 great variations among them, as far as the relations are 
 
 * Huxley in Philos. Transactions for 1851. Paper on /S'aZpo?, p. 579. 
 t Mr. Lnbbock in Philosophical Transactions. Jany. 29, 1857. 
 
ALTERNATION OF GENERATIONS. 1 1 1 
 
 coiiGerned in which the budding process stands to the sexual 
 act, and to the full development of the specific type — rela- 
 tions depending on the period of the life-history of the 
 species, at which the act of gemmation is interpolated in 
 the genetic cycle. The contrast lies especially between the 
 cases in which the alternation of form is due to zooids 
 being budded off in the Protomoiyhic stage of the life- 
 history — that is, during the early progTCss of germinal de- 
 velopment — and those in which it arises from the detach- 
 ment of gemmae in the fully developed or typical phase, as 
 a preliminary step to the evolution of reproductive organs 
 — the latter zooids belonging to the Gamomorphlc stage, or 
 that of sexual maturation. The two classes — as has been 
 already observed — differ wddely in their structure and rela- 
 tions. In the one case they are the primary products of 
 impregnation, precursors of the perfect form, and without 
 sexual characters — in the other derivative, and wiWi dis- 
 tinct sex. Zooids of both kinds, indeed, may have cer- 
 tain organs superadded, varying in their nature and com- 
 pleteness with the circumstances of their life as indepen- 
 dent beings. In those of the protomorphic stage, the ad- 
 ventitious organization probably does not go beyond the 
 development, externally, of cilia, or of a contractile integu- 
 ment for locomotion, and internally, of a rudimentary di- 
 gestive apparatus ; but in many gamomorphic zooids, both 
 the locomotive and alimentary systems may be rather 
 highly organized, and the whole structure occasionally 
 larger and more complex and elaborate than that of the 
 parent stock. On the other hand, such is the structural 
 degradation of some zooids of both kinds, that they might 
 readily pass for mere proliferous cysts or egg-sacs. This 
 variability in the kind and extent of organization proves 
 of itself its adventitious nature, and shows it to be of no 
 value as a distinctive feature. The real points of distinc- 
 tion are those before referred to — their position in the 
 
112 THE NATURE AND VARIETIES OF 
 
 genetic cycle, and their gemmiparous or sexual character in 
 consequence. They both, however, have this in common, 
 that the great end of their existence is the multiplication of 
 the race — an end to which the nutritive and animal func- 
 tions are always subordinated. 
 
 § 2. The distinctions now referred to among the cases 
 of alternation will appear more clearly by noticing the phe- 
 nomena which are actually met with in such tribes of ani- 
 mals as afford well marked examples of their occurrence. 
 The case of the Trematode Entozoa furnishes a fair illus- 
 tration of the variety in which gemmation occurs, as a 
 feature in the , progress of the development of the most 
 typical form of the species. The reproduction of these 
 Entozoa, as observed in the well-knov,Ti parasite Distoma, 
 has had the attention of naturalists strongly drawn to it, 
 from being the case on which Steenstrup chiefly enlarged in 
 his original work on " Alternation of Generations." The 
 species of Distoma are very numerous ; they are bisexual, as 
 is the case with the Trematoda generally, and probably also 
 self-impregnating. The young, on escaping from the ^gg — 
 which does not commonly happen till the ejection of the latter 
 from the system of the animal in which the parent was a pa- 
 rasite — appear in the guise of infusorial animalcules, which 
 swim about freely by the play of the cilia, covering their ex- 
 terior. Some of them have been traced into the interior of 
 water snails. This infusorial form never advances to any 
 higher development; it is in fact merely the matrix of another 
 animalcule of a very different character, resembling a Gre- 
 garina, in its uniformly granular structure and smooth con- 
 tractile integument, and the function of the original ciliated 
 envelope is mainly, as it would seem, to introduce the Gre- 
 garina into the body of the snail. This gregariniform 
 parasite itself is a mere cyst or capsule, whose gelatinous 
 walls have generally a certain degree of contractility, but 
 which never acquire more than the most rudimentary in- 
 
ALTERNATION OF GENERATIONS. 1 1 3 
 
 temal organs, though there is a certain gradation observ- 
 able in this respect. In some there is a distinct head, witli 
 a mouth opening into a sort of bUnd gullet, representin<T 
 perhaps the commencement of an alimentary canal, and 
 posteriorly the tail is marked off from the cylindrical body 
 by a pair of processes like rudimentary limbs ; others 
 again are merely elongated sacs, not always endowed even 
 with contractility. The former Filippi terms Redice, the 
 latter Sporocysts* 
 
 In the farther course of development, the redia or sporo- 
 cyst forms in its interior a number of growing points, which 
 assume the form of Cercaria?, or microscopic tadpoles. The 
 parent cyst in time gives way, under the pressure caused by 
 the growth of its progeny, which are thus set at liberty, and 
 boring their way out of the snail by hooks on their heads, 
 they swim about for a time freely in the water. Their re- 
 lations and farther progress are thus graphically described 
 by Prof. Owen. " No sexual organs exist in these Cercaria% 
 any more than in their animated ' coat,' the Grecjarina, or 
 in their ciliated ' great coat,' the Infusorial embryo. After 
 the larval Cercarise have passed some time in the water, first 
 creeping and then swimming about with great restlessness, 
 they either enter directly the body of the waterfowl,*!" or 
 bore their way into some aquatic insect, or they may fail in 
 both these instinctive efforts, and remain in the water. In 
 any case they undergo a metamorphosis. The Cercaria 
 gathers itself up into a ball, and exudes a mucous secretion 
 from its surface, which soon hardens ; and since the worm, 
 inside this mucous mass, turns round without stopping, it 
 
 * Siebold's Compar. Anatomy, § 118, n. 7. Huxley, in Medical Times, 
 XIII., 133-134. Busk's Translation of Steenstrup on Alternation of 
 Generations, (Ray Soc. Pub.), p. 63. 
 
 t The Monostomnm imdahile, a Trematode, whose development is 
 quite parallel to that of Distoma, has for its habitat the eyelids of ducks 
 and other waterfowl. 
 
Hi THE NATURE AND VARIETIES OF 
 
 invests itself with a kind of egg-sliell ; during tliis process 
 the tail is cast off.* 
 
 " Should this process take place within the body of an 
 insect, the encysted Cercaria might be introduced into the 
 body of an insectivorous bird or beast. In the act of di- 
 gestion by the engulpher, the body of the insect is destroyed, 
 together with the capsule of the cercarian pupa ; but this by 
 virtue of its "vitality remains unharmed, and is thus trans- 
 planted into a new sphere, and fitted for its farther change into 
 a sexual entozoon of the Trematode or ' fluke-worm' order. 
 
 "Then again commences the strange and complex genetic 
 cycle, from the Harveian point — the impregnated ovum. 
 
 " Three different species of animal may contribute — two 
 are essential — to the successful progress of the ordinary and 
 Parthogenetic processes of propagation, manifested by the 
 three distinct forms of Infusory, Gregarina, and Cercaria, 
 intervening between the egg and the perfect parasite fluke- 
 worm. ""I" 
 
 If the hypercriticism be excusable of objecting to the 
 accuracy of the figurative language, in which this author 
 gives so lively a representation of these strange mutations, 
 it may be remarked that the terms " coat" and " greatcoat" 
 are out of point here in two particulars. 
 
 1. That such articles of dress never envelope more than 
 one wearer at a time, whereas the Gregarina-form at least 
 encloses a whole brood of Cercarise ; and 
 
 2. That these garments are worn simultaneously, whereas 
 the Gregarina does not develope the Cercarise till it has 
 escaped from its infusorian cyst. Indeed in some cases it 
 
 * Sometimes tliis appendage appears to be torn oflf at the first entrance 
 of the parasite, in the act of boring through the integument. It would 
 appear, however, that some Distomata never pass through the Cercaria 
 stage at all. Huxley, in Medical Times, III., 133-134. Siebold's Compar. 
 Anatomy, 118 [note]. 
 
 t Address to Brit. Assoc, 1858, 23-24. 
 
ALTERNATION OF GENERATIONS. 1 1 5 
 
 would seem that the Cercarise are not formed in the first 
 Gregarina-zooid at all, but in those of an intermediate 
 brood, derived from it, and of the same general character.* 
 
 Till the recent researches of Professor Van Beneden of 
 Louvain, the whole series of changes liad never been traced 
 out in the same species, or by one single observer, but, as 
 the author just quoted remarks in another place,i" ^^^^ tes- 
 timony of different good and independent witnesses, at 
 different periods, to different stages of the successive genera- 
 tions, which, when compared with one another, are seen to 
 link together and complete the metagenetic cycle, was per- 
 haps the best foundation for scientific confidence in the 
 truly marvellous result. 
 
 "Siebold observes the development and birth of the 
 ciliated monadiform embryo from the egg of the oviparous 
 Trematode Entozoon, and the escape of the gregariniform 
 non-ciliated worm from the ciliated one. 
 
 " Bojanus and V. Baer trace the development of the 
 cercariform individuals from the 'King's yellow worm,' 
 which in its form and simple structure corresponds with the 
 vermiform offspring of the ciliated embryo. 
 
 " Nitsch traces the Cercariform progeny of that worm to 
 their pupa state. 
 
 '' Steenstrup, confirming the origin of the Cercarire from 
 the multiparous ' King's yellow worm,' completes the obser- 
 vation of their metamorphosis through their pupa state, 
 into the Trematode Entozoon." 
 
 In the development of the Trematoda, as exemplified in 
 the case of a Distoma, there are two points of especial inte- 
 rest in their bearing on the general question of Alternation : 
 
 1. The imperfection and variability in the amount of 
 organization acquired by the zooids, which originate directly 
 from the infusorian form, as compared with that of the 
 
 * Steenstrup on " Alternation," pp. 69-93. 
 f Parthenogenesis, p. 17. 
 
116 THE NATURE AND VARIETIES OF 
 
 Distomata, derived from them in turn. The former never 
 exhibit clearer indications of animaUty than a power of 
 peristaltic motion, and some rudimentary organs, external 
 and internal ; and they range from this down to simple rigid 
 tubes — mere bud-sacs, quite destitute of organization and 
 all power of motion. The latter, again, possess as complex 
 a structure as is found anywhere in the class of animals to 
 which they belong — and this not as an occasional develop- 
 ment, but uniformly in all cases, and quite irrespective of 
 the organization of the precursory form from which they 
 have been derived. The derivative zooid, indeed, is not 
 only much more highly organized than the primary, but it 
 is truly the typical form of the species, as appears by its 
 correspondence with the fully developed condition of those 
 Trematoda in which '^ alternation" does not prevail, and 
 consequently but one form occurs in the same species. 
 
 2. The second point is that not only are the precursory 
 zooids destitute of all sexual characters, but that no such 
 organs are developed even in the derivative forms, till some- 
 time after they have acquired the typical conformation in 
 all other particulars. The appearance of these organs, in 
 fact, constitutes a new epoch in the life-history of the 
 typical form, quite as observable as its derivation from the 
 preceding one, and admits of our dividing the whole succes- 
 sion of changes into the three stages to which the terms 
 Protomorphic, Orthomorphic, and Gamomorphic, were ap- 
 plied in the Introductoiy Chapter. 
 
 From the consideration of these points, we may assign the 
 foUomng as the characters — positive and negative — of that 
 modification of " alternation," which prevails among the 
 Trematoda : — 
 
 1. That the " alternation" consists in the derivation of 
 sexual and oviparous zooids, from the last generation of a 
 series of others which are sexless and gemmiparous. 
 
 2. That the later set of zooids, which eventually acquire 
 
ALTERNATION OF GENERATIONS. 117 
 
 sexual organs, represent the typical or orthomorphic form 
 of the species. 
 
 3. That the process of gemination in this case represents 
 a particular step in the course of embryonic development, 
 marking the transition from the early germinal or proto- 
 morphic, to the first beginning of the orthomorphic or 
 typical stage ; and that it has no direct bearing on the evo- 
 lution of the sexual organs — the process which distinguishes 
 the gamomorphic stage. 
 
 The first of these characters belongs to all forms of '' al- 
 temation ;" the latter two are distinctive of that now de- 
 scribed, which may, therefore, be termed " Alternation from 
 gemmation in the Protomorphic stage," or, more shortly, 
 " Protomorphic Alternation." Its distinctness will appear 
 at once, on comparing it with other forms, particularly with 
 that which prevails among the lower or polypiferous section 
 of the Coelenterate division of the Animal .Kingdom (Hy- 
 drozoa of Huxley). 
 
 § 3. In more than one family of Polypes, the true ova 
 are frequently produced by zooids, varying much in size, 
 but having the general structure of the Medusa?, or common 
 Jelly-fishes of our seas. From the ovum a cup-shaped 
 embryo proceeds, which is transformed into a polype, and 
 from this, as from the original shoot of a plant, there is 
 generally developed, by a series of successive sprouts, a 
 polypidom supporting a whole colony of polypes like the 
 original — variously disposed according to the species, but 
 all organically connected together. At certain seasons, and 
 under favourable circumstances, there are developed either 
 from the polypes or from the polypidom, peculiar bud-like 
 processes, which sometimes acquire the characters of regu- 
 larly organized Medusoids, but at others remain in the ru- 
 dimentary condition of mere spermatic and ovarian sacs. 
 It is fi'om these that the ova are derived, whose course of 
 development has just been noticed. 
 
118 THE NATURE AND VARIETIES OF 
 
 Now, while this case agrees with that of the Trematoda, 
 in the first of the three characters before given — that of a 
 derivation of sexual and oviparous zooids (the medusoids) 
 from others which are sexless and gemmiparous (the polypes, 
 or their common stem, or its capsular developments) — I 
 think it may be clearly sho^^^.l to differ in the other two ; 
 that is to say, in the zooids which represent the typical 
 form being here the earlier or gemmiparous set, not the 
 later or oviparous ; and in the process of gemmation being 
 ancillary to the act of sexual reproduction, instead of re- 
 presenting a step in the development of the typical form — 
 belonging to the Gamomorphic, instead of to the Proto- 
 morpldc stage. 
 
 Certainly it is the polypiferous phase which in the great 
 majority of the species impresses us as the representative of 
 the typical form, for in the Coryniform and Sertularian 
 zoophytes, as well as in the Calycophoridae and Physopho- 
 ridse, the individual polypes, though small, are sometimes 
 not so minute as the resulting medusoids ; while the zoo- 
 phytic growths, which are developed by their repeated pul- 
 lulation, are clearly the most conspicuous phase in the life- 
 history of the species, and, in the two orders last mentioned, 
 have often such individuality of character about them, that 
 they suggest the idea not so much of a colony of aggregated 
 zooids, as of a body composed of various organs, like that 
 of one of the higher animals.* 
 
 And as in these cases the polype phase is the most con- 
 spicuous, so is it always the most permanent condition, for, 
 after throwing off a swarm of medusoids, it goes on in as 
 vigorous a state as before, and at intervals, varying with the 
 
 species or with accidental circumstances, may give origin to 
 
 * 
 
 * This is especially tlie case in such forms as Physalia, Velella, and 
 Parpita. 
 
ALTERNATION OF GENERATIONS. 1 1 9 
 
 many successive crops of gemmae* ; whereas the rudi- 
 mentary forms of the Trematoda seem to pass away as soon 
 as they have thrown off all their freight of gemma?, whose 
 production is the great object of their existence. The con- 
 trast is equally marked in the derivative zooids, though in 
 the opposite way. In the Trematoda, where they are re- 
 presented by the distoma-form, it is these that have the 
 greater length of life ; for a considerable time generally 
 elapses before they go through their metamorphosis and 
 acquire sexual organs — while the medusoids of the zoo- 
 phytes, which are developed for the very purpose of repro- 
 duction, have a correspondingly brief duration, their term 
 of life coming to a close as soon as the spermatic and ger- 
 minal products are matured and discharged. 
 
 There is besides a fragmentary and subsidiary character 
 attaching to these medusoids in many cases, which of itself 
 suggests the idea of their being merely detached organs for 
 the formation and fecundation of ova. It is true that there 
 are gTcat differences among them in this respect — gTeater 
 even than among the precursory zooids of the Trematoda. 
 The variability is such that while some of the medusoids 
 have an organization apparently much more complex than 
 that of the polype-stock, in other cases the sexual zooids are 
 reduced to mere sperm and germ-sacs, of the most rudi- 
 mentary description, without any trace of medusoid struc- 
 ture, though the correspondence of the two extremes is 
 established by a continuous series of intermediate forms. 
 
 There is an equal variability in the isolation or attachment 
 of the sexual structures. In general these are thrown off 
 as free zooids, but in many species they are never detached, 
 forming fixed appendages of the parent stock, and gradually 
 merging into the character of mere organs of reproduction. 
 So completely is this the case in the common Hydra, that 
 
 * Carpenter's Compar. Pliysiology, 4tli EJ., p. 559. 
 
120 THE NATURE AND VARIETIES OF 
 
 the species presents but a single form, very slightly modi- 
 fied even at the breeding period. The single fonn of the 
 Hydra may, of course, be as fairly taken to indicate the 
 type of the allied polypes, as that of the viviparous Trema- 
 toda to determine the type of the order of worms to which 
 they belong. So long, therefore, as we confine our atten- 
 tion to the orders of Hydrozoa above mentioned, there 
 seems no difficulty in determining that here the " alterna- 
 tion" is due to gemmation in the gamomorphic stage, or in 
 the course of the evolution of the sexual organs — that the 
 oviparous zooid is not here the typical form, but a sub- 
 sidiary offset from it, for the development of those organs of 
 reproduction which never make their appearance in the 
 former — and that the gemmiparous zooid is not here the re- 
 presentative of the gemmiparous or protomorphic zooid of 
 the Trematoda, but is itself the typical form, which in 
 polypes is produced by the transformation rather than the 
 gemmation of the primary infusorial product of the ovum ; 
 or, as we recognise in both cases a principal or typical 
 and a subsidiary form, the difference might otherwise be 
 expressed by saying, that in the Trematoda the subsidiary 
 zooid is gemmiparous and preliminary to the typical, while 
 in the Polypifera it is oviparous and supplementary. 
 
 But there is one order of Hydrozoa — the Lucernariadse — 
 some of the reproductive phenomena of which seem at first 
 sight much opposed to this view. Certain Lucernarian 
 polypes, particularly that termed Scyphistoma by Sars, 
 (Hydra Tuba of Dalzell) give off gemmae, which are even- 
 tually developed into Hood-eyed Medusse — the common 
 Jelly-fishes of our seas — animals of colossal dimensions, 
 compared with the original polype stock, and, apparently at 
 least, of much higher organization.* Here it seems natural 
 
 * On the Lucernarian affinities of the polype phase of the large Me- 
 dusge, see Huxley in Med. Times, XII., 506, and Oceanic Hydrozoa, p. 21. 
 See also Dr. J. Reid's Physiolog. and Patholog. Researches, p. 445. 
 
ALTERNATION OF GENERATIONS. 121 
 
 to consider tlie polype form as a rudimentary phase, com- 
 parable to that occurring among the Trematoda, and to re - 
 gard as typical the Medusa form, which is an animal of 
 much more conspicuous appearance, of apparently higher 
 organization, endued with the power of . locomotion, and 
 havinor true sexual ors^ans in distinct individuals. Such, 
 indeed, is the view taken by Steenstrup and several other 
 authors, even by those who occasionally speak of the medu- 
 soid progeny of the Hydraform polypes as mere detached 
 generative organs. Thus Prof. Owen observes — " The 
 nutritive gemmiparous polypiform individuals in all the 
 compound Radiaries would seem, rather than the oviparous 
 medusiform ones, to manifest the typical form of the 
 species. . . . Superadd, however, distinct nutritive 
 and circulating organs to the free-moving ovigerous indi- 
 vidual from the rooted polype, and prolong its existence, 
 and it would then cease to have the ancillary character of a 
 nurse to the ova of the fixed individuals, and would assume 
 that of the perfected form of the species ; and such in fact 
 is the case with the larger gelatinous Eadiaries called 
 Medusse." * 
 
 Now, in so far as perfection means the possession of a 
 more conspicuous organization, it is not of course to be 
 denied that the Medusa is in advance of the polype ; but 
 as regards the selection of the phase to be taken as the 
 typical form of the species, I do not see how we can avoid 
 these conclusions — 
 
 1. That the Medusoids derived from the compound 
 polypes (Sertularida and others) — formerly ranked as a dis- 
 tinct order under the name of Gymnophthalmatous (or bare- 
 eyed) Medusae — are really homologues of the parts of re- 
 production, inasmuch as they pass by a continuous grada- 
 tion into generative organs of the simplest kind. 
 
 * PartlienogenesiSj p. 12. 
 
 Q 
 
122 THE NATURE AND VARIETIES OF 
 
 2. That in so natural a group, tlie relative position as- 
 sumed for the puny bare-eyed Medusae must hold also for 
 their portly brethren of the hood-eyed kind. 
 
 A few details may here be given of the declension re- 
 ferred to, from fi'ee Medusae to germ-sacs of so simple a 
 kind, that they might fairly be termed mere tunicated ova. 
 The transition is so gradual, that Prof Huxley considers it 
 impossible to draw any definite line of distinction between 
 true Medusoids and mere proliferous cysts, or sporosacs, as 
 they are termed by Prof. Allman.* The distinction, how- 
 ever, is a convenient one, if not strictly philosophical. A 
 Medusoid is a gemma, usually detached as a free zooid, and 
 consisting of a bell-shaped mantle or umbrella, fringed with 
 tentacles at its margin, and having a cylindrical process 
 (manubrium) depending from the centre of its concavity. 
 The manubrium in its most complete form is itself a polype- 
 like organ, sometimes tentaculated at its free extremity. 
 The umbrella may be regarded as a hemispherical swim- 
 ming disc developed, round the base of the central struc- 
 ture, after the prevailing type of arrangement in these ani- 
 mals. In its full development it contains canals in its sub- 
 stance radiating from the central or gastric cavity of the 
 manubrium, and opening into a circular canal at the free 
 margin of the bell. The ovaries are usually situated at the 
 points of origin of these canals. The umbrella in some 
 species is converted by the cohesion of its edges into a shut 
 sac, which serves as a marsupium or uterus for the nur- 
 ture of the ova after impregnation. In the sporosac, which 
 is never detached as a free zooid, the manubrium is gene- 
 rally represented by a central imperforate columella, and 
 
 * Huxley's Oceanic Hydrozoa (Ray Soc), p. 137. AUman's terms are 
 meduscB and sporosacs — tlie last lias an unfortunate similarity to Filippi's 
 term Sporocyst, applied to tlie gemmiparous tubes of the Trematoda, 
 structures of a totally different import. 
 
ALTERNATION OF GENERATIONS. 1 2.*> 
 
 the umbrella by an investing sac, in which the canals are 
 imperfect or altogether wanting. 
 
 Even in allied species, it is to be noticed, that there is a 
 great diversity in the development of these structures. 
 Thus in Laomedea geniculata the reproductive elements are 
 contained in free swimming metdusoids with marginal 
 cirrhi, and a central proboscidiform mouth, round the at- 
 tachment of which the ovarian chambers are situated. In 
 Laomedea Loveni,^ they assume the form of an inflated 
 bell surrounding the ovary, and fringed at its free edge with 
 minute tentacles ; and they remain during their brief period 
 of life attached to the edge of the horny " o vigorous cap- 
 sule" characteristic of the gToup, and there emit the sper- 
 matozoa or ova with which they were charged ; after which 
 they wither like blossoms, to be succeeded by a new expan- 
 sion. In Laomedea lacerata the ovarian sac advances to 
 the mouth of the capsule, but instead of a bell-shaped en- 
 velope becomes invested merely by a thick gelatinous coat. *(' 
 Even in the same species there is sometimes as great a 
 diversity in the opposite sexes ; thus in L. geniculata the 
 ova are formed in free swimming medusoids, the sperma- 
 tozoa in simple cysts, permanently attached. J 
 
 Professor Allman refers to the reproductive sacs of 
 Tubular ia indimsa, which never become detached, as of 
 
 * Allman in Annals of Nat. Hist., 3d Ser., IV., p. l-tO — tlie same 
 species apparently which Dr. Wright refers to as confounded by Johnston 
 with another having free medusoids, under the name of L. dichotoma . 
 (Edin. Philos. Journal, Jany, 1859, p. 110). This form of extracapsular 
 medusoid, Allman terms vieconidiuin, from its resemblance to a poppy- 
 head. 
 
 t Dr. Wright, Op. Cit. 
 
 X At least Professor Schultze is quoted by Dr. Wright (Edinburgh 
 Philosophical Journal, July, 1856, p. 85, note) as having discovered 
 sperm capsules in this zoophyte, but there is a degree of confusion among 
 the species which somewhat invalidates the conclusion iu the text. 
 
 G 2 
 
124 THE NATURE AND VARIETIES OF 
 
 special interest in establishing the relations between medu- 
 soids and sporosacs. He describes them as closed cap- 
 sules, each containing in its interior a second sac, with four 
 canals in its walls, radiating from the base, and communi- 
 ating mth another circular canal round an opening at its 
 apex. An imperforate columella or manubrium projects 
 into the interior from the centre of its concavity, so that 
 we may be said to have all the parts represented which are 
 found in the free medusa, except the marginal tentacles, 
 the eye-spots, and some lesser details.* The genital pro- 
 ducts are formed in the wall of the manubrium. In Sertu- 
 laria the medusoid conformation is less discernible, and the 
 sacs generally mature and discharge their contents while 
 still within the outer capsule. In Cordylophora the only 
 medusoid features presented, either by the spermatic or the 
 ovarian cysts, are the manubrium and some irregular longi- 
 tudinal canals in the wall of the sac ; there is no aperture 
 (at first) nor any circular canal. In Hydractinia we have 
 the columella without the canals ; and the sporosacs of some 
 species of Plumularia and Eudendrium are if possible of 
 still simpler structure, the latter containing but a single 
 ovum.'f The progress of degradation finally reaches its 
 maximum in the common Hydra, in which the large me- 
 dusae of the " Hydra Tuba' are represented only by sper- 
 matic and ovarian cysts of the most rudimentary organiza- 
 tion, attached to the exterior of the polype. 
 
 An equally great variety is presented by the reproductive 
 organs of the allied orders of Calycophorida and Physo- 
 phorida, ranging from the form of mere sacs to that of free 
 moving bodies (as in Velella), precisely resembling medusse, 
 
 * Annals of Nat. Hist., 3d Ser., IV., 48. 
 
 t In E. hacciferum, Allman (Op. Cit.) describes short blind radiating 
 canals. Tbe closely allied species of Atractylis detacli well formed me- 
 dusoids. See many interesting details on this bead by Dr. T. S. Wright, 
 in Edinb. Philos. Journal, 1856-57-58. 
 
ALTERNATION OF GENEllATIONS. 125 
 
 and developing their generative elements subsequent to their 
 liberation. Even in the same species the male and female 
 apparatus are not always alike in structure. Mr. Huxley 
 remarks, that '' the female organs in Athorybia are sacs con- 
 taining a single ovum, arrested, as it were, in the first stage 
 towards the medusiform condition, while the male orofans 
 become completely medusiform, but are probably not de- 
 tached. In Physalia, on the other hand, the female organs 
 are free swimming medusoids, while the male organs are 
 simply pyriform sacs."* 
 
 There is an equally great variety in the mode of orijiiii 
 of the gamomorphic structures — whether medusoids or 
 sporosacs — from the polype stock. In the Hydroid group 
 they spring from papillary outgrowths of the gelatinous 
 basis either of the polypes or of the common axis of the 
 polypidom. When the papilla is prolonged into a iieshy 
 column, it is called by AUman a hlastostyle, and generally 
 bears a cluster of sporosacs or medusoids. Sometimes the 
 blastostyle and polypes are naked, as in Clava and Tu- 
 bular ia ; but more frequently they are surrounded by a 
 gonophore, or involucral capsule, derived from the horny 
 sheath of the polypidom, as in species of Campanularla, 
 Laomedea, smd Anten?iidaria. In Hydractlnla and Cordy- 
 lophora we have gonophores Avithout any blastostyle, the 
 capsule containing a single sessile sporosac. In Plumu- 
 laria cristata the gonophores occur in clusters, in peculiar 
 receptacles formed, as Prof. E. Forbes has shown, by a mo- 
 dification of the ordinary ramuscules of the zoophyte. "(" 
 
 * Huxley, Medical Times, XII., 566. English Cyclop. Nat. Hist., 
 I., 38. 
 
 t Ann. Nat. Hist., 1st Ser., XIV., 385. 
 
 In tlie homology of these structui-es, it is the manubrium which ap- 
 pears to be the representative of an ordinary poh-pe, the umbrella being 
 a superadded organ for natatory or other purposes. The simple gono- 
 phore may be taken as the homologue of the horny polyp cell, and tlie 
 blastostyle as a rudimentary polj^piferous ramusculc. The compound 
 
126 THE NATURE A2JD VARIETIES OP 
 
 The gamomorpliic gemmae, in the case of the hood-eyed 
 Medusae again, are detached from their polyp stock as a 
 strohila or pile of zooids, by a successive transverse fissuring 
 of the body of the polype just below the tentacles. When 
 the segmentation is completed, there is developed round the 
 remaining portion of the body, immediately below the pile 
 of medusoids, a new circle of tentacles, so that when the 
 whole are thrown off the polype is enabled to resume its 
 pristine form and mode of life.* 
 
 Such variations as have just been noticed, though per- 
 plexing to the systematic zoologist, are especially valuable 
 to the physiologist, as indicating the true relations of the 
 forms which occur in dimorphous species ; and I think they 
 are sufiicient fully to bear us out in the conclusion, that 
 both the bare-eyed and the hood-eyed Medusse are to be 
 considered as gamomorphic zooids, and the polype-stock 
 from which they spring, as the typical form in each case. 
 In the one the orthomorphic form is, as usual, the most 
 conspicuous phase of the species, while in the other it is 
 quite eclipsed by the resulting gamomorphic zooid, which 
 is really a part of itself — a detached and overgrown organ 
 
 gonophore is coBsidered by Prof. Allman to represent the concrete cells 
 of the polypes of such a rarauscule. (Edin. Philos. Journal, VII., 294, 
 IX., 111.) Mr. Huxley professes to adopt the term " gonophore" from 
 Dr. Allman, but the two authors do not appear to use the word in the 
 same sense. The latter applies it to the horny vesicle or urn which con- 
 tains one or more sporosacs or medusa, and speaks consequently of vne- 
 dusiferous gonophores ; the other applies it to the medusoid itself, and 
 speaks of medusiform gonophores. 
 
 * According to Desor, the strobila or pile of nascent medusoids is 
 formed inside the oral circle of tentacles; at the expense of the probos- 
 cidiform mouth, while the figures and description of Dalzell and Eeid 
 represent it as external, the original tentacles being elevated on its sum- 
 mit, and a new one formed on the residuary base, when the whole pile 
 has been detached. Does this indicate a specific difference, as suggested 
 by Dr. A. Thomson in the Cyclop, of Anat. and Physiol. (Art. ovum 
 p. 22) ? 
 
ALTERNATION OF GENERATIONS. J 1^7 
 
 of its o-WTi system. That is to say, as all these structures 
 are admitted to be strictly homologous, the large and 
 elaborately organized Medusae, instead of ranking as the 
 typical forms of their species, must be reduced to the level 
 of their humbler representatives in the Hydra fmsca, and 
 regarded as mere spermatic and ovarian appendages, which, 
 like the staminiferous flowers of the Valis7ieria, accomplish 
 their special function after being detached from the parent 
 organism.* 
 
 It is in farther support of this view, that in other Lucer- 
 nariada — includinoj the o-enus Lucernaria itself — no medu- 
 soids are thrown off, but the ova and spermatozoa are 
 formed in immediate connection with the polypoid stock, 
 which, as being the only form in these species, must be 
 taken as the characteristic type of the group. 
 
 But, besides such analogical arguments, the contrast be- 
 tween the permanence of the polypiform, and the evanes- 
 cence of the medusiform state, already noticed, as an argu- 
 ment for the typical character of the former, appUes with 
 quite as much force to these Lucernarian polypes as to 
 those of the Coryniform and Sertularian groups. The 
 '' Hydra Tuba," indeed, is often spoken of as the '' larva" 
 of the Medusa, but there is no true analogy between their 
 mutual relations, and those of the vermiform larva} among 
 the Articulata to the perfect insects. The larva developes 
 but a single insect, and, with the exception of its lifeless 
 integument, is wholly transfonned into it, but the *' Hydra 
 Tuba," after throwing off a whole pile of Medusa? from its 
 oral extremity, regenerates its original tentaculated month, 
 and returns to the common condition of polype life, till cir- 
 cumstances occur to develope anew a similar reproductive 
 process."!* 
 
 * British and Foreign Med. Chir. Review. I., 203-212. 
 t Steenstrup on Alternation of Generations, p. G. British and Foreign 
 Medico Chirurgical Review, as above quoted. 
 
1'28 THE NATURE AND VARIETIES OF 
 
 § 4. The conclusion, therefore, to which a fair compari- 
 son of the reproductive process in the two cases now cited 
 — the Trematoda and the Polypifera — seems to lead is 
 this, that though in both we certainly have an alternation 
 of forms in the genetic cycle, still we cannot treat them as 
 parallel. It does not seem possible to do so without leav- 
 ing out of view two points of obvious contrast. 
 
 1. That the polype stock has a much greater perma- 
 nence than the trematode redia or precursory zooid, and 
 may throw off many successive broods of medusoids. 
 
 2. That the concluding links of the respective series have 
 really nothing in common but the single point of sexual 
 completeness — the medusoids being sometimes of the most 
 rudimentary structure, more comparable to detached organs 
 than to perfect animals. For the parallel indeed, the single 
 character of sexual completeness must be taken to mark 
 the culminating point of the development of the species, 
 however defective the general organization ; and this is 
 precisely what some naturalists contend for. Thus Siebold 
 in his concluding note on the Comparative Anatomy of the 
 Acalepha remarks — " However various the developing forms 
 may be, that one must be regarded as the real one, which 
 exists during the development of the testicles and ovaries." 
 So also Dr. A. Thomson — ''Some [Hydrozoa] we have 
 been accustomed to see principally in their largest and most 
 developed condition, as Medusse ; others are best knowm in 
 that polypoid condition, in which they remain for the 
 longest time ; but we must regard that condition in which 
 sexual reproduction takes place as the complete one, and 
 this we have seen is in both the Acaleph or Medusa form, 
 while the polype or polypoid state, however permanent it 
 may appear, is to be looked upon as a preparatory stage."* 
 
 But the general analogies of living beings surely indicate 
 
 * Cyciopasd, Anat. and Physiol., Art. Ovum, p. 22. 
 
ALTERNATION OF GENERATIONS. 120 
 
 tlie completeness of the whole organization, according t<i 
 the type of the species, as a juster criterion of the culmi- 
 nating point of development than the possession of any on( 
 function, however important. It is true that where the in- 
 dividuality is much broken up, there may exist a difficulty 
 in determining what particular zooid does really represent 
 most correctly the typical organization of the species — a 
 difficulty which can, of course, have no place, where, such 
 zooids not being budded off, all the structures characteristic 
 of the species are united as organs of one individual. Yet 
 as it rarely, if ever, happens that alternation prevails so 
 universally in any natural family as wholly to exclude the 
 more common course of reproduction, the cases — whether 
 many or few — in which this function is performed without 
 disturbance of the integrity of the organism, generally 
 furnish us with sufficient data for selecting the truly typical 
 form, and for determining whether it does or does not coin- 
 cide m.th that phase of development characterised by the 
 sexual peculiarities. 
 
 Nov/ the viviparous Trematoda, in which there is no 
 " alternation" — the ovum being at once developed into the 
 sole foiTji of the species — clearly indicate that in this group 
 the typical form is that represented by the Distoma ; and 
 this is never dissociated from the sexual phase, though in 
 the great majority of the order the culminating point of 
 development is not attained till after a more or less pro- 
 longed course of gemmation in a rudimentary stage. 
 
 Among the Poly pif era again, we have the case of the 
 common Hydra to determine the polype form as the typi- 
 cal, because in that species the only form ; and therefore I 
 conceive we must hold it to be the typical form also in tlie 
 Sertularian and other alternating species, though no longer 
 that of sexual completeness.* 
 
 * A much more pert)lexiug fiict — if itljo really a fact — is the occasioral 
 
 G 3 
 
130 THE NATURE AND VARIETIES OF 
 
 In the Protom Orphic alteniation, therefore, of the Tre- 
 matoda, we speak of the typical organism and its genn-like 
 matrix ; in the Gamomorphic alternation of the Polypifera, 
 of the typical organism and its sexual offset. Both the 
 matrix and the offset may assume, indeed, the form of in- 
 dependent beings, but their life is always transitory and 
 provisional, having reference to one common end — the 
 multiplication of the race — though by different means. 
 
 development of Medusae from the egg without passing througli the polype 
 stage. It is said to occur in Pelagia noctiluea (Krohn), (Eginojpsis Me- 
 diterranea (MiiUer), and Trachynema ciliatum (Gegenbaur). Annals 
 of Nat. Hist., 2d Ser., IX., 37, XVII., 285. Huxley in Medical Times, 
 XII., 506. 
 
 Professor Huxley, in retaining the term Medusidse for such cases, re- 
 marks — " It is not yet proved that any of them are developed directly 
 from the eggs of similar organisms. I by no means vdsh to question the 
 great probability of the supposition that those ciliated embryos which 
 were observed by MuUer and Gegenbaur to pass directly into the Medusae, 
 proceeded from the eggs of similar Medusae. But, I repeat, there is no 
 proof of the fact." — Oceanic Hydrozoa, p. 21, andj note. I am equally 
 unable to harmonize some of the statements of Mr. Lewis. He cites Pro- 
 fessor Kolliker as ha^dng " seen the same species of CampaTiularia prb- 
 ducing both eggs and Medusae," and goes on to mention that he himself 
 had "on the same polypidom found some of the capsules filled with eggs, 
 and some with Medusae," and that in different specimens of one species 
 (Plumularia MyriophyllumJ " dredged at the same time, and from the 
 same place, he found capsules containing eggs and also Medtisoe ; 
 and others — ^but not on the same polypidom — containing eggs and 
 polypes, i.e., the ciHated gemmules which we know to be the infusorial 
 stage of the polype." These observations — though unfortunately not 
 stated with the fulness and precision necessary on such a point — seem to 
 point either to the conclusion, that the same species may bear sporosacs 
 with true ova, and free medusoids, the latter developed from gemmae 
 closely resembhng ova — or to another result, still more at variance with 
 our received views — viz., that true ova, formed within the capsules 
 (sporosacs ?) of the polype, and actually impregnated, may undergo di- 
 rect development into Medusae. — Sea-side Studies, p. 296. 
 
 Van Beneden, it may be observed, is quoted by Carpenter for the ob- 
 servation that in some Tubularida both attached ovarian cysts and free 
 medusoids are developed, with no difference that can be traced in their 
 respective products. Compar. Physiol., § 539. 
 
ALTERNATION OF GENERATIONS. 131 
 
 The great function of the germinal or protomorphic zooids 
 is the evolution of the embryos of higher forms, of 
 which they serve as budding-stocks ; that of the sexual or 
 gamomorphic zooids is the development of ova and sperma- 
 tozoa. These ends accomplished, their vitality ceases, 
 while the typical organism, the offspring of the former class, 
 or the parent stock of the latter, as the case may be, has a 
 much more permanent duration, and may go on for a long 
 time in perfect vigour, sending off crop after crop of ova, 
 or of sexual gemmae, according to its mode of propagation. 
 § 5. The distinctness of these varieties of " alternation ' 
 is further shown by their occasional co-existence in the same 
 species. Such an association occurs, for instance, in some 
 Cestoid worms. This is apparent from the sketch before 
 given of the development, first of the Cysticercus, and then 
 .of the Taenia, from the six-hooked contractile vesicle, 
 discharged from the egg of the latter. The vesicle, as was 
 shown, is first transformed into the " cyst," which represents 
 the Eedia or protomorphic zooid of the Trematoda, and 
 then buds off the Tsenia-head (the orthomorphic or typical 
 form). From the latter are again derived, by a second 
 gemmation, the cucurbitiform or sexual segments making 
 up the body of the Tapeworm, which represent the gamo- 
 morphic zooids of the Polypifera. 
 
 This species was selected in illustration, as the best known, 
 and, in some respects, the most characteristic of the order. It 
 certainly exemplifies as well as any the development of the 
 gamomorphic structures, but the gemmation in the precur- 
 sory or protomorphic stage is a much less conspicuous fea- 
 ture in it than in many other species, from the circumstance 
 that there is ordinarily formed but one gemma, and that 
 this is never detached from the primary cyst, till tlie latter 
 disappears on the animal entering on its ta}ni()id phase. In 
 the allied species (7a?/iwrM5, numerous Ta?nia-heads are budded 
 off fi:om the same cyst, each of which may originate a separate 
 
132 THE NATURE AND VARIETIES OF 
 
 Tapeworm. In Echinococcus, several successive gemmations 
 of simple cysts may occur before Tsenia-heads are formed 
 at all ; and it is by its cystic growth that the parasite 
 becomes formidable, the resulting Tsenise being minute three- 
 jointed worms, of no importance on their own account. 
 
 Of the two kinds of alternation thus exhibited by the 
 Cestoidea, it is obviously only the protomorphic or cystic 
 that corresponds to the alternation of the Trematoda — 
 a point which seems to have escaped the notice of Professor 
 Van Beneden, as he applies the term scolex alike to the 
 protomorphic Redia or Sporocyst of the Distoma, and the 
 oithomorphic Tsenia-head of the Cestoid worm ; and that of 
 proglottis to the Cercaria, or larval stage of the typical 
 Distoma, and to the ovigerous segments budded off in the 
 gamomorphic phase of the Tapeworm. As this application 
 of the nomenclature confounds fonus which I cannot but 
 consider of different significance, I have thought it best to 
 avoid using these terms, though fully sensible of the 
 advantage of having short names to express corresponding 
 stages in the cycle of development and reproduction in 
 different species.* 
 
 The association of these two kinds of alternation may 
 be traced in a more latent form in the Polyzoa, as will 
 be more fully noticed afterwards. Such co-existence, 
 however, is, on the wliole, exceptional, for it would appear 
 that organisms, which are propagated by protomorphic 
 gemmation, do not ordinarily throw off sexual zooids, and 
 that species, in which the latter phenomenon occurs, do 
 
 * In the use of the terra Strohila there seems to be an equal ambiguity, 
 as it is sometimes applied to the typical form (as of a polype), from 
 which sexual zooids are eventually to be budded off, sometimes to the 
 aggregate of these zooids, already formed, but still adhering in a chain 
 or pile to the typical stock. Its derivation (strohilus, a fir cone) is, of 
 course, suggestive of the latter meaning, and it was to an animal in this 
 transition stage that the name was first applied by Sars. Steenstrup on 
 Alternation, p. 19. 
 
ALTERNATION OF GENERATIONS. 133 
 
 not usually furnish instances of pro-embryonic forms. We 
 may observe indications, indeed, of such a tendency even in 
 the Cestoid order, which has been referred to as furnishin"- 
 the most satisfactory examples of the association, for we 
 lind that when gemmation is very marked in one stage, 
 whether protomorphic, as in Echinococcas, or gamomorphic, 
 as in the common Tapeworm, it is in general proportionally 
 in abeyance in the other. 
 
 § 6. There are, however, I conceive, certain cases of 
 alternation, which are not properly referable either to the 
 protomorphic or gamomorphic stages of the genetic cycle, 
 but depend rather on the occurrence of gemmation in the 
 intermediate or orthomor]^)hic stage — that is, during the sub- 
 sistence of a more fully developed condition of the typical 
 organization, but prior to the maturation of the sexual 
 org-ans. This I believe to be the case with the alternation 
 which is so striking a feature in the reproduction of the 
 Ajj/iides. The remarkable phenomena attending the propa- 
 gation of these insects is too well known to require any 
 detailed account to be given here, and I shall conhne myself 
 therefore to such points as have some bearing on its relation 
 to the other forms of alternation, especially as farther 
 reference will have to be made to the case, in connection 
 with the enquiry into the difference between ova and gemmie. 
 
 The eggs of the Aphis are laid in autumn, and hatched, 
 as usual, in spring, but the primary larvas nevei^'attain the 
 full completeness of the insect type. They resemble the 
 woridiig bees in neutrality of sex, though certainly not in 
 sterility, as by a process of internal gemmation they 
 produce large broods of young, resembling themselves both 
 in their low grade of development and in their unassisted 
 powers of increase.* But as the larvse are incapable of 
 
 * As this process of multiplication may go on the whole summer for 
 nine or ten generations, an easy calculation will show that many millions 
 of Aphides may spring from a single larva. 
 
134^ THE NATURE AND VARIETIES OF 
 
 withstanding the winter cold, all this increase would not 
 avail to the perpetuation of the race, were it not for the 
 provision that, towards the end of summer, a brood 
 appears capable of complete transformation into perfect 
 insects of both sexes, precisely similar to those of the 
 preceding season, which were the progenitors of the 
 original neuter brood hatched in the spring. 
 
 Now, if we compare this case of alternation with the two 
 previously noticed, we cannot but observe that it is more 
 closely allied to that of Trematoda, than to the modification 
 occurring among the Polypifera, for of all the successive 
 forms in the series the one which bears the sexual organs 
 is undoubtedly that which approximates most to the ideal 
 of the insect type.* So much is admitted by the general 
 phraseology applied to the case, all the sterile forms which 
 proceed being, by common consent, termed larvce. But this, 
 at the same time, suggests the suspicion that the gemmation 
 is referable rather to an early stage of the orthomorphic 
 than to the protomorphic or germinal phase of development. 
 For if the zooids are really equivalent to the larvse of insects 
 generally, their condition corresponds to the embryonic state 
 of other animals — for a larva is simply a naked embryo. 
 Now, the larval or embryonic state decidedly belongs, as a 
 whole, rather to the typical than to the germinal stage of 
 development. For the former must be held to include the 
 whole pericjd, from the first commencement of permanent 
 organization till it attains the standard of the adult. The 
 commencement of the permanent organization is a definite 
 
 * It seems not to be the case, however, as is sometimes assumed, that 
 the precursory forms are all without wings, and only the terminal males 
 and females furnished with these organs. It is doubtful if the true 
 females are ever winged, but both neuters and males appear to occiir in both 
 guises, the determining conditions being yet unknown. It is much the 
 same with the alternating species in the group to which Cliermes belongs. 
 (Huxley, in Annals of Nat. Hist., 3d Ser., II., 214. Leuckart, in do., 
 IV., 321.) 
 
ALTERNATION OF GENERATIONS. 135 
 
 epoch in the Hfe history ; we can readily distinguish a 
 point of time when the cellular germ-mass first presents 
 the incipient traces of that structure which is characteristic 
 of the Vertebrate, Articulate, or other leading type of or- 
 ganization ; but we cannot draw such a definite line of 
 demarcation between any two successive periods of the 
 ensuing embryonic development : the subsequent changes 
 are of degTee rather than of kind — a gradual, and, on the 
 whole, a continuous unfolding of the perfection of the type 
 from the rudimentary traces which constitute its first com- 
 mencement. Undoubtedly, we meet occasionally witli 
 arrests of development more or less complete and extended 
 — and nowhere more markedly than in the class of insects 
 — but these are all of an irregular or adventitious nature, 
 as is shown by the entire absence, in many cases, of any 
 break in the continuity of the process, and by their varia- 
 bihty when they do occur. If, then, we regard embryogeuy, 
 or lai^'al development, as constituting the initial state of the 
 typical or orthomorphic stage — but as, on that very account 
 strictly belonging to it — then, we must refer the alternation 
 of the Aphides to the commencement of this stage rather 
 than to the protomorphic, because the organization has 
 already acquired that partially advanced development cha- 
 racteristic of the larvae of other insects, before the process 
 of gemmation comes into play. We cannot say here that 
 the primary product of impregnation buds off a set of em- 
 bryos of a higher organization ; it is rather a larva — that 
 is, a naked embryo — already so far advanced on the insect 
 type, that buds off a series of similar larvse, the last only 
 of which become perfect insects.* 
 
 * Dr. Carpenter, while he virtually admits the distinction of the tbmis 
 of alternation here termed Protomorphic and Griimomorpliic, by compar- 
 ing the zooids of the latter to detached reproductive organs, and by term- 
 ing the former a process of " larval gemmation," at the same time uses 
 this expression to include the development of the precursory forms botli 
 
136 THE NATURE AND VARIETIES OF 
 
 § 7. The COD elusion, therefore, at which we arrive is 
 this, that each of the three stages into which the life history- 
 has been divided (protomorphic, orthomorphic, and gamo- 
 morphic), may become the scene of a process of gemmation, 
 attended bv an alternation of forms : and, under one or 
 other of the varieties of alternation thus admitted, I am 
 persuaded all the cases knowTi, in both kingdoms of nature, 
 may readily be ranged. 
 
 To the protomorphic, I would refer, along with the 
 Trematoda, the Echinodermata among animals, and the 
 Mosses and Hepaticae among plants ; to the orthomorphic, 
 I would refer such Crustacea as Daphnia and Cyclops, 
 whose reproduction is, to some extent, parallel Tvdth that of 
 the Aphides^ ; and to the gamomorphic, the Salpw in the 
 animal, and the Ferns and their allies in the vegetable 
 kingdom. 
 
 It is not common, as has been stated, to meet with the 
 concurrence of more than one kind of alternation in the 
 same species. The Cestoid worms, however, have been 
 already mentioned, as furnishing examples of alternation, 
 
 of the Trematoda and tlie Aioliides. Very probably, indeed, notwith- 
 standing the distinction now indicated, the two modifications may be con- 
 nected by a series of intermediate gradations. All such precursory forms, 
 being sexless, come under the term " agamozooid,' used by Huxley and 
 Lubbock. See Carpenter's Compar. Physiology, 4th Ed., p. 558, 597, 
 529. 
 
 * The species of the allied family of Coccida, and of the transitional 
 genus Chennes, present, according to Leuckart, phenomena somewhat 
 analogous to those occun-iog in the reproduction of the Aphides (Annals 
 of Nat. Hist., 3d Ser., lY., 321). Among the cases of orthomorphic al- 
 ternation should probably be included also that of the Pteromalus, as de- 
 scribed by Fihppi. Here a caterpillar is developed within a maggot-like 
 larva, which by its growth it reduces to a mere sac, and in due time 
 passes into the pupa state, and comes forth as an insect of the Ichneumon 
 tribe. The case may possibly be one of parasitism, but the uniformity of 
 the occurrence is opposed to this view. See Annals of Nat. Hist., 2d 
 Ser., Vol. IX., -IGl, and Carpenter's Priucip. of Compar. Phys., 4th Ed.,. 
 597. 
 
ALTERNATION OF GENERATIONS. 137 
 
 both in the protomorphic and gamomorphic stages ; as also, 
 in a more latent form, the Polyzoa, which will come under 
 consideration again, as illustrating the connection between 
 alternation of generations and certain phenomena occurring 
 in the higher animals. 
 
 § 8. Some Annelida may be said even to present pheno- 
 mena akin to those of alternation in all the three. The 
 earlier alternations are most readily to be traced in the 
 branchiated species. In these the primary infusorial form 
 in which the young quit the egg may be compared to a 
 protomorphic zooid, such as the *' six-hooked embryo" of 
 the Cestoidea. As the latter buds oif a tienia-head, so 
 this infusorian gives origin, on one side, to the cephalic, 
 and, on the other, to the caudal and penultimate segments 
 of the Annelidan — conjointly representing the commence- 
 ment of the typical form — after which the ciliated part 
 gradually wastes away. There now follow a series of suc- 
 cessive acts of gemmation, the penultimate segment budding 
 off a new joint on its caudal aspect, which in turn repeats 
 the process, and so ^on, till there is formed eventually a 
 long train of such segments, each of which (except the tail 
 piece), is derived by gemmation from the one immediately 
 in advance of it. Hence, all the hnks of this later gem- 
 mation are as distinctly referable to the orthomorphic phase 
 as are the successive gemmations of Aphides, from which 
 they differ only in continuing in organic union with each 
 other, instead of assuming the position of free zooids. 
 
 This correspondence is much closer than that which 
 subsists between the Annehdan and the Cestoid worm. 
 Much as these resemble each other in the composite cha- 
 racter of the long vermiform body, made up of a series of 
 derivative and semi-independent gemma), there are two 
 important points of difference between them. 
 
 1. The segments of the Cestoid worm, though of cUfferent 
 ages and degrees of maturity, are all originally budded off 
 
138 THE NATURE AND VARIETIES OF 
 
 from one point — the back part of the Tsenia-head — and 
 therefore, except in so far as they have multiplied after- 
 wards by sub-division, may be said to constitute but a 
 single generation, being all the progeny of one parent stock, 
 while the segments of the Annelidan are a succession of 
 generations, each being derived from that immediately in 
 front of it ; so that the hinder ones are the youngest, not, 
 as in the Taenia, those nearest the head. 
 
 2. The segments of the Cestoid worm are clearly gamo- 
 morphic or sexual gemmae, for as soon as they show any 
 distinct organization at aU, it tends to the development of 
 the reproductive elements. Those again of the Annelidan 
 are, as has been observed, orthomorphic, tending to the 
 completion of the typical body, which attains some con- 
 siderable elongation before it enters on the sexual stage. 
 As in general it is only the later segments that develope 
 reproductive organs, these indeed may with some reason be 
 considered as constituting a new series of gemmae, really 
 corresponding to the gamomorphic segments of the Tape- 
 worm, In Syllis, Myrianida, and some other species, it is 
 obviously so, for the later segments become, as has been 
 already noticed, so many new centres of a budding process, 
 resulting in the formation and detachment of distinct sexual 
 zooids. In this case the primary Annelidan has no sexual 
 organs, but the caudal zooids become gorged with ova, even 
 before actual separation takes place. In the same way 
 other individuals of the species, equally destitute themselves 
 of sexual parts, throw off from their posterior extremity 
 secondary Annelida, with voluminous spermatic organs. 
 When impregnation has been effected, and the ova have at- 
 tained a certain degree of development, the female zooid 
 becomes completely detached from the parent stock. Its 
 separate existence, however, is of limited duration, for it is 
 ruptured by the growth of the eggs, which are thus dis- 
 persed. As M. Quatrefages expresses it, the zooid ''is an 
 
ALTERNATION OF GENERATIONS. 139 
 
 animal formed solely to serve as a reproductive ma- 
 chine."* 
 
 The zooids, it is to be observed, are not derived from 
 each other, as the rings themselves are, but are the results 
 of a separate budding process in certain of tlie posterior 
 segments ; and the conversion of segments into zooids takes 
 place in the reverse order of their original development — 
 that is, from behind forwards. Though the liindmost joint 
 is the last formed, its derivative Annelidan is the first ma- 
 tured.-|- 
 
 The sequence of alternation here is, therefore, parallel 
 to that occurring in the Polypifera, only there is less dif- 
 ference between the sexual zooids and the parent stock — 
 the annelidan zooids are neither so rudimentary as some of 
 the medusoids, nor do they ever rise so much above the 
 level of the stock as the large hood-eyed Medusaj. Both 
 the parent animal and its offsets have the obvious annelidan 
 structure, yet there are certain minor distinctions between 
 them — such as mio-ht even indicate a o-eneric difference, and 
 it has been ascertained that the young produced from the 
 ova resemble, not the immediate parents, but the primary 
 Annelida, in their general conformation, as well as in their 
 want of sex and their tendency to caudal gemmation. J 
 
 Among the Annehda, therefore, we seem warranted in 
 saying that gemmation may occur in all the three stages 
 before specified,§ though it is only as an occasional occur- 
 
 * Rambles of a Naturalist, I., 217. 
 
 f Hence the facetious remark of Mr. Lewis is hardly in point, that the 
 family inheritance of the parental tail, in passing to the progeny, re- 
 verses the law of primogeniture, and like the stock of baby linen, descends 
 always to the youngest. Sea-side Studies, p. 62. 
 
 X Milne Edwards, Ann. des Sciences Nat., 3d Ser., Zool., torn iii., p. 170. 
 
 § Terehellay in which the gemmation of segments from the infusorial 
 germ, and from each other, has been most distinctly observed, presents 
 also, according to Mr. Lewis, the formation and detachment of caudal 
 zooids. Sea-side Studies, 62. 
 
140 THE NATURE AND VARIETIES OF 
 
 rence and in the gamomorpliic stage, that it appears as a 
 case of distinct alternation, because in the two former the 
 gemmae remain in union mth the parent stock, instead of 
 assuming the character of free zooids. 
 
 The remarks now made, and those which the course of 
 the argument will yet call for, touch, I think, upon all the 
 cases of alternation in the Animal Kingdom, above referred 
 to, with the exception of the Salpce, to which, therefore, a 
 passing reference may here be made. 
 
 § 9. Notwithstanding that the reproduction of the Salpoe 
 was the first case of " alternation" to attract notice, and 
 that it has ever since been res-arded as among; the most 
 striking instances of it, it is at the same time one concern- 
 ing the exact relations of which some doubt may be enter- 
 tained. From the associated forms having, along with 
 perceptible differences in external configuration, such a close 
 similarity in internal structure, and from their locomotive, 
 circulatoiy, digestive, and nervous systems being so entirely 
 on a par in the scale of organization, it would be hazardous 
 to pronounce one more than the other the typical represen- 
 tative of the species, so that we are in a sort of difficulty to 
 decide whether the alternation is due to the interpolation 
 of a protomorphic zooid — the solitary asexual form which 
 originates directly from the ovum — or of a gamomorphic 
 zooid — the catenated sexual form budded off from the 
 former. In point of organization there is nothing to indi- 
 cate to us whether the gemmation precedes or follows the 
 orthomorphic stage of development. From all that we can 
 gather from a comparison of the two forms, we might either 
 compare the solitary Salpa to the gregariniform phase of 
 Trematode life, and the catenated Salpcc derived from it to 
 the brood of Distomas — both alike maturing their reproduc- 
 tive structures as simple organs in the continuity of their 
 own bodies — or, on the other hand, we might consider the 
 solitary form as the typical one— elaborated out of the 
 
ALTERNATION OF GENERATIONS. 141 
 
 germ-mass without any breach of structural continuity — 
 and compare it to the Tsenia-head of a Cestoid worm, or the 
 zoophytic phase of polype-life ; in which case the chain of 
 sexual Salpa? would represent simply an aggregation of 
 generative structures, provided (like the proglottides of the 
 Twnia or the medusoids of the polype) with accessory 
 organs of nutrition and locomotion. Either of these com- 
 parisons perhaps might stand of itself, but the weight of 
 analogy is much in favour of the latter ; the parallel between 
 the chain of sexual ^alpce, tlie pile of medusoids, the 
 jointed " body" of the Tapeworm, and tlie caudal train of 
 some Annelida — all alike made up of segments furnished 
 with proper sex-organs, and maturing true ova — is too dis- 
 tinct to be overlooked. In this direction accordingly it is 
 that we find those naturalists who have made this class 
 their especial study are the most inclined to look for illus- 
 trations. Mr. Huxley, in particular, is very decided in 
 favour of this view. In his paper in the Philosophical 
 Transactions on the Anatomy of Salpa and Pyrosoma, he 
 characterizes the aggregated zooids as merely highly indivi- 
 dualized generative organs,* and in a lecture at the Royal 
 Institution he ranks amono; their homolonues the medusiform 
 zooids of Physalia and Velella, the medusiform organs of 
 Diphyes and Tubidaria, and the egg-capsules of Hydra.'\ 
 
 In this view, of course, we cannot recognize any example 
 of protomorphic alternation among the Salpcu. It is by no 
 means clear, however, that all the derivative Tunicata are 
 on a footing in this respect with the catenated Salpce. Ac- 
 cording to MM. Lowig and Kolliker, the stellate clusters 
 of the Botryllida are formed by a sort of fissiparous divi- 
 sion of the original germ. In this case their formation 
 would be parallel to the protomorphic gemmation of the 
 Trematoda, or as Dr. Carpenter remarks, " to the free gem- 
 
 * Phil. Transac. for 1851, p. 5 11. 
 t Ann. Nat. Hist., 2d Ser., IX., p. 506. 
 
142 THE NATURE AND VARIETIES OF 
 
 mation of mosses whilst yet in the confervoicl state. The 
 fact, however, is denied by Professor Milne Edwards, who 
 considers that the cluster is formed by subsequent gemma- 
 tion from the first individual ; and the matter remains open 
 for further investigation."* 
 
 § 10. A few remarks may be made, in conclusion, in re- 
 gard to the cases of '' alternation" which occur in the Ve- 
 getable Kingdom. Here marked phenomena of this kind 
 are confined to the Cryptogamia. In the lower section of 
 this division — including Algae, Fungi, and Lichens — in- 
 stances probably occur of all the forms of alternation above 
 referred to, as will appear from the summary of the repro- 
 ductive process in these orders, given in Chapter 11. But 
 as no one form occupies a preponderating place, and as 
 most of the phenomena of reproduction are still so imper- 
 fectly known in these plants, it would be premature to at- 
 tempt any generalizations as to the character of the process 
 as a whole. 
 
 The higher Cryptogamic species fall very naturally into 
 two groups, corresponding to the Muscales and Filicales 
 of Lindley, and distinguished by differences alike in struc- 
 ture, habit, and development. The structure of the repro- 
 ductive organs themselves (antheridia and archegonia) is 
 very similar in these groups, the diversity, as already no- 
 ticed, lying in their direct connection in the former with the 
 leafy axis, while in the latter they are contained in detached 
 gemmae or phytoids. It was remarked, at the same time, 
 that from these relations of the reproductive organs, some 
 botanists would argue a correspondence on the one hand 
 between the structures from which they spring, that is, be- 
 tween the leafy axis of the fern and the stalked capsule of 
 the moss ; and on the other, between the bodies into which 
 the spores germinate, i.e., the prothallium and the leafy 
 
 * Compar. Physiol., 4tli Ed., p. 571. 
 
ALTERNATION OF GENERATIONS. 143 
 
 axis of the moss. But a comparison of objects of siicli 
 prima facie diversity — objects more unlike than even the 
 large Medusce, and the ovarian cysts of the Hydra, and 
 what is more, without any intermediate connecting forms — 
 ought not, I conceive, to be adopted, except on the most 
 convincing evidence. But there is no such cogency in the 
 case, if we assume that the interpolation of a derivative 
 form occurs at a later stage of the genetic cycle in ferns 
 than in mosses ; and for this view we have ample warrant, 
 in the analogy of the Animal Kingdom, where we find cor- 
 responding differences between the Cestoid and Trematode 
 Entozoa, and between these and the Polypifera ; while 
 among the latter, even nearly allied species differ in this 
 matter of the interpolation of gemmation. Such a view, I 
 submit, is a less tax on our powers of conception than to 
 regard the minute and fugitive capsule of the moss as the 
 equivalent of the perennial and towering stem of the tree 
 fern. And no less real is the contrast between the evan- 
 escent prothallium of the fern and the foliaceous axis of the 
 moss, which, humble as is its mode of gro^vth, has yet such 
 permanent vigour of vegetative power, that its pidlulations 
 may eventually come to cover a larger space than that over- 
 shadowed by many a spreading forest tree ; for the leafy 
 shoots w^hich, year after year, cover the mossy bank with 
 verdure, and send forth each its annual clusters of capsules 
 from the impregnated archegonia, are often all of them the 
 ultimate twigs or branchlets of one original moss-plant, 
 whose primary axis and its immediate ramifications have 
 long since mouldered away, and gone to form the accumula- 
 tion of soil in which the present shoots vegetate.* 
 
 * Mr. Jenner, in some respects, supports this view, though his idea of 
 the homologies of these orders differs in some important points from that 
 here adopted. See Edin. Philos. Joiimal, April, 1856, p. 269 ; and 
 Annals of Nat. Hist., 2d Ser., xv. 245. 
 
 See also the Translation of Radlkofers' Observations on the Function 
 
144 THE NATURE AND VARIETIES OF 
 
 In mosses, then, as in the Trematoda, the gemmation 
 must be held to occur in a germinal or rudimentary (proto- 
 morphic) stage, whereas in ferns, as in the Polypifera, it is 
 delayed till the formation of an axis, in which the general 
 organization reaches its culminating point, though without 
 the development of organs of fructification, which make 
 their appearance only subsequently in the prothallia — de- 
 rived from it, as the medusoids are from the zoophyte — 
 both being, as it were, supplementary structures, and having 
 for their main end to supply the deficient organs. In the 
 moss the parts of fructification are attached to the axis 
 more persistently, and with less intervention of floral enve- 
 lopes than in any other plants, while in the fern they are 
 not produced at all, till after the fall of the fern, spore, and 
 the development from it of their matrix by a subsequent 
 process of independent growth. However disguised by this 
 detachment and growth — the prothallium, as the ma.trijj of 
 the spermatic and germinal elements, must remain the real 
 homologue of the floral organ of a phenogamous plant, and 
 the illustration furnished by the floating flower of the 
 Valisneria comes in here even more appositely than in the 
 case of the Polypifera. 
 
 It will be observed, however, that in thus indicating a 
 relation between ferns and mosses, similar to that subsist- 
 ing between the Polypifera and Trematoda, arguments of 
 analogy only have been made use of. No reference has 
 been made to transitional forms, such as those which furnish 
 so important a clue in the last mentioned case, for in fact 
 no such forms have yet been recognised among the Crypto- 
 gamia, though, as their existence is quite conceivable, their 
 discovery may possibly reward the labours of some future 
 botanist. A case could readily be imagined, for instance, 
 
 of Keproduction in the ABimal and Vegetable Kingdoms, Annals of 
 Nat. Hist., 2d Ser., xx. pp. 241, 344, 439. 
 
ALTERNATION OF GENERATIONS. 145 
 
 in which the impregnated archegonium of a moss shouM 
 mature but a single spore, germinating directly into its own 
 protonema and moss, as the egg of the viviparous Trema- 
 tode is at once developed — without the intervention of any 
 nurse animal — into the likeness of its parent. Or again, we 
 might conceive the " feni-spore," while still attached to the 
 frond, developing a prothallium, which might be compared 
 to the flower of the Buscus aculeatus ; such a prothallium 
 would then stand in somewhat the same relation to the 
 original axis, as the spermatic and ovarian sacs do to the 
 body of the common Hydra. 
 
 Though the discovery of cases like these would no doubt 
 confirm the parallel just indicated, yet, even as the case 
 stands, there seem to be sufficient gTOunds for assuming 
 the existence among Vegetables, as well as in the Animal 
 Kino^dom, of varieties of the so-called alternation of s^enera- 
 tions, distinguished from each other by the period at which 
 the budding process is interpolated in the cycle of successive 
 forms. 
 
 H 
 
146 INTERPOLATION OF A CONTINUOUS 
 
 INTERPOLATION OF A CONTINUOUS. 
 PULLULATION IN THE GENETIC CYCLE. 
 
 § 1. To complete our survey of the Genetic Cycle in the 
 alternating species, it is necessary to advert more specifi- 
 cally than has yet been done to the fact, that this cycle is 
 at times much extended by a continuous succession of gem- 
 mations, all of the same general character. Thus we 
 find that in some of the best marked cases of alternation 
 of generations, the offsets produced in a particular stage of 
 development are not transformed immediately into the next 
 phase in the life-history of the species, but that there occurs 
 a continuous series of zooids [or phytoids], budded off from 
 each other, and all referable to one phase of development, 
 which is succeeded in due time by that next in order, as if 
 there had been but a sino^le intervenino- link. In these 
 cases, instead of a regular alternation of free gemmae with 
 true embryos, we find the general propagation of the species 
 effected by gemmae alone ; the sexual zooids, which give 
 origin to the fecundated germs, recurring only at longer or 
 shorter intervals, which are occupied by continuous suc- 
 cession of non-sexual zooids, bearing a general resemblance 
 to each other, though mth differences frequently in details. 
 In certain cases — as among the Trematoda — the links 
 are but few in number, and apparently fixed in each species, 
 and there are generally appreciable differences between the 
 forms which succeed each other in the series ; in others we 
 have an indefinite succession of like forms, and the periodic 
 recurrence of the sexual zooids, which tenninate the series, 
 seems to depend on circumstances, being a provision to 
 
PULLULATIOX IN THE GENETIC CYCLE. 11-7 
 
 meet contingencies which would otherwise imperil the con- 
 tinuance of the race. Thus in the Aphides the male and 
 female insects appear at the close of the season, when it is 
 necessary for the preservation of the species that true ova 
 should he formed, more capable of resisting the winter cold 
 than the rudimentary forms, which are propagated from eacli 
 other in such quick succession during the summer. 
 
 § 2. Such a process of continuous gemmation may 
 occur, as it would seem, at any period in the life-history of 
 a species. We have an instance of it during the course of 
 germinal development in Distoma and Echinococciis among 
 animals, and in the successive forms of the capsule and 
 protonema of moss-plants ; and we meet with it also 
 at the other extreme of the cycle, in the medusoid offsets of 
 the Polypifera. Professor E. Forbes makes mention of four 
 modes of gemmation among the Medusae : — 1. From the 
 ovaries, as noticed by Sars in Thaumantias ; 2. from the 
 peduncular stomach [manubrium] in Lizzia \^Cyta:'is\, the 
 gemmae coming off from each of its four sides in a some- 
 what symmetrical way ; 3. from the walls of a tuljulav 
 proboscis into which the manubrium is extended, in a 
 species of Sarsia, the gemmai coming off in an irregular 
 manner from its whole lenoth ; and 4. from the bases or 
 tubercles of the four marginal tentacles, in another species 
 of the same genus.* 
 
 * Naked-eyed Medusae (Ray Soc), pp. 17, 65, 59, 58. See also En<^- 
 lish Cyclop. Nat. Hist., I., 25, and Carpenter's Principles of Comp. 
 Physiol., 4th Ed., p. 558. 
 
 Dr. T. S. Wright, indeed, regards every medusa as composite, looking 
 on its component memloers as so many modified polypes. He terms the 
 oral 'protubei'ance an alimentary polype, and the contractile marginal 
 filaments and the ovaries, tentacular and sexual j^olji^es, comparing them 
 to the parts fulfilling the same functions in Hydractinia — of whose ge- 
 neral polype nature there can be no doubt (Ed. N. Phil. Jour., 1857, 
 pp. 315 and seq.) Huxley again regards the whole medusa as a modified 
 polype, and he demonstrates very clearlj' its agreement in the general 
 plan of structure. The truth seems to be that in proportion as the diffuse 
 
 n 2 
 
148 INTERPOLATION OF A CONTINUOUS 
 
 A sort of gamomorphic pullulation may be traced in the 
 very development of the reproductive organs of some medu- 
 soids, for while generally in this family the ova and sper- 
 matozoa are formed directly in the substance of the walls 
 of the manubrium or central polype, in a few species se- 
 condary sacs are budded off as their matrices.* The same 
 idea has suggested itself to Professor AUman, as appears 
 from the following passage iu his Notes on the Hydroid 
 Zoophytes : — " In Laomedea dicJiotoma, L. penicidata, &c., 
 the generative elements are never formed in the manubrium 
 of the Medusa bud, but in peculiar bodies situated on the 
 course of the radiating canals. Now these bodies, at least 
 in the Medusa of L. dickotoma, which I carefully examined 
 with regard to this point, are constructed precisely on the 
 plan of the sporosacs in Clara, Hydractinia, &c. These 
 sporosacs must be viewed as special zooids, representing one 
 term in the ' alternation of generations' of the individual. 
 Just so must the reproductive bodies (sporosacs) which bud 
 from the radiating canals of the Medusa of Laomedea 
 dichotoma, be regarded as special zooids, and as represent- 
 ing a term in the life-series of the Zoophyte. 
 
 " In Eudendrium \atractylis\ ramosum, for example, we 
 * 
 
 vitality of the lower species favours gemmation, in the same degree it 
 tends to confound all the appendages of the body with gemmae. The de- 
 tachment of a part may decide its being a gemma (though not absolutely, 
 as we see in the case of the Hectocotylus), but so long as parts continue 
 iu adhesion, it must often be impossible to determine between a gemma 
 and a hypertrophied appendage, as all parts tend with development of 
 their organization to take on the typical form of the group, which in the 
 case of the Ccelenterata is that of a bell-shaped polype. See in connection 
 Avith this the speculations of M'Cosh on the relation between the vena- 
 tion of a leaf — the vegetable unit or phyton — and the ramifications of the 
 corresponding tree. Typical Forms, Bk. II., ch. 2. 
 
 * Compare Huxley's account of the development of ova and sperma- 
 tozoa in the Hydrozoa generally (Oceanic Hydrozoa, pp. 21-22), and Dr. 
 Wright's remarks on the medusoids of certain species of Laomedea (Edin- 
 burgh Philos. Journal, Jany., 1859, p. 111). 
 
PULLULATION IN THE GENETIC CYCLE. 1 41J 
 
 have, therefore, this series represented by two terms — 
 [ovum] polype, medusa ; while in Laomedea dlclwtonm it 
 is represented by three — [ovum] polype, medusa, sporosac. 
 In Eudendrium the series stops with the production of a 
 sexual zooid, in the form of a medusa ; in Laomedea it goes 
 on through the non-sexual medusa-bud, until it finds its ter- 
 mination in the sexual sporosac of the latter."* 
 
 But the course of pullulation is most usually interpolated, 
 after the general typical character of the species has been 
 first acquired in all respects, save the peculiarities of sex. 
 
 § 3. In fact, the orthomorphic g'emmation, already no- 
 ticed as one form of alternation, almost always runs on into 
 a continued course of pullulation, the result being either a 
 swarm of free zooids, as in the case of the Aphides, or else 
 a composite structure, like the polypidom of a zoophyte, or 
 the leafy stem of a plant. In the last mentioned case, the 
 seed, derived from the impregnated ovule, emits in germi- 
 nation the primary leaf-shoot of the plant ; but, in the ma- 
 jority of instances, before reproductive organs are formed, 
 this shoot produces leaf-buds, from which other leaf-shoots 
 are developed, and from these again others originating in 
 the same way, and so on, till at last that form is acquired 
 proverbially known as a vegetation. As Professor Braun 
 remarks, " only a small proportion of plants reach the goal of 
 the metamorphosis (blossom and fruit) in the first genera- 
 tion, the majority attain this term only in the second, third, 
 fourth, or sometimes not till the fifth generation of sprouts. + 
 
 * Annals of Nat. Hist., 3d Ser., IV., 368, note. 
 
 t Rejuvenescence in Nature, (Henfrey's Trauslat., Ray Soc), p. 32. 
 Braun recognizes three orders of gemmations — Cataphyllary (root and bud- 
 scales, nieder-hldtterj , eupliyllary (leaf-shoots, lauh-hldUerJ, and hypso- 
 phyllary (floral shoots, hoch-bldtterj . He holds also that when blossoms 
 are formed, they occur after a definite number of gemraatioiis, verj' cou- 
 staut in the same species, and frequently throughout a wliolo order. 
 
 See also Dana in Silliman's American Journal of Science, Nov., 185(1, 
 and the Annals of Nat. Hist., 2d Ser., VII., 'SiH. 
 
150 INTERPOLATION OF A CONTINUOUS 
 
 At first a general similarity prevails in the successive 
 shoots, amounting in most cases almost to identity — the 
 instances of diversity of leaves on the same tree being quite 
 exceptional — but in by far the majority of plants, the 
 floAver-shoots, on which alone reproductive organs are pro- 
 duced, differ widely from the leaf-shoots, though the argu- 
 ments on which the science of Vegetable Morphology is 
 based prove clearly an essential community of nature be- 
 tween them. In all normal development these floral leaves 
 or bracts immediately precede the evolution of the repro- 
 ductive organs, but the number of successive leaf-buds of 
 the common form seems to be to some degree dependent on 
 external conditions — many plants vegetating vigorously in 
 situations where they never flow^er. 
 
 All that has now been said of such gemmation in plants 
 wdll apply also to zoophytes among animals, if w^e merely 
 substitute " pol}^e-bud" for " leaf-bud," and " ovigerous 
 capsule" for '' flower-bud." 
 
 That the different leaf-shoots in the plant, and the polype 
 shoots in the zoophyte, are so far distinct individuals that 
 they possess a certain independent life of their own, is now 
 so generally admitted, that it is needless to spend time in 
 adducing arguments in its support — the well-kno^vn practice 
 of propagating plants by cuttings must occur to every one. 
 The majority of plants, indeed, are equally entitled with 
 zoophytes to be termed compound organisms.* 
 
 § 4. From the gemmae in such cases so frequently re- 
 maining attached to each other and to the parent stock, it is 
 proposed — for want of a better expression — to distinguish 
 
 * It lias been already sliown that the conipoTind stnieture does not 
 necessarily imply the derivation of its component units from each other 
 by gemmation, for it may also depend on their aggregation by a common 
 derivation from the same stock, as in the Catenated Sal/pee, the pile of 
 Medusae, derived from a " Hydra Tuba," or the caudal zooids of some 
 Cestoidea. See again in Ch. IX. 
 
PULLULATION IN THE GENETIC CYCLE. 1 .") 1 
 
 the plienomenon bj tlie term pullidation, in allusion to the 
 sprouting of leaf-shoots in a tree, which is, in fact, merely 
 a special case of a process of this kind. But the expression 
 is here employed simply to denote a continuous succession ( »f 
 gemmse in the same phase of development, ^vithout restriction 
 to cases in which they remain in this state of adhesion to each 
 other. No such distinction, indeed, could be well carried out ; 
 for gemmse ordinarily attached sometimes become separate, 
 so as to originate distinct organisms ; and variations in this 
 respect are met with not only in comparing allied species, 
 but even in the same species under altered circumstances. 
 
 On the whole, however, such a general rule as this seems 
 to prevail — that in the Vegetable Kingdom, and in the 
 lower divisions of the Animal Kingdom, whose diffuse vita- 
 lity favours such development, the outgro\\i:hs do, witli 
 some exceptions, remain in adhesion to form compound organ- 
 isms, while from the incompatibility of such structures with 
 the more concentrated vitality of the higher animals, such 
 pullulation is either wholly excluded, as in Vertebrata, or, 
 as in Articulata — where it manifests itself exceptionally 
 — the gemmse are detached as soon as matured, and 
 assume the guise of independent animals. Such an excep- 
 tional case is that of the Aphides among insects, already 
 referred to. However great the prima facie diversity be- 
 tween the successive swarms of free insects which we here 
 meet with, and the clustered buds of the plant or the zoo- 
 phyte, the physiological identity of their relations has been 
 well demonstrated by Owen, Carpenter, and otliers, who 
 clearly show that the only difference lies in a character, the 
 variable and accidental nature of which has just been no- 
 ticed — viz., the bond of connection between the gemmje, 
 whose presence in the form of a common axis associates in 
 organic union the successive puUulations of the plant or 
 zoophyte, and whose disappearance in the Aphides disso- 
 ciates the derivative zooids, as the snapping of the tliread 
 
152 INTERPOLATION OF A CONTINUOUS 
 
 of a necklace would scatter the beads of which it is made up. 
 " The wingless larval Aphides are not very locomotive ; 
 they might have been attached to one another by continuity 
 of integument, and each have been fixed to suck the juices 
 of the part of the plant where it was brought forth. The 
 stem of the rose might have been encrusted with a chain of 
 such connected larva, as we see the stem of a Fucus encrusted 
 with a chain of connected polypes, and only the last deve- 
 loped winged males and oviparous females might have been 
 set free. The connecting medium might even have per- 
 mitted a common current of nutriment, contributed to by 
 each individual, to circulate through the w^hole compound 
 body. But how little of anything essential to the animal 
 would be affected by cutting through this hypothetical con- 
 necting and vascular integument, and setting each indivi- 
 dual free. If we perform this operation on the compound 
 zoophyte, the detached polype may live and continue its 
 gemmiparous reproduction. This is more certainly and 
 constantly the result in detaching one of the monadiform 
 individuals, which assists in composing the seeming indivi- 
 dual whole called " Voltox globator ;" and so likewise with 
 the leaf-bud. And this liberation Nature has actually per- 
 formed for us in the case of the Aphis, and she thereby 
 plainly teaches the true value or signification, in morphology, 
 of the connecting links that remain to attach together the 
 different gemmiparous individuals of the Vohox, the zoo- 
 phyte, and the plant."* 
 
 Though it may be convenient therefore, as proposed by 
 Dr. Lankester,*!" to have appropriate terms to distinguish 
 attached gemmae of all kinds from those detached from the 
 parent stock — such as isozoids and isophytoids for the 
 former, and allozooids and allophytoids for the latter — w^e 
 
 * Prof. Owen's Partlienogenesis, p. 60. The correspondence is in- 
 geniously shown by the comparative diagrams in the Frontispiece, 
 t In a communication to the British Association, 1857. 
 
PULLULATION IN THE GENETIC CYCLE. 153 
 
 must not allow this terminology to blind us to the uoci- 
 dental nature of the distinction. 
 
 § 5. The repetition of many successive gemmations — or 
 what has been here termed pullulation — must be considert-tl 
 a much more variable feature in the reproductive cycle, than 
 the simple alternation of gemmation with sexual generation 
 under any of its modifications ; and the extent to which it is 
 carried is still more variable. Thus in the protomorphic al- 
 ternation of most Cestoid worms, we have but a single pri- 
 mary cyst, which directly originates the Ttenia-head ; but in 
 the Echinococciis there always is one, and frequently are se- 
 veral derivative cysts, interposed before the appearance of 
 the typical form. In the Trematoda again, we have two 
 intermediate forms as a general rule (the infusorial and the 
 gregariniform), but, according to Steenstrup, the latter is oc- 
 casionally repeated, and that perhaps more than once, be- 
 fore the appearance of the cercariform zooids.* In the 
 
 * It is this variable mixltiplication of links wliicli lias been the sonrce 
 of ambiguity as to the con-esponding forms in the genetic cj'cle of the 
 Trematoda and Cestoidea respectively. Professor Van Beneden correctly 
 identifies the immediate product of the ovum in each case, under the 
 name of proscolex (the " infusorial embryo of the Distoma, and the 
 "six-hooked vesicle" of the ToeniaJ, but he is less satisfactory in his 
 identification (under the name of scolex) of the forms immediately suc- 
 ceeding — that is, of the Redia of the Distoma and the Taeuia-head of the 
 Cysticercus — because the length of the preliminary pullulation difiers in 
 these species. If Filippi is correct in stating (Ann. Nat. Hist., 2d Ser., 
 XX., 130) that in some instances the primary infusorian zooid is itself 
 ti'unsformed into the redia, rather than that it generates the latter in its 
 interior, in tliis case the comparison would stand, for the infusorian and 
 Redia are as much amalgamated as the " six-hooked vesicle" of the Ttenia- 
 egg is with the primary cyst of the Cysticercus, But the majority of the 
 species of Distoma, which have two Hnks in their preliminary develop- 
 ment, should be compared, not with the Cysticercics, which has but one 
 — the primary cyst budding off the Taenia-head directly — but with the 
 Echinococcus scolicvpariens of Kuchenmeister, in which the first cyst buds 
 off secondary cysts as the immediate progenitors of the heads. Those Dis- 
 tomata which have more than one Redia might in like manner be con - 
 pared to the Echinococcxis oJtricipariens of Kuchenmeiator, in which 
 
 H 3 
 
154 INTERPOLATION OF A CONTINUOUS 
 
 Hepatic^e, among Cryptogamic plants the spores produced 
 by the protomorphic gemma which becomes the capsule, 
 give origin directly to the typical frond, but in mosses we 
 have a second form interposed — viz., the Protonema. 
 
 In the orthomorphic gemmation the number of hnks is 
 still more variable, reaching perhaps their maximum among 
 animals in the ten or twelve generations of larval Aphides, 
 but in plants running on to an indefinite extent, and pro- 
 bably depending much on external circumstances, while 
 the remarks which have been already made on the pro- 
 liferous Medussg show that pullulation, though less common, 
 is not less variable in the gamomorphic stage. 
 
 Various other facts might be adduced to show that the 
 processes do not stand at all on the same footing. Thus 
 we find that even in species in wiiich the sexual gemmae are 
 detached as independent organisms, it is comparatively 
 rare for the non-sexual shoots, which have pullulated from 
 the original typical form, to be detached in the same w^ay.* 
 
 We may observe farther, there are, numerous cases in 
 
 there is a succession of cystic forms before the characteristic heads of the 
 Echinococcus are produced. In this view the Scolex of the Cestoid worm 
 — the Tsenia-head — is represented, not by any Trematode Eedia, primary 
 or secondary, but by the early condition of the Disto'rna itself, inchiding 
 the cercarian phase through which it passes in the usual course of its de- 
 velopment (but not, as it would seem, universally in all the species), and 
 the 'proglottides of the Tapewonn have no farther representations among 
 the Trematoda than what may be furnished by the reproductive organs 
 developed at a later period in the fully formed Distoma. 
 
 * The exceptions are unimportant, and occur principally in the aber- 
 rant cases before noticed among the Articulata, or, again, among phanero- 
 gamic plants, as in the deciduous bulbs of Begonia j Allium^ and various 
 Lilies, MarcJiantia, and some other HepaticcB, &c. In a few plants such 
 deciduous buds may occasionally take the place of seeds, especially if the 
 maturation and impregnation of the ovules is prevented by force of cir- 
 cumstances. An inflorescence bearing such bulbs is termed by botanists 
 vivipa/rous, though in the received signification of the word it is here mis- 
 applied, the only truly viviparous plants being such as the Mangrove, in 
 which the embryo germinates while still attached to the plant. 
 
PULLULATION IN THE GP:NETIC CYCLE. 1 oS 
 
 which the puUiilation seems to lie out of the primary cycle 
 of propagation altogether. So it is in plants, witli what 
 Braun calls the " inessential sprouts," that is, shoots over 
 and above those which are necessary to the full carrying out 
 of the series of formations up to blossom and fruit. These 
 inessential shoots are mostly formed subsequently to those 
 essential to the cycle, and in some species are very numerous 
 and regular, constituting the great mass of the vegetation, 
 and enabling the plant to rise up in new generations from 
 the same stock, year after year, and thus repeatedly to pro- 
 duce flower and fruit ; or, again, they may become detached, 
 and serve the purpose of dispersing the plant.* We have 
 phenomena of a like kind among animals also, both in the 
 growth of the ramose polypidoms, and in the reversion of 
 the " Hydra Tuba" to the gemmation of common polype- 
 buds, after having thrown off swarms of Medusa-buds. "f- 
 
 * Eejuvenescence, p. 36. 
 
 t Dalzell's Remarkable Animals of Scotland, Vol. I., ch-. 3. Dr. J. 
 Reid's Anat. and Physiol. Researches, pp. 652-656. 
 
lot) REPRESENTATION OF PROTOMORPHIC ALTERNATION 
 
 VL 
 
 REPRESENTATION OF PROTOMORPHIC ALTER- 
 NATION IN THE EMBRYOGENY OF THE 
 HIGHER ANIMALS. 
 
 § 1 . In the foregoing remarks traces of reproduction by the 
 co-operation of the sexes have been noticed, in all the leading 
 groups of both kingdoms of nature. This process still con- 
 tinues to exist, side by side with that of gemmation, even in 
 those lower forms of Hfe, in which the latter is much the 
 most conspicuous mode of propagation. Hence the enquiry 
 naturally suggests itself, whether in the higher species, in 
 which sexual generation is the only weU-marked agency for 
 the purpose of propagation, any associated phenomena 
 occur which can be considered as corresponding to the gem- 
 mation of the inferior classes ; and whether the alternation 
 of the two processes, so striking in some of the lower forms, 
 has any representation in the case of the higher organisms, 
 and of those generally in which naturalists have recorded 
 no change in the forms propagated from each other. In 
 reply, it may be observed that on a careful survey of the 
 phenomena of reproduction in the principal groups of or- 
 ganized beings, indications do present themselves of a ge- 
 neral tendency in this direction, as will appear from some 
 illustrations which will now be offered, and which go to 
 show that in the phenomena of embryological development, 
 and of the maturation of the sexual organs, processes occur 
 which have a certain correspondence with those observed in 
 the best marked cases of alternation of generations. 
 
IN THE EMBRYOGENY OF THE HIGHER ANIMALS. 1.")? 
 
 § 2. We may consider first the phenomena of embry- 
 ogeny as presenting a certain parallelism with the (proto- 
 morphic) gemmation which occui's in some of the lower 
 species (Trematoda, Mosses, &c.) before the period wht'ii 
 the typical form is attained. 
 
 No point in embryogeny is better established than this, 
 that the first result of impregnation is the formation in the 
 ovum of a cellular mass, from one point of wliich is subse- 
 quently developed a fresh axis of gTowth, destined for evolu- 
 tion into the organization typical of the species, while the 
 original germ-mass disappears as a distinct structure. The 
 embryo, in short, may be said to be budded oft' from the 
 primordial germ-mass or " mulberry body," much as the 
 cercariform larva of the Distoma is from the oreoariniform 
 product of the Trematode ovum. 
 
 There are, however, two striking points of diversity 
 which must not be overlooked. In ordinary and normal 
 development the original germ-mass gives rise only to a 
 single embryo, and no separation takes place between them ; 
 the later growth appears simply as a more advanced state 
 of the former, wliich w^astes away, pari passu, with the 
 growth of the embryo, becoming a mere appendage of the 
 latter, or, it may be, disappearing altogether. In the cases 
 a^ain of alternation of Q-eneration, which w^e have had under 
 review, the immediate product of impregnation gives origin 
 to numerous gemmse, every one of which may acquire the 
 characters of a typical individual of the species. We find 
 also that these gemma? generally become completely sepa- 
 rated from their germ-parent, and assume the form of inde- 
 pendent organisms. 
 
 § 3. But although the detachment of the later growth, 
 and its multiplication, give an apparent distinctness to the 
 cases in which they occur, they can scarcely be considered 
 as characters of sufficient constancy to establisli, of them- 
 selves, an essential diversity of nature between them and 
 
158 REPRESENTATION OF PROTOMORPHIC ALTERNATION 
 
 the phenomena of ordinary embryogeny ; for we shall have to 
 notice instances of alternation in which they no longer pre- 
 sent themselves, while they reappear — at least as an occa- 
 sional abnormality — in the reproduction of the higher 
 species. 
 
 As in the former case, we have examples of alternation, 
 where the form immediately developed from the fecun- 
 dated germ originates but a single gemma, which never 
 becomes detached from its matrix ; so in the latter, a sin$!;le 
 ovum has been observed to originate two distinct axes of 
 embryonic growth. Cases of a double primitive trace of 
 organization have been met with in the bird's egg, by Dr. 
 Allen Thomson and others, and it is probably in some such 
 way that we may most feasibly account for the origin of 
 what are termed ''double monsters."* At all events we 
 have in these, as much as in the best marked cases of al- 
 ternation of generations, a production of two more or less 
 typical organisms from a single original germ ; for it is 
 now generally agreed that such monstrosities cannot be well 
 explained on any supposition of the fusion of two inde- 
 pendent embryos. 
 
 This conclusion rests principally on the following con- 
 siderations : — 
 
 1. In all such monsters the duplicated parts are con- 
 nected together, and derive their vessels from a common 
 trunk ; we never find a face springing out of the chest, legs 
 implanted on the head, or any such mal-position of parts. 
 
 2. Double monsters form a continuous series, in which 
 the degrees and modes of deviation from singleness gTadu- 
 ally increase, and pass, without any abrupt steps, from the 
 addition of a single ill-developed limb to the nearly com- 
 plete formation of two perfect beings ; so that no theory 
 can be tenable that will not account for the simpler as well 
 
 * Edin. Monthly Jouni. Med. Science (1844), lY., pp. 479, 56S, 639. 
 See also Vrolik's article on Teratology, in Cyc. Anat. and Phys, 
 
IN THE EMBRYOGENY OF THE IIIGHER ANIMAL.S. i:>9 
 
 as the more complete instances of duplicity — that cannot 
 explain, for example, the existence of supertiuous limbs. 
 As M. Vrolik remarks, " the limbs are mere off-shoots, and 
 are produced at so late a period, that if we could imafrinc 
 two embryos to come in contact by their shoulders or pelvis, 
 and a fusion of those parts to take place, we should still 
 have to explain how one of them, leaving only an arm or a 
 leg behind him, could for the rest of his substance, head, 
 trunk, and all, wholly disappear." 
 
 3. The two monsters are always of the same sex, which 
 we know, from the case of twins, is very fiir from being a 
 constant rule with associated embryos. 
 
 The theory of the furcation of a germ or embryo, origi- 
 nally single, is farther supported by an observation of Va- 
 lentin's, that an injury inflicted on the caudal extremity of 
 an embryo on the second day was found on the fifth to 
 have produced the rudiments of a double pelvis and four 
 inferior extremities.* 
 
 Reference may be made also to the observations on the 
 development of the ova of fishes by M. Lereboullet, accord- 
 ing to whom, in particular species — as the Pike — the for- 
 mation of such monstrosities may be determined at pleasure, 
 by placing the eggs in certain conditions unfavourable to 
 development. In this case the blastodermic ridge forms 
 on its surface two tubercles instead of one, and from each 
 of these an embryonic fillet is produced, the farther deve- 
 lopment of which gives rise to- double embryos of various 
 kinds, i* 
 
 The detachment of a portion from the body of the ger- 
 minal mass has not unfrequently been observed in the em- 
 bryogeny of the MoUuscan Gasteropoda. In this case the 
 isolated segments may become clothed with cilia, and re- 
 
 * Vrolik, Op. Cit. 
 
 t Annals of Nat. Histoiy, 2d Ser., XVI., 19. 
 
160 REPRESENTATION OF PROTOMORPHIC ALTERNATION 
 
 tain a proper vitality for some time, but tliey have never 
 been observed to undergo any farther development. It 
 would appear to be different, however, when the general 
 mass divides by a process of fission into two or more equal 
 segments, as is stated by Agassiz to occur occasionally in 
 the ovum of a species of Eolis, for in this case he has ob- 
 served each segment to dev elope a distinct embryo of its 
 own. * 
 
 § 4. This multiplication of embryos in the ovum of 
 Eolis shows that it is not among monstrosities only that 
 we meet with cases establishing a transition between the 
 phenomena of alternation and those of ordinary embry- 
 ogeny ; and the evolution of the Polyzoa furnishes us with a 
 farther confirmation of the same, for in some of this group 
 we have as a normal occurrence w^hat may be compared to 
 the formation of a double primitive trace, or a double 
 monster, in the development of the vertebrate ovum. In 
 the Polyzoa, as has been already noticed, the immediate 
 product of the ovum is a ciliated germ-mass, like an infu- 
 sorial animalcule, from a protrusion of which a pair of 
 polypes are budded off in succession, the phenomena pre- 
 senting, as Professor AUman observes, '' some remarkable 
 analogies, which would seem to bring the whole process of 
 generation and gemmation in these animals within the do- 
 main of the so-called Law of Alternation of Generations. ""(* 
 Yet the case is not commonly reckoned one of " alterna- 
 tion," and in fact agrees with it only in the multiplication 
 of the secondary products of development, for in the ma- 
 jority of the group, neither the two first formed gemmae. 
 
 * Lectures on Comparative Embryology, quoted by Dr. A. Thomson, 
 in Cyclop, of Anat. Physiol., art. Ovum, p. 2-i. Such a division of the 
 yolk after segmentation into several (foui-) globular masses, I have ob- 
 served myself in the ova of a Nudibranchiate Mollusc, though I have had 
 no opportunity of tracing the development farther. 
 
 t Allman's Polyzoa, p. 41 (Kay Soc.) 
 
IN THE EMBllYOGENY OF THE HIGHER ANIMALS. IGI 
 
 nor those which aftenvards pulhilate from tliem, ever be- 
 come quite detached ; the whole cohering together to form 
 a compound animal — while the original germinal matrix 
 becomes as completely reduced to the condition of a mere 
 appendage of the structures derived from it, as in the case 
 of any vertebrate ovum. 
 
 § 5. For another illustration of a reproductive process, 
 intermediate between the continuous embryogeny, as it may 
 be termed, of the higher species, and ** alternation of gen- 
 erations," we may turn to the Cystic Entozoa, which, prior 
 to their most notable change— r the transformation into 
 Cestoid worms — present us with a series of successive 
 forms, all referable to the Cystic phase. The typical form 
 — the Tsenia-head — is not, as has been shown, produced at 
 once from the egg, but is budded off as an aftergrowth from 
 the cyst which is the primary development. With consider- 
 able differences of detail, this general relation is to be 
 traced in all the species. In Echinococcus the Ta3nia-heads 
 are developed in large numbers, by a sort of gemmation, from 
 the Hning membrane either of the primary cyst, or of others 
 derived from it by an intervening process of puUulation. 
 In Coenurus also there is a formation of numerous heads 
 from the original cyst ; only they are budded oft' from a 
 special thickening of the membrane, not from the whole 
 interior, and they subsecj[uently become evaginated so as to 
 protrude from its exterior. In both these cases there is an 
 obvious " alternation," attended with a midtiplication of 
 the brood, but in Cysticercus the germ-mass is resolved into 
 a simple cyst, from which is evolved a single Tixjuia-head, 
 the whole process having somewhat the character of a con- 
 tinuous development, like the formation of the embryo of a 
 vertebrated animal.* Indeed, not only is the latter formed 
 
 * A detailed account of the primary development of the vesicle nnd 
 head of the Cysticercus is given by Mr. Raiuey in the Philosoph. Transact . 
 for 1857. 
 
162 KEPRESENTATION OF PROTOMORPHIC ALTERNATION 
 
 much in the same ^Yay on the investing or blastodermic 
 layer of the germ-mass, but it gradually becomes invagi- 
 nated within the amniotic folds of that membrane, some- 
 what as the head and neck of the Cysticercus are within the 
 primary cyst, in the early stage of its development. In 
 such cestoid forms as the Bothrioceplialus, the progressive 
 development is, if possible, of a still more continuous kind, 
 the Tsenia-head appearing to be formed from the original 
 contents of the ovum, by as direct a process of organiza- 
 tion as is anyAvhere met with in animal embryogeny, and 
 the act of gemmation not being obviously represented by 
 any one particular event in the course of evolution. 
 
 We have, then, in this single order, a series of cases 
 establishing a transition from a well-marked '' alternation," 
 attended with multiplication and detachment of gemmae, to 
 ordinary continuous embryogeny. This argument is of all 
 the greater cogency if Coenurus be, as Siebolcl contends, a 
 mere variety of Cysticercus. Even in admitted forms of 
 Cysticercus, however, it is probable such multiple gemma- 
 tion of T^enia-heads may at times occur, for when the cyst 
 developes itself in the brain (the usual seat of Coenurus,) it 
 occasionally buds off secondary cysts, all of which, it would 
 seem, may bear T^enia-heads.* 
 
 § 6. The Echinodermata afford another interesting illus- 
 tration of such a transition series. In some species of the 
 class, the primary germ -mass has so much the character of a 
 complete animal as to have been mistaken for one of a 
 totally different family, and named accordingly ;"j* while 
 the new axis of growth, which appears at one point, and in- 
 creases pari passu with the decline of the matrix, has all 
 along such a distinct character, and so much individuality 
 of its own, that nothing but actual observation could im- 
 
 * Siebold's Memoir is translated in the second volume of tlie Ear So- 
 ciety's Edition of Kiiclienmeister's work on Parasites. 
 
 t " Pluteus," in Echinus and OpMura. "Bipinnaria" in the Starfish. 
 
IN THE EMBRYOGENY OF THE IIIGIIKR ANIMALS. Ki.S 
 
 press the conviction that the one is but a farther advanced 
 stage of the other. Here the majority of naturalists reheard 
 the process as a modification of alternation, differino- oidy 
 from that of the Trematoda in the gemmation developintr 
 but a single offset from the primary zo(jid, instead of 
 a numerous brood, each individual of which is in turn 
 equally prolific* 
 
 Yet in this same class there are other species (Ech bl- 
 aster and Holothuria) in which the organization of the 
 original germ-mass is so little advanced, and that of the 
 typical Echinoderm is so confounded w4th it, that there is 
 positively less distinction between the two, than exists in 
 the evolution of the higher animals, between the so-called 
 mulberry body, and the proper embiyonic organization which 
 subsequently originates from it. Dr. Carpenter, indeed, 
 points out differences in the embryogeny of the Vertebrata, 
 in some degree analogous to those just referred to in the 
 development of the Echinodermata, observing that the um- 
 bilical vesicle, which is cast off from the foetus of the j\Iani- 
 mal — like the Bipinnaria of the Starfish — is gTadually 
 taken — like the Pluteus of the Echinus — into the body of 
 the Bird ; while he finds in the mode of evolution of the 
 Batrachian Reptiles, the whole of whose vitelline mass goes 
 at once to be converted into the embryo, a representation 
 of the type of development occurring in Echinaster.'f 
 
 * There may be added one otlier point of difference — namely, that in 
 all cases, even where there is the greatest extent of change, certain parts 
 of the original structure — particularly the alimentary canal — arc incorpo- 
 rated into the new growth. 
 
 t Piinciples of Comparative Phj^siology, § 555. A practical difficulty 
 which results from this diversity in the development of the Echinoder- 
 mata, is that it becomes impossible to apply the same terms with perfect 
 accuracy to all the cases, for while there may be liltle reason to object to 
 Auricularia being spoken of as the larva of Holothuria, we cannot so 
 well apply the same name to the Bipinnaria of the Starfish, which, after 
 it has parted from its derivative Echinoderm, continues for some time its 
 
IG-i REPRESENTATION OF PROTOMORPHIC ALTERNATION 
 
 § 7. Additional illustrations might be cited, but those 
 just given appear sufficient to establish a certain community 
 of nature in all cases of the kind, provided the survey be 
 extended over the whole course of phenomena intervening 
 between two successive returns of the act of digenesis. In 
 all cases it is probable that two successive steps can be dis- 
 tinguished, which may be termed respectively germinal and 
 embryonic — the later structure, which alone acquires the 
 typical characters of the species, arising from the earlier by 
 a more or less appreciable process of gemmation. In what 
 is called alternation of generations, this gemmation, in the 
 first place, is remarkably definite, the product frequently 
 becoming detached, and acquiring in some sort a distinct 
 individuality ; and, in the second place, it is generally 
 multiple, so as apparently to give rise to a new generation 
 of many separate zooids. We find, too, that the gemma- 
 tion is occasionally repeated many times over, so that a 
 whole race or series of o-enerations seems to orio-inate from 
 a single ovum. But however striking these points of dif- 
 ference may be, the transitional cases just cited indica.te 
 that the diversity is less in the essential nature of the func- 
 tion than in its being exaggerated, as it were, in the lower 
 species, so as to diverge from what may be considered, in 
 some sort, a process common to them and the higher — viz., 
 the gemmation, just referred to, of the embryonic structure 
 from the germinal mass. So long as the exaggeration is 
 merely in its distinctness (as in the Echinodermata) the af- 
 finity of the process to the normal course of embryogeny is 
 sufficiently apparent. Even when a new element of dis- 
 crepancy is introduced by multiple gemmation, we can still 
 find a parallel in the embryogeny of the higher species, 
 
 own independent life, and may even, for ouglit that is known to the con- 
 trary, be capable of developing another Starfish, by a repetition of the 
 same process of gemmation, for evisceration, which is so readily bom by 
 the adult Holothuria, can hardly of itself be fatal to the Bipinnaria. 
 
IN THE EMBKYOGENY OF THE HIGHER ANIMALS. Hi.') 
 
 tliouoli now only as an occasional abnorniallty. But when 
 the breach is yet farther widened by one or more repetitions 
 of the process of gemmation, we have a result so totally un- 
 like the ordinary course of reproduction in the majority of 
 animals, that it is with some difficulty we can realize the 
 existence of any community between them. The case 
 seems to stand thus : Gemmation of the embryonic struc- 
 ture may be said to occur in all cases, though in the higher 
 animals only in a latent form, and without trenchinc; on 
 the unity of the organism ; while multiple gemmation 
 exists in the higher only as a monstrosity, and a repetition 
 of it is wholly unkno-wn. Still as the difference is due to a 
 progressive exaggeration of a feature conmion to all, we 
 must regard it as one rather of degree than of kind, and 
 therefore not such as to interfere wdth a certain essential 
 though hidden community of nature — and this even when 
 we come to apply it to such cases as the series of precur- 
 sory zooids among the Trematode Entozoa. 
 
 This way of viewing the case has a bearing on the ques- 
 tion of " zoological individuality," before referred to, for as 
 we consider the germinal mass and the embryo which suc- 
 ceeds it in the light not of two animals, but of mere suc- 
 cessive stao-es in the existence of one and the same animal, 
 so the whole succession of rudimentary Trematoda or 
 Echlnococci may also, in a certain [embryological] sense, be 
 considered as making up but one animal with the typical 
 Distoma or Toenia in which the series terminates. The 
 separate links of the chain of succession, at all events, have 
 not the same distinctness of organic individuality in cases 
 of alternation, as belongs to the consecutive generations of 
 animals high in the scale of organization, in whose develop- 
 ment the embryonic stage — when the typical conformation 
 begins to take shape — is never broken off from the ger- 
 minal in any similar way. 
 
166 REPRESENTATION OF THE 
 
 VII. 
 
 REPRESENTATION OF THE OTHER FORMS OF 
 ALTERNATION IN THE HIGHER ANIMALS, 
 ESPECIALLY IN CONNECTION WITH THE 
 MATURATION OF SEX. 
 
 5^ 1 . Reasons have been given in the last Chapter, for drawing 
 a parallel between protomorphic alternation in the lower 
 animals, and a particular feature in the embryogeny of 
 those higher in the scale — viz., the implantation of the 
 rudiments of the typical organization on the blastodermic 
 membrane, which after cleavage is formed on the surface of 
 the vitelline mass. On similar grounds of analogy we 
 might look for some representation of the other forms in 
 the period of typical development, and in connection with 
 the evolution of the sexual organs. 
 
 The same analogies, however, would lead us to expect 
 that the traces of such phenomena would be far from evi- 
 dent in the former. Even in the lower animals, as we have 
 seen, gemmation in the orthomorphic stage rarely puts on 
 the form of alternation, because the gemmae seldom sepa- 
 rate as free zooids, generally remaining in adhesion to the 
 common stock, and going along with it and with each other 
 to make up a more or less composite structure. We find 
 further, that, as we ascend to the higher forms, the individu- 
 ality of the associated parts becomes always less marked, 
 the zooids assuming more and more the position of mere 
 organs, and the budding process gTaduaUy merging into 
 one of continuous gTowth. In the higher animals, indeed, 
 
OTHER rORMS OF ALTERNATION. KIT 
 
 any indications of gemmation, in the orthomorpliic stap,e, 
 as distinct from growth, are very equivocal ; possibly, how- 
 ever, we may trace them in such phenomena as the renewal 
 of the hair, teeth, antlers, and other cutaneous appendafi;es, 
 or of the whole integument in certain species — the limited 
 reproduction of lost parts — the abnormal sprouting of su- 
 pernumerary limbs — and the still rarer monstrosity termed 
 foetus in foBtu. Perhaps, too, some of the normal struc- 
 tures of foetal life may be considered as early orthomorpliic 
 or larval gemmae ; e.g., the placenta of Mammalia, the 
 allantois, the branchial tufts of Batrachia, and the ciliated 
 lobes of Gasteropoda. 
 
 § 2. We come next to enquire into the phenomena 
 which, in the higher animals, may be regarded as standing 
 in the place of the variety of alternation depending on gem- 
 mation in the gamomorphic stage. To this a certain 
 analogy has just been indicated in the processes connected 
 with the development of the reproductive elements, which 
 may be held to represent this modification of alternation, 
 somewhat in the same way that the succession of forms in 
 embryogeny shadow^ out the budding off of zooids in the 
 rudimentary or protomorphic stage. 
 
 Some of the points which suggest such a correspondence 
 will now be briefly noticed. 
 
 § o. To begin Avith one of minor importance, it may be 
 observed that the periodicity whicli so commonly charac- 
 terizes the development of the sexual organs seems to as- 
 sert for them, even in the higher species, a relation to the 
 body at large somewhat different from that hold by the 
 other members. Much in the same way, for instance, that 
 the " Hydra Tuba," after a certain lapse of polype life, 
 matures a succession of reproductive structures, in the guise 
 of medusa-buds, and on tlieir detachment relapses again 
 into the ordinary polype life, till other periods of reproduc- 
 tive activity occur, marked by similar phenomena ; so we 
 
168 REPRESENTATION OF THE 
 
 find tliat among animals generally the parts ministering to 
 the generative function have regularly recurring periods of 
 increased action, dependent on the development or gemma- 
 tion, as it were, in their substance, of swarms of cells, bear- 
 ing the reproductive corpuscules, and comparable in a de- 
 gree to the piles of medusoids budded off from the polype 
 stock. During the intervals the function is commonly en- 
 tirely suppressed, and the parts, so largely developed dur- 
 ing the period of action, are in some cases not to be dis- 
 tinguished at all. Even in species characterized apparently 
 by continuous fertility, the phenomena of ovulation in the 
 female, which are always more or less periodic, are gener- 
 ally admitted to indicate corresponding differences in the 
 proclivity for conception. 
 
 Another argument in the same direction, and one pro- 
 bably of greater force, may be drawn from the lateness of 
 the development of the reproductive organs. In some 
 species they would seem actually not to be formed at all 
 till the breeding period arrives. This has been already 
 noticed in the case of the Distoma, in which the appear- 
 ance of these organs constitutes almost as marked an 
 epoch, as the previous budding off of the Cercariw from the 
 interior of their gregariniform matrix. In some instances 
 it is equally dependent on the transference of the parasite 
 to an animal of different species from its former victim. 
 The Cercaria which has quitted the snail, on its discharge 
 from its parent sac, for the body of an aquatic insect, may 
 in this position complete its larval development, and yet 
 may not mature its sexual organs, till, by its new host 
 falling a prey to the voracity of some bird, it is transferred 
 to the intestine of a warm-blooded animal. 
 
 Another peculiarity in the development of the sexual 
 organs may be noticed in this connection — viz., that among 
 insects which live in communities — such as Bees, Ants, and 
 Termites — these organs are never perfectly developed at all, 
 
OTHER FORMS OP ALTERNATION. 109 
 
 except in a few individuals, the majority remaininn; neuter 
 in function, if not in all cases absolutely devoid of the 
 structural characters of sex. 
 
 Even, however, when such organs are normally matured 
 in all the individuals of the species, and when, as is ge- 
 nerally the case, traces of them do make their first appear- 
 ance alons: with the nei2:hbourino- viscera * it is still a con- 
 stant rule that they lie in a latent condition long after the 
 full development of other parts, and are the last to take on 
 a state of functional activity. This only occurs on the for- 
 mation in their substance, at the proper period, of numerous 
 cells containing the peculiar reproductive corpuscules (sper- 
 matozoa and ova) ; and it is not till the development of 
 these, that the bodies in question, which up to this time 
 have been mere masses of parenchyma, can rightly he 
 called organs of reproduction. Hence probably the dif- 
 ference between the common case, and that of the species in 
 which these organs appear to be formed pro re nata, may 
 not amount to more than this, that in the former the gem- 
 mation extends only to the cells producing reproductive 
 corpuscules, while in the latter it embraces also the general 
 envelope or viscus in which they are contained. Or per- 
 haps in propriety we ought to make such a distinction be- 
 tween these formative cells and the stroma in which they 
 lie, as to regard the latter as merely a proliferous tract of the 
 parent's body — like the base of the Ta3nia-head, or the cap- 
 sule of the Sertularian polypidom, or like the " funiculus" 
 of the Polyzoon presently to be noticed — and to consider 
 
 * This, however, is probably conceding too much, for it is now well 
 ascertained that the generative glands are not part of the organization aa 
 originally laid down, at least in Mammalia and Birds, but that the large 
 masses occupying each side of the abdomen of the embryo at an early 
 stage of development, which are known as the Wolffian bodies, and have 
 themselves but a provisional part to fulfil, form the primordial matrices, 
 upon which both the uriuarj^ and genital organs are developed. See a 
 farther reference to this point in the concluding Chapter. 
 
 I 
 
170 REPRESENTATION OF THE 
 
 the former, that is, the sperm-sacs and ovisacs, which are 
 in due time developed in this matrix, as the true organs of 
 reproduction. In this view the medusoids of the Poly- 
 pifera, and other such sexual zooids, would differ in them- 
 selves from the organs of reproduction of the higher 
 species only by the gi-eater complexity of their internal 
 structure, and the possession of certain appendages, required 
 for their maintaining an independent existence. 
 
 § 4. In support of such a relationship reference may be 
 made to the reproductive organs of the Polyzoa, as occupy- 
 ing a position intermediate in some respects between that 
 of derivative gemmge, and that of mere organs of the par- 
 ticular polypes in connection with which they are developed. 
 Such at least is the view of Professor AUman. " If the 
 formation of the ovary," he remarks, " be attended to, it will 
 be seen that this body is developed at a later period from 
 the walls of the original sac-like embryo, which have under- 
 gone slight changes and have become the endocyst [inner 
 coat] of the more mature Polyzoon, and it will be at once 
 perceived that this development of the ovary takes place i^j 
 a way which may obviously be compared with the forma- 
 tion of a bud, that — at least in Alcyonella — it occupies 
 exactly the position in certain cells that the buds destined 
 to become polypides [polypes] do in others, and that at an 
 early stage of polypide and ovary it is scarcely possible to 
 distinguish one from the other ; so that the idea is imme- 
 diately suggested that the body here called ovary is itself a 
 distinct zooid, in which the whole organization becomes so 
 completely subordinate to the reproductive function as to 
 be entirely masked, and apparently replaced by the genera- 
 tive organs. This would then constitute a third zooid, 
 which w^ould therefore be a sexual zooid ; it is, however, 
 unisexual (female). Again, we find that upon the /"Mmcz^/w^ 
 [or suspensory ligament of the stomach] there is developed 
 the mass described as testis. Now, if w^e view this mass 
 
OTHER FORMS OF ALTERNATION 171 
 
 as a mere organ of the polypide, we must regard the latter 
 as the second or male zooid ; but the testis may perhaps be 
 more correctly considered, like the ovary, as a distinct 
 sexual bud, having the generative system so enormously 
 predominant as to overrule and replace all the rest of the 
 organization ; this bud, like the ovary-bud, being also uni- 
 sexual, but with a male function."* In support of this 
 view he points out that certain undoubted buds, known by 
 the name of statoblasts, are actually at times produced in 
 the same species by this very part — the funicidus — while 
 in another species the testis is developed more in the situ- 
 ation of the ovary, i.e., from the endocyst. As instances 
 of such a dominant development of the generative system 
 as to supplant that of the other organs, he quotes the males 
 of some Rotifera (Asplanchia) ; and probably still more 
 striking illustrations might be found among the Cirrhipedes. 
 Dr. Allman observes in conclusion, that in this view " the 
 complete comprehension of a Polyzoon will involve the con- 
 ception of a ciliated sac-like embryo as a starting point, and 
 a series of buds, of which the last term will consist of 
 a pair of sexual buds, the others being non-sexual ; from 
 the sexual buds a new embryo, like the first, is again pro- 
 duced, which affords a point of departure for another simi- 
 lar cycle . . . analogies, which would seem to bring 
 the whole series of generation and gemmation within tlie 
 domain of the so-called ' Law of Alternation of Genera- 
 tions.' ""f According to this view a twofold interpolation of 
 gemmation must be recognized in the Polyzoa, first in the 
 protomorphic, and again in the gamomorphic stage — and 
 this over and above the continued pullulation of the polypes, 
 throughout the duration of the typical or orthomorj)hii' 
 phase, by which the ramified structure is formed, known as 
 the polypary or polypidom. It is to this sequence Allman 
 
 * Allman, Op. Cit., p. 41. f Op. Cit., pp., H- J2. 
 
 I 2 
 
172 REPRESENTATION OF THE 
 
 seems to refer above, wlien he calls one of the generative 
 organs " a third zooid." 
 
 § 5. Another illustration of the semi-independent posi- 
 tion of the sexual organs is offered by some aberrant forms 
 of the Crustacean type, especially by species of Cirrhipedes 
 and Lerneans, which undergo what is termed a retrograde 
 metamorphosis. These species commence life as active 
 Entomostraca, but afterwards lose the power of locomotion, 
 attaching themselves to the integuments of marine animals 
 or to other bodies, while at the same time they become va- 
 riously transformed — or deformed, as we should say, in the 
 majority of cases — by the obliteration of certain parts of 
 the typical organization, and the disproportionate develop- 
 ment of the reproductive organs. Here the nature of the 
 change is such as to suggest doubts of the correctness of 
 the common view of the Entomostraceous stao^e beino- a 
 larva state, and the subsequent transformation, though of 
 a retrograde kind, one analogous to the metamorphosis of 
 an insect. Another view at least ma^/ be taken — namely, 
 that the transformation is a sort of gamomorphic alterna- 
 tion, the reproductive structures in many respects standing 
 more in the position of superadded sexual zooids than of 
 constituent organs. Prof. Owen ranks the case as one de- 
 cidedly of the nature of metagenesis,* and there is at all 
 events a much more complete change in the relations of 
 the parts than in any case of undoubted metamorphosis. "f* 
 The greater tendency of the males to retain their original 
 
 * Partheuogenesis, p. 25. 
 
 t The only cases in Insects whicli are at all similar are those before 
 referred to in the gregarious species, where the procreation of ova for the 
 whole community devolves on a single fertile female or queen. The 
 ovaries may then attain an enormous size, as happens most remarkably in 
 the queen of the Termites, whose abdomen at the time she commences 
 laying is from 1500 to 2000 times larger than the rest of the body, the 
 eggs being subsequently deposited at the rate of 80,000 a day for several 
 successive weeks. 
 
OTHER FORMS OF ALTERNATION. 178 
 
 form is nowise opposed to this view, for we have seen a cor- 
 responding diversity in some polypes which form their ova 
 in free well-developed medusoids, but the spermatozoa in 
 simple attached cysts. 
 
 § 6. From such cases we pass by an easy transition to 
 the Cestoid Entozoa with voluminous caudal sesmients, of 
 later growth, containing the reproductive organs. In the 
 foregoing remarks these have been unhesitatingly considered 
 as gamomorphic zooids — a view adopted by Van Beneden 
 and others of the first authority in helminthology, and one, 
 as it would seem, fully borne out by their disproportionate 
 development, and their ultimate detachment while still re- 
 taining their vitality.* At the same time it must be ad- 
 mitted that they may also be regarded as being, for a time 
 at least, integral members of the vermiform body, from their 
 connection with each other and with the "head," by two 
 sets of so-called vascular canals and by continuity of tissue 
 generally. 
 
 § 7. It is ob"saous that if this gradation through the 
 Polyzoa, Lerneada, and Cestoidea, be admitted as showing a 
 community of nature between the ordinary development of 
 the reproductive organs in the majority of animals, and 
 well-marked cases of alternation of generations, we must in- 
 clude in our generalization all the gamomorphic zooids fall- 
 ing under the latter head ; so that even the large hood- 
 eyed Medusae must be regarded as representing the repro- 
 ductive organs of the small Lucernarian Polypes from wliich 
 they have been budded off — not being after all much more 
 disproportionate in size than the voluminous caudal seg- 
 ments of a large Tapeworm, in comparison with its minute 
 denticulated head. 
 
 The same conclusion, indeed, as has been already shown. 
 
 * Kiiclienmeister describes the joints as depositing their ova as they 
 wriggle along with a sori; of spontaneous movement. 
 
17:i REPRESENTATION OF THE 
 
 may be amved at by a comparison of tlie different modifi- 
 cations of reproductive apparatus occurring among the 
 Polypifera themselves, as in this single group we find a 
 transition, and that even among closely allied species, from 
 cases in which the structures ministering to reproduction 
 are integral parts of the system, and organs of very simple 
 form, to others in which they appear as detached zooids, 
 having the characters of distinct and well organized ani- 
 mals. A gradation is here presented to us of the most 
 continuous kind, from the spermatic and ovarian follicles of 
 the Hydra fusca to the Medusae just mentioned, whose iso- 
 lation from the parent stock, free powers of locomotion, 
 colossal size, and development of organization, appear almost 
 to raise them to a higher type of animal life. As Professor 
 Huxley remarks, '' in passing from Hydra to RJiizostoma, 
 we thus see the reproductive organs acquiring a gTeater and 
 greater relative mass, when compared with the organism 
 from which they spring, and, as it were, grouping round 
 themselves and subordinating to their own perfection a 
 greater and greater number of morphological elements. 
 First, they are parts of the body wall, indistinguishable in 
 form from the rest ; then they are distinct sacs ; then they 
 are sacs with a gonocalyx [beU-shaped envelope] ; then 
 that gonocalyx becomes a well developed contractile organ ; 
 next the reproductive apparatus is detached, and swims 
 about independently by means of its gonocalyx or umbrella ; 
 and, finally, it acquires total independence, feeding and 
 nourishing itself, and attaining the most complex organiza- 
 tion exhibited by the class to which its originator belongs."* 
 § 8. Granting, however, on the gTounds now alleged, 
 that a general community of nature may be admitted be- 
 tween the reproductive organs of the higher animals, and 
 the gamomorphic zooids of the lower species in which alter- 
 
 * Oceanic Hydrozoa, p. 18. 
 
OTHER FORMS OF ALTERNATION. 175 
 
 nation prevails, still tlie great amount of apparent diversity 
 seems to call for some enquiiy into the causes to which tliis 
 may be due. These appear to be mainly the two following : — 
 
 1. The detachment of the parts of reproduction from the 
 organism producing them, much in the same way that the 
 typical form is separated as a free zooid from the original 
 germ-mass, in the protomorphic form of alternation. 
 
 2. The development, in connection with these parts of 
 reproduction, of accessory organs of alimentation, locomo- 
 tion, &c. 
 
 From the influence of these processes on the gcnenil or- 
 ganization, the phenomena of reproduction are, in many 
 cases, made to assume a character as unlike that of the 
 higher animals as can well be conceived ; but the instances 
 of transition forms just noticed are sufficient to show that 
 differences in these points cannot be allow^ed any weight in 
 determining for or against their essential community "f 
 nature. 
 
 In regard particularly to what may be termed the adven- 
 titious organization of the reproductive zooids, as com- 
 pared with mere organs fulfilling the same function, thi« 
 conclusion is strengthened by the contrast of phenomena 
 of an opposite kind — the degradation of individuals in cer- 
 tain species to the position of mere sexual mechanisms. 
 Wonderful, as it undoubtedly is, to find the homologues of 
 the reproductive organs at times so elaborately organized as 
 to present the characters of distinct animals, and even to 
 simulate species higher in the scale than those of which 
 they are really but detached members, it is not perhaps 
 more wonderful than to meet with animals of undoubted 
 zooloo'ical distinctness — as the males of some Rotifera and 
 Cirripedia — whose organization seems almost limited to tlie 
 parts required for the performance of the sexual function.* 
 
 ♦ From the observations of Mr. Gosse in the Phil. Traus. for 1837, it 
 
176 REPRESENTATION OF THE 
 
 111 some of the latter the animal certainly has more the ap- 
 pearance of a mere detached organ, being, by defect of the 
 apparatus of alimentation and locomotion, reduced to the 
 condition of a minute spermatic cyst. Yet its status as a 
 distinct animal is established by its having the same origin 
 from the impregnated ovum, and passing through the same 
 intermediate larva form, as its more highly organized mate ; 
 as well as by the gradation through different species from 
 tliis extreme of degradation up to the entire fulness of the 
 type of the order.* 
 
 In the structures now contrasted — the so-called parasitic 
 males, on the one hand, which have just been noticed, and 
 the large Medusse on the other — we have examples of the 
 two extremes of organization ; in the one case we have a 
 member, organized above par, so as to simulate a complete 
 
 would seem that an absence of alimentary organs is a general feature in 
 the males of the Rotifera — he has found it in all he has ascertained, or 
 has reason to believe, to stand in this relation. The first observations 
 were those made on the genus Asplanchna. See Brightwell, in Ann. 
 Nat. Hist., N.S., II., 154; Dalrymple PhU. Trans., 1849, p. 340 ; and 
 Gosse An. Nat. Hist., N.S., 2d Ser., 18. 
 
 * In Ihla there is a certain amount of embryonic or rudimentary or- 
 ganization ; some species of Scalpellum have the ordinary structure of 
 the class, but others are extremely rudimentary, and when mature " may 
 be said to be essentially mere bags of spermatozoa," having no mouth, 
 or other viscera, but those of reproduction. The males of Crypto2:>Malxis 
 and AlciiJpe are, if possible, still more rudimentary, for they are reduced 
 to an outer envelope, a single eye, a spermatic gland and vesicle, and an 
 intromittent organ eight or nine times their own length, coiled up Kke a 
 great worm ; there is neither mouth, stomach, throat, abdomen, nor 
 cirri. All these rudimentary males are microscopic, sometimes not ex- 
 ceeding the size of one of the ova which they have to impregnate. They 
 are in some cases attached in numbers at the same time — as many as 14 
 in Alcippe — and their existence being transitory, fresh relays attach 
 themselves as the ova become ready successively for impregnation. See 
 Darwin's Cirripedia (Ray Soc), I., 291, II., 26, 561, 586 ; Carpenter's 
 Comparative Physiology, 4th Ed., p. 606. Some prior observations of 
 Mr. Goodsir of a similar import will be found in the Edinb. Philos. 
 Journal for 1843, v. 83, XXXV. 
 
OTHER FORMS OF ALTERNATION. 177 
 
 animal ; in the other we have a true animal, so far below 
 par in its structural development as to resemble a mere 
 organ. The contrast shows in a striking way that the sup- 
 pression of normal parts in an animal, or the development 
 of adventitious structures in connection with any particular 
 organ, are not of essential importance in determining wliat 
 has been termed by some authors *' zoological individu- 
 ality." 
 
 The other character — the detachment of the sexual 
 structure — is not, as it would seem, of more importance 
 than its amount of organization, allied species both of Poly- 
 pifera and of Cestoid worms differing among themselves in 
 tliis respect. It is even said that in some Tubularian 
 polypes there occur in the same species both sporosacs and 
 medusoicls.* 
 
 It may be mentioned, too, that even so high in the scale 
 of organization as among the Decapod Crustaceans, we meet 
 with something analogous to the elaboration of the repro- 
 ductive corpuscules after their envelope has become de- 
 tached, for in the case of certain crabs it would seem that 
 the spermatozoa are not fully matured till after the vesicles 
 in which they are formed have been introduced into the 
 spermatheca of the female. "t* 
 
 In fact the whole question of detachment hinges on the 
 proportionate development of the somatic life, i.e., the life 
 of the body as one whole, and the more or less indei)endent 
 life of its several organs, or what we may term the topical 
 or regional life. In the higher animals the special actions 
 of the several organs are as completely subordinated t(j that 
 of the body as a whole, as are the powers of local corpora- 
 tions to the central government in any well-ordered state, 
 yet there still remains sufficient evidence of the real exist- 
 
 * Carpenter's Comparat. Pbysiol,, '1th Ed., p. 552. 
 
 t Goodsir's Anatomical and Patliolo'^ioal Observations, p. 39. 
 
 I 3 
 
178 REPRESENTATION OF THE 
 
 ence of a distinct topical life. The liairs and teeth of ani- 
 mals generally, and the antlers of the deer, have already 
 been cited as furnishino: illustrations of it. The first set of 
 teeth, for instance, are formed each in its own capsule by a 
 process of local growth, quite independent of that of the 
 neighbouring tissues, nay, in so far opposed to it, that at a 
 certain stage of development the integuments of the gum 
 are partially disintegrated to allow of their eniption. A 
 tooth, thus geiierated by independent growth, some time 
 after attaining maturity, undergoes a process of decay, end- 
 ing in its ultimate removal, when a new tooth of the second 
 dentition takes its place by a similar process of local gTO\^i;h. 
 In its turn this tooth also is shed, and though in most 
 species it has no successor, yet in a few there is a constant 
 succession durins: the whole lifetime of the animal ; and 
 this is the general rule in the case of the hair.* Hence in 
 such local formations as teeth, hair, &c., we have, in the 
 way they are marked off from the neighbouring parts, and 
 in this succession of growth, maturation, a] id decay — re- 
 peated again and again, and epitomizing, as it were, the life 
 of the animal on which they gTow — evidence of a vitality, 
 quite as defined perhaps in itself as that presented by the 
 free zooids of the lower species, though their functional 
 dependence on the common circulation, and the mechanical 
 bond of a common integniment, prevent their exhibiting the 
 more obvious phenomena of a separate life. But as we 
 descend in the scale of organization we come to species, 
 where, from the absence of centralizing influences, the se- 
 veral organs — which are possessed of a vitality, less ener- 
 getic perhaps, but more enduring than in the higher — be- 
 come emancipated, as it were, from the control of the 
 general system, and appear as zooids, that is, in the guise 
 
 * Paget' s Lectures on Sm-gical Pathology. Kirkes' Handbook of 
 Physiology, Ch. X. 
 
OTHER FORMS OF ALTERNATION. 17!) 
 
 of independent beings, rather than as integral parts of the 
 same animal — suggesting a comparison to a loose confeder- 
 ation of Indian tribes, or to the feudal system of the middle 
 ages, rather than to a well-ordered polity of our own day* 
 And though the proper organs of reproduction, from 
 their partial independence even in the higher animals, seem, 
 as "v^e might expect, to manifest most clearly this emanci- 
 pation from the controlling influence of somatic life, yet it 
 is seen very distinctly in others also, as, for instance, in the 
 peculiarly modified tentacle of the Argonauta, which, when 
 filled with spermatic fluid, is detached from the body, and 
 finds its vfay spontaneously to the female for the purpose of 
 impregnation. "f* The organs of alimentation in the Poly- 
 pifera may also be considered as an illustration in point. 
 It is quite a tenable view of the compound polypes to re- 
 gard the whole polj^idom as one body, of which the several 
 polypes are organs, combining the characters of mouth and 
 stomach ; yet such is their independence of each other, and 
 of the whole group of associated organs, that the play of 
 their functions is not arrested by their separation, it being 
 indeed in some cases the normal course for a polype to de- 
 tach itself from the rest and become the nucleus of a new 
 community. This relation is suggested especially by such 
 cases as that of Hydractinia, in which the various appen- 
 
 * Some appropriate remarks on the general question here referred to 
 mil be found in Professor Laycoek's recent Avork on " Mind and Brain," 
 Vol. II., Ch. VIII. 
 
 t The worm-like appearance led at first to its being described as a 
 parasite of this organ under the term of Hedocotylus ; and even after its 
 sexual relations were determined by KoUiker, it was still considered as 
 an integral, though rudimentary animal, and in this point of view was 
 employed by Darwin (in the first vol. of his monograph of the Cirrhi- 
 pedes) in illustration of the nature and relations of the minute parasitic 
 males occurring in certain genera of that group. The discoveiy of its 
 true nature as a mere tentacle of a Cuttlefish is due to Verany and H. 
 Miiller. 
 
180 RKPllESENTATIOX OF THE 
 
 dages — which we may term either organs or zooids — are 
 adapted to fulfil diflereiit functions for the benefit of the 
 wdiole — the outer polypes being metamorphosed into tenta- 
 cular organs of offence and defence, the inner into stomachs, 
 and certain others into spermatic or ovarian cysts.* The 
 same remark will apply to many of the compound Physo- 
 phorida and Calycophorida. 
 
 With such cases before us, it seems very clear that the 
 detachment of reproductive zooids, as in one form of alter- 
 nation of generations, is a point even of less importance 
 than their elaborate oro-anization, in marlvino; them out as 
 of a different nature from the reproductive organs of the 
 higher animals ; for when we come to species in which the 
 organs of alimentation, prehension, &c., acquire a sort of 
 independent vitality, it is only to be expected that those of 
 reproduction should also appear as free zooids. *|" 
 
 § 9. If from the Animal we turn to the Vegetable 
 Kingdom, we shall find that there likewise a correspondence 
 may be traced between certain processes in the fructifica- 
 tion of the Phanerogamia and the alternation of the ferns 
 and allied Cryptogamia. 
 
 * Dr. T. S. Wriglit, Ed. N. Phil. Jour., April, 1857, p. 305. See also 
 a former note in Chapter V., 2. 
 
 f The view here contended for — viz., that the gamomorphic zooids are 
 merely reproductive organs, isolated and hyper-organized into the simiH- 
 tude of distinct animals, may appear to be opposed by certain facts in the 
 alternation of Syllis and aUied Annelida. Dr. A. Thomson quotes obser- 
 vations of Leuckart and Schultze to the effect that the parent annelidan 
 arrives itself eventually at sexual perfection, after having given off a num- 
 ber of sexual zooids by the caudal gemmation. (Note to Article on the 
 " Ovum" in the Cyclopaedia of Anatomy and Physiology, p. 33). As the 
 animal, therefore, comes ultimately to possess reproductive organs wdthin 
 ts own body, we have not, it may be said, to seek for them in the free 
 Zooids. Not knowing the exact details, I can only suggest thatif the for- 
 mation of these organs is preceded by a process of gemmation from a 
 local centre, as in the case of the detached zooids, then the region of the 
 body in which they occur ma}^ fairly rank as one of the series, which re- 
 mains attached simply because it is the last formed. 
 
OTHER PORMS OF ALTERNATION. \b\ 
 
 The development of tlie pollen in tlie anther, and the 
 embryosac in the ovule of the former division, may be shown 
 to present a distinct analogy in essential points with the 
 antherozoids and archegonial corpuscules in the protliuUium 
 of the latter, that is, in the cellular mass which is first 
 formed in the germination of the spore. The resemblance, 
 it must be admitted, does not lie on the surface ; the short 
 summary given in the second Chapter shows but little 
 prima facie similarity between the cases, but it exists not 
 the less in those points which are of most essential import- 
 ance in the reproductive process, and a closer comparison 
 will indicate many points of analogy. 
 
 Thus, starting w^th the assumption that the spore-bearing 
 capsule of the fern corresponds to the ovuliferous carpel of 
 a flowering plant, it is interesting to observe that they are 
 both modifications of leaves ; though tliis is a subject on 
 which it is unnecessary to enlarge here, as full reference has 
 already been made to the circinate vernation and other 
 points of relation between the spore-cases and the ordinary 
 leaves of ferns, in comparing these plants with mosses. 
 The connection of the capsules with the fronds has a paral- 
 lel in the case of the Riiscus aculeatus. But the principal 
 analogies of the reproductive process lie in the changes oc- 
 curring in the germination of the spore itself, and in the 
 transformation of the ovule into the seed. The main 
 feature of this development is that in the cellidar substance 
 of the ovule, or the cellular outgrowth of the spore (as the 
 case may be) minute capsules are generated, — known respec- 
 tively as embryosac and archegonium, — witliin which pecu- 
 liar corpuscules are formed, fitted to become tlie subjects 
 of impregnation. These corpuscules, whicli, from the tes- 
 timony of some able observers, appear to have at first no 
 distinct boundar}^ walls, are converted by fertilization into 
 true cells, and afterwards by a process of endogenous growtli 
 into clusters of cells. The part of the cell-mass first formed 
 
182 REPRESENTATION OF THE 
 
 has but a temporary existence, and is known as the suspen- 
 sor ; that subsequently generated is the true embryo, which 
 in the course of development protrudes an extension down- 
 wards (the radicle), and one directed upwards (the plu- 
 mule). 
 
 The particulars now referred to appear to be the essen- 
 tial points in the process, and there is undoubtedly a close 
 correspondence in them, between the two kinds of plants. 
 The differences, which at first appear so great, seem to be 
 reducible to the following : — 
 
 1 . The shedding of the fem-spores before any of the cel- 
 lullar gTowths are formed — and, of course, before impreg- 
 nation — while the phanerogamic ovule continues in situ till 
 the embryo is matured. 
 
 2. The development from the spore, in its primary ger- 
 mination, of an external cellular growth or prothallium, 
 which afterwards simulates a cotyledon — whereas generally 
 in the ovule no cellular body is formed distinct from the 
 common tissue of the nucleus. 
 
 3. The formation of numerous archegonia in the sub- 
 stance of the prothallium, each with a germinal corpuscule 
 in its interior — whereas in the ovule there is normally but 
 one such capsule — viz., the embryo-sac. 
 
 4. The fi^equent co-existence of spermatic capsules and 
 of archegonia in the Cryptogamia within the same prothal- 
 lium ; whereas in phanerogamic plants, the organs contain- 
 ing the corresponding elements — i.e., the anthers and 
 germens — are from the very first quite distinct structures. 
 
 To estimate the importance of these diversities they ^^dll 
 require to be considered seriatim. 
 
 That mentioned first — the premature dispersion of the 
 seed-like bodies — is certainly a very constant point, but it 
 cannot be held to be of a kind to destroy the general cor- 
 respondence of the course of phenomena in the two cases, 
 for it is evidently a phenomenon of the same nature as the 
 
OTHER FORMS OF ALTERNATION. 18;} 
 
 detachment of gemmse, and like it connected with tlie more 
 diffused vitality of the lower organisms, owing to wliich the 
 spore has sufficient intrinsic plastic energy to develupe its 
 derivative cellular mass, even when severed from that con- 
 tinuity with the parent stock, which seems absolutely essen- 
 tial to the maturation of the ovule. 
 
 The second diiferential character, on the other hand — 
 that of the great development of the cellular mass during 
 the germination of the spore, so as to form an external pro- 
 thallium — is not a constant one ; for, though it is well 
 marked in the ferns and Equisetacea3, it is absent in the 
 allied cryptogamic orders of L^^copodiace^e and Khizocarpea*. 
 In these orders the general course of phenomena is very 
 similar, only the cellular mass is never so much devebjped 
 as to rupture the spore -coat and appear externally, but is 
 limited to a stratum lying immediately beneath that por- 
 tion of the investing membrane of the spore which is per- 
 forated by a sort of micropyle. Hence the term endothal- 
 loid has been applied to these spores, and that of escothal- 
 hid to those of the true ferns.* Neither ao-ain is the ab- 
 sence of a prothallial structure universal among the Pha- 
 nerogamia, for in the ovule of the Coniferas a peculiar mass 
 of cellular tissue of a very analogous kind — the albuminous 
 body — is formed within the nucleus, but, like the prothal- 
 lium of the Ehizocarp, it never protrudes externally. The 
 ovule of the Coniferae being naked, like the spore of the 
 Cryptogamia at the time of impregnation, the additional 
 protection of a prothallial structure may possibly be re- 
 quired as a substitute for the germen, which encloses the 
 ovules in the higher Plianero2;amia till the embryo is fully 
 formed. 
 
 A similar inconstancy attaches to the third point of dif- 
 ference — the multiplication of archegonia in the prothallium 
 
 * Jennerin Ed. New PliO. Jour., III., 279 (April, 185G). 
 
184- REPRESENTATION 0¥ THE 
 
 — as is illustrated in the same natural order, for within the 
 prothallial formation, or " albuminous body," above no- 
 ticed, there occur in the ovules of the Conifera? three or 
 four capsular cavities — the C07yuscula — intermediate in 
 their characters between the embryo-sacs of other Phanero- 
 gamia and the archegonia of the Cryptogamia. 
 
 Cases are not absolutely unknown in other phanerogamic 
 orders of the presence of more than one embryo-sac in the 
 ovule. *' Visciim has two or three embryo-sacs ; these 
 may all have their germinal vesicles fertilized, and the de- 
 velopment of the embryos may go on to a certain point, 
 until one takes the lead and the others disappear."* This 
 is just what occurs in the cryptogamic spore, for though 
 -two or more of the archegonia may be impregnated, they 
 generally all abort but one. Polyembryony may occur even 
 in cases where there is but a single embryo-sac in the ovule, 
 owing probably to more than one of the contained vesicles 
 being impregnated. This is not uncommon among the 
 Orchidace^e, and also it is said in the genus Citrus, in one 
 species of which (the orange) seeds are occasionally met 
 with, containing more than one mature embryo. "[* That 
 polyembryony should be of rarer occurrence among Phane- 
 rogamia than Cryptogamia admits of a very feasible expla- 
 nation, from the difference in the mode of reproduction, for 
 one result of the enclosure of the fertilizing particles of the 
 fovilla in the pollen-tube must be to concentrate their action 
 on a single germinal focus, and prevent the impregnation of 
 any other, except in the rare case of two pollen-tubes enter-* 
 ing the same ovule. 
 
 The last of the differential characters above mentioned 
 — the association of antheridia with archegonia in the pro- 
 thalhum — is certainly a remarkable one. It is as if in a 
 
 * Griffith and Henfrey, Microg, Diet., p. 521. 
 t Op. Cit., p. 521. 
 
OTHER FORMS OF ALTERNATION. 185 
 
 phanerogamic plant the pollen, instead of being generated 
 in anthers, as distinct floral organs, were formed in cells 
 within the ovule, lying side by side with the embryo-sac 
 containing the germinal corpuscules. It is of course need- 
 less to say that no such arrangement is met with in any 
 plant ; but, at the same time, there is observable a great 
 variety in the mutual relations of the sexual organs. Their 
 location in distinct individuals, by what is termed a dioe- 
 cious arrangement, though common in animals, is rare 
 among plants. So is also that rather closer approximation, 
 known as monoecious, in which, though the stamens and 
 pistils are in distinct flowers — or when these arise from dif- 
 ferent buds, may even be said to be in distinct phytoids — 
 yet they always co-exist within the limits of the entire 
 plant, or as some would term it, the physiological inditi- 
 dual — i.e., the product of the same original act of di- 
 genesis. But in plants it is by far most usual to have both 
 kinds of organs within the same floral envelopes ; while in 
 what are termed gynandrous flowers, the anthers and the 
 ovuliferous carpels are more or less fused together. We 
 have only to suppose the approximation carried a little 
 farther to have an arrangement comparable to that met 
 with in the prothallium of a fern. 
 
 The comparative unimportance of this arrangement is 
 farther shown by its absence in the allied cryptogamic 
 orders of Rhizocarpea3 and Lycopodiacese, in which the 
 general course of embryogeny so much resembles that of 
 ferns. In Rhizocarpea3 the spore-case contains two kinds 
 of bodies, the larger answering in so far to the fem-spores, 
 that in germination they develope a prothallial layer con- 
 taining archegonia ; only, as already remarked, this is of 
 comparatively small size, and never protruiles beyond the 
 spore-coat. It has this farther peculiarity, more relevant 
 to our present subject, that it developes no antherozoids. 
 these corpuscules being the exclusive product of the smaller 
 
186 REPRESENTATION OF THE 
 
 seed-like bodies contained in the sporocarp, which may 
 therefore be compared to a sort of gynandrous flower,* and 
 as the Rhizocarp fructification has this analogy to the bi- 
 sexual flowers of the phanerogamia, so have some of the 
 Lycopodiacese to the monoecious inflorescence, as the an- 
 theridial bodies — represented by the " small spores" — are 
 generated in capsules quite distinct from the oophoridia, 
 or those yielding the large spores, which form prothallia. 
 
 Hence the resemblance between the reproduction of such 
 cryptogamic plants as Selaginella or Pilidaria, and the pha- 
 nerogamic Conifer83, is very close in essential points, however 
 diverse in many accidental features. In both the germinal 
 body (the ovule or the large spore) is formed in connection 
 with a bract or rudimentary leaf, but is quite naked, during 
 the later stages at least of its maturation — in both there is 
 formed in its interior, before impregnation, a peculiar cel- 
 lular body, distinct from the rest of its parenchyma, (the 
 albuminous body or tlie pro thallium), lying just under- 
 neath the micropyle or opening in the outer coat, through 
 which the spermatic particles gain access for fecundation — 
 in both this new growth forms within it a certain number 
 of cellular capsules, (the corpuscula or the archegonia), 
 each mth a germinal cell in its interior, capable of becom- 
 ing an embryo on fecundation — but in both also, only one 
 is nonnally so transformed, the rest aborting. In both, 
 moreover, the spermatic cells (pollen gTains or microspores) 
 are formed in distinct organs of fructification — and in both 
 their development is interrupted by a latent interval, repre- 
 sented in the former by the arrest of the growth of the 
 2}ollen-tube during the winter, in the course of the two 
 years over which the maturation of the fir-seed is extended 
 
 * Hence these two orders are termed Heterosporous by Munter, and 
 the Ferns and Equisetaceee Hornoiosporous, as producing but one land of 
 spore, in whose cellular outgrowth are formed both archegonia and anthe- 
 ridia. Comptes Rendus, Dec, 1857. 
 
OTIIER FORMS OF ALTERNATION. I .S7 
 
 — and represented in the latter by the dormant condltioh 
 of the microspore for some time after being shed.* Of all 
 the points of difference, therefore, above enumerated, tlu* 
 only one left outstanding in this comparison is the per- 
 sistence of the ovule in sit it, till the maturation of the 
 embryo, as contrasted with the early shedding of the " large 
 spore." Even the coniferous pollen-tube presents, as we have 
 seen, changes in its contents corresponding in some degree 
 with those which occur in the small spore of these species 
 of Cryptogamia. We seem warranted, therefore, in arriving 
 at the general conclusion that the spore of the higher Cry})- 
 togamia corresponds to the phanerogamic ovule, on account 
 of the strong analogies in their progress to maturation — 
 analogies which the distinctive characters appear quite in- 
 adequate to overbalance. •[* 
 
 But it is to be observed that the comparison does not 
 extend to the so-called spores of mosses, any more than 
 to those of the lower Cryptogamia or thallogenous plants. 
 In fact, as has already been pointed out, there is no kind of 
 affinity between the corpuscules going under this name in 
 the two groups. As the whole process of development pre- 
 liminary to the formation of archegonia is absent in mosses, 
 the gap between them and ferns is wider — so far as the 
 function of reproduction is concerned — than that separating 
 the latter from the Phanerogamia. The prothallium of the 
 fern has been shown to have its homologue within the 
 ovule even of some flowering plants — the Coniferte — as 
 traceable through a distinct chain of intermediate forms, 
 but neither to fern-spore nor to its prothallium have we any 
 homologue whatever in the moss, where the antheridia and 
 archegonia are directly attached to the leafy axis like the 
 
 * Sanderson, in Cyclopaidia of Anat. and Physiol., lY. (Vcg. Ovum.) 
 t See the abstract before given of the points both of agreement and di- 
 versity, in the notice of the lleproduction of the Coniferce, Cb. II., § 9. 
 
188 REPRESENTATION OF THE 
 
 sporangia of the ferns — reminding us of the contrast be- 
 tween the common Hydra among the Polypifera, with its 
 simple genital cysts, and the complex gonophores of other 
 species, developing free medusoids. 
 
 The complexity of the genetic cycle of mosses is not in 
 the processes which precede, but in those which immediately 
 follow on impregnation, as was before shown at some length 
 in contrasting the phenomena of alternation in these two 
 gTOups. In fact there is almost as much difficulty in 
 pointing out, in the flowering plant or fern, any homologue 
 to the spore-case of the moss, as in demonstrating in the 
 latter any part corresponding to an ovule or a prothallium.* 
 
 § 10. It would apppear, therefore, that the results of 
 the examination of the reproductive process in the Vege- 
 table Kingdom are quite in harmony with those before 
 dra'wn from a survey of the corresponding phenomena 
 among animals ; both leading to the conclusion that some- 
 thing which may stand for a representation of an alternation 
 
 * It may be tliought tliat the suspensor of tlie embiyo represents the 
 seta and tlieca ; but in the mosses and the foliaceous Hepaticse there is, 
 besides this, another form — the confervoid protonema — interposed before 
 the development of the leafy axis, so that one at least of these structures 
 must be wholly unrepresented in the higher species. In the Couifera) 
 there is something analogous to the multiplication of spores in the theca 
 of the moss, for the primary " embryonal vesicle" originates four sus- 
 pensors, each vrith its proper embryo, all, however, normally aborting but 
 one (as in the case of the " Corpuscula" themselves), so that here, as in 
 other plants, but a single embryo is eventually developed from the seed. 
 On the other hand, it may be observed, that in some species of Mo/ir- 
 chantia among the Hepaticse there is a stalked receptacle of the organs 
 of fructification, which may admit of comparison vsdth the floral organ of 
 the Phanerogamia, or the capsule spore and prothallium of ferns. The 
 peduncle in these cases has obviously very different homological relations 
 from those of Jungermannia, for though both, when in fruit, support the 
 spore-cases, that of Jungermannia is a much later formation, being 
 evolved from the archegonial corpuscule, while that of Marchantia pre- 
 cedes the archegonia, which are developed from the parenchymatous 
 mass of its summit. 
 
OTHER FORMS OF ALTERNATION. 189 
 
 of forms is as generally recognizable at an advanced stage of 
 the life of the higher organisms, in the phenomena atten- 
 dant on the maturation of the reproductive organs, as we 
 have seen it to be in the initial period of tlieir embryonic 
 development. 
 
 The rationale of the difference is this, that in the higher 
 species the prevailing law of centralization prevents the 
 structures developed for the performance of the sexual func- 
 tion, from ever acquiring the automatic organization and in- 
 dependent position that would entitle them to be recognised 
 a« distinct zooids. Such a result is confined to the lower 
 forms of life, and indeed occurs but exceptionally even 
 among them. Even in tribes, where alternation is the rule, 
 there occur species in which this process of sexual matura- 
 tion is so curtailed, by the suppression of structures com- 
 monly present in their congeners, that instead of separate 
 zooids we have merely organs of reproduction of the simplest 
 possible construction. 
 
 But the instances which have been given of transition 
 forms, concur with the general considerations just adverted 
 to, in suggesting the conclusion of an essential community 
 of nature in the processes connected with the development 
 of the structures ministering to this function, whether they 
 put on the exceptional character of distinct zooids, or ap- 
 pear in the more usual form of constituent organs, in the 
 unity of the body which produces them. 
 
190 RELATIONS OF OVA AND GEMMAE. 
 
 VIII. 
 
 RELATIONS OF OVA AND GEMM^. 
 
 § 1. The arguments which have now been advanced for 
 establishing a homology between the sexual zooids of some 
 alternating species, and the more ordinary form of repro- 
 ductive organs, have proceeded on the assumption that a 
 difference between gemmse and ova, or corresponding bodies, 
 may in all cases be clearly ascertained, however much they 
 may resemble each other in general appearance ; and that 
 ill the latter we have a satisfactory basis from which to 
 estimate the relative import of other structures. So much 
 has indeed been generally admitted by naturalists, for it has 
 been commonly held that these bodies may be recognized 
 both by the necessity of impregnation for their farther de- 
 velopment, and by certain peculiarities of structure. 
 
 It is allowed that these peculiarities are not always ap- 
 parent at first. Thus it has been remarked — especially in 
 orders noted for a proliferous tendency, as the Polyzoa and 
 Polypifera — that the nascent ovum bears a close resem- 
 blance to an ordinary gemma, both in itself and in its place 
 of origin, and other relations to the surrounding tissues. 
 When the development, however, is complete, the most re- 
 cent observations go to show that in Animals a true ovum 
 always contains in its interior a characteristic nucleated ger- 
 minal vesicle, and that in Vegetables the germ, (from which 
 after fertilization by the spermatic particles the embryo is 
 formed), though differing widely in different cases — as in 
 cryptogamic and phanerogamic plants — yet admits of having 
 
RELATIONS OF OVA AND GEMM/E. 101 
 
 its homological identity established, on structural gr«)unds 
 alone, by means of various transitional forms. 
 
 But the other great character (as generally considered) 
 of bodies homologous with the ova of the higher animals — 
 viz., their dependence on impregnation for their farther de- 
 velopment, would seem, from recent researches, to be tenable 
 only with considerable qualification. The facts now re- 
 corded by several independent and trustworthy observers 
 leave no room to doubt that ova — or bodies undistintruish- 
 able from ova both in structure and relation — do occasion- 
 ally undergo development independently of impregnation. 
 
 § 2. Hence there may, under certain circumstances, be 
 a difficulty in deciding whether the phenomena are of the 
 nature of gemmation or of ovulation. In fact, one of the 
 cases — that of the Aphides — quoted as an example of gem- 
 mation, in the course of the foregoing remarks on the dif- 
 ferent forms of alternation, has been the subject of much 
 controversy on this very point. The question has been 
 particularly studied by Owen, Cams, Leydig, Burnett, Hux- 
 ley, Lubbock, and Leuckart, but these authors differ in 
 some important particulars. 
 
 It is admitted that there is a general correspondence be- 
 tween the internal organs of generation in the o\iparou.s 
 and viviparous individuals; and though, as Siel)old was the 
 first to point out, there is also an important difference in 
 the absence, in the latter, of the collet erial (/la /ids and 
 spermatheca, yet, as these are organs ministering exclusively 
 to the impregnation and encasing of the eggs, their defi- 
 ciency does not touch on the question of essential identity 
 or otherwise, in the process of their first formation. Tlii.s 
 is distinctly denied by Dr. W. Burnett, but, with some qua- 
 lifications, is rather supported by most of the other ob- 
 servers. 
 
 Burnett maintains that the viviparous Aphides have no 
 proper sex — that they possess no organs, external (►r inter- 
 
192 RELATIONS OF OVA AND GEMM^. 
 
 nal, strictly corresponding to those of true females — 
 neither ovaries nor oviducts. T]ie germs are situated in 
 moniliform rows, like the successive joints of confervoid 
 plants, and are not enclosed in a special tube. These rows 
 of germs commence each from a single germ-mass, which 
 sprouts from the inner surface of the animal, and increases 
 in leng-th, and the number of its component parts, by the 
 successive formation of new germs by a process of constric- 
 tion. These rows of germs, indeed, closely resemble, in 
 general form, the ovaries of some insects, but they are not 
 continuous with any uterine or other female organ ; they are 
 simply attached to the inner surface of the animal, and 
 their component germs are detached into the abdominal 
 cavity as fast as they are developed, and thence escape out- 
 wards through ?iporus genitalis. Farther, he states that 
 the germs have none of the structural characteristics of 
 true ova — such as a vitellus, or a germinal vesicle and dot ; 
 on the other hand, they are at first simple collections, in 
 oval masses, of nucleated cells, and the appearance of or- 
 ganization is not preceded by the phenomena of segmenta- 
 tion. But he admits that soon after their formation " a 
 vitellus-looking mass is formed in connection with each."* 
 Carus takes a somewhat similar view ; Leydig again main- 
 tains that the germs of the AjyMs do possess a germinal 
 vesicle and macula, and that they appear to have in other 
 respects the same internal structure as the ova. Mr. Lub- 
 bock, while admitting that he has not been able to detect 
 these parts, appears inclined rather to ascribe this to their 
 indistinctness in the eggs of insects generally. f Huxley and 
 Leuckart arrive at the same conclusion, that histologically 
 there is no difference in the germs of the oviparous and 
 
 * Dr. Burnett's observations are given in Ann. and Mag. of Nat. Hist., 
 Aug., 1854, in Silliman's American Journal, Jany., 1851, and in his con- 
 cluding note to his Translation of Siebold's Conipar. Anatomy. 
 
 t Philos. Transact., 1857, p. 95. 
 
RELATIONS OF OVA AND GEMM.E. 193 
 
 viviparous Aphides, though they state that tliere are obvious 
 differences both in the form of the ovarium, and in some 
 collateral phenomena, such as the absence in the latter of 
 those intermediate clusters of cells commonly termed vitel- 
 ligenous, which are regarded by Dr. A. Thomson as a sort 
 of normally abortive ova, and are compared by Dr. Carpenter 
 to the sterile yolk segments, which form so peculiar a feature 
 in the development of some Gasteropodous Mollusca.* 
 
 The preponderance of testimony, therefore, is decidedly 
 in favour of the germs of the viviparous Aphides having 
 essentially the structure of ova. 
 
 The same is maintained by Leuckart of the " eggs" of 
 some Coccida, which, though not impregnated, are found 
 to contain embryos, immediately on being laid. The re- 
 production of Coccida has also been examined by Mr. Lub- 
 bock, who arrives at the same conclusion — namely, that 
 there is absolutely nothing, so far as our knowledge at pre- 
 sent extends, to distinguish the e^g formation, from that 
 which occurs in any other Hemipterous insect.-(- 
 
 It appears, too, from the recent observations of Leuckart, 
 that in the genus Chermes, which is also gemmiparous, and 
 is intermediate in some deoree between the two families 
 just referred to, all the parts concerned in the formation 
 and development of true ova are more or less represented, 
 for the germ, which contains a very distinct vesicle, lies in 
 an ovary of the usual type, and furnished with appendages 
 resembling the accessory glands and spermatheca of ordi- 
 nary female insects.j 
 
 § 3. All this must incline us, as the author just quoted 
 
 * Huxley, iu Annals of Nat. Hist., 3d Ser., II., 215. Lubbock on the 
 Ova of Insects, Op. Cit., III., 499 ; and Philosopl.. Tniusact., Nov. 1858. 
 Thomson, in Cyclop, of Anat. and Physiol. (Ovum). 
 
 f Philosopli. Transact., Dec, 1858. 
 
 X Annals of Nat. Histor}-, 3d Ser., IV., 321-111, " ou the Reproduction 
 of the Bark-lice." 
 
 K 
 
194 RELATIONS OF OVA AND GEMMiE. 
 
 remarks, to regard tlie germ cells and ova of the Aphides 
 as morphologically identical structures ; and the conclu- 
 sion is strongly corroborated by the researches of Mr. Lub- 
 bock into the process of reproduction in Entomostraca, and 
 particularly in the genus Daphnia. 
 
 In Daphnia, Cypris, and probably others of this order, a 
 production of young has been observed to take place mth- 
 out impregnation — somewhat as in the case of the Aphides, 
 — ^and, as in them, it may be repeated for many generations 
 in succession ; only the young are not born alive, but 
 hatched from eggs. In these genera there are known to 
 occur two kinds of egg-like bodies, one capable of spon- 
 taneous development, and the other dependent on impreg- 
 nation. The eggs of the first kind are laid at frequent 
 intervals, and in large numbers, during the summer, and 
 very speedily develop their contents ; those of the other 
 kind are formed in sparing numbers at the close of the 
 season, and are termed winter eggs, as they serve the pur- 
 pose of continuing the race through the winter, being 
 defended by their dense envelopes against the cold, which 
 proves fatal to the parent animals, and not undergoing their 
 evolution till the following spring. In Daphnia, the winter 
 eggs are termed also ephippial, from their being carried for 
 some time in an ephippium, or saddle-shaped mass, nearly 
 in the same situation as the matrix for the ordinary ova, on 
 the back of the animal, under the shell, with which they are 
 thrown off in the process of moulting. Mr. Lubbock has 
 shown, that while the common sort of eggs in the Daphnia 
 are agamic — that is, capable of spontaneous evolution — the 
 ephippial, or winter eggs, probably require impregnation. 
 They differ also in their later development ; they are 
 then of larger size, they are enclosed in hard horny 
 bivalve shells, and they lie in a mass of dark coloured 
 pigment ; but both kinds of eggs seem, from the observa- 
 tions of Huxley, and of Lubbock, to be formed originally 
 
RELATIONS OF OVA AND GEMMiE. I95 
 
 from the same mass of parenchyma. The latter observer 
 distmctly states that no difference can be detected in their 
 initial development. If the common eggs are, from their 
 producing young without impregnation, to be considered as 
 really gemmed, and of a different nature from the ephippial 
 there is nothing at first to indicate this in their structure' 
 any more than in their substance or place of origin, for they 
 contain an equally distinct germinal vesicle, and'' are formed 
 side by side with the others, so that it is impossible to 
 determine at first which line of development any particular 
 germ will follow.* 
 
 In the Eotifera, there is a similar distinction of com- 
 mon and winter eggs, though here there is some reason to 
 beheve that it is the latter which are developed without fe- 
 cundation. In this group, according to Kuxley, the true 
 ova are single cells, which have undergone a special develop- 
 ment ; the winter eggs are aggregations of cells, larger 
 or smaller portions — sometimes, in fact, the whole — 
 of the ovary, which become enveloped in a shell, and 
 simulate true ova.f 
 
 § 4. For cases affording, if possible, still more cogent 
 arguments for the essential identity of gemmre and ova? we 
 may turn again to the class of Insects, where some iate 
 researches go to show that bodies, not only having all the 
 structural characters of true ova, as in the cases^ quoted, 
 but under certain circumstances acquiring, as it would 
 seem, a capacity for impregnation, or, indeed, actually be- 
 coming impregnated, and thereupon undergoing the usual 
 embryonic development, may at other times be evolved into 
 normal organisms, without ever coming in contact with the 
 spermatic particles. Phenomena of this kind have been 
 rigorously demonstrated by Siebold, who proposes to restrict 
 
 * Lubbock in Philos. Transact, for Jan., 1857, and Dec, 1858 ; Buird's 
 British Entomostraca (Ray Soc), pp. 79, 87, 149. 
 
 t Quarterly Journal of Microscopic Science, vol. I., pt. 1, p. 16. 
 
 K 2 
 
196 BELATIONS OP OVA AND GEMMiE. 
 
 to them the term Parthenogenesis, originally employed in a 
 wider sense by Professor Owen. 
 
 Siebold's remarks refer principally to some Lepidopterous 
 insects, (Psyche Helix, Solenobia, <^c.), and they have 
 been confirmed by Leuckart, who has satisfied himself that 
 the parents are true females, with ovaries of the ordinary 
 type, and with the usual adaptations in the appendages for 
 the impregnation of the ova, such as spermathecae, or re- 
 ceptacles for the seminal fluid. The ova also have the 
 normal structure, even in such details as the micropyle, or 
 aperture in the shell for the entrance of spermatozoa.* But 
 it appears to have been positively determined by both these 
 observers that these ova may develop young without im- 
 pregnation. The progeny in such cases was always female. 
 Siebold does not appear to have determined whether these 
 females can themselves propagate without impregnation ; 
 and there are theoretical reasons against the probability of 
 a continuous succession of the race being maintained inde- 
 finitely, without the recurrence of impregnation from time to 
 time. Indeed, the ascertained facts of the adaptation, both 
 of the ova and of the maternal organs for receiving impreg- 
 nation, and of the unfecundated progeny being always 
 female, make it highly probable that in the natural course 
 of things some are impregnated, and that in this case males 
 are developed. 
 
 Such a conjecture is strongly confirmed by the results of 
 Siebold's researches into the details of the reproduction 
 of the Hive Bee, in verification of the views of Dzierzon. 
 In this species the only perfect female and normal producer 
 is the queen, who seems to be impregnated once for aU on 
 her marriage flight — the contents of the spermatheca 
 sufficing for the fertilization of aU subsequent ova, as re- 
 quired. But it would seem that only the ova destined to 
 
 * Microscop. Journal, Jan. 1859. 
 
RELATIONS OF OVA AND OEMMii:. 197 
 
 produce females are so fertilized, and that those ^coing to 
 form males (drones) are expelled without contact with the 
 spermatic fluid — its access being cut off by a contraction of 
 the sphincter of the spermatheca, which is induced in the 
 reflex way, by a peculiar impression made on the abdomen, 
 when inserted into such a cell as is prepared for the nurture 
 of a drone larva.* The impregnated ova again all give origin 
 to female larvae, which, according to their diet and general 
 treatment, become either fertile queen bees, or sterile workers. 
 The evidence on which Siebold founds his conclusion as 
 to the non-impregnation of drone-ova is principally the 
 following : — 
 
 1. Workers, whose organs do not admit of copulation, 
 though generally sterile, do occasionally produce ova, but 
 these always develope drone-larvae. In some species fertile 
 workers form a large proportion of the whole. "f* 
 
 2. It may be regarded as an ascertained fact that bees 
 copulate in the air, and never in the hive ; and, in connec- 
 tion with this, it has been observed that the ova produced 
 by queens, which, from imperfect development of their 
 wings, are incapacitated for the marriage flight and conco- 
 mitant impregnation, are also always drone. 
 
 3. The ova produced at the close of the season, even by 
 a fuUy impregnated queen, are drone, the contents of the 
 spermatheca being by this time exhausted. 
 
 4. They are found to be drone also when the spermathec.a 
 is destroyed by any injury to the abdomen. 
 
 * Kuchenmeister, observing that it is only wlien the abdomen is com- 
 pressed that fluid escapes from the spermatheca, suggests that the 
 fecundation of the eggs which yield the larvao of queens and workers 
 may be due to the mechanical pressure of the edge of the cell on the queen's 
 body : such pressure would not occur when the abdomen is inserted into 
 the more roomy cells provided for the larvM of the drones. Annals of 
 Nat. Hist., 3d Ser., II., 490 
 
 t Leuckart, quoted in Quart. Journal of Microscop. Science, Jan., 
 
 1859, p. 104. 
 
198 RELATIONS OF OVA AND GEMM^. 
 
 5. It is known that congelation destroys the vitality of 
 the spermatozoa ; and, in connection with tliis, it is found 
 that though a queen, when revived after being frozen, may 
 deposit ova, they are only such as will give origin to drone- 
 larvse. 
 
 6. A queen, when crossed with a male of another variety, 
 will produce a hybrid progeny, but ail the di'ones will be of 
 her own variety. 
 
 7. AVhile spermatozoa are readily discoverable in female 
 ova, all attempts have been unsuccessful to find them in 
 those of drones.* 
 
 The case of the hive bees goes to prove an actual conver- 
 tibility of gemmse and ova. Other cases show, with varying 
 distinctness, a sameness of origin and of development up to 
 a more or less advanced stage ; nay, even it may be, a pro- 
 bability that the egg-like bodies, which ordinarly develope 
 embryos of themselves, are occasionally impregnated ; but, 
 in the reproduction of the bee, it would seem that, up to 
 the time when the eggs come to be laid, it is still undeter- 
 mined whether they are to be impregnated or not. The 
 Entomostraca and Rotifera lay two kinds of eggs — identi- 
 cal in their origin, though differing in their later develop- 
 ment — one of which is agamic and the other not ; but, in 
 the case of the hive bee, the same ova appear to be agamic 
 or not, according to circumstances. Out of the same brood, 
 all ripe for fecundation, some are fecundated, some not — 
 the selection depending on causes quite extrinsic to the 
 organism — and both alike develop embryos, with only a 
 corresponding difference in sex.*f* Phenomena such as these 
 
 * A true Parfhenogenesis in Moths and Bees — Transl. by W. S. Dallas. 
 An abstract of the paper is given in the Edinb. Philos. Journal for April, 
 1857, p. 319, by Prof. Goodsir. 
 
 f Hence, the term " agamic ovum" seems preferable to that of " pseud- 
 ovum," proposed by Prof. Huxley, for it is a contradiction in terms to say 
 that such a body may have already left the ovary, before it is decided 
 whether it is to become an ovum or a pseud-ovum. 
 
RELATIONS OF OVA AND GEMMAE. 199 
 
 certainly compel us to qualify the commonly received state- 
 ments as to the universal dependence of ova, (or bodies 
 having the structure and relations of ova), on impregnation 
 for their farther development. For, though we may con- 
 tinue to hold such to be the only bodies capable of impreg- 
 nation, yet we cannot maintain, with absolute universality, 
 the converse proposition, that every body, having the struc- 
 ture and relations of an ovum, requires impregnation as 
 the starting point of its development ; although we know 
 that, in general, this is so essential, that a mature ovum, 
 if not fertilized, very speedily degenerates, and entirely 
 loses its vitality. In fact, the cases now referred tu 
 — confined, as \nll be observed, to two classes of the 
 Articulata — are the only known exceptions to the non- 
 development of unimpregnated ova in the Animal King- 
 dom. 
 
 § 5. Similar facts, however, to these have been alleged 
 by botanists from the time of Camerarius (1694). Spallan- 
 zani, Henschel, Bernhardi, Thuret, and many others, have 
 adduced evidence in this direction, and more lately the 
 question has been made the subject of special attention by 
 Mr. John Smith of Kew, and Professor Braun of Berlin. 
 As instances of Plants which occasionally form perfect 
 seeds without access of pollen, Gaertner, Lehocq, and Braun 
 cite certain dioecious species of Zea, Mercurlalis, Cannabis, 
 Spinacia, Bryonia^ Trinia, Datlsca, and Fistacia ; and 
 among monoecious species, the common fig, the Roman 
 nettle, and certain varieties of melon. It appears to have 
 been ascertained that some of these unfecundatcd seeds 
 produce both male and female plants, up to the fourth and 
 fifth generations. At the same time, it is admitted that 
 these observations are not all rigorously demonstrative, for 
 want of due precautions in some of them to prevent the 
 access of pollen from extraneous sources, and to ascertain 
 that no male flowers had appeared among the female ones — 
 
200 RELATIONS OF OVA AND GEMM.E. 
 
 an abnormality of not unfrequent occurrence. The most con- 
 clusr;e observations are those made by Smith and Braun, 
 on Gcelehogyne ilicifolia, a dioecious Euphorbiaceous plant 
 from Australia, of which the male has never been intro- 
 duced into this country, and in which there is no tendency 
 to the occasional development of stamens. In this plant 
 the maturation of seeds without pollen has now been a 
 subject of notice for upwards of twenty-seven years, and it 
 appears, from the observations of Deecke and Radlkofer, 
 that the structure, both of the ovule and of the mature 
 seed, are perfectly normal, and that the embryo follows the 
 usual course of development, with the exception of the 
 absence of the pollen tube. Radlkofer thus sums up the 
 arguments in proof of a " true parthenogenesis" in this 
 plant : — 
 
 1. The ascertained absence of all male flowers of the 
 same species. 
 
 2. The absence of all indications of hybridization by 
 males of allied species. 
 
 3. The development of the embryo, without any trace of 
 a pollen tube in the ovule. 
 
 4. The stigma not withering, as it always does after 
 impregnation. This mark indicates parthenogenesis in 
 some of the other plants experimented on, especially 
 Cannabis and Mercurialis. The seeds thus raised have 
 never yet given origin to any but female plants. Braun 
 thinks that similar phenomena can be shown to occur in 
 some dioecious species of Chara* 
 
 § 6. Intermediate between cases such as these, of the 
 
 * Radlkofer, in Annals of Natural History, 2d Ser,, XX., 216. 
 Balfour, in Edinburgh Philosoph. Journal for June, 1858, vol. VIII., 159. 
 Lubbock, in PhUos. Transact, for 1857, page 97. 
 Owen's Address to British Association at Leeds, 1858, p. 26. 
 For Regel's arguments against such Parthenogenesis, see Annals Nat. 
 Hist., 3d Ser., III., 104. 
 
RELATIONS OF OVA AND GKMMiE. 201 
 
 development of the ovule without impregnation into a fertile 
 seed, and ordinary gemmation, may probably be ranged 
 what are called viviparous flowers. In these buds are 
 formed within organs having the general character of floral 
 envelopes, where they occupy commonly the position <tf 
 the ovary in a normal flower. This peculiarity sometimes 
 constitutes a specific or constant character, as in the Polif- 
 gon am vivipariim, in which, while the upper bracts of the 
 floral spike bear the sexual flowers, the lower ones bear 
 gemmse, ripening without impregnation into deciduous 
 bulbils, and acting the part of pliytoids in the propagation 
 of the plant. More commonly, perhaps, the viviparous 
 condition is induced by the force of circumstances, as a 
 compensating provision under a state of matters liable to 
 interfere with the maturation of the essential parts of fi'uc - 
 tification — the stamens and pistils. Thus certain grasses 
 which have regular flowers in genial habitats, are found to 
 present the viviparous inflorescence in alpine situations ; 
 and cases are even met with in which the same individual 
 plant forms at one time gemmae, and at another time ovides, 
 within its floral envelopes, according to variations in climate 
 or other external circumstances. If we may assume in such 
 cases that the viviparous condition is in compensation for 
 the inability of the plant to form perfect stamens, there 
 would arise a certain proljability of the actual transfiu-ma- 
 tion of the rudimentar}" ovule into a gemma, capable of 
 vegetating into a new plant, apart from any fertilizing ac- 
 tion of the pollen. 
 
 For farther arguments on the essential identity of ovidts 
 and gemmae, reference may be made to works on Vegetable 
 Morphology, in which this view is almost universally adopt- 
 ed. So much at least appears to be shown by the occurrence 
 of viviparous flowers, that the same ft^cus of vital action 
 may be capable of assuming the form of a gemma, to pro- 
 pagate the plant by its unaided pla.stic powers — or of be- 
 
 K 3 
 
202 RELATIONS OF OVA AND GEMMAE. 
 
 coming an ovule, whose development is dependent on im- 
 pregnation. In such cases it would seem that, though in 
 the normal course of development preference is given to the 
 seed as being the surest means of perpetuating the species 
 in all its integrity, and as possessing a more enduring vi- 
 tality when separated from the parent plant, yet under pe- 
 culiar circumstances, the growing point may be transfonned 
 into a gemma whose early evolution makes less demand on 
 the parental vitality, than the impregnation of the ovule 
 and the formation of the embryo. 
 
 § 7. Though it is, no doubt, quite exceptional to meet 
 with cases such as have now been cited, in which a body, 
 with the structure and relations of an ovum, either passes 
 into a true gemma, or acquires the power of self-develop- 
 ment characteristic of gemmae, traces of an incipient ten- 
 dency in this direction are not wanting in many cases, in 
 which impregnation is absolutely essential to full develop- 
 ment, and may possibly turn out to be a more frequent 
 characteristic of the sexual elements of both kinds than is 
 generally supposed. Thus though in ordinary cases unimpreg- 
 nated ova do certainly soon lose their vitality, yet they have 
 been seen to make in the interval some abortive attempts, 
 as it were, in the way of development. Thus it has been 
 observed, that, though the unimpregnated spores of Fucus 
 never produce fronds, yet they may put forth irregular pro- 
 longations as if about to germinate.* And so in the un- 
 impregnated ova of animals, the preliminary phenomena of 
 segmentation have been observed by Loven and Schultze in 
 Campanularia.'f by Quatrefage in Hermella and Unio,^ 
 and by Vogt in Firola.^ 
 
 * Carpenter's Comparat. Physiol., 4th Ed., p. 493. (Thuret.) 
 f Quar. Jour. Micr. Sc, III., 65 (from Muller's Archives). 
 X Rambles of a NaturaHst, II., 244, and Comptes Rendus, July 23, 
 1849. 
 
 § Siebold on Parthenogenesis, 106. 
 
RELATIONS OF OVA AND GEMM^. 208 
 
 In the Batracliian ovum, on the other hand, Mr. New- 
 port's researches led liim to conclude that segmentatiun 
 never takes place without impregnation, but only certain 
 preliminary changes of a less obvious kind. Even in im- 
 pregnated ova, when, from the excessive dilution or the 
 momentary contact of the spermatic fluid, this process is 
 inefficiently performed, the segmentation stops at its in- 
 cipient stages.* But this result is only what we should 
 anticipate in the ovum of the Vertebrata, in accordance 
 with the general abeyance of gemmation in that division of 
 the Animal Kingdom. 
 
 These facts seem to indicate rather an evanescence, or a 
 feebleness of vitality, than an absolute want of develop- 
 mental nisus in the unimpregnated ovum, as the cause of 
 its general abortion. 
 
 But that the spermatic element is something more than 
 a mere stimulus is shown conclusively by the phenomena of 
 hybridization, and the general fact of the transmission of 
 the paternal peculiarities to the offspring. There are not 
 wanting indications also of a certain intrinsic capacity of 
 development in the spermatic element, at least in plants. 
 Setting aside the power of germination, asserted by some 
 for the spermatia of Fungi, ■!- and antheridia of Mosses,:): 
 the continued growth of the extremity of the pollen-tube in 
 impregnation, even after the decay of the gTanule itself, and, 
 according to Schacht, its occasional branching,^ are well 
 attested facts w^hich look in this direction. It will probably 
 be found also, as observations are multiplied, that tlie 
 zoospores or motile gemmae of Algse merge by as gradual a 
 
 * Phil. Transact. (1851), p. 169. 
 
 f Berkeley's Introduction to Cryptogamic Botany, 217, 259, note, 
 
 % Lindley's Natural System of Botany, p. 407. 
 
 § Schacht on the Microscope (Currey), p. 144. Keissok maiutixins tho 
 occasional development of pollen grains into fungoid vegetations. Quoted 
 by Sanderson in Cyclopaed. Anat. and Physiol. "Vegetable Ovum," p. 255, 
 note. 
 
20-i RELATIONS OF OVA AND GEMMiE. 
 
 transition into tlie pliytozoa or ciliated spermatic particles, 
 as the fixed gemmae of some species of articulated animals 
 do into true ova. 
 
 It may be observed also that altliougb tbe vitality of the 
 spermatozoa is soon lost on exposure, it may be protracted 
 indefinitely under more favourable conditions, as by trans- 
 ference to the female organs. One charge of the sperma- 
 theca will enable a queen-bee to lay impregnated eggs for 
 several years, during the whole of which time the sperma- 
 tozoa continue in a state of activity. Siebold quotes 
 Dzierzon for the statement that a queen may acquire the 
 power of laying fertilized eggs for fi^'e years by a single 
 normally executed copulation.* The evolution of the sper- 
 matozoa, indeed, is only in progress in some cases at the 
 ejaculation of the seminal fluid, and is thus perfected in the 
 normal course of things after their removal from the male 
 organs. Thus in Spiders these particles are not matured 
 till after the fluid is transferred to the cavities of the palpi, 
 and in the higher Crustacea not till its introduction into 
 the passages of the female. "f" 
 
 § 8. May not the true theory be, that each of the sexual 
 elements is essentially a gemma, endowed with a high de- 
 gTee of vitality, which confers upon it a capacity of develop- 
 ment, but which is, at the same time, of a self-exhausting 
 nature, unless tempered by combination with its pre- 
 arranged complement of the other sex — the fusion of the 
 two elements being a sort of physiological illustration of 
 the connubial relation of the sexes, " ordained for the 
 mutual society, help, and comfort, that the one ought to 
 have of the other." 
 
 * True Parthenogenesis in Moths and Bees, p. 61 , note. It is the same 
 also with several Araehnida, according to Blanchard. Comptes Rendus 
 (April 9, 1860), p. 127. 
 
 f Wagner and Leuckart, Cyclop, of Anat. and Physiology, article, 
 " Semen." H. Goodsir, Anatomical and Physiol. Observations, p. 39. 
 
RELATIONS OF OVA AND GEMM/E. 205 
 
 Such a view harmonizes with other results ohtaiued by 
 Mr. Newport * Thus he has observed that a deticiency 
 affecting one of the elements may be supplemented by an 
 increased action of the other, for he found that when the 
 spermatozoa w^ere applied in a very concentrated form, even 
 immature ova became segmented and produced embryos. 
 Again he found that the procreative force both of the ova 
 and the spermatozoa was augmented by increase of he<at, 
 but the duration of the force was lessened. Now, in the 
 primordial germs, that physiological law may well be sup- 
 posed to have full play, which appears even in the adult 
 state — though there masked by the continual renewal of 
 the system, which it is the very object of its (jrganizatiou to 
 effect — namely, that the endurance of vital action is in the 
 inverse ratio of its intensity. 
 
 On the whole, after a careful survey of the part taken by 
 ova and gemm?e respectively in the propagation of organic 
 beings, I think we can hardly avoid adopting Professor 
 Owen's conclusion, that there is no essential difference be- 
 tween the two, and that the one may pass into the other by 
 insensible gradations. It cannot at least be any longer 
 maintained as an invariable law — though it is strongly con- 
 tended for by some — that there is such an incompatibility 
 betw^een these tw^o modes of propagation, that in proportion 
 as any part of the parenchyma of the parent body is en- 
 o-ao-ed in the one course, it is in so far disabled for tlie other. 
 Such a statement, if admitted at all, must be held open to 
 many exceptions. We may assume perhaps, that, up to a 
 certain point, the development of the new focus of vital 
 action may go on all the same for a gemma or an ovum ; 
 but that towards the period of maturation the changes 
 which take place in the latter, to lit it for impregnation, 
 cause such a tension, as it were, of its vitality, as is incom- 
 
 * Philos. Transac. (1851), pp. 206-209. 
 
206 RELATIONS OF OVA AND GEMMiE. 
 
 patible mth its continuance, in the majority of cases, 
 unless re-invigorated by the access of the spermatic element. 
 
 § 9. This doctrine of an essential community of nature 
 between ova and gemmae has an obvious bearing on our 
 views regarding the modes of propagation in which they 
 are respectively concerned. If the nascent bodies approxi- 
 mate so much in their real nature as to pass into each 
 other, the processes of development can hardly be so widely 
 diiferent in the two cases as is held by some. 
 
 The prevailing view in this direction seems to be that 
 gemmation perpetuates the individual rather than the 
 species, the successive zooids or ph}i:oids preserving, more 
 completely than the progeny of embryonic origin, the cha- 
 racters of the parent stock ; and it has been thought, too, 
 that there is a tendency for the plastic power to wear out 
 in process of time, so that a recurrence of sexual generation 
 at intervals is necessary to preserve the pristine vigour of 
 the species. The more highly organized the species, the 
 more dependent it is supposed to be on the frequent recur- 
 rence of sexual reproduction in the genetic cycle. In the 
 higher animals we meet with no obvious phenomena at all 
 of the nature of gemmation, while in the lowest there may 
 be a very prolonged pullulation of gemmae, the sexual act 
 recurring only at distant intervals. Still it is held that 
 even in these it must recur from time to time, to give a 
 fresh start, as it were, to the organizing process. It is true 
 there are species in which we have no positive knowledge 
 of any sexual act occurring at all — such is the case with 
 most of the Protozoa. There are species, too, in which no 
 males have yet been detected — so it is with some Insects 
 and Entomostraca.* But such negative evidence is not 
 held of sufficient weight to counterbalance the argument 
 
 * Certain species of Cynips, Apus, Limno.diaj and Polyphemus are in 
 this case. Siebold's Parthenogenesis, 105. 
 
RELATIONS OF OVA AND GEMMiE. 207 
 
 from analogy, being put down to the account of imperfect 
 observation. 
 
 The great difficulty, indeed, in the way of admitting a 
 total and continued absence of the sexual act in any species 
 is its apparent contrariety to the general analogy of the 
 organic creation. The constancy of the presence of both 
 sexes in almost every species, and the remarkable adapta- 
 tions which are provided in particular cases to ensure im- 
 pregnation, certainly suggest the idea that the act is one of 
 essential importance to the perpetuation of race. The act 
 may take place with less frequency in certain cases — in- 
 deed it is well known that in some species the occurrence of 
 males is rare and intermittent — but still it is one which we 
 have difficulty in conceiving ever to be wholly dispensed 
 with.* 
 
 Now the cases of Parthenogenesis, above referred to, do 
 not appear materially to affect this conclusion. They still 
 leave the question open of the necessity of an act of sexual 
 reproduction recurring from time to time in the continued 
 propagation of a species. In the case of the bees it is 
 clear that the act of monoQi:enesis must alternate with one 
 of a sexual kind, as the unimpregnated ova produce only 
 male insects. In all instances, indeed, yet observed, agamic 
 broods have been always of one sex in the same species, a 
 circumstance which is in favour of the occasional recurrence 
 of the sexual act, as the probable determining cause of tlie 
 development of the other sex.i* 
 
 * Professor Braun of Berlin, in the Transactions of the Royal Prussian 
 Academy (Annals of Nat. Hist., 2d Ser., XVI., 234), mentions as a some- 
 what parallel case to the intermittent recurrence of male Entomostraca, 
 the casual appearance of staminiferous flowers in the weeping willow 
 (Salix, BahylonicaJ , which has always been propagated by cuttings de- 
 rived originally from one female plant, and which ordinarily bears only 
 pistilliferous catkins. 
 
 t This may hold of normal agamic broods, but Sicbold found that when 
 the unimpregnated eggs of the silkworm-moth proved fertile, the resulting 
 
208 RELATIONS OF OVA AND GEMMAE. 
 
 In regard to the leiigtli of time for which agamic 2)ropa- 
 gation may run on, our observations are as yet very imper- 
 fect. Lacordaire has followed the parthenogenesis for three 
 generations in Liparis dispar,^ and Davis to the same ex- 
 tent in the Egger Moth ; all the progeny in both cases 
 appear to have been female."|* 
 
 Many plants, it is known, may be propagated by buds or 
 cuttings for a long series of years, without ever flowering or 
 seeding ; in some species of shrubs and trees, which have 
 long been cultivated in our gardens, only one of the sexes 
 is kno^Aai to exist in this country — the Aucuha Japonica 
 and the Weeping Willow are instances in point.j 
 
 § 1 0. In conclusion, a few remarks may be made on the 
 bearing of these phenomena of " true parthenogenesis" on 
 the theory of alternation of generations. Startling as are 
 many of the facts recorded by Siebold and others, and much 
 as they have tended to modify the opinions formerly held 
 on the relationship of ova and gemmae, they do not seem 
 to be at all opposed to the parallel which has been traced 
 in the different forms of alternation, and the pheno- 
 mena of embryogeny and sexual maturation in the higher 
 species. On the contraiy, they appear to supply the very 
 links wanting to the completeness of the aro-ument. 
 
 Ox O 
 
 caterpillars developed both male and female moths. The inferiority, 
 however, of the organizing force in the unimpregnated eggs was clearly 
 shown by the small proportion in which an embryo was formed, and by 
 its often aborting even when formed ; this, of course, must militate 
 against the perpetuation of the species independently of the sexual act. 
 " True Parthenogenesis," p. 100, &c. 
 
 * Lubbock, in Philosoph. Transact. (1857), p. 96. 
 
 t Siebold on Parthenogenesis, p. 99. 
 
 X Among the lower plants instances of this kind are even more striking. 
 The Gulfweed, which accumulates in such quantities as to acquire for its 
 oceanic habitats the name of " floating meadows," multiplies solely by the 
 detachment of offshoots, and has never been found in fructification (R. 
 Brown, in Annals of Nat. Hist., 2d Ser., VII., 327). So it is also with 
 many mosses, as noticed in Chap. II. 
 
RELATIONS OF OVA AND GEMxM.E. 209 
 
 The formation of ova has been here considered as in its 
 initial stage a modification of gemmation, in connection 
 with the maturation of the reproductive organs — these 
 forming the parent stock, as it were, from which the gemmae 
 in question may be said to sprout. But, had we no ex- 
 amples of ova undergoing development in virtue of their 
 own plastic energy, we should miss in them one of the 
 most essential characters of gemmse. As the matter stands, 
 however, nature has provided us with a complete series of 
 examples, establishing a well-marked transition from simple 
 gemmse, undergoing evolution in the ordinary way, to per- 
 fectly normal ova, absolutely dependent on fertilization by 
 the spermatic element. 
 
 The view of the genetic cycle, which has been put forward, 
 is based on the existence of three successive stages in the 
 life-history of all organic beings, of which the first is pre- 
 liminary to the full development of the typical organization 
 of the species in the second, and the last has for its great 
 object the perpetuation of the race, by elaborating and 
 providing for the fecundation of ova endowed with a special 
 retentiveness of vitality and aptitude for development. In 
 one point of view, these three stages in the life of each in- 
 dividual may rather be regarded as a succession of so many 
 distinct individuals, each derived from the preceding by an 
 act of gemmation : — using this word in its widest sense, to 
 imply simply the establishment of a new focus of construc- 
 tive and other vital action, in an extension of the substance 
 of the parent body. The new growth may be single or 
 multiple ; and it may separate from the parent as a 
 distinct organism, or it may in some way absorb it or take 
 its place. From variations in these points we may have 
 the alternation and multiplication of diverse forms, or we 
 may have merely successive phases of development in a 
 single individual. But, in all cases, the derivation of each 
 stage from the preceding may be held to be by some process 
 
210 KELATIONS OF OVA AKD GEMM^. 
 
 of the nature of gemination ; and the close affinity, if not 
 identity, which has now been shown to exist between the 
 processes of ovulation and gemmation is of especial interest 
 in this respect, that it indicates a parallelism between the 
 origination of the protomorphic stage, from the gamomorphic 
 stractiireoi the preceding cycle, by the process of generation, 
 and the derivation of each of the other phases from that 
 which immediately precedes it in the same cycle. Just as 
 the typical fonn is budded off from the germinal, and as 
 the gamomorphic form itself is budded off from the or- 
 thomorphic, so is the germinal stage of the next generation 
 budded off in the form of an ovum from the female ovary. 
 That there should be certain specialities in this particular 
 gemmation is only what might be anticipated, when we 
 consider that the great function of this stage of existence is 
 the perpetuation of the race. Whenever the continuity of 
 the vital processes is broken in upon by a period of latency, 
 we find almost universally that this break follows close upon 
 ovulation, which is the characteristic gemmation of the 
 gamomorphic stage. Such a state of latent vitality is of 
 essential importance in the great majority both of animals 
 and vegetables, serving as it does to bridge over seasons 
 and circumstances which would otherwise prove fatal, and 
 affording, in the form assumed — that of eggs or seeds — 
 peculiar facilities for the dispersion of the species. An in- 
 termediate process of puUulation may occasionally occur in 
 the gamomorphic stage, but eventually eggs or seeds a.re 
 formed in almost every case.* An egg is itself essentially 
 a modified gemma., derived from a gamomorphic structure ; 
 a seed is the persistent wall of such a gemma which has 
 already developed other structures in its interior; but both, 
 being destined for the continuation of the species, under 
 
 * The Ferns and their allies constitute, perhaps, the only case in which 
 the reproductive organs remain permanently in adhesion to the t^-pical 
 structures developed by their instrumentality. 
 
RELATIONS OF OVA AND GEMM.E. 211 
 
 special conditions, have naturally certain peculiarities in 
 their mode of origin different from those of ordinary buds. 
 Among such peculiarities is their development, in connec- 
 tion with the organs of sex. If there be any truth in the 
 opinion before referred to of the necessary recurrence of the 
 sexual act from time to time in every species, this of all 
 seems the fittest season, when bodies of such importance 
 are to be formed. Such, at least, is the case ; whether the 
 explanation be in point or not, it remains a fact, that the 
 proper gemmae of the gamomorphic stage have always a 
 sexual character. Ordinarily, impregnation is a necessary 
 condition of their ulterior progress ; the transformation by 
 which the gemmae are converted into spermatic and germi- 
 nal elements being apparently incompatible, in most cases, 
 with the farther development of either singly. But in- 
 stances, as we have seen, do occur, in which, either in 
 compensation for the failure of the spermatic element, or 
 for other reasons, the co-related gemma is fitted to retain 
 the power of self-development. Still, however, it acquires 
 somewhat of the sexual character, and may, indeed, in some 
 cases, take on all the structural peculiarities of tlie ovum, 
 and even its capacity, in certain contingencies; for impreg- 
 nation. In every case, there probably remains at least such 
 a speciality of character as clearly to distinguish these 
 gemmae from those developed in any other stage of the 
 genetic cycle.* 
 
 * An exception possibly occurs, in a few species of Polypifera, in the 
 development of the gamomorphic structures themselves (the medusoids) 
 from gemmae having a general resemblance to ova — but the facts of the 
 case are not clear of doubt. See before, in the note at page 129. 
 
212 SUMMARY OF CONCLUSIONS. 
 
 IX. 
 
 SUMMARY OF CONCLUSIONS. 
 
 § 1. Having discussed, in tlie preceding chapters, the distinc- 
 tions observable among cases of alternation of Generations, 
 and the phenomena which may be thought in some way to 
 represent them in the higher species, and having stated 
 the general results of later observations in reference to the 
 relations of ova and gemmae, it may be advisable to give 
 here a short summary of the conclusions arrived at, as 
 affording that explanation of the facts which appears, on 
 the whole, the most probable, if not in all cases positively 
 ascertained. They may be stated as follows : — 
 
 I. — The function of reproduction is performed in two 
 ways — by gemmation (monogenesis), and by sexual union 
 (digenesis.) In the former, a portion of the body of the 
 parent becomes the seat of a certain independent vitality, 
 and may eventually be detached and transformed, by a pro- 
 cess of self-development, into a distinct organism (zooid or 
 phytoid). In the latter, the germ of the new being is the 
 result of fecundation — that is, of the fusion of two highly 
 organized portions (speimatic and germinal) of the same or 
 of kindred organisms, which stand in the relation of 
 parents. 
 
 II. — There is reason to believe that the same portion of 
 the parenchyma of the parent may be organised in either 
 of these ways ; but, in general, in proportion as it is engaged 
 in the one course it is disabled from the other ; thouo:h a 
 few cases are known in which a part already organized as 
 an ovum may yet be developed as a gemma, that is, with- 
 out impregnation. 
 
SUMMARY OF CONCLUSIONS. 213 
 
 III. — Eeproduction, by fecundated germs, appears to be 
 of a higher kind than that by gemmse, and has been regard- 
 ed as the special agency for the propagation of the 
 species, the other serving rather for the extension of the 
 individual.* 
 
 IV. — There may be reason to believe that the recurrence 
 of sexual generation, at least occasionally, is necessary for 
 the long-continued propagation of every species ; but, in 
 many of the lower forms of life, it occurs but rarely, and at 
 distant intervals. In the higher, again, it is the prevailing 
 mode, and the counter process of gemmation is minimized, 
 and its manifestations often very obscure. 
 
 V. In those in the lower species, in which both modes of 
 propagation are well marked features, we find that they 
 have a tendency to succeed each other in a regular order, 
 to which the term of " alternation of generation" (meta- 
 genesis) has been applied. 
 
 VI. — The phenomena of alternation of generations pre- 
 sent certain remarkable diversities, dependent in great 
 measure on the period of the life-history of the species at 
 which a distinct process of gemmation is interpolated. 
 
 VII. — In some cases the interpolation takes place in 
 what has been termed here the protomorphic stage — that 
 is, in the course of development prior to the appearance of 
 the typical character of the species (as in Trematoda and 
 Mosses.) 
 
 VIII. — More frequently, perhaps, a process of gemmation 
 is interpolated in the later or gamomorphic stage — that is, 
 in connection with the development of the reproductive 
 
 * This idea, based partly on the greater resemblance to the parent, in 
 most cases, of the progeny developed by the budding process, has the 
 support of many great authorities. " Gemmce individium continuant, 
 cum semina speciem propagent,* is an aphorism of Link (Elem. Philos. 
 Bot., p. 208) ; that of Linnaeus is different — " Gemmcn totidem herbce." 
 Braun's Rejuvenescence, pp. 19, 24. 
 
214 SUMMARY or CONCLUSIONS. 
 
 organs, after the typical form of the species has been 
 acquired (as in the Polypifera and Ferns.) 
 
 IX. — In the orthomorphic or intermediate period, the 
 gemmee generally remain in adhesion, to form a compound 
 organism (as in zoophytejand most plants), but a few cases 
 are kno^vii in which they give rise to a well-marked alter- 
 nation of distinct forms (as in the Aphides.) 
 
 X. — It is but rarely that alternation occurs in more than 
 one stage of the development of the same species. Even 
 in the larger groups or orders characterized by such pheno- 
 mena, their marked occurrence is mostly confined to one of 
 the life periods above specified. Among the Cestoid worms, 
 however, we find distinct alternation, both in the protomor- 
 phic and gamomorphic stages ; and in the Polyzoa, and 
 some Annelida, less obvious processes of the same kind 
 appear to occur in all the stages. 
 
 XL — The gemmation, which occurs in any stage, may oc- 
 casionally be lengi:hened out by the successive puUulation of 
 a series of zooids or phytoids of the same general character, 
 previous to the supervention of the characteristic pheno- 
 mena of the next succeeding stage. The number of inter- 
 polated links is fixed in some species, and variable in others. 
 Such pullulation may occur at any stage, but is most com- 
 mon in the orthomorphic, giving rise in it to the compound 
 ramified structures characteristic of plants and zoophytes. 
 
 XII. — In the embryogeny of the higher species, a certain 
 parallel may be traced to the first or protomorphic form of 
 alternation, in the implantation of the primitive trace of the 
 typical organization, on the cellular mass into which the 
 contents of the ovum are resolved, by the process of cleav- 
 age foUomng immediately on impregnation. This view is 
 founded on the following considerations : — 
 
 1. The duplication, in whole or part, of the embryonic 
 axis, as an occasional abnormality, even in the higher 
 species, resulting in the formation of a double monster. 
 
SUMMARY OF CONCLUSIONS. 215 
 
 2. The normal formation of a double embryo from the 
 ovum, in the case of the Polyzoa. 
 
 3. The variable character of the gemmation in the Cystic 
 Entozoa, commonly solitary, as in Cystkercus ; but multiple 
 in some, as in Coenurus and EcMnococcus. 
 
 4. The co-existence among the Echinodermata of cases 
 of ordinary embryogeny, with others, in which the embryo, 
 though still solitary, has a character of distinctness from 
 the primary matrix, or so-called larva, wliich has led to its 
 being regarded as an independent zooid. 
 
 XIII. — To the gamomorphic form of alternation, a similar 
 parallel may be traced in the development of the reproduc- 
 tive organs of the higher species. Such a correspondence 
 is suggested in particular by the follo^ving considerations : — 
 
 1. The periodicity and lateness of development of the 
 organs of reproduction in most species; and their greater or 
 less independence of the rest of the system in some cases, 
 as in the Polyzoa. 
 
 2. The transition, among nearly allied species of certain 
 families, from cases in which the reproductive organs are 
 integral parts of the system, to others in which they occur 
 in detached zooids having the character of distinct and 
 well-ora;anized animals. 
 
 .3. The accidental or non-essential nature of the charac- 
 ters of detachment and organization, which principally 
 distinguish these zooids from common organs of reproduc- 
 tion, as is illustrated in the orders just referred to ; and as 
 is indicated, further, in respect of the latter point, by the 
 contrast of such forms as the rudimentary males of the 
 Cirripedia and Rotifera, which, though truly distinct ani- 
 mals, have their structural development limited almost 
 exclusively to the generative organs. 
 
 4. The correspondence traceable between the emhryosacs 
 of the onules in phanerogamic plants, and the archegonia 
 in the prothalUa of ferns and allied Cryptogamia. 
 
216 SUMMARY OF CONCLUSIONS. 
 
 § 2. If it is desired to have a formulated expression of 
 the sequence of phenomena in the genetic cycle, the follow- 
 ing may be taken as a sort of medium statement : — 
 
 I, PROTOMORPHIC STAGE. 
 
 Development of the fecundated Germ into a rudimen- 
 tary asexual organism, serving as the matrix of 
 the typical form. 
 
 Gemmation, or formation in connection with this 
 matrix of one or more growths of a new and 
 different kind. — (Scolex, Redici.) 
 
 II. — ORTHOMORPHIC STAGE. 
 
 Development of such a growth into an organism of the 
 
 typical form of the species. 
 Gemmation, or formation in the typical organism of 
 
 new points of growth, for the development of 
 
 reproductive organs. 
 
 III. — GAMOMORPHIC STAGE. 
 
 Development of the new growth into a more or less 
 complex structure, serving as a receptacle of true 
 sexual organs (Medusoid, Prothallium, &c.) 
 
 Gemmation, or formation in such structures of sper- 
 matic and germinal bodies, the latter, on fecunda- 
 tion by the former, constituting the starting point 
 of a new cycle. 
 
 § 8. In applying this formula to the case of the higher 
 species, the protomorphic matrix must be held as repre- 
 sented by the cellular mass, resulting from the cleavage of 
 the germ on impregnation, and serving as the basis of the 
 
SUMMARY OF CONCLUSIONS. 217 
 
 true embryonic structures. And so, in the gamomorphic 
 stage, the representatives of the reproductive receptacles 
 must be sought for in certain organs of the body, often not 
 at all conspicuous, the spermaries and ovaries, or, perhaps, 
 rather the minute spermatic cysts and ovisacs which are 
 developed in their interior at the appropriate season. 
 
 Hence, the formula, modified to the case of the higher 
 animals, would stand as follows : — 
 
 I. — PROTOMORPHIC STAGE. 
 
 Development of the fecundated germ into a peculiar 
 cellular mass, by a process of cleavage — ('' Mul- 
 berry body") 
 
 Gemmation, or implantation of the primitive trace of 
 embryonic organization in the area pellucida of 
 this germinal mass. 
 
 II. — ORTHOMORPHIC STAGE, 
 
 Development of this primitive trace of organization, 
 through the successive stages of embryonic 
 growth, into the typical conformation of the 
 species. 
 
 Gemmation, or formation, in the typical form, of a 
 matrix, which is subsequently to originate repro- 
 ductive organs of greater or less complexity — 
 ( Wolffian Body t) 
 
 III. — GAMOMORPHIC STAGE. 
 
 Development of the true organs of reproduction — 
 spermsacs and ovisacs. 
 
 Gemmation or formation, in their interior, of vesicles of 
 evolution containing spermatozoa, and of ova 
 with germinal vesicles ; by the joint action of 
 
 L 
 
218 SUMMARY OF CONCLUSIOKS. 
 
 which, in impregnation, a basis is formed for a 
 new cycle of changes of the same kind. 
 
 § 4. On the other hand, a ffarther expansion must be 
 given to the formula, to adapt it to cases of repeated 
 puUulation. For this purpose a middle term must be in- 
 serted under each head ; for, as has been showTi, a process 
 of puUulation m.ay be interpolated in any of its three stages. 
 Thus modified, the formula will stand as follows : — 
 
 I. PROTOMORPHIC STAGE. 
 
 Detelopment of the fecundated germ into a rudimen- 
 tar}^ form. 
 
 PuUulation^ or production of a continued series of 
 gemm93, which are either detached, or remain in 
 connection with the stock as a compound organ- 
 ism — (Protonema.) 
 
 Gemmation, or formation, in the concluding links of 
 the series, of new points of growth. 
 
 . II. — ORTHOMORPHIC STAGE. 
 
 Development of such gemmae into organisms of the 
 
 typical form of the species. 
 PuUulation to a variable extent in this form — (a Poly- 
 
 pidom or Vegetation.) 
 Gemmation, in the concluding pullulations, of fresh 
 
 points of growth, for the evolution of sexual 
 
 org^ans. 
 
 III. — GAMOMORPHIC STAGE. 
 
 Development of the latter gTowths into sexual structures 
 of greater or less complexity. 
 
SUMMARY OF CONCLUSIONS. 219 
 
 Pulliilation of similar derivative structures to a 
 
 variable extent. 
 Gemmation ultimately of the proper reproductive 
 
 organs — sperm sacs and germ sacs — containing 
 
 their characteristic corpuscules, for the purpose of 
 
 fecundation. 
 
 § 5, This formula, and that at p. 216, as constructed to 
 include the different forms of alternation of generations 
 above referred to, of course has not, in general, all its 
 details obviously represented in any one species. The 
 alternation comes out prominently in one stage, wliile the 
 con-esponding changes are more or less suppressed or cur- 
 tailed in the others. It is, perhaps, of most frequent 
 occurrence in the gamomorphic stage, next in the proto- 
 morphic, and least so in the orthomorphic ; while there 
 appear to be but few cases, as already mentioned, in which 
 it is distinctly met with in all the three stages. 
 
 In one of the tables given in the Appendix, the orders 
 best known, for examples of this kind, are arranged under 
 the heads of the life periods in which the more obvious- 
 phenomena of alternation occur. In those that follow, an 
 attempt has been made to arrange, under the same heads, 
 some of the most striking phenomena in the genetic cycle, 
 both of alternating and non-alternating species of plants 
 and animals. 
 
 It may be mentioned, in conclusion, that however great 
 
 the effect of these processes of gemmation and puUulation 
 
 may be in modifying the external form of those species 
 
 in wliich they prevail extensively, little or no relation ca,n 
 
 be traced between the peculiarities of the genetic cycle and 
 
 the affinities of the species, as recognized by systematic 
 
 naturalists. We have seen that totally different laws of 
 
 gemmation prevail in nearly allied orders, as in Cestoid and 
 
 Trematode worms among animals, and in mosses and ferns 
 
 L 2 
 
220 
 
 SUMMARY OF CONCLUSIONS. 
 
 among plants ; and we find that, even in the same families 
 — and these highly natural ones — free zooids occur in some 
 species and not in others, closely allied ; of this, many 
 illustrations have been given in the course of the foregoing- 
 remarks. The occurrence of pullulation is even more irre- 
 crular, not serving always even as a generic character ; 
 thus, we have arborescent, herbaceous, and even annual 
 species in the same genus, as in Solanum, Veronica, and 
 Hibiscus. 
 
CASES SIMULATING ALTERNATION OF GENEllATIONS. 221 
 
 X. 
 
 CASES SIMULATING ALTERNATION OF 
 GENERATIONS. 
 
 § 1. In connection with the subject of alternation of gene- 
 rations, a short reference may be made here to various 
 cases, which, without being really of the same nature, have 
 some apparent resemblance to it, or have for some reason 
 been confounded with it. 
 
 Most properly the expression is used to imply a certain 
 regularity of recurrence of sexless and sexual forms in tlie 
 succession of progeny, and a certain diversity in their 
 general character. It cannot be regarded as a proper case 
 of alternation of generations, when the interchange of the 
 two modes of propagation is casual and not a fixed cha- 
 racter of the species — as may be the case, for instance, in 
 plants with bulbiferous stems or viviparous flowers, which 
 propagate by gemmae in seasons when they cannot mature 
 their seeds. 
 
 § 2. Nor again does an interchange of different modes 
 of budding belong to the class of cases we have been con- 
 sidering, for this would be an alternation of peminatiotis 
 rather than of generations. Instances of such a kind occur 
 in the alternation of attached and deciduous buds in plants. 
 Thus a grass raised from one of the bulbils thrown off by a 
 deciduous infloresence multiplies its stems into a large 
 tussock by a succession of leaf-shoots which vegetate in 
 connection with the primary axis, and may all bear gemmi- 
 parous flowers, like that which furnished the original de- 
 ciduous gemma. 
 
222 CASES SIMULATING ALTERNATION OF GENERATIONS. 
 
 In many of the lower algae we find a similar alternation 
 of free and attached gemmse, in the form of zoospores, and 
 of cells cohering to form confervoid filaments. And much in 
 the same way we have in the Polyzoa, besides the attached 
 Polype-bud, a peculiar form of deciduous gemma — the stato- 
 hlast. 
 
 In the cases cited, the two forms of gemmae which 
 thus take part in the propagation of the species differ in 
 the matter of attachment to the parent stock as well as in 
 their own character, but cases occur in w^hich both are fixed, 
 as well as others in which both are free. Thus, in some 
 species of Sertularia we may have a frond of seaweed 
 covered with a miniature forest of small poljrpidoms, each 
 ■\vith its own polype-buds, but all at the same time organi- 
 cally connected by stolons proceeding from radical gemmae, 
 which creep in a network over the surface of the frond. 
 Two forms of free gemmae again appear to co-exist in 
 some Algae, for there is reason to believe that the stato- 
 spore, which is often associated with the zoospore, and is in- 
 tended for the reproduction of the species after a consider- 
 able lapse of time, is not in every case the result of impreg- 
 nation, but is sometimes rather a true gemma, modified to 
 meet the peculiarities of the case. 
 
 § 3. As an alternation of different forms may thus occur 
 in a succession of gemmations, without the intervention of 
 any sexual process, so it has been thought that a periodic 
 recurrence of certain peculiarities may be observed in the 
 course of generations, even where the only mode of propa- 
 gation is by the formation and impregnation of ova. In 
 our own species something of this kind has been recognized 
 under the term atafclsm, by which is meant the reappear- 
 ance of particular features, tempers, morbid diatheses, &c., 
 in the progeny of the second generation, passing over the 
 immediate offspring. Facts of this kind are of frequent 
 observation — a man's resemblance to his grandfather is a 
 
CASES SIMULATING ALTERNATION OF GENERATIONS. 2'2o 
 
 common subject of remark, as well as the tendency of cer 
 tain hereditary diseases, as gout, to reappear in the grand- 
 son, rather than in the immediate issue. 
 
 § 4. By some authors the phenomena of Metamorphosii<y 
 as they occur in Insects, Crustaceans, Batrachians, &c., have 
 been confounded with those of alternation. Such meta- 
 morphosis is described by Dr. A. Thomson as a breach 
 of continuity in the progress of embryonic development, 
 *' marked by some change in the mode of life, or some dif- 
 ference in the structure of the individual"* — a definition 
 which might perhaps be stretched to include cases of 
 alternation. In almost all cases of metamorphosis there is 
 a separation of what was originally a single body into more 
 parts than one, inasmuch as there is always something 
 cast off — either, as in Insects and Crustaceans there is 
 ecdysis or casting of the skin (vvdiat Huxley terms concentric 
 fission-f) — or, as in the Ascidians and some Batrachians, 
 the casting off of a member, as the tail. The difference in 
 so far is perhaps one rather of accident than of essence, and 
 seems to consist in this, that in the metamorphosis none of 
 the parts but one is capable of continuing its existence, so 
 that, disregarding all the others, we at once identify the 
 living segment with the animal wliich has been the subject 
 of the metamorphosis ; whereas in weU-marked cases of 
 alternation, the vitality being more equally divided, we 
 have in the swarm of resulting zooids, so many candidates 
 for identity with the pre-existing structure, that we in- 
 voluntarily cancel their claims as destructive of each other's 
 validity, and regard them all alike as the progeny of the 
 pre-existing structure, and not as a continuation of its very 
 self. That there is not merely this community in theory, 
 but that in actual nature the two cases do tend to merge 
 into each other has already been pointed out in speaking of 
 
 * Cyol. Anat. and Phys. Sup. [131] (ovum). 
 
 f Lect. at Royal lust. Ann. Nat. Hist., 2 J Ser., IX., 505. 
 
224 CASES SIMULATING ALTERNATION OF GENERATIONS. 
 
 the Echinodermata. WTienever, as in tliis class, but one 
 new zooid results from the alternation, it is obvious that 
 the great difficulty of identifying it with the prior structure 
 is removed, and in some of the species of Echinodermata 
 the process has in fact much more the character of a me- 
 tamorphosis than of an " alternation." In the develop- 
 ment, for instance, of the Echinus from its "Pluteus" there 
 is less rejection of the pre-existing structure than occurs in 
 the exuviation of the skin of the Caterpillar, the casting off" 
 of the tail of the Tadpole, or even in the removal of the 
 placenta of the Mammalian foetus ; but in the Starfish — 
 a close ally of the Echinus — though we still have but a 
 single new zooid, our sense of continued identity is obscured, 
 if not destroyed, by the structure in which it originated, re- 
 taining its own vitality, and appearing as a distinct animal, 
 side by side with that which has issued from it. 
 
 After all, it is not metamorphosis which is proved in 
 this way to be akin to alternation, but only that casting off 
 of old structures simultaneously with the formation of new, 
 which, though a common accompaniment of metamorphosis, 
 is far from being its prominent characteristic ; for the de- 
 velopmental changes in which the process essentially con- 
 sists tend much more to the fusion of parts previously dis- 
 tinct, than to the breaking up of prior continuity of struc- 
 ture. This is particularly remarkable in the embryogeny 
 of those species, in which metamorphosis is best marked, 
 as Insects and some of the Crustaceans. On the other 
 hand, it is not in metamorphosis merely, or as a progressive 
 step towards higher organization that we have a casting off 
 of certain parts of the body ; exuviation at least of the 
 tegumentary tissues is a phenomenon, which, continuously 
 or intermittently, and in a greater or less degree, goes on 
 durino; the whole lifetime of the individual in almost all 
 species, and is in fact absolutely the same in kind with that 
 constant molecular renewal of the body, in which the very 
 
CASES SIMULATING ALTERNATION OF GENERATIONS. 225 
 
 essence of organic life consists. One does not see wliy, for 
 instance, the exuviation of sheets of cuticle after scarlet 
 fever is not as much entitled to be called ** a concentric 
 fission" as the ecdysis of an insect in the course of its me- 
 tamorphosis. 
 
 § 5. Another class of cases which in some degree simi- 
 late those of alternation consist in the formation of sper- 
 matophores and nidimentary etivelopes. These structures, 
 which are sometime elaborately organized, have been met 
 with in Cephalopoda, Gasteropoda, Insecta, Crustacea, 
 Annelida, Planaria, and perhaps other Invertebrata. In 
 the Cephalopoda the spermatic corpuscules, when generated 
 in tlie usual way, become enclosed in peculiar cases or re- 
 ceptacles, which in the case of the Lolligo have been long 
 known to naturalists under the name of " filaments of 
 Needham." They are of a very complex structure, but 
 their motile powers, chiefly shown in the ejection of their 
 contents, may probably be accounted for on physical prin- 
 ciples.* In the Argonauta, in which the spcrmatophore is 
 a simple sac, its active functions are discharged by the pe- 
 cidiarly modified tentacle (Hectocotiflus) in the cavity of 
 which it is lodged previously to the member being thrown 
 off from the body of the Cephalopod.*|" Sperm atophores of 
 
 • 
 
 * In Nautilus the spermatopliores after ejaculation appear to be coiled 
 up witliin the funnel iuto peculiar laminated vesicles. When uncoiled 
 they appear as attenuated filaments about half a line in diameter, but of 
 great length — e.g., 27 to 34 centimetres in Nautilus, 3 feet in Octopus 
 Carena (Leuckart), 8 centimetres in Octopus vulgaris (M. Edwards). 
 Hoeven, in Ann. Nat. Hist., 2d Ser., XIX., 72. 
 
 t Annals of Nat. History, 2d Ser., IX., p. 492. Ann. des ScienceB 
 Nat., i. XVI., No. 3. From the observations of Steenstrup it seems 
 probable that in all male Cephalopoda one of the eight shorter arms i.s 
 different one side of the body from its fellow on the opposite side, and ia 
 developed for a certain extent of its length in a manner more or less 
 analogous to that of the Hectocotylus-arm of the Argonauta. The par- 
 ticular arm and the side of the body afibcted vary in diflcrent species. 
 Anuals of Nat. Hist., 2d Ser., XX., 81. 
 
 L 3 
 
226 CASES SIMULATI^^G ALTERNATION OF GENERATIONS. 
 
 a simpler structure are met with in some Insects, Crus- 
 taceans, and other Invertebrate animals.* 
 
 Much in the same way the eggs of some Insects, Anne- 
 lidans, and Molluscs,'!' after acquiring the usual character of 
 impregnated ova, become enclosed in peculiar envelopes ; 
 and some of these structures also are said, though on rather 
 doubtful evidence, to have certain motile powers. 
 
 In the simple fact of the enclosure of the reproductive 
 bodies in appropriate receptacles there is nothing very pe- 
 culiar ; it is merely, so to speak, the application to masses 
 of spermatozoa and ova, of what we are familiar with in the 
 case of sinfrle ova, in the formation of the shell of the bird's 
 ^^^% by the lower portion of the oviduct, or of the decidua of 
 the mammalian foetus by the uterus. It is more difficult to 
 decide on the proper relations of the receptacles in those 
 cases in which they exhibit spontaneous motions, or other 
 indications of independent vitality. They may perhaps be 
 considered in the light of special organs- of the parent's body, 
 destined to receive the corpuscules, and to be afterwards 
 thrown off for their protection and dispersion, like the 
 Hectocotylus-arm of the Cuttlefish, just referred to. 
 
 But such egg-sacs, or spermatophores, though in a certain 
 sense distinct forms in the genetic cycle, intermediate between 
 
 * Siebold's Compar. Anatomy, I. § 290-348. Annals of Nat. Hist., 
 2d Ser., XVI., 150, XIX., 165. In some Crustacea the spermatophore 
 eeems to be formed by the coagulation of the outer film of the seminal 
 fluid, on coming in contact with sea- water, the shape depending on that 
 of a groove in the shell in which the spermatophore is modelled, as it 
 were. Coste — Annals 3d Ser., II., 197. In Geoioliihis — a genus of 
 Myriapoda — the impregnation seems to be effected by the female 
 coming in contact with the spermatophore, which is suspended in the 
 centre of a net stretched across one of the subterranean galleries of 
 the insect. Annals, XIX., 165, 2d Ser. 
 
 f Blatta among Insects, Purpura and other genera of the Pectini- 
 branchiate Mollusca, Nemertini, Hirudinei, and Lumbricini, among 
 Annelida. The egg-sac of the earthworm (its so-called egg) contains two 
 embryos — that of the leech as many as eighteen. 
 
CASES SIMULATING ALTERNATION OF GENERATIONS. 22 
 
 
 the parent and the embryo, cannot be considered as pro- 
 perly constituting a link of the series. However elaborate 
 their organization, they are not really zooids, either proto- 
 morphic or gamomorphic, for they originate neither the 
 embryos, nor the sexual elements of the embryonic exist- 
 ence ; they serve merely to give a temporary protection to 
 germs which are really of a date of formation anterior to 
 their own. As the gamomorphic zooids have been com- 
 pared to free spermaries and ovaries, so these receptacles 
 may, according to the nature of their contents, be compared 
 to spermathecae, such as occur in insects, only free, or to 
 free uteri, with broods of embryos enclosed — their office 
 being not generation but gestation. 
 
 They do, however, simulate some of the more rudimen- 
 tary zooids, both germinal and sexual, so that, under cer- 
 tain circumstances, they may be confounded, if the deve- 
 lopment be overlooked. Thus in the case of Planaria it 
 appears still doubtful whether the bodies from which the 
 broods of young issue are merely nidimentary envelopes of 
 true ova, or germinal bodies, themselves derived from ova, 
 and originating a fresh progeny by a proper act of gem- 
 mation.* 
 
 Many zooids, indeed, of both orders are known to na- 
 turalists, which, in a structural point of view, are little 
 more than mere egg-sacs, and which in fact are, in some 
 works, designated by this or an equivalent term, such as 
 sporocysts, sporophores, sporosacs, &c. Such expressions, 
 however, are, in strictness, open to objection, being in- 
 
 * Siebold's Comparative Anatomy, Cli. IX., § 129, mtb Dr. W. Bur- 
 nett's note. 
 
 As Dr. Carpenter remarks, in discussing the embryogcuy of Pnrpxiray 
 the development of Planaria may prove to be parallel to tbat of the 
 Pectiuibrancbiate Mollusca, [noticed in Chap. III.] Trans. Micros. 
 Soc, III., 17. See also Sicbold, § 293, note 20, on the simulation of 
 the parent cells of spermatozoa, by the spermatophores of some Crustacea. 
 
228 CASES SIMULATING ALTERNATION OF GENERATIONS. 
 
 consistent with precision of language, as well as with the 
 true theory of development. A medusoid, for instance, 
 is something more than an egg-sac or egg-carrier, it is an 
 egg-producer, and the precursory form of a Trematode is 
 neither one nor other — it is indeed a producer of its brood, 
 not a mere carrier, but the brood consists neither of eggs, 
 nor of embryos produced from eggs, but of zooids formed 
 by a fresh act of gemmation. 
 
 Such objections are perhaps hypercritical, but the im- 
 portance can hardly be over-rated, in a perplexed subject 
 like the present, of avoiding the use of expressions which 
 may in any way become a fresh source of confusion. 
 
HOMOLOGICAL RELATIONS, &C. 229 
 
 XL 
 
 HOMOLOGICAL RELATIONS OF THE PARTS 
 CONCERNED IN REPRODUCTION. 
 
 § 1. In order to complete our survey of tlie process of re- 
 production, it remains to offer some remarks on the cor- 
 respondences or homological relations of the structures con- 
 cerned in it, with reference to differences both of sex and 
 species, and by way of making subsequent enquiries more 
 intelligible, a few words may be premised concerning the 
 principal modifications and general nature of the ultimate 
 reproductive particles. 
 
 Having already adverted to the development' of these 
 corpuscules in both Kingdoms of Nature, the following 
 summary of their principal modifications will be sufficient 
 here, in connection with the remarks which have to be made 
 on their essential nature, and on their homoloo-ical relations. 
 The Spermatic Corpuscules in the Vegetable Kingdom 
 are — 
 
 In the Protophyta, merely the condensed endo- 
 chrome of certain cells, and undistininiishable 
 from the germinal element. 
 In certain Algae (Florideae), Lichens and Fungi, 
 ellipsoidal or cylindrical motionless bodies, 
 without cilia (microgonidia^ spermatia, &c.) 
 In the Alga? generally, ciliated ovoid bodies like 
 
 minute zoospores ( anther ozoids, phvtozoa). 
 In the Charace?e, and in the higher Cryptogam ia 
 generally, (Hepaticse, Mosses, Ferns, Equise- 
 tacese, Lycopodiacese, and Marsileacea}), lila- 
 
230 HOMOLOGICAL RELATIONS OF THE 
 
 mentous motile corpuscules, somewhat resem- 
 bling the spermatozoa of animals ( Anther o- 
 zoids, Phi/tozoa). 
 In Phanerogamic plants, secondary cells formed in 
 the anthers, and protruding, through openings 
 in their outer or cellulose coat, tubules which 
 are outgrowths from the inner coat, or rather 
 from the protoplasmic granular matter which 
 the latter encloses (Fotilla in Pollen g7'ains). 
 In the Animal Kingdom, as a general rule, these corpus- 
 cules appear to be developed as the nuclei of secondary 
 cells (vesicles of evolution), generated in variable numbers 
 ^vithin larger parent cells. But in some Chilopoda, Aca- 
 rina, and Entozoa, the wall, as well as the nucleus of the for- 
 mative cells, seem to enter into their constitution ; and in 
 some Nematoid worms, and in Hydrozoa, it is alleged that 
 they are formed directly as primary cells within the sper- 
 matic gland.* 
 
 The spermatozoa are generally motile filaments, often 
 clavate — the larger extremity in some cases assuming the 
 character of a distinct " body," rounded or acuminated — 
 but in some Ci'ustacea, in Chilopoda, and in Nematoid 
 
 * Huxley's Oceanic Hydrozoa, p. 22. The secondary cells are de- 
 scribed by some as being formed by the breaking up of the large nucleus 
 of the primary cell in a way somewhat similar to the cleavage of the 
 vitellus of the ovum. It cannot be considered absolutely determined that 
 the secondary spherules, within which the spermatozoa originate, are 
 always true cells. See Burnett's note to Siebold's Comp. Anat. Invert., 
 § 127. Quatrefages Ann, des Sci. Nat., 4th Ser., II., 152. The develop- 
 ment of the spermatic particles in the higher Crustacea is described by 
 H. Goodsir (Anatomical and Pathological Observations, p. 39), and more 
 fully by Wagner and Leuchhart, as quoted below. According to the latter 
 authors the spermatozoa are formed singly in projections from the 
 primary ceU [which may possibly represent the vesicles of evolution]. 
 In the primary cell there is also an obvious nucleus, projecting externally, 
 but it is eventually thrown off, without itself undergoing any farther de- 
 velopment. 
 
PARTS CONCERNED IN REPRODUCTION. 231 
 
 Avorms, they are motionless and of various forms, as specu- 
 late, clavate, elliptical, semi-lunar, &c. In the majority of 
 animals these corpuscules are suspended in a peculiar 
 seminal liquor, but this is wanting in many Insects, Worms, 
 and other Invertebrata.* 
 
 The Germinal Corpuscules in Vegetables are — 
 
 In the lower Cryptogamia the condensed granular 
 contents of certain cells, which in the Proto- 
 phyta are indistinguishable from the sperma- 
 tic element. 
 In the higher Cryptogamia the central corpuscules 
 
 of the structures termed arche2:onia. 
 In the Flowering plants, protoplasmic corpuscules 
 lying within the embryo-sac, or central cavity 
 of the ovule. 
 In the Animal King-dom the almost universal arrano;e- 
 ment is a nucleated cell, termed the germinal vesicle, occu- 
 pying the interior of a larger one knoA\Ti as the ovum. 
 
 In both sexes there is reason to believe that the ultimate 
 reproductive corpuscules are essentially mere homogeneous 
 particles of the fundamental organic matter or protoplasm 
 of the species, but so related to it and to each other, that 
 neither is complete in itself, the conjunction of the 
 two being required to constitute a true representative of 
 the species. They are often termed cells, but a cell-wall is 
 certainly not always present, and when present does not 
 appear to be essential, but to serve only for the elaboration 
 or protection of the real reproductive matter which it con- 
 tains ; for the true end of the latter cannot be attained till 
 the impediment which the wall offers to the fusion of the 
 corpuscules of opposite sexes is removed by its deliquescence, 
 rupture, or penetration. This, indeed, is generally ad- 
 
 * Wagner and Leuckart, in Cyclopoedia of Anatomy and PLysiology, 
 Vol. III., article, " Semen." 
 
232 HOMOLOGICAL RELATIONS OF THE 
 
 mitted in the case of the spennatic particles, the only 
 instance in which they are walled cells being that of the 
 pollen grains of plants, the real value of which cannot be 
 positively determined till we have greater certitude as to 
 the behaviour of the extremity of the pollen-tube within 
 the ovule. But the female germ is generally regarded as a 
 true walled cell, and is considered moreover to be identical 
 with the primordial cell of the future embryo, passing into 
 it, when fertilized by some material or influence derived 
 from the spermatic particles. 
 
 Yet the grounds are very slender for either of these assump- 
 tions — that is, either for admitting that the female corpuscule 
 is — any more than the male — essentially a true walled cell, 
 or that one of these corpuscules is more continuous than the 
 other with the resulting embryo. The real state of the case 
 appears to be tha;t the embryo is formed out of the combina- 
 tion of masses of protoplasm representing the two sexes, and 
 that it assumes afterwards the form of a true cell by its own 
 progress of groTii;h, the first steps of organization being — at 
 least in animals — what is termed segmentation, and the 
 formation of a wall round the exterior of the mass. 
 
 While it is true that these acts commonly take place within 
 the cell-wall which originally surrounded the unimpregnated 
 germ, this is not to be considered as an essential of their 
 performance, but as due to the accidental circumstance that 
 the commixture of the particles generally takes place by the 
 spermatic corpuscules gaining access to the interior of this 
 protecting cell, through a perforation in its wall ; for when 
 the commixture is effected otherwise the result is different. 
 Thus, while in some of the conjugating Algee the proto- 
 plasmic contents of one cell are transferred to another, with 
 the contents of which they combine and form a spore to be 
 matured in that same cell, in other species of the family 
 Iwth cells effuse their protoplasmic contents, and the spore 
 resultino; from their combination is either matured in a new 
 
PARTS CONCERNED IN REPRODUCTION. 233 
 
 provisional cell formed by an outgrowth from the walls of 
 the conjugating cells, or is developed without the protec- 
 tion of any extrinsic cell-wall, though after a time it forms 
 one for itself, by the induration of its exterior layer. 
 
 That in many at least of the higher Alga?, in which the two 
 combining elements are differentiated into the representa- 
 tives of sexual corpuscules, the germ is at first a mere proto- 
 plasmic mass, would certainly appear from the observations 
 of Pringsheim, which go to show that it is not till after its 
 combination with the phytozoa in the act of impregnation 
 that a cell-wall is formed round it.* There is reason also 
 to believe that the germinal bodies lying within the central 
 cell of the archegonium of the higher Cryptogamia,*|* and 
 the embryo-sac of the Phanerogamia, j are at first mere pro- 
 toplasmic masses, which only after impregnation form on 
 their exterior a true or distinct cell-wall. 
 
 In animals although in the reproductive organs of the 
 female we have generally two well-marked cells, (the ovum 
 and the germinal vesicle), one within the other, and each 
 with a proper wall, neither seems to be the true homologue 
 of the protoplasmic body of the vegetable, but rather the 
 contents of the innermost — that is, the macula or nucleus 
 of the germinal vesicle. Impregnation is effected by the 
 spermatic particles diffusing themselves among the contents 
 of the outer cell or ovum, either through a special aperture 
 (micropyle) or in some of the other ways noticed before 
 (Chap. III., p. 70) at the same time that the genninal 
 vesicle dissolves and discharges its contents from within 
 into the same cavity, so that the two sexual elements, lying 
 
 * Kemarks on the spores of Algae in Eep. of Berlin Academy (Quar- 
 terly Journal of Microsc. Science, IV., 126). AJso Braun, Rejuvenes- 
 cence in Nature (Hay Soc. Publ.), p. 150, and seq. 
 
 t So at least they would seem to be in Buxhaumia. See also Prings- 
 heim, as quoted above. 
 
 X Griffith and Henfrey — Miscrograph, Dictionary, p. 432. 
 
234 HOMOLOGICAL EELATIONS 01 THE 
 
 free within the ovum, readily coalesce. Then follows the 
 cleavage of the yolk, and the formation of a wall on its ex- 
 terior — the blastodermic vesicle. 
 
 § 2. If we turn now to the homological relations of the 
 germinal element in the two kingdoms of organic nature, 
 and take for our starting point the protoplasmic corpus- 
 cules of the embryo-sac of the plant, and the contents of 
 the germinal vesicle of the animal ovum, we may consider 
 the '' formative yolk" of the latter as the equivalent of the 
 vegetable endosperm, and its primordial wall (zona pellu- 
 clda) as representing the embryo-sac of the ovule of the 
 Phanerogamia or the archegonium of the Cryptogamia. 
 Among the adventitious parts or those met with only occa- 
 sionally, we might compare the "nutritive yolk" of the bird's 
 ovum, which is really derived from the contents of the ovisac, 
 to the nucleus of the ovule or to the perisperm of the seed ; 
 and the albumen and shell of the egg (equivalent perhaps to 
 the tunica granulosa and shaggy chorion of Mammalia) to 
 the seed coats, arillus, &c. The ovary of the animal would 
 represent the ovary or germ en of the plant with its loculi. 
 
 In animals, on account of the germ not being generally 
 — like that of the plant — impregnated in situ, that is to 
 say, not coming in contact with the spermatic particles 
 till it has escaped from the ovary, we have no aperture cor- 
 responding to the micropyle of the seed. The term " mi- 
 cropyle" has indeed come into use in connection with the 
 animal ovum, but the aperture so called does not corres- 
 pond to the micropyle of the seed, and is nowhere repre- 
 sented in the majority of j)lants, for though the canal of 
 the archegonium of the Cryptogamia may fairly be taken to 
 represent the micropyle of the Qgg in Fishes, Insects, Echino- 
 dermata, &c., there exists no such opening in the embryo- 
 sac of the phanerogamic plant, the manner of fusion of the 
 reproductive elements being as obscure as in the imperforate 
 ova of the hioher Vertebrata. 
 
 I 
 
PARTS CONCERNJilD IN REPRODUCTION. 
 
 235 
 
 The oviduct — to complete the parallel — may he compared 
 to the canal of the stjde mthe flowering plant; while a certain 
 analogy may even be suggested between the cleavage of the 
 vitellus — giving rise to the cellular germ mass, which serves 
 as the point of origin of the embryo of the animal — and the 
 process of cell-multiplication by which is formed the suspen- 
 sor, at one of whose extremities the embryo of the future 
 plant is developed. 
 
 The following is a tabular statement of the correspon- 
 dences now indicated ; to push them farther would be a 
 
 matter of pure fancy : — 
 
 Egg Structures. Seed Structures. 
 
 Germinal Vesicle, with Macula. 
 
 Formative Yolk. 
 
 [Cicatricula of Bird.] 
 
 Corpiiscules of Embryo-sac, 
 
 [Nucleus of Ai'cliegonium . ] 
 Endosperm. 
 
 Primitive boundary of true 
 ovum. 
 
 Adventitious YoLk. 
 
 Micropyle, 
 
 Ovary and follicles. 
 
 Oviduct. 
 
 The Adventitious Yolk and 
 Vitelline Membrane of the 
 Bird's egg are derived from 
 the contents of the Vesicle. 
 
 Embryo-sac, 
 
 [Wall of Archegonium. ] 
 
 Perisperm, 
 
 [Canal of Archegonium. ] 
 
 Ovule, [Fern Spore.] 
 
 Canal of Style. 
 
 The Perisperm and Seed- 
 coats are derived from the 
 tissue and coats of the 
 Ovule. 
 
 In regard to the homologues of the spermatic elements, 
 the foUowino; is suo:2:ested as on the whole the most satis- 
 factory parallel. Kegarding the fovilla or contents of the 
 pollen grain as the essential spermatic element, and there- 
 fore as the equivalent of the animal spermatozoon, the 
 inner membrane of the pollen grain (intine) and its tubular 
 outgrowth may be considered as adventitious structures — 
 like the wall of the germinal vesicle — provided for the pur- 
 pose of securing the advance of the effused fovilla in a re- 
 gular column to its appointed destination, the embryo-sac 
 
236 HOMOLOGICAL RELATIONS OF THE 
 
 of the ovule,* and may be regarded as homologous with 
 the vesicle of evolution, whose nucleus in most animals be- 
 comes the spermatozoon. On this supposition the pollen 
 grains would correspond to the parent cells within which 
 the " vesicles of evolution" are generated, while the primary 
 cells of the anther would represent the tubules, follicles, or 
 other secreting cavities of the spermatic gland — relations 
 which may be expressed in a tabular way, as follows : — 
 
 Animal Structures. 
 Vesicles of evolution and 
 
 Spermatozoa. 
 Spermatic parent cells. 
 Seminiferous tubules, folli- 
 cles, &c. 
 Anther. I Spermatic gland. 
 
 On the same principles the corresponding relations of 
 the opposite sexual elements may be represented as fol- 
 lows : — 
 
 Vegetable Structures. 
 Pollen-tube and Fovilla. 
 
 Pollen grain. 
 
 Primary cells of Antber. 
 
 Animal Spermatic. 
 
 Vesicles of evolution ) 
 
 and Spermatozoon. ) 
 Parent Sperm-cell 
 Spermary and follicles. 
 
 Animal Germinal. 
 
 Germinal vesicle 
 
 and Macula. 
 Ovum. 
 Ovary and Ovisacs. 
 
 * Danvin notices another provision for a like object in the long probos- 
 cidiform introraittent organ of some of the " parasitic males" among the 
 Cii-ripedia. Speaking of this organ in Cryptophialus minutus, he re- 
 marks that its use " obviously is that the spermatozoa of these males, 
 which are so extremely small in size, compared to the female, should all 
 be conveyed within the sac, and none be lost. It should be borne in 
 mind that the whole male, including every part, is scarcely larger than a 
 single ovum, of which sometimes sixty have to be impregnated by only 
 two or three males." The spei-matozoa, he goes on to observe, have to 
 pass a distance of about l-7th of an inch from the gland to the lower 
 ova — but of this about two-thirds would be along the canal of the intro- 
 mittent organ (Monograph, II., 586). The envelopes of the female germ, 
 in the Phq,nerogamia and Cryptogamia respectively, have already fur- 
 nished us with a parallel case of the application of organs of very different 
 homological import, to the discharge of similar functions. 
 
PARTS CONCERNED IN REPRODUCTION. 23* 
 
 Vegetable Spermatic. 
 Fovilla within the Pollen- 
 tube. 
 Pollen grain. 
 Primary Pollen-cells. 
 
 Parenchyma of Anther. 
 
 Vegetable Genninal. 
 Protoplasmic Corjjuscules. 
 
 Embryo-sac. 
 Nucleus of O^Tile. 
 Ovule. 
 
 § 3. By way of applying the principles of homological 
 correspondence to the specialities of the several groups of 
 organized beings, a few tabular statements are here sub- 
 joined, based on the notices of the reproductive process in 
 Chapters II. and III. : 
 
 PROTOMORPHIC STAGE. 
 
 The primary product of fecundation, (pro-scolex passing 
 into scolex,) is represented 
 
 In Diatomace?e, by the large frustules. 
 
 In Algse, Fungi, and Lichens, by the composite 
 
 spores. 
 In Mosses and Hepatic?e, by the seta and theca de- 
 veloped from the archegonial cell. 
 In the higher plants, only by the cellular suspensor 
 of the embiyo of the seed. 
 It is^ represented in Animals by the primary germmass, 
 which in many Invertebrata has the characterof a ciliated 
 animalcule. In general it attains no higher organization ; 
 but 
 
 In Echinodermata It is developed into such zooids 
 
 as Auricularia, Pluteiis, and Bipinnaria. 
 In Trematoda, into the primary gregariniform zooid 
 
 (redia or sporocyst). 
 In Cestoidea, into the Cysticerciis or the primary 
 vesicle of the Echinococcus. 
 
238 HOMOLOGICAL RELATIONS OF THE 
 
 The second and following intermediate foims ('meta-scolea:) 
 are represented 
 
 In Mosses, by the spores, and filaments of the pro- 
 
 tonema into which they germinate. 
 In Trematoda, by the second and subsequent gre- 
 
 gariniform zooids. 
 In Cestoidea, by the secondary and subsequent 
 
 vesicles of the EcJiinococcus. 
 But in the majority of Plants and Animals, not at 
 
 all. 
 
 ORTHOMORPHIC STAGE. 
 
 The rudimentary condition of the typical form is re- 
 presented in plants and animals generally by the embryo. 
 
 In Fungi, by the confervoid filaments of the nascent 
 
 mycelium. 
 In Lichens, by those of the hypothallus. 
 In Echinodermata, by the " disc." 
 In Ascidium, by the Spinula. 
 In Distoma, by the Cercaria. 
 In Insects, by the " maggot" or " caterpillar." 
 In Batrachia, by the " tadpole." 
 When naked, the embryo is termed a lar^a ; w^hen ex- 
 truded from the body of the parent, but still invested with 
 its own envelopes, it is termed a seed or egg. 
 
 Secondary and subsequent phytoids or zooids, more or 
 less of the typical form, are represented — 
 
 In Vegetables, by the successive pullulations of ad- 
 herent leaf-shoots, making up the ramose vege- 
 tation of the majority of plants. 
 In the Polypifera and Polyzoa, by the successive 
 polypes, which, with their connecting stalks, 
 form the polypidom. 
 In Annelida, by the ''joints" of the body. 
 
PARTS CONCERNED IN REPRODUCTION 230 
 
 In Insects, by the " viviparous Aphides' and other 
 
 like forms. 
 The ultimate phase of the typical stao-e is reprcscr.tcd — 
 In Fungi, by the fruit-bearing plant. 
 In other lov;er Cryptogamia, by the thallus. 
 In Mosses, by the perichfetial leaves. 
 In Ferns, Equisetacese, Lycopodiaceie, &c., Ijy the 
 
 sporangium. 
 In the higher plants, by the floral organs. 
 In the Polypifera, by the " urn" (gonophore) and 
 
 blastostyle. 
 In the Trematoda, by the Distoma-fonn. 
 In the Cestoidea, by the mature Tainia-head. 
 In Insects, by the Imago, generally winged. 
 In Animals generally, by what is recognised as the 
 
 adult form. ^ 
 
 GAMOMORPHIC STAGE. 
 
 The proper sperm or germ stock (strohlla, proglottis) is 
 represented — 
 
 In Algse, by the androspore of Bulhochwte. 
 
 In Fungi, by the hymenium. 
 
 In Lichens, by the apothecium. 
 
 In Mosses, scarcely at all. 
 
 In the higher Cryptogamia by the spore, and the 
 
 prothallium developed from it. 
 In the Phanerogam ia, by the pollen grain and ovule. 
 In the Polypifera, by the medusoid, or the sporosac. 
 In the Cestoidea, by a proglottis, or cucurbitiform 
 segment, as in Tcbnla. 
 
 * In the higlier Aniraa-s, liowever, as -n^ll be presently noticed, tbf 
 adult state represents, in addition to the tjj^ical form, the rudiments 
 also of the gamomorphic, in the parts of sex, implanted at a coinpam- 
 tively early period of mbryonic development, on the pre-existiug struc- 
 ture known as the Woljjiaji body. 
 
240-. HOMOLOGICAL RELATIONS OF THE 
 
 In the Tunicata, by a catenated zooid, as in 
 
 Salpa. 
 In Annelida, by a caudal zooid, as in Syllis. 
 In Animals generally, by the spermary and ovary. 
 
 The sperm-sacs and germ-sacs are represented — 
 In the Protophyta, by the conjugating cells. 
 In Algse, by the antheridium and the sporangium. 
 In Fungi and Lichens, by the spermagonium and 
 
 ascus. 
 In the higher Cryptogamia, by the antheridium and 
 
 archeo;onium. 
 In the Phanerogamia, by the pollen-tube, and the 
 
 embryosac of the ovule. 
 In Animals generally, by the primary sperm-cell 
 
 and ovum. 
 
 The ultimate sexual elements are represented — 
 
 In the Protophyta, by the endochrome of the con- 
 jugating cells. 
 
 In Algae, by the antherozoids and germinal corpus- 
 cules. 
 
 In Fungi and Lichens, by spermatia and endothecal 
 nuclei. 
 
 In the higher Cryptogamia, by the filaments in the 
 cellules of the antheridia, and the central cor- 
 puscule of the archegonium. 
 
 In the Phanerogamia, by the fovilla in the pollen- 
 tube, and the germinal corpuscules of the 
 embryosac. 
 
 In Animals generally, by the spermatozoa in the 
 vesicles of evolution, and the macula of the 
 germinal vesicle. 
 Tabular views are given in the Appendix of the points of 
 correspondence as above indicated. 
 
PARTS CONCERNED IN REPRODUCTION. 211 
 
 § 4. In conclusion, a few observations may be made on 
 the relations of the sex to the individual. 
 
 If this term individual be applied to eveiy isolated or- 
 ganism, then it is only in cases in which — as in the higher 
 species — no process of detachment of gemmae is interposed, 
 at any period of the life-history, so as to interfere with the 
 integration into a single body of the successive phases of 
 organization, that the character of sexuality can attach to 
 every individual of the species. On a first view, indeed, 
 its limits appear even more restricted, for, though in the 
 higher animals — except in circumstances of immaturity, or 
 of mutilation, or other abnonnality — all the individuals 
 have true sexual powers, yet, in certain families of the 
 Invertebrata — as Bees and Termites, among insects — the re- 
 productive faculty is not diffused over the whole species, 
 the majority being destitute of all power, either of impreg- 
 nation, or conception, and hence termed neuters, as being 
 neither males nor females. This sterility, however, is rather 
 functional than organic, the so-called neuters being, in fact, 
 females, in which the reproductive organs have remained in 
 a rudimentary condition. 
 
 Generally in the animal kingdom, the development is 
 one-sided, the same indvidual not producing both sexual 
 elements. In the normal condition of the higher animals, 
 we never find the sexes united, each individual being 
 either simply male or simply female. This applies uni- 
 versally to Vertebrata, except as a rare monstrosity.* 
 It applies also very generally to the typical Articulata, 
 except in aberrant orders, as the Cirripedia, but in the 
 vermiform tribes, and in the sub-kingdom of Mollusca, the 
 union of the sexes, by what is termed a hermaphrodite or 
 bi-sexual arrangement, is common enough. 
 
 * It seems to occur more frequently in fishes than in auy of the hi^'her 
 classes, and is said to be a normal phenomenon in the perch. — (Dufoss* 
 Annales des Sciences Naturelles, 1857.) 
 
 M 
 
242 HOMOLOGICAL RELATIONS OF THE 
 
 With these qualifications, it still remains true that where 
 the unity of the organic structure is not broken in upon by 
 an interpolated process of gemmation, all the individuals of 
 the species, as their normal constitution, present indications 
 of sexuality. They may not all be endowed with reproduc- 
 tive power, but they all normally possess organs, either 
 male or female, or both combined. 
 
 It has been contended, indeed, that the original unifor- 
 mity of type is even more absolute than this — that sexual 
 organs, of both kinds, exist at first normally in all the in- 
 dividuals of a species, though the full development of one 
 sex is usually associated with the non-development of the 
 opposite — a view originally suggested by Dr. Knox,* and 
 one which has several theoretical considerations in its 
 favour. It goes far to harmonize the existence of the sexual 
 peculiarities of individuals with the general laws of repro- 
 duction, in those species whose continuity of organization 
 is not broken up by any separation of free zooids ; for it 
 certainly seems more natural in this case to regard all the 
 individuals as having an original structural identity, and 
 to ascribe the sexual differences to the non-development of 
 certain parts, than to suppose the admitted rule of like pro- 
 ducing like to be continually broken in upon by essential 
 differences of organization from the very first in the parts of 
 generation. It also serves to soften the abruptness of the con- 
 trast between the normal hermaphroditism of some species, 
 and the arrangement of separate sexes, which is the ordinary 
 rule in the animal kingdom. And it affords, farther, a ready 
 explanation of the occasional appearance of hermaphrodites, 
 even in species in which the sexes are normally separate. 
 
 This is, indeed, a rare occurrence, for the individuals so 
 termed are commonly only malformed males or females. 
 But a monstrosity, consisting of a real intermixture of sex, 
 
 * Brewster's Edinburgli Journal of Science, II., 322 — 1830. 
 
PARTS CONCERNED IN REPRODUCTION. 2V6 
 
 does at times occur, and may, on this view, be explained in 
 accordance with the general principles of teratology. i\m- 
 genital malformations are generally the result either of 
 defect or excess of development, or of the irregular associa- 
 tion of both influences ; and the latter is exactly the 
 condition calculated to induce such a monstrosity, on the 
 hypothesis in question. The most common fonn of inter- 
 mixture is probably the development of male organs on one 
 side, and female on the other — a monstrosity which has 
 been observed in Fishes and Insects.* In the latter, it 
 reveals itself by a coiTesponding disparity in the external 
 characters of sex, as in the markinii-s of the wiiic;s of Butter- 
 flies."!* -B^^t there are not wanting instances of a true 
 intermixture of male and female organs on the same side of 
 the body. I Such cases aff'ord a strong argument in favour 
 of the orio-inal co-existence of the oro;ans of both sexes as 
 a normal arrangement, for otherwise we must first assume 
 the co-existence of another malformation — viz., the dupli- 
 cation of the organs on one or both sides — and then their 
 sexual development in opposite ways ; a view which is 
 quite opposed to the general rule, that in double monstcr.s 
 the two individuals are always of the same sex. 
 
 It does not appear, however, that the speculation of Dr. 
 Knox is borne out by the embryonic development of the 
 parts in the higher animals, in which alone the point ha^n 
 been carefully examined. It is true it cannot be said either 
 to be disproved by this test ; only there is an entire absence 
 
 * Siebold's Comparative Anatomy, § 318, uote 1. 
 
 Dr. Simpson, on HermapLroditism. Ob.stetric Works, Vol. II-, 
 pp. 242-304 — a reprint, -with some additional cases and remarkp, from an 
 article in the Cyclopaedia of Anatomy and Physiology, "Vol. III. 
 
 t An illustration of this bi-sexual livery is given in Humphrey's Butter- 
 fly Vivarium, page 142, and plate II. fig 6. 
 
 X Simpson Op. Cit., pp. 280-339. 
 
 Dr. Blackman and Dr. W. J. Burnett, in the Anioricau Journal of the 
 Medical Sciences, N. Ser., Vol. XXVI., pp. 63-3G7. 
 
 M 2 
 
244* HOMOLOGICAL RELATIONS OF THE 
 
 of any evidence in support of the co-existence of the 
 essential organs of the two sexes — the spermatic and ovarian 
 glands — which is the more remarkable from there being a 
 very complete representation of the associated structures, 
 both male and female.* 
 
 The organs of both sexes are developed on the basis of 
 prior embryonic structures, the Wolffian bodies. In con- 
 nection with these the embryo exhibits on each side two 
 hollow filaments or tubules — the efferent duct of the 
 Wolffian body and the Mullerian cord. According to 
 Kobelt, in the male the former is converted into the vas 
 deferens, while the latter almost disappears. In the fenipJe, 
 the latter is converted into the fallopian tube, while, in the 
 human species, the duct entirely disappears, though in 
 Ruminantia and Pachydermata, it remains as the rudi- 
 mentary structure known by the name of the canal of 
 Gartner. -f- Morphologically, the uterus is merely a dila- 
 tation of the common inferior termination of the two 
 oviducts or fallopian tubes, and is represented in the 
 male by the prostatic vesicle, which, though a mere 
 follicle in the human species, assumes, in some of the lower 
 animals, so much the character of a miniature uterus, with 
 two filaments or tubules going off from its upper angles, 
 alongside the vasa deferentia, that Weber gives it the name 
 of " Uterus Masculinus."J Up to a certain period of 
 
 * Tliis coiTespondence becomes still more striking, if we extend our 
 survey to tlie other Mammalia, in some of wliicli we find the scrotum cleft, 
 in others the clitoris traversed by the urethra. Simpson on Hermaphro- 
 ditism, Obstretic Works, Vol. II., pp. 220-307. It is to an abnormal 
 development of these accessory parts that the multiform disguises of sex 
 are due, which are popularly confounded with tme hermaphroditism. 
 
 t Valentin's Text-book of Physiology, 661. 
 
 "^ Zusiitze zur Lehre vom Bau and den Verrichtungen der Geschlechtsor- 
 gane. Leipsic, 1846. 
 
 The development is well marked in the Beaver, Eabbit, Boar, Horse, 
 Ass, Badger, Goat, Sheep, and Deer. 
 
 But, perhaps, as is pointed out by Leuckart, the part may be more ac- 
 
PARTS CONCERNED IN REPRODUCTION. 2\'> 
 
 embryonic development, both sets of organs continue 
 equally apparent, so that the sex is witli (liltunihy distin- 
 guishable, as is particularly remarked by Weber in the case 
 of the Rabbit. 
 
 The Wolffian body itself, there is reason to believe, lias 
 a much more permanent existence than was at one time 
 supposed, for a structure, which is probably to be regardetl 
 as its residuum (parovarium) has been discovered by Rosen- 
 miiller in the broad ligament of the uterus of the foetus 
 and infant,* and has been shown by Kobelt to continue to 
 exist in the same situation, even in the adult female,"[" while, 
 in the male it is converted into the epididymis, and, per- 
 haps, in part (superiorly) into a peculiar body, to whicli 
 Giraldes has called attention, in the spermatic cord (Corpus 
 Innomine.) 
 
 So far, therefore, as appears from the facts of develop- 
 ment, we may either assume, in conformity with Knox's 
 view of the primordial duplicity of sex, that in the whiti>h 
 spot on the inner margin of the Wolffian body, where tlie 
 
 curately compared to the whole genital sinus of the female — that is, to 
 the uterus and vagina taken together. (Cjclopajdia of Anatomy and 
 Physiology, Art. Vesicula Prostatica, Suppl., p. 112.) The Prostrate 
 Gland, in which it is imbedded, has been held to represent the glandular 
 substance of the cervix uteri, but this view is negatived by its occasional 
 occurrence conjointly with a distinct uterus. (Dr. Wan-en, in Amer. Journ. 
 of Med. Science, July, 1857, p. 127.) Its homologues, therefore, as well 
 as those of the vesiculae scmiuales, are somewhat uncertain. Dr. Simpson 
 suggests that the former may be represented by the foUicles of the waUn 
 of the female urethra, while the latter may be regarded as analogous ap- 
 pendages of the seminal canals. The relations of the external organs aro 
 more obvious, but it is not necessary for our subject to enter upon them. 
 A faU tabular view of the homologies of all the parts, lioth external and 
 internal, is given in Dr. Simpson's article on Ilermaphroditisni, a8 re- 
 printed in the second volume of his Obstetric Works, p. 320. 
 * " Qusedam de ovariis embryonum et foetuum humanomm." 
 t Philosophical Transactions, April, 1858. See also Dr. A. Faire, in 
 Supplement to the Cyclopa}dia of Anatomy and Physiology, Art. 
 « Uterus," p. 593. 
 
246 HOMOLOGICAL RELATIONS OF THE 
 
 generative gland first appears, there are distinct foci of de- 
 velopment for both sexual elements — though the normal 
 development of one suppresses that of the other ; — or we 
 may adopt the more common theory, that there is but a 
 single focus of this kind, whose development is, in some un- 
 known way, directed exclusively to the evolution of one or 
 other sex. The latter view, certainly, is that most naturally 
 suggested by the facts of the case in the higher species, and 
 also by the development of the gonophores of the Hydrozoa. 
 In the lower animals, generally, the primordial condition of 
 these organs has not yet been much studied in this point 
 of view. 
 
 "Wlien the sexes are separate, two individuals — male and 
 female — are required for an adequate representation of the 
 species ; but, in cases where they are united, each indivi- 
 dual of the species becomes a complete type of the whole, 
 so far as structure is concerned. Functionally, however, 
 it is only so, when the bi-sexual organism has the power of 
 self-impregnation ; and this is comparatively seldom the 
 case, most hermaphrodites impregnating each other, either 
 by a reciprocal act (as in Helix), or by their aggregation 
 into chains, the individuals composing which receive fecun- 
 dation from those in advance, and communicate it to those 
 behind.* 
 
 On the other hand, in the cases in which the oneness of 
 the organism is broken in upon by an interpolated process 
 of gemmation, the sexual characters attach themselves ex- 
 
 * In some bi-seraal Cin-ipedes, it lias been shown by Mr. Darwin that a 
 sort of supplementary impregnation is effected by separate males of mi- 
 croscopic size and parasitic habits, which he terms complementary males. 
 
 In aquatic animals, intromission of the spermatic particles is by no 
 means so regular a phenomenon as in terrestrial species, impregnation 
 being frequeutly effected by the diffusion of the seminal fluid through 
 the water in the neighbourhood of the previously deposited spawn of the 
 female. The process may be imitated artificially, and this is now done to 
 some extent in the breeding of fish. 
 
PARTS CONCERNED IN REPRODUCTION. 21^7 
 
 clusively to those of the resulting zooids or phytoids, whicli 
 represent, or are more or less incorporated with that pha.s»* 
 of development to which, in the foregoing pages, the term 
 gamomorphic has been applied.* The other links, which 
 help to make up the entire series intervening between the 
 successive acts of sexual reproduction, are truly neuter — 
 that is, not only incapable of exercising sexual function!*, 
 but destitute of all trace of sexual orrjans, and multiplying 
 simply by some modification of the budding process. 
 
 Protomorphic organisms thus isolated from those of tlie 
 succeeding phases have not yet been shown to have their 
 neutrality even indirectly affected by their giving rise, in in- 
 dividual cases, exclusively, to male or female gamomorphic 
 forms ; but analogous differences have been satisfiietorily 
 determined as occurring in the orthomorpliic or typical 
 phase. In the vegetable kingdom particularly, they have 
 long attracted the attention of botanists, who apply the 
 term dmclous to species whose sexual phytoids or iiowei-s 
 are exclusively of one sex on any single plant, and that <if 
 mGnoecious to species whose sexual ph}i;oids, though them- 
 selves exclusively either male or female, occur of both kinds 
 in connection with the same plant. A word of the same 
 general character-^such as synoeclous — might be devised to 
 distinguish plants bearing bi-sexual flowers, to which as yet 
 no special term has been applied. The expressions might 
 farther be extended with advantage from phanerogamic 
 plants, not only to those organisms — like Mosses, and some 
 of the Polypifera, in wliich the reproductive organs are in 
 obvious connection with the vegetative stock, — but to other 
 cases also, in both kingdoms of nature, in wliich the sexual 
 forms are quite isolated. In the case of Ferns or Polyjii- 
 fera, for instance, we should call a species synrecious, in 
 which the prothallia or medusoids are bi-sexual; another 
 
 * Nurses (Amme) of Stoeustrup ; Agamozooids of Uuxlcy. 
 
248 HOMOLOGICAL RELATIONS OF THE 
 
 monoecious, in which they are of separate sexes ; and 
 another, again, dioecious, in which those of one sex only are 
 derived from the same axis or polype stock. It is believed 
 that illustrations of all these arrangements may be found 
 in the two groups referred to, as well, perhaps, as in some 
 others. 
 
 The sexual relations, now indicated, may be represented 
 in a tabular form as follows : — 
 
 Reproductive Organs present, as integral parts of the system : — 
 Male and Female in different indivi- 
 duals, each of wliicli is IMonosexual. 
 
 Male and Female in the same indivi- 
 
 ( Bi-sexual or 
 dual, which is, therefore | Hermaphrodite, 
 
 but not necessarily seK-impregnatmg. 
 Organs appearing as distinct gemm{?e : — 
 
 Male and Female in the same gemma. . . Synoecious. 
 Male and Female in different gemmae, 
 
 from the same stock , Monoecious. 
 
 Male and Female in different gemmte, 
 
 from different stocks Dioecious. 
 
 Organisms, normally incapacitated for sexual 
 
 action, are termed... Neuter. 
 
 True neuters occur only in the preli- 
 minary phases of species which 
 have the sexual organs in detached 
 gemnise ; 
 
 False neuters are either rudimentary 
 or larval conditions of organisms 
 which afterwards form true sexual 
 
 organs ; 
 
 Or, individuals in wliich the latter re- 
 main permanently in a rudimen- 
 tary condition, as in the female 
 working Bees. 
 
 § 5. It is with some hesitation that I have used the 
 term homologous with reference to the correspondences 
 above suggested, as they are obviously of a different nature 
 
PARTS CONCERNED IN HITUODUCTION. 240 
 
 from tliose to Avliicli the expression was originally applied 
 by Professor Owen. In comparative anatomy, the tenn 
 homologous is employed to indicate parts which occupy 
 corresponding positions in that general plan of conformation 
 traceable throughout large groups of animals. Such part.s 
 have no farther community of office than arises from tlieir 
 physical adaptation. The work which they are naturally 
 adapted to perform, in the more typical species, they must 
 be suited for in all, in some degree, so long as there is no 
 wide departure, on the one hand, from the ordinaiy fonn of 
 the organ, or, on the other, from the ordinary habitat of 
 the gi'oup of animals. But, when this does occur, we 
 have numerous examples of their being turned to totally 
 different uses, or left in a rudimentary state, without any 
 office to perform at all. It is sufficient to cite, in illustra- 
 tion, the rudimentary condition of the pelvis of the whale, 
 or the transference of the respiratory function in the fish 
 from the lung to the gill, the rudimentary homologue of the 
 former organ being left to do duty as a swimming bladder. 
 But, in the correspondences which have been under con- 
 sideration in this chapter, the function or olhce to which 
 the parts minister is a point of prime importance in esti- 
 mating their relations. The spermatic and germinal organs, 
 for instance, have throughout been assumed as the corre- 
 sponding parts in the economy of the two sexes. Yet, there 
 is reason to believe, they are not always really structural 
 homologues ;* and all that is meant by instituting a com- 
 parison between them, is to indicate that they occupy 
 corresponding or equivalent positions in the reproductive 
 process, in as much as they are similarly related to the 
 orthomorphic phase of development on the one lianil, and 
 to the ultimate spermatic and germinal corpusculcs on the 
 other. Hence, it may appear that the term analocjoa* 
 
 *■ See Sanderson in Supplement to Cyclop. Anat. and Physical " Voget. 
 Eeproduct.," p. 252. 
 
 M 3 
 
250 HOMOLOGICAL RELATIONS OF THE 
 
 would be more suitable, as now commonly restricted to 
 correspondences in function. There is a wide difference, 
 however, between the reproductive function and others, in 
 the constancy of its structural relations. ^A-liether it is 
 that the process, whereby are laid the foundations of the 
 organized fabric, has, as it were, reflected back upon it some 
 of the uniformity of system, which is so striking a character- 
 istic of the latter, or whatever other explanation may be 
 suggested, so it is, as a general rule, that not only have 
 the reproductive organs as definite relations in each great 
 group as any part of the fundamental framework of the 
 skeleton, but that even in anim^als of totally different types 
 of organization, there prevails a close uniformity of struc- 
 ture, even in very minute details of these parts, the evolu- 
 tion, both of ova and spermatozoa, presenting — with some 
 few exceptions — the closest resemblance throughout the 
 whole Animal Kins^dom. 
 
 It is true that the interpolated process of gemmation 
 observes no such constancy, so that the uniformity is very 
 much confined to the gamomorphic or sexual stage ; but as 
 the phenomena of this stage form the starting point of the 
 cycle of reproduction, the use of the term homologous 
 appears to indicate, at least, the general character of the 
 process, better than any other in common use. 
 
 I have only, in conclusion, to repeat my regret, if the 
 spirit of system has in any respect given a false bias to the 
 interpretation of the facts of nature. Impressed, as I have 
 long been, with the conviction of the prevalence of an 
 orderly arrangement throughout the works of the great 
 Creator, who " hath made all things double one against 
 another ;" and, believing that some such guiding principle 
 has been successfully used by the most cautious explorers 
 of nature, as a clue to her more intricate mazes, I freely 
 admit having proceeded, in the examination of the com- 
 parative details of the process of reproduction, with a strong 
 
PARTS CONCERNED IN REPRODUCTION. 251 
 
 prepossession in favour of the existence of a real, thoii;:!! 
 hidden unity, in the essentials of this important function 
 throughout the Avhole range of organised beings. Feeliuir, 
 however, at the same time, that the very consciousness of 
 such a prepossession is some protection against its leading 
 into serious error, I now submit my conclusions, such ns 
 they are, for the judgment of those whose position auKjn;: 
 the cultivators of Natural Science entitles them to pronounce 
 upon them. 
 
APPENDIX. 
 
 It appears the most conv^enieut arrangement to put the followiiii^ 
 Tables in an Appendix by themselves, as referred to in ditiorent 
 parts of the work. 
 
 Tables I. — IV. are slightly altered from those appended to my 
 paper on the Genetic Cycle, in the Edinburgh Philosojihicjil 
 Journal for January, 1860. Table V. is a modification of quo 
 given by Dr. Sanderson, in the Cyclopaedia of ^Vnatomy ami 
 Physiology (Art. Vegetable Ovum) ; the explanation ai)pend«.d 
 to it shows in what resjiects his views have been departed from. 
 
 The three succeeding give a conspectus — arranged a.s much ii."< 
 possible in the same plan, for the sake of comparison — of tlio 
 theory of relations which I have been led to adopt in thi« 
 work. 
 
OPtDINAEY REPRODUCTION". 
 
 
 
 >. 
 
 
 
 t 
 
 
 GQ 
 
 
 
 e 
 
 « 
 
 oa 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1"- 
 
 
 
 1 
 
 
 
 
 
 
 
 D 
 ^ 
 
 
 a 
 
 
 
 
 
 
 0) 
 
 a. 
 
 
 
 
 
 «« 
 
 
 1 
 
 
 ^^-^H 
 
 
 
 -a 
 
 • •-« 
 
 
 
 
 
 3 
 
 DO 
 
 
 S 
 
 (4^ 
 
 
 
 
 
 a 
 
 >> 
 
 3 
 
 
 • 
 
 
 
 
 OS 
 
 
 
 
 
 
 s of Embrj 
 Larvse or 
 \secta, and 
 
 
 
 > 
 
 
 T3 
 
 
 
 
 
 
 +3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 -•J 
 
 OS 
 1 
 
 
 a 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CM 
 
 
 
 ► 
 
 
 
 P4 
 
 
 52; 
 
 w 
 
 ent of the Cellu] 
 Body." 
 
 
 
 Ah-S 
 
 - tD 
 
 
 
 m 
 
 
 ical Form, 
 
 1 the successive pi 
 orphis in the case 
 in some Crustacea 
 
 
 
 n of the matrix 
 'olfl&au Body.) 
 
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256 
 
 APPENDIX. 
 
 TABLE III. 
 
 PERIODS OF INTERPOLATION OF GEMMATION 
 IN THE GENETIC CYCLE 
 
 IN SEVERAL TRIBES OF PLANTS AND ANIMALS. 
 
 PROTOMOPvPHIC. 
 
 ORTHOMOSPHIC. 
 
 GAMOMORPHIC. 
 
 Mosses ife Hepaticse. 
 
 Plianerogamia 
 
 Ferns & Equiseta. 
 
 Echiiiodermata 
 (Polyzoa) 
 
 Trematoda 
 
 Cestoidea 
 
 (Aimelida) 
 
 Polypifera 
 Polyzoa 
 
 (Annelida) 
 Apliides 
 
 • 
 
 Polyi)ifera 
 
 Polyzoa 
 Salpjje 
 
 Cestoidea 
 
 Annelida (Syllis, 
 &c.) 
 
 Gemmation is exceptional in any stage among the higher Ar- 
 ticulata and Mollusca, and is unknown, as a normal arrangement, 
 among Yei-tebrata. 
 
APPENDIX. 
 
 2:. 7 
 
 TABLE IV. 
 RESTING PERIODS IN THE GENETIC CYCLE. 
 
 Mosses and Hepaticas } 
 protospores ) 
 
 Ferns and Eqiiiseta \ 
 gamospores ^ 
 
 In the middle of the Protomorphic 
 stage. 
 
 Between the Orthomoi'pliic and Ga- 
 momorphic. 
 
 Between the Protomorphic (einljr}'- 
 ogeny) and the Ortliomorphic (vege- 
 tation commencing with germina- 
 tion). 
 
 Coniferse present also another resting period, in the middle of 
 
 the Gamomorphic stage (during the 
 maturation of the fruit). 
 
 Phanerogamia 
 seeds 
 
 AnimalB in general, 
 eggs or ova, 
 
 Insects, Trematoda, 
 
 &C.J 
 
 Between the Gamomorphic (maturation 
 of the reproductive organs), and the 
 Protomorphic (embryogeny). 
 
 Have also a resting period (pupa or en- 
 cysted state) during their metamor- 
 phosis, in the early part of the Oi-tho- 
 morphic stage. 
 
 Mammalia have no obvious resting period, the mature ova re- 
 quiring immediate fecundation, which is at once followed 1>y seg- 
 mentation and the development of the embryo. 
 
 The bodies which, under the names of statoblasts, bulbs, restiiiff 
 spores, (fee. , perform the part of eggs or seeds in some species of 
 animals and plants, appear occasionally to be gemma?, which 
 may be termed accessory, as Ipng out of the direct genetic cycle. 
 
TABLE V. 
 
 Abstract of Dr. Sanderson's Table of the Analogies 
 
 Algfe, Fungi, 
 Liclieues. 
 
 SPOEOID BODY 
 
 Germination 
 
 Coiiferva,Mjcelium, 
 
 or Hypothallus 
 
 Hepaticae, Musci. 
 
 SPORE-CELL 
 
 G. into a 
 
 Filamentous Pro- 
 
 tonema 
 
 Filices, Equiseta. 
 
 SPORE-CELL 
 
 G. into an 
 
 Exosporous Pro- 
 
 tliaUium 
 
 Rliizocarpeffi. 
 
 MACROSPORE 
 
 G. into an 
 Endosporous Pro- 
 -( thallium 
 
 MICROSPORE 
 
 G. by the 
 
 protrusion of the 
 Inner Spore-coat 
 
 ThaUus 
 
 Frond or Leafy Stem 
 
 Protliallium 
 (Bi- sexual) 
 
 Protliallium 
 (Female) 
 
 Nuoule (of Cliara) 
 
 Archegonium 
 
 Archegonium 
 
 Arcliegonium 
 
 GERM-CELL 
 
 GERM-CELL 
 
 GERM-CELL 
 
 GERM-CELL 
 
 Glohule (of Chara) 
 
 Antheridiivin 
 
 Antheridium 
 
 Absent 
 
 SPERM ATI A, Sfc. 
 
 ANTHEROZOIDS 
 
 ANTHEROZOIDS 
 
 ANTHEROZOIDS 
 
 
 Division of Germ- 
 cell 
 
 D. of Germ-cell 
 
 D. of Germ- cell 
 
 • 
 
 
 From lower segment 
 
 Formation of 
 
 Formation of 
 
 
 Fruit-Stem 
 
 Embryo 
 
 Embryo 
 
 
 
 
 SPORE-BEAR- 
 ING PLANT 
 
 
 SPORE-BEAR- 
 ING STEM 
 
 SPORE-BEAR- 
 ING PLANT 
 
 Sporangium 
 Spore 
 
 
 Sporangium 
 
 Sporangium 
 
 
 
 
 Spore 
 
 Spore 
 
 and 
 
 Microspore 
 
TABLE V 
 
 in the Development of the Different Classes of Plants. 
 
 Lycopodiaceoo. 
 
 Gymuospermous 1 liaucro- 
 gamia. 
 
 AngiospennouH Phauero- 
 gaiiiiii. 
 
 MACROSPORE 
 
 ALBUMINOUS BODY 
 
 EMBllYO-SAC 
 
 G. into an 
 Endosporous Protliallium 
 
 
 
 MICROSPORE 
 
 POLLEN- CELL 
 
 POLLEN.CELL 
 
 G. ly the 
 X>rotrusion of the 
 Inner Spore-coat 
 
 G. by the 
 
 protrusion of the 
 Pollen -tube 
 
 G. hy the 
 
 protrusion of the 
 
 Pollen-tube 
 
 Protballinm 
 (Female) 
 
 Absent 
 
 Absent 
 
 Arcliegonium 
 
 Corpnsculnm 
 
 Absent 
 
 GERM-CELL 
 
 GERM-CELL 
 
 GERM-CELL 
 
 Absent 
 
 Abse7it 
 
 Absent 
 
 ANTHEROZOIDS 
 
 Absent [FOVILLA^ 
 
 Absent [FOriLLA'\ 
 
 D, of Germ-cell 
 
 D. of Germ -cell 
 
 D. of Genn-cell 
 
 From upper segment 
 
 From upper segment 
 
 From upper segment 
 
 Suspensor, 
 
 Suspensor, 
 
 Suspensor, 
 
 From lower segment 
 
 From lower segment 
 
 From lower segment 
 
 Embryo 
 
 Embryo 
 
 Emukyo 
 
 SPORE-BEARING 
 PLANT 
 
 OVULIFEROUS PLANT 
 
 OVULIFEROUS PLANT 
 
 Sporangium 
 
 Ovule 
 
 Ovulo 
 
 Spore 
 
 Albuminous Body 
 
 Embrvo-sac 
 
 also 
 
 ANTHERIFEROUS 
 PLANT 
 
 ANTIIERIFKROVS 
 PLANT 
 
 Microsporangium 
 
 Anther 
 
 Antlwr 
 
 Microspore 
 
 Pollen 
 
 Pollen 
 
260 APPENDIX. 
 
 In the foregoing Table the embryo-sac of the higher Phanero- 
 gamia is taken as representing the ' ' albuminous body" of the 
 Coniferse — or rather its wall, for its cellular contents would 
 answer more to the endosperm. Hofmeister farther considers 
 this body to represent the prothallium of the Crj^^togamia. 
 
 The view here adopted is distinct from both, regarding the 
 following as homologous plants : — ■ 
 
 1. The spore and the ovule. 
 
 2. The prothaUium and the ' ' albuminous body. " 
 
 3. The Archegonium, the Corpusculum, and the Embryo-sac. 
 In this view the endosperm is unrepresented in the Coniferoe 
 
 and Cryptogamia, and the prothaUium and ' ' albuminous body" 
 in the Angaospermese. 
 
 But the principal point, in which the relations represented in 
 this table differ from those advocated in the present work, is 
 the identification of the alternation of the Mosses with that of 
 the Ferns — as has been explained before at some length. 
 
 To make the points now referred to more intelligible I have 
 represented in a tabular form the relations here adopted, break- 
 ing up Dr. Sanderson's Table into three, for the sake of con- 
 venience, but keeping to his general arrangement, as much as 
 the necessary changes allow. In these tables, as well as in the 
 one just given, the male structures are printed in italics. 
 
APPENDIX. 
 
 2G1 
 
 TABLE VI. 
 
 TABLE OF THE ANALOGIES IN THE GENETIC CYCLE 
 OF THE LOWER CRYPTOGAMIA. 
 
 Structures. 
 
 Algiie, Fungi, Lichenes, (tc. 
 
 Hepatica', Musci. 
 
 Protopli}i:e 
 
 Compound Spore (Xenodochus) 
 
 Fruit-stem 
 
 Protospore 
 
 Uredo-spore (^Ecidium) 
 
 Spore 
 
 2d Protoplijiie 
 
 
 Protonema 
 
 Embryo 
 
 Mycelium 
 
 Nascent Mosa 
 
 Typical form 
 
 ThaUus 
 
 Moss-stem 
 
 
 PuUulation of Fronds 
 
 PuUul of Shoots 
 
 Matrix of Pe- ^ 
 productive > 
 
 Hymenium 
 
 Pericha-tium 
 
 organs ) 
 
 1 
 
 
 
 
 (F) 
 
 (M) 
 
 
 Gamospore 
 
 Secondary 
 Spores 
 
 Microrfonidia 
 (fEdogonium) 
 
 absent 
 
 Gamopliyi;e 
 
 Gynotliallium 
 (Ceramiura) 
 
 AndrothaUium 
 (CEdogonium) 
 
 abs 
 (F) 
 
 ent 
 (M) 
 
 Sex Capsule 
 
 Ascus (Fungus, 
 Lichen) 
 
 Nucule (Chara) 
 
 Sj^emiagonium 
 (Lichen) 
 
 Globule (Cliara) 
 
 Arche- 
 gonium 
 
 Anthc- 
 ridium 
 
 Sex Elements 
 
 True Spores 
 
 Sjycrmatla 
 
 Germ- 
 cell3 
 
 Anthe- 
 rozoida 
 
 
 F E C U N D A T I 
 
 ON. 
 
2G2 
 
 APPENDIX. 
 
 TABLE VII. 
 
 TABLE OF THE ANALOGIES IN THE GENETIC 
 
 Striictiires, 
 
 Protophyte .... 
 Protospore 
 
 Embryo 
 
 Typical Form 
 
 Filices, Equisetacese. 
 
 Matrix of the 
 Reproductive Organs 
 
 Gamospore 
 
 Gamopliyte 
 Sex Capsule 
 Sex Elements 
 
 .Suspensor 
 .absent 
 
 ...Embryo 
 
 Fern-stem and Fronds , 
 Pullulation of Shoots., 
 
 Sporangium 
 
 Spore germinating into a 
 
 (F) 
 Prothallium 
 Archegonium 
 Germ-cell 
 
 (M) 
 
 Protlialliuni 
 
 Antheridium 
 
 Cellules luith 
 Antherozoids 
 
 FECUNDATION. 
 
APPENDIX. 
 
 2C3 
 
 TABLE YII. 
 
 CYCLE OF THE HIGHER CRYPTOGAMIA. 
 
 Ehizocarpeje. 
 
 .Suspensor 
 .absent 
 
 .Embryo 
 
 .Leafy Axis 
 
 •Pullulation of Shoots 
 
 . Sporangmm 
 
 (F) 
 Maerospore 
 
 Prothallium 
 
 Archegonium 
 
 Germ-cell 
 
 (M) 
 
 Microspore 
 
 absent 
 absent 
 
 Cellules rvith 
 Antherotoids 
 
 Lycopodiaceae. 
 
 .Suspensor 
 .ab.seut 
 
 .Embryo 
 
 .Leafy Axis 
 
 .Pul. of Shoots and Spikes 
 
 (F) 
 
 (M) 
 
 .Oophoridium A ndrospo- 
 rcuKjiiini 
 
 Maerospore ' Microsjiore 
 
 Prothallium 
 
 absent 
 
 Archeiionium ' absent 
 
 Germ -cell 
 FECUNDATION. 
 
 CeUuhs tHfh 
 AntherozouU 
 
26i 
 
 APPE^'DIX. 
 
 TABLE VIII. 
 
 TABLE OF ANALOGIES IN THE GENETIC CYCLE 
 OF THE PHANEROGAMIA. 
 
 Structures. 
 
 Gymnosperm eae. 
 
 Angiospermeae. 
 
 Protoj^hyte . . 
 Protospore ... 
 
 . . . Suspensor 
 
 ...Suspensor 
 
 ...Absent 
 
 ...Absent 
 
 Embryo 
 
 Embryo 
 
 Embryo 
 
 TyiAcal Form 
 
 Female and 
 
 Male Plants 
 
 Female and 
 
 Male Plants 
 
 
 Pullulation 
 
 of Leaf- 
 shoots 
 
 PuUulation 
 
 of Leaf- 
 shoots 
 
 Matrix of the 
 Reproductive 
 
 Ovuliferous 
 Flower 
 
 Antherif. 
 Floiver 
 
 Ovuliferous 
 Flower 
 
 Antherif. 
 Flower 
 
 Organs 
 
 
 
 
 
 Gamospore 
 
 Ovule 
 
 Anther 
 
 Ovule 
 
 Anther 
 
 Gamoph}i;e 
 
 Albuminous 
 body 
 
 Pollen- 
 grain 
 
 Absent 
 
 Pollen- 
 grain 
 
 Sex Capsule 
 
 Corpus- 
 culum 
 
 Pollen-tuhe 
 
 Embryo-sac 
 
 Pollen-tuhe 
 
 Sex Elements 
 
 Germ-cell 
 
 Cellules with 
 Fovilla 
 
 Germ-cell 
 
 Fovilla 
 
 
 FECUNL 
 
 >ATION. 
 
APPENDIX. SfJ.') 
 
 The three foregoing Tables (VI., VII., VIII.,) are in ru)>- 
 stance the same as Tab. I., but the differences in arrangement 
 allow some points to be brought out more clearly — such a.s the 
 extent to which the sexual characters affect the sequence of foruu*. 
 Omitting the Thallogenous group — of which our knowledge in 
 still too fragmentary and conjectural to allow us to gcnerahze 
 upon it — there will be seen to be a progressive increase iii tlie 
 extent of the genetic cycle, over which this influence prevails, a-s 
 we rise from the lower Cryptogamia to the Phanerogam ia, and 
 especially to the dioecious species of the latter. The dilierence of 
 manifestation is even greater than can be measured in this way, 
 as the sexual characters of tlie lower forms are not only more 
 limited in extent, but also of a less apparent kind — fully justify- 
 ing the expressive term given by Linnjeus to the lower of the two 
 great divisions of the Vegetable Creation. 
 
 GENETIC CYCLE IN ANIMALS. 
 
 For the Animal Kingdom, on account of the great variety in 
 the Genetic Cycle, it would be difficult to construct convenient 
 and manageable tables arranged in parallel columns like the fore- 
 going, but I have appended in their stead tabular views of the 
 sequence of development in the families which are of most in- 
 terest in respect of their mode of propagation. 
 
 In the following Tables (IX. -XVIII.), the division into 
 columns indicates the existence of sexual distinctions in that 
 part of the cycle where it occurs — the left-hand column giving 
 the spermatic, and the right, the germinal structures. Unless 
 contra-indicated by the punctuation, the reading is to be carried 
 across the page. The horizontal lines indicate a breach in the 
 continuity of structure. This may sometimes affect only one 
 sex, as in the detachment of the spermatozoa of animals gene- 
 rally, while the ovum is commonly impregnated, and often 
 incubated, within the body of the female. 
 
 Brackets are used to imply that the parts or processes men- 
 tioned are only of occasional occurrence in the group. 
 
 N 
 
26o APPENDIX. 
 
 TABLE IX. 
 GENETIC CYCLE OF THE POLYPIFERA. 
 
 mOTOMOPvPHIG STAGS, 
 
 (merged in the following). 
 The ciliated Germ — (planula). 
 
 ORTHOMORPHIC STAGE. 
 
 The Tohjj>e. 
 [The Ramifications of the Zoophyte]. 
 The gemmiparous Vesicles [gonopJwres of Allman]. 
 
 GAMOMORPHIC STAGE. 
 
 Mednsoids or Sporosacs, 
 [and Secondary Medusoids and Sporosacs budded off from these,] 
 (male and female.) 
 
 Spermatic, and Ovigerons Sacs. 
 
 Primary Sperm Cell ? The Ovnm (unwalled). 
 
 Special S]perm Cells ? "^ ( The Germinal vesicle 
 and Spermatozoa. 3 I and Macula. 
 
 FECUNDATION. 
 
APPENDIX. i*»;7 
 
 TABLE X. 
 
 GENETIC CYCLE OF THE ECHINODERMATA. 
 
 PROTOMOPHIC STAGE. 
 
 The ciliated Germ, passing into the condition of au Anrun- 
 
 laria, Bipinnaria, or Plutetts. 
 
 ORTHOMORPHIC STAGE. 
 
 The Echinodcnn, 
 (male and female). 
 
 GAMOMORPniC STAGE, 
 
 (merged in the foregoing). 
 Spermary, Ovary. 
 
 Primary Sperm Cell, Ovum. 
 
 Special Sperm Cells ) (The Germinal Vesicle, 
 and Spermatozoa. ) { and Macula. 
 
 FECUNDATION. 
 
 TABLE XL 
 GENETIC CYCLE OF THE POLYZOA. 
 
 PROTOMORPHIC STAGE, 
 
 (merged in the following). 
 The ciliated Germ. 
 
 ORTHOMORPHIC STAGE. 
 
 Double Polype-embryo. 
 Polypes. 
 Ramose Zoophyte — monoecious or dicecion.n ; 
 with male and female polj-pe.s. 
 
 GAMOMORPHIC STAGE, 
 
 (merged in the foregoing). 
 Spermary, Ovary. 
 
 Primar}^ Sperm Ccl], Ovum. 
 
 Special Sperm Cells ) C he Germinal vesicle 
 and Spermatozoa. 3 ^ and IMacula. 
 
 FECUNDATION. 
 
268 APPENDIX. 
 
 TABLE XII. 
 GENETIC CYCLE OF THE SALP^. 
 
 PROTOMORPHIC STAGE, 
 
 (merged in the following). 
 The primordial Germ-mass. 
 
 ORTHOMORPHIC STAGE. 
 
 The Embryo, transformed into 
 
 The solitary Salpa. 
 
 GAMOMORPHIC STAGE. 
 
 Catenated SalpcB. 
 
 Spermary, Ovary. 
 
 Primary Sperm Cell, Ovum. 
 
 Special Sperm Cells "^ ( Germinal Vesicle 
 and Spermatozoa, j ( and Macula. 
 
 FECUNDATION. 
 
 TABLE XIII. 
 GENETIC CYCLE OF THE TREMATODA. 
 
 PPOTOMORPHIC STAGE. 
 
 The Infusorial Germ. 
 The primary Gregariniform Zooid (Bedia or Sporocyst. ) 
 
 [The secondary Gregariniform Zooid]. 
 
 ORTHOMORPHIC STAGE. 
 
 Cercaria, penetrating into the tissues of animals. 
 
 The same encysted, 
 
 And then metamorphosed into a Distoma. 
 
 GAMOMORPHIC STAGE, 
 
 (distinguished from the former by the acquisition of sexual organs). 
 Spermary, Ovary. 
 
 Primary Sperm Cell, Ovum. 
 
 Special Sperm CeUs \ ( Germinal Vesicle 
 and Spermatozoa. ) \ and Macula. 
 
 FECUNDATION. 
 
APPENDIX. -2 no 
 
 TABLE XIV. 
 GENETIC CYCLE OF THE CESTOIDEA. 
 
 PROTOMORFHIO STAGE. 
 
 The six-hooked Germ, penetrating into the tissues and converti-d 
 into a cyst, which becomes 
 
 The Cysticercus, or the primary Eclihvococais-vcsirU'. 
 [Secondary and subsequent Echinococc'i]. 
 
 ORTHOMORPHIC STAGE. 
 
 T^enia-liead (Sc(Acx). 
 
 GAMOMORPHIC STAGE. 
 
 Cucurbitiform Proglottides. 
 
 Spermary, Ovary. 
 
 Primary Sperm Cell, Ovum. 
 
 Special Sperm Cells ") ( The Germinal Vesicle 
 and Spermatozoa, j \ and Macula. 
 
 FECUNDATION. 
 
 TABLE XV. 
 GENETIC CYCLE OF ANNELIDA 
 
 PROTOMORPHIC STAGE. 
 
 The ciliated Germ, which is converted into 
 The Head-segment. 
 
 ORTHOMORPHIC PHASE. 
 
 Segments of the Body of the Annelidaii. 
 
 Caudal Zooids [of SijUis, dr. ] 
 Male and Female. 
 
 Spermary, Ovary. 
 
 Primary Sperm Cells, Ovum. 
 
 Special Sperm Cells ] ( Gcnuinal Vesicle 
 and Spermatozoa, j I and Macula. 
 
 FECUNDATION. 
 
270 APPENDIX. 
 
 TABLE XVI. 
 GENETIC CYLE OF THE ARTICULATA GENERALLY 
 
 PROTOMORPHIC STAGE, 
 
 (merged in the following). 
 The Germinal Mass. 
 
 ORTHOMORPHIC STAGE: 
 
 The Embryo, 
 [passing through the conditions of Larva and Pupa . ] 
 Imago or perfect form, 
 Male and Female, 
 
 GAMOMORPHIC STAGE, 
 
 (merged in the foregoing). 
 Spermary, Ovary. 
 
 Primary Sperm Cell, Ovum. 
 
 Special Sperm Cells | f Germinal Vesicle 
 and Spermatozoa, j \ and Macula. 
 
 FECUNDATION. 
 
 TABLE XVII. 
 GENETIC CYCLE OF THE APHIDES. 
 
 PROTOMORPHIC STAGE, 
 
 (merged in the following). 
 The Germinal Mass. 
 
 ORTHOMORPHIC STAGE. 
 
 The Embryo, extruded from the Egg as a 
 Hexapod Larva. 
 
 Repeated pulhdations of other like Lar^'^f^. 
 
 Larvae at the close of the series passing into 
 Perfect Insects, 
 (Male and | Female). 
 
 GAMOMORPHIC STAGE, 
 
 (merged in the foregoing). 
 
 Spermary, j Ovary. 
 
 Primary Sperm Cells, Ovum. 
 
 Special Sperm Cells ) ( Germinal Vesicle 
 
 and Spermatozoa, j \ and Macula. 
 
 FECUNDATION. 
 
APPENDIX. t>71 
 
 TABLE XVIII. 
 
 GENETIC CYCLE OF THE HIGHER ANIMALS 
 GENERALLY, IN THE NON-ALTERNATING SPECIKS 
 
 PROTOMORPHIC STAGE, 
 
 (merged in the following). 
 The Germinal Mass. 
 
 ORTHOMORPHIC STAGE. 
 
 The Embryo, passing into 
 The T^qiical Form, 
 Male and j Female. 
 
 G AMOMORPHIC* STAG E, 
 
 (merged iu the foregoing). 
 Spermary, Ovary. 
 
 Primary Sperm Cell, Ovum. 
 
 Special Sperm Cells ) f Germinal Vesicle 
 and Spermatozoa. ) ( and Macula. 
 
 FECUNDATION. 
 
 I 
 
PLATE /. BATmi'L/VrMV OF ALffjE AND FMGl. 
 
 FIG.1 
 
EXPLANATION OF THE PLATES. 
 
 Plate L — Reproduction in ALOiE and Fungi. 
 
 Figs. 1 and 2. —Filamentous Algae in conjugation, (p. 23) after 
 Smith. In Fig. 1, ( ATesocarjms, ) the endoohrome of both the 
 conjugating cells is evacuated into the comiecting tube formed 
 by the fusion of their papillary outgrowi^hs, and tlie spore i» 
 matured in the same place ; in Fig. 2, only one of the conjugat- 
 ing cells evacuates its contents, which are received into the 
 other, where the spore is formed from the fusion of the two 
 endochromes. In this figure conjugation is sliown between the 
 ceUs of distinct filaments, as well as between two adjoining cells 
 of the same filament — a circumstance showing, j\s Mr. Smith 
 remarks (Trans. Microsc. Soc, II. 70), that the importance of 
 variations in this respect, as distinctive characters, has been 
 over-rated by some NaturaHsts. 
 
 Fig. 3 (from RaKs) shows the process of conjugation in the 
 Desmidieee (Clostermm acerosum). The evacuation of the cells 
 takes place by the separation of their valves, and the spore is 
 formed, as in Mesocarpus, midway between the cells. 
 
 Fig. 4 (also from Ralfs) represents a process of endogenous 
 multiplication in the germination of the spore of ClosUrium 
 
 (p. 27). 
 
 Figs. 5 and 6 (Eunotia turgida, from Thwaites), ilhistrato the 
 process of conjugation in the Diatomacea?, in wliich the effused 
 endochromes are resolved either at once, or at a very early 
 l>eriod, into two spore-masses, which are ultimately trans- 
 formed into frustules of a much larger size than their i)ari^uts. 
 The genetic cycle is supposed to be completed l>y their breaking 
 up into frustules, Uke those originally concerned in the process 
 
 of conjugation (p. 28). 
 
 
 
274 EXPLANATIOIT OF THE PLATES. 
 
 Fig. 7. — Ciliated zoospore or motile gemma of (Edogonium 
 vesicatum. 
 
 Fig. 8. — The same in germination. Having lost its crown of 
 cilia, it has begun to emit radical filaments from its base (p. 32). 
 (Both from Thuret). 
 
 Figs 9 and 10 (from Thwaites and Berkeley), illustrate repro- 
 duction by androspores, or minute phji;oids, formed by the ger- 
 mination of a kind of zoospores, and consisting of a pedicle and 
 two antheridial cells, containing each a single antherozoid. 
 In Fig 9, a filament of (Edogonium is shown, with several an- 
 drospores, and in Fig. 10, a similar body is seen attached to a 
 spore cell of Bulboclicete crassa — (p. 33). 
 
 Fig. 11. — Reproduction in Vaucheria (from Pringsheim) ; a, 
 the " hornlet," or antheridium ; 6, the sporangium, both at 
 first diverticula of the general cavity of the filament, but after- 
 ward shut oS" so as to form distinct cells ; c, micropyle or ter- 
 minal pore in the sporangium, by which the antherozoids gain 
 access, when liberated by the dehiscence of the point of the horn- 
 let. The germinal body is at first covered only by a layer of 
 mucus, penetrable by the spermatic particles, but after impreg- 
 nation, this becomes consolidated into the proper coat of the 
 spore — (p. 34). 
 
 Fig. 12. — Reproductive organs of Sporoclinus A driaticihs (from 
 Kutzing), illustrating the arrangement in the higher Algse. — a, 
 antheridial filament ; 6, sporangium. These parts are more 
 generally separated, and are frequently situated on difierent 
 plants — (p. 36). 
 
 Fig. 13. — Antherozoid of Fucus vesiculosus (from Thuret) — 
 (p. 32.) 
 
 Fig. 14. (from Berkeley). — Part of the hymenium of Agaricus 
 velutinus, illustrating the acrogenous fructification of the higher 
 Fungi, a, basidium, with four stalked spores on its summit — 
 (p. 42-45). 
 
 Fig. 15. (after Currey). — Compound spore of Phragmidium 
 hnlhosum in germination, showing the production of threads of 
 mycelium from each of the compartments into which it has be- 
 come divided, and the secondary spores formed on these fila- 
 ments in the acrogenous way — (p. 44). 
 
EXPLANATION OF THE PLATES. 275 
 
 Plate II. — Reproduction in the other Cryptogamic Orders. 
 
 Fig. I. — One of the valves of the globule of Chara fragilis 
 (from Berkeley). 6, cells forming the valve, radiating from the 
 summit of the supporting cell or pedicle, a ; c, bases of other 
 pedicles springing from the summit of the central stalk of the 
 globule ; d, one of the tuft of articulated tubules, which spring 
 from the same point, each of the articulations developing a bi- 
 cilated spermatic filament. — (p. 39). 
 
 Fig. 2. — Section of a part of the frond of Sticta pulmonaria 
 (after Tulasne), showing spermagonia a, b — the latter empty — 
 and an apothecium c. 
 
 Fig. 3. — Section of part of an apothecium oi Lecidea luguhris, 
 (after Lindsay,) showing immature asci at a ; and asci with- 
 eight mature spores at h; sterile filaments or paraphyses at c; the 
 subjacent layer of gonidia at d; and the hypothallus or stratum 
 of mycelial filaments at e — (p. 48). 
 
 Fig. 4. — Germination of a Moss (Funaria hygrometrica. ) a 
 protonemic filaments, the first outgrowths from the spore ; c, a 
 nascent moss-bud ; d, another bud which has begun to develope 
 a leafy axis, and to emit below radical filaments b. — (from 
 Schimper). 
 
 Fig. 5. — Perpendicular section of the monoecious fructifica- 
 tion of a Moss (Phascum cuspidatum from Hof meister), showing 
 antheridia at a, and archegonia at b, both intermixed with ar- 
 ticulated filaments or paraphyses — (p. 50). 
 
 Fig. 6. — Antheridium of a Moss, emitting the cellules which 
 contain the motile filaments. 
 
 Fig. 7. — The Antherozoid of a Moss coiled up in its cellule. 
 It is a long simple filament, with one extremity enlarged, and 
 the other tapering away to a fine point. 
 
 jTjg^ 8. — An antherozoid of Pellia (from Thuret). 
 
 jTjg^ 9, — Archegonium of Jungermannia bivaricata (from Hof- 
 meister) showing the central corpuscule and the styloid canal 
 formed of four columns of cells. At its outer extremity are re- 
 presented antherozoids, free and in cellules. 
 
 Yi(r, 10. — Capsule of P olytriclmm (ironi Balfour), showing the 
 veil, which is derived from the upper wall of the archegonium, 
 
 o 2 
 
276 EXPLANATION OF THE PLATES. 
 
 calyptra or wliile the fruit-stalk, capsule, lid, and contained 
 six>res, are all developed out of the germinal corpuscle, which 
 occupied its central cavity. 
 
 Fig. 11. — Section of the germinating spore of Pilularia (after 
 Hofmeister). At the lower part of the figure are seen the nu- 
 cleus and two coats of the spore. The pyramidal body at the top 
 is the prothallium, a structure of later growth, here represented 
 as protruding through the micropyle. The section shows an 
 archegonial cavity in its interior — (pp. 57, 183). 
 
 Fig. 12 and 13 (after Suminski) illustrate the process of ger- 
 mination in Ferns — (p. 52, 183). Fig. 12. — ^A tetrahedral fem- 
 sj)ore. 
 
 Fig. 13. — Prothallium or cellular outgrowth from the spore 
 (Pteris serrulata). a, remains of the spore ; 6, radical filaments ; 
 e, antheridial cells containing cellules with ciliated filaments in 
 their interior ; d, archegonia. 
 
 Fig. 14. Shows the connection of a young Fern (Pteris 
 paleacea) developed from the archegonial corpuscule, with its 
 prothallial matrix. 
 
I 
 
nATL ///. FHANEROGAM/C JiEPBODLfCTION. 
 
 ANIMAL OVUM. 
 
EXPLANATION OF THE PLATES. 277 
 
 Plate III. — Embryogeny in Phanerogamic Plantb. 
 
 Figs. 1-4 (from Hofmeister) illustrate the process in the Coni- 
 ferae (pp. 57, 183). 
 
 Fig. 1. — A section of the naked ovule of Pimis sylvestrie in 
 the spring of the year after impregnation. In the niicropyle at 
 c are seen two poUen grains, with theii* tubes turned in the direc- 
 tion of the internal cellular mass b, going under the name of 
 the alhumhwus body, and corresi)onding to the prothallium of 
 the higher Cryptogamia. 
 
 Fig. 2. — Part of a similar section of the ovule of Pinus 
 Strobios, in early summer ; a upper part of the nucleus, which 
 the pollen-tube, after a long period of inaction, has now netirly 
 traversed, in its way to impinge on the wall of the albuminous 
 body b, immediately over one of the clusters of flask-shaped 
 cavities or corpuscula d, which have just been formed in tliat 
 body, and which seem to correspond to the archegonia of the 
 higher Cryptogamia on the one hand, and to the embryo-sacs of 
 the majority of the Phanerogamia on the other. 
 
 Fig. 3. — A magnified view of a corpusculum of Pinus ^ijlvts- 
 tiis, showing at e the germinal particle which is developed into 
 the embryonic structures on impregnation, and, at ti, two of 
 the four cells which represent the canal of the archegonium — b 
 tissue of the nucleus, c cellular contents of the corpusculum. 
 
 Fig. 4 illustrates the result of impregnation, in the formation 
 of a cluster of four pro-embryos, three of which have been cut 
 away near the base ; b proper embryo formed by a new process 
 of cell formation at the lower extremity of the suspensor o. 
 (Pinus Strobus). 
 
 Figs. 5-8 illustrate the same process in the Angiospernions 
 Phanerogamia — (p. 61). 
 
 Fig. 5 (from Schleiden) shows the emission of tubules by tlie 
 pollen grains, and their penetration through the conducting cel- 
 lular tissue of the style. 
 
 Fig. 6.— Section of an ovule of Polygonum divaricaiumy (from 
 Schieiden) showing the seed-coats, the micropyle c, and the 
 nucleus a, with its large embryo-sac 6. 
 
 FicT. 7.— Ovule of CEnotli^ra (from Hofmeister), showing 
 
278 EXPLANATION OF THE PLATES. 
 
 a pollen tube d, passing down from tlie micropyle c, through 
 the tissue of the nucleus a, to the enibryosac 6, whose summit is 
 occupied by protoplasmic masses e, one of which on impregna- 
 tion developes the embryo. 
 
 Fig 8. — Embryogeny of Orchis Morio (from Henfrey), a the 
 pro-embryo formed from the upper of the two cells, into which 
 the germinal body divides on impregnation, but, unlike the 
 suspensor of the Coniferse, growing upwards into a blind fila- 
 ment, which projects through the micropyle ; h the true embryo, 
 produced by the sub-division of the lower of the two primary 
 cells. 
 
 Animal Embryogeny. 
 
 Fig 9. — Part of the egg of Musca vomitoria (from Meissner), 
 showing the micropyle occupied by a cluster of spermatozoa — 
 (pp. 69-70). 
 
 Fig. 10. — Ovum of Unio (from Hossling), in which the aper- 
 ture of the hollow pedicle serves the purpose of a micropyle — 
 (pp. 69.70). 
 
 Figs. 11-13. — Successive stages of the cleavage of the yolk, 
 after impregnation in the Mammalian ovum (from Kirkes) — 
 (p. 72). 
 
Plate IV. — Eeproduction in Polypifera and 
 
 ECHINODERMATA. 
 
280 EXPLANATION OF THE PLATES. 
 
 Plate IV, — Reproduction in Polypifera and 
 
 ECHESrODERMATA. 
 
 Fig. 1. — Hydra vhidis (from Thomson), showing sexual organs 
 of both kinds and of very simple structure ; a spermatic capsule, 
 & ovarian cyst containing a single ovum — (pp. 120-124). 
 
 Fig. 2. — Reproductive organs of Campanularia Loveni (from 
 Steenstrup, after Loven). The ovigerous capsule or gonophore 
 is surmounted by two sessile sporosacs or meconidia, a, b, more 
 complicated in structure, and more approaching to the organiza- 
 tion of free medusoids — a immature sporosac containing two 
 ova ; b sporosac discharging the young in the guise of ciliated 
 infusorians — (p. 123). 
 
 Fig. 3. — ^Another species of Campanularia, detaching free 
 medusoids (from Desor) — a polype-cell, b immature gonophore, 
 c gonophore discharging free medusoids d. 
 
 Fig. 4. — Medusoidof C. gelati7iosa{irom.'Beiieden) — « umbrella, 
 
 b manubrium, c marginal tentacles. — (p. 122). 
 
 Fig. 5. — Infusorian zooid from the ovum of a MedA'sa — 
 (pp. 120-126). 
 
 Fig. 6. — Hydraform phase of a Medusa — {Scyiyhistomci. of 
 Sars — Hydra Tuba of Dalzell.) 
 
 Fig. 7. — Hydraform stock detaching from its summit a pile of 
 nascent Medusae, (from Dalzell). 
 
 Fig. 8. — B'ipinnaria or precursory zooid of a starfish (from 
 Miiller) — (pp. 85,162). At the upper extremity is seen the 
 rudiment of the starfish. The zooid has a mouth and vent of 
 its own, a, 6, but internally its alimentary canal becomes con- 
 tinuous with that of the Echinoderm. 
 
 Fig. 9. — Plutens or precursory zooid of an Ophiura — (from 
 Miiller) — at a is seen the rudiment of the young Echinoderm, 
 with a distinct mouth of its own in the centre of the disc. 
 
FLAIEIV. HEFROnUCrm IN mYFJFFBA MD i:cmmDERMA7'A 
 
PLATE V. 
 
 ALTEIIITATIOI/ IN TM ENTOZOA 
 
 FIG. 6. 
 
 FIG. 7. 
 
EXPLANATION OF THE PLATES. 1>M 
 
 Plate V.— Altehnation in the Extozoa, <kc. 
 
 Figs. 1-3 illustrate tlio successive pliasos in the dovolopim-ut 
 of the Tapeworm— (pp. 9G, 131, IGl). 
 
 Fig. 1.— The egg of a species of Tapewonji, T(rtn4i PUtHlum, 
 (from Dujardiij), \\ith its six-hooked contractile enil)r}'o. 
 
 Fig. 2. — The Cysticenis (from Bremser), now known to l>e tlu- 
 cystic phase of the Tcenia Solium ; a the head, formed originiilly 
 within the cyst b, and then extruded by the evagination of it« 
 hollow pedicle or neck. In tlie farther development within the 
 alimentary canal, the cyst is throwai off, and the neck extended, 
 by the gemmation and multipHcation of its joints, into the long 
 body of the Tapeworm. 
 
 Fig. 3. — Ultimate development of the Tttnia risfillnm of the 
 Shrew (from Dujardin) — a, the head ; b, the neck, formed of un- 
 developed segments ; c, the body, formed of segments which 
 iiave acquired their full size, and become filled with ova. 
 
 Figs. 4-7 illustrate the development of the Echhiococcus ur 
 Hydatid— (p. 131). 
 
 Fig. 4. — A diagram of the simple Hydatid cyst — (EchiiU)CoccHs 
 scolicipariens) — the first result of the transformation of the con- 
 tractile vesicle discharged from the egg of a minute species of 
 TcBnia. Derivative Taenia-buds are represented in the course of 
 development from the interior of the cyst — (p. 131). 
 
 Fig. 5. — A diagram of the compound Hydatid {Echiiwcoccuif 
 altricipariens)^ resulting from the intermediate gemmation of 
 secondary cysts, prior to the formation of proper Tfenia-buds. 
 
 Fig. 6. — A Tsenia-bud, with its denticulated head a in proce.';s 
 of development, on an invagination of the wall of the cystic poi-- 
 tion b ; c pedicle of attachment to the parent cyst. 
 
 Fig. 7. — A fully-formed Tsenia-bud, with its head everted 
 (both from Wilson). 
 
 Figs. 8-11 (mostly from Steenstrup) illustrate the successive 
 forms in the alternation of the Trematoda — (pp. 95, 112). 
 
 Fig. 8. — Egg of Mo'Tiostomiim mutabile (from Siebold) with its 
 infusorian embryo. 
 
 Fig. 9. — Redia or intermediate form of Distoma, derived from 
 the infusorian, and forming in its owii interior an agamic brood of 
 
 3 
 
/ 
 
 282 EXPLANATION OF THE PLATES. 
 
 Cercarice : a oesophogeal csecum, or rudiment of an alimentary. 
 canal. This is really the second of the redial forms figured by 
 Steenstrup. 
 
 Fig 10, — Cercaria, or larva form of the Distovna, being one of 
 the brood figured in the last. 
 
 Fig. 11. — Ultimate form of Distom,a, produced by a transfor- 
 mation of the last during its stage of encystment. 
 
 Fig, 12, — Myrianida fasciata from M, Edwards — showing the 
 formation of caudal zooids, as described at page 101. 
 
-*«• 
 
 I 
 
PL A TE vl. ALTERNATION IN MOTLUSCA AND MTICIITATA . 
 FIG.I X. ^. FIG 
 
EXPLANATION OF THE PLATES. 2KI 
 
 Plate YI. — Alternation in Mollusca xnd Autk-tlata. 
 
 Figs. 1-4. (from Allman) illustrate the eiubryogcny of the 
 Polyzoa(p.p. 88, 160.) 
 
 Fig. 1. — Ovum of Alcyonella fungosa, containing an embryo in 
 an early stage, with the rudiment of a single polype ; a, ciliat^-d 
 coat of the embryo ; h, protrusible non-ciliated portion ; f, uas- 
 cent polype. 
 
 Fig. 2. — The same, farther advanced Avith the rudimeni^ «-i 
 two polypes c. d. 
 
 Fig 3. — The same, still farther advanced, with botli polyjtt^ 
 fully formed. 
 
 Fig. 4. — A polypidom of Loplwjyns crystallinuSy containing 
 wo polypes. This is altered from Professor Allman'H figure, no 
 far as to show one of the polypes exserted. 
 
 Figs. 5 and 6 (from Sars) illustrate the alternation of the 
 Salpce^i-p-p. 90, 140). 
 
 Fig. 5. — A "solitary" Salpa, possessing no organs of sex, but 
 budding off from a sort of internal stolon, connected with the 
 nucleus a, a pile of sexual zooids h. 
 
 Fig. 6. — Pile of zooids more enlarged ; a, the first fonned por- 
 tion of the pile, composed of well developed zooids, and now 
 ready to break oflf as a Salpa-chain ; b, middle portion of lew* 
 advanced zooids ; c, last formed portion, in which the segments 
 have not yet acquired proper organization ; d, point of origin 
 from tlie nucleus. 
 
 Fig. 7. — An Ovum (of Eolis ?), which, after undergoing th«' 
 usual segmentation, has divided into four lobes, as if for th»- 
 development of as many distinct embryos — (p. ItiO n.) 
 
 Figs. 8-10 (from Nordmann) illustrate the metamorithosih i.f 
 the Lernean Crustacea — (p. 172). 
 
 Yig. 8. — Larva of Achtheres, a parasite on the Perch. 
 
 Figs. 9 and 10. — The fully-developed male and female of tht- 
 same — the latter acquiring a much greater proportionate hiie. 
 Here the abdominal region, a, developed in the c(»urse of the me- 
 tamorphosis, may be considered as a gamomorphic structure for 
 the evolution of the organs of reproduction. In the female, 
 
284 EXPLANATION OF THE PLATES. 
 
 besides the large external egg-sacs, h, the dissection in fig. 10 
 shows the cavity of the abdomen to be mainly occupied by the 
 voluminous internal ovaries. 
 
INDEX. 
 
 Pago. 
 Acineta-forms - - 80 
 
 Achlya, Reproduction - SI 
 
 Algoid or fungoid nature 47 
 
 Adventitious organization of 
 
 zooids - - 175 
 
 JEcidium, Reproduction - 43 
 
 Affinities in relation to Alter- 
 nation - - 219 
 Agamic eggs - - 191-, 198 
 Agamozooid - ■ 136, 2 17 
 Albuminous body - 58, 183 
 Alcippe, Defective Organization 176 
 Algse, Reproduction - 20, 37 
 Varieties of Gemmae - 222 
 AlLman, Prof., Organs of 
 
 Hydrozoa - 122, 124, 148 
 
 Development of the Polyzoa 160 
 
 Reproduction of the Polyzoa 170 
 
 Allopbytoids and Allozooids 152 
 
 Alternation of Geminations 221 
 
 Alternation of Generations 11, 212 
 
 Varieties of - 12, 19, 109, 136 
 
 Formula? of - - 216 
 
 Contrast in Plants and 
 
 Animals - - 107 
 
 Concurrence of varieties in 
 
 tlie same species 131, 137, 219 
 Representation in the higher 
 
 species - 109, 144, 157 
 
 Simulation of - - 221 
 
 Casual - - 221 
 
 Ambiguities of Nomenclature 
 
 126/1, 132, 153 n, 227 
 Analogies in Vegetable Ro- 
 
 production, Tables 258, 264 
 Androspore - - 33 
 
 Angiospermous Phanerogaraia, 
 
 Reproduction - 61 
 
 Animals, Survey of Roprodoction 68 
 
 Tabular views - 254, 265, 271 
 Annelida, Reproduction • 99 
 
 Altcniation - - 137 
 
 Tabular view - - 269 
 
 Antheridium - 33, 36, 5<.» 
 
 Autherozoids - 32, 5() 
 
 Access of - • 34, 63 n 
 
 Ants, Metamori)ho8i8 - 105 
 
 Neuters - - 168 
 
 Aphis, Reproduction 15, 133, 119 
 
 Nature of germs - 191 
 
 Tabular ^^ew • 270 
 
 AjyiSy sec Boc. 
 
 Apothecium of Lichen -W 
 
 Ajyus, Absence of Mules -<'6 
 
 Archegouiuni - - 21 
 
 Of Moss . - 60 
 
 Homologue of the Kmbryo-wc 181 
 Argonauta, Ilectocotylua 179 n 
 
 Articuluta, Roproduction 102 
 
 Tabular view - 27o 
 
 A.'icaris, Iuij)regnntion - 69 
 
 Genniuol Development 71 
 
286 
 
 INDEX. 
 
 Page. 
 Ascidia, Metamorpliosis - 91 
 
 Ascomycetes, Reproduction 42 
 
 Ascospore - - 42 
 
 Ascus of Fungus and Lichen 42 
 Asexual Reproduction - 9 
 
 Asplanchna, Defective Or- 
 ganization - - 176 
 Asteracanthion, Reproduction 84 
 Asteridae - - 85 
 Atavism - - 222 
 Auricularia - - 85 
 Baird, Reproduction of Ento- 
 
 mostraca - - 195 
 
 Balbiani, Reproduction of In- 
 fusoria - - 77 
 Bark-lice, Reproduction - 193 
 Barry, Dr. M., Penetration of 
 
 Spermatozoa - 69 n 
 
 Bary, Reproduction of Fungi 46 
 
 Vegetable Impregnation 62 
 
 Basidium of Fungus - 42, 45 
 Batraeliia, Penetration of 
 Spermatozoa 
 Cleavage of Ovum 
 Bee, Neuters - - 105, 168 
 
 Drone Ova - - 196 
 
 Protracted fertility of tlie Queen 204 
 Beneden, Prof. Van, Nomen- 
 clature - - 9 ir, 132 
 Reproduction of Trematoda 95 
 Of Cestoidea - 98 
 Berkeley, Rev. M. T., Mor- 
 phology of Chara - 88 
 Reproduction of Fungi 40, 46 
 Bipinnaria of Starfish. - 85 
 Birds' Ovum - - 73 
 Birth in relation to other epochs 107 
 Bisexual arrangement - 241 
 BischofF, Penetration of Sper- 
 matozoa - - 69 w 
 Blastostyle - - 125 
 
 70 n 
 203 
 
 Page. 
 Bothriocephalus, Development 162 
 
 Botryllida, Reproduction 141 
 
 Bovista, Fructification - • 45 
 Braun, Prof., Conjugation 26, 27, 35 
 PuUulation - - 149 
 
 Vegetable Parthenogenesis 199 
 Brightv^eU, Organization of 
 
 Asplobnclma - 176 
 
 Bryozoa, Bryozoaria, see Polyzoa. 
 Bulhochcete, Reproduction 33, 34 
 Bulbs, Deciduous - 154 
 
 Burnett, Dr. W., Heterogony 
 
 of Synapta . - 93 
 
 Germs of Ax)liis - 191 
 
 Calycophoridse, Gemmae, and 
 
 Medusoids 83, 118, 124 
 
 Carpenter, Prof.,Embiyogeny 
 
 of MoUusca . - 91, 92 
 
 Metamorphosis of Insects 104 
 Gemmation of Polypes 119, 177 
 Larval Gemmation - 136 
 
 Embryogeny of the Echino- 
 
 dermata - - 163 
 
 Of Planaria - - 227 n 
 
 Carter, Reproduction of Volvox 28 
 
 Of (Edogonium - 34, 63 
 
 On the Tank worm and the 
 
 Guinea worm - 198 
 
 Cams, Germs oiApMs • 192 
 
 Casting of Skin and Limbs 223 
 
 Casual Alternation - 221 
 
 Caterpillar - - 105 
 
 Caryopliylleus - - 96 
 
 Cephalopoda, Embiyogeny 91 
 
 Cerainium, Reproduction 86 
 
 Cercaria of Trematoda - 95, 113 
 
 Cestoidea, Development - 96 
 
 Contrast with Trematoda 153 
 
 Gemmation of Embryos 161 
 
 „ of Sex Organs 173 
 
 Tabular view 
 
 269 
 
INDEX. 
 
 287 
 
 Page. 
 1)0 
 38 
 200 
 39 
 
 13i 71 
 
 Cliamisso, Alternation of Salpa 
 Characea?, Reproduction 
 Parthenogenesis 
 Morphology 
 Chermes, Reproduction - 
 Development of uninipreg- 
 
 nated Ova - 193 
 
 Cirripedia, Retrograde Meta- 
 morphosis - 106, 172 
 Defective Organization 175 
 Complementary Males 17G, 2 16 n 
 Citrus, Polyembryony - 18 i 
 Claviceps, Development - 44 
 Closterium, Development 27 
 Coccida, Reproduction - 136 n 
 Unimpregnated ova - 193 
 Cocoon, intra-ovular - 104 
 Coelenterata, Reproduction 81 
 Ccelohogyne, Parthenogenesis 200 
 Ccenurus, Development - 131, 161 
 Columella of Medusa - 122 
 Comatula, Development 87 
 Complementary Males 176, 246 n 
 Concentric fission - 223 
 Conceptacle of Florideae 36 
 Conclusions, Summary of 212 
 Concurrence of different forms 
 
 of Alternation - 219 
 
 Confervoideae, Reproduction 32 
 
 Coniferse, Reproduction 57, 183 
 
 Analogies mth Ciypto- 
 
 gamia - - 186 
 
 Coniomycetes, Reproduction 42 
 
 Conjugatse, Reproduction of 25 
 
 Coujugate-spore - 27 
 
 Conjugation - - 20, 23 
 
 In Fungi - - 47 
 
 In Infusoria, &c. - 79 
 
 Table of Modifications 26 
 
 Cordyceps, Cordyliceps, De- 
 velopment - - 4i 
 
 Corpusculnm of Conifprae 58, 183 
 Cosmariuvi, Gommaiion of Spores 27 
 Coste, Sperinatophores of 
 
 Crustacea - - 226 n 
 
 Crustacea, Spermatozoa] 68, 177, 
 
 230 n 
 
 Spcrmatophorcs - 226 n 
 
 Crust of Lichen - - 49 
 
 Cryptogamia, Reproduction, 21 ctseq. 
 Contrast with Phanerogamia, 65 180 
 
 Tabular view . - 258, 263 
 
 Cryptophiahts, Defective Or- 
 ganization - - 176 n 
 
 Impregnation - 236 n 
 
 Cupressince, Pollen - 59 
 
 Currey, Reproduction of Fungi 42 
 Ctenophora - - 83 n 
 
 Cycle, see Genetic. 
 Ci/ciops, Reproduction • 136 
 
 Cydippe, Reproduction - 83 n 
 
 Cylindrospermum - 28 
 
 Cynips, Absence of Males 2(i6 
 
 CypHs, Absence of Males lilt 
 
 Cysticercus, Development 161 
 
 Cystic Worms, Development 96, 161 
 Cytceis, PuUulation - 1 17 
 
 Daa'ymyces, Proliferous spores 15 
 Dalrymple, Males of Rotifera 176 
 Danielssen, Reproduction of 
 
 Gasteropoda - 91 
 
 Daphnia, Reproduction • 136 
 
 Ephippial ova - 191 
 
 Darwin, Male Cirripedes 176, 236, 
 
 240 n 
 Dauben}', Prof., Experiments 
 
 on Spontaneous Generation 3 
 Davis, Parthenogenesis of 
 
 Eggcr Moth - 2(t8 
 
 Decapoda, Development of 
 
 Spermatozoa - 177 
 
 Deciduous Gemnios - 151 
 
288 
 
 INDEX. 
 
 Page. 
 Deecke, Observations on Ve- 
 getable Parthenogenesis 200 
 Defective Organization - 175 
 
 Dentition - • 178 
 
 Derivation of Organic beings 1 
 
 From one or two parents 9 
 
 Desmidiese, Eeproduction 24, 31 
 Desor, Eeproduction of Poly- 
 
 pifera - - 99, 126 
 
 Detachment, Physiological 
 
 Import . - 177 
 
 Development, Epochal acts 107 
 
 Of Unimpregnated ova 194 
 
 Incipient - 202 
 
 Diatomacese, Reproduction 24, 28, 31 
 Digenesis - - 9 
 
 Dioecious arrangement - 247 
 
 Dvporpa, Conjugation - 79 ?i 
 
 Distoma, Reproduction 95, 112 
 
 PuUulation - - 147 
 
 Maturation of Organs - 168 
 
 Double Monsters - 158 
 
 Drone ova, agamic - 197 
 
 D'Udekem, Development of 
 
 Infusoria - - 80 
 
 Dualism - - 42 
 
 Duplicity, Malformation 158 
 
 Dzierzon, Reproduction of theBeel96 
 Earthworm, Penetration of 
 
 Spermatozoa - 70 
 
 Egg-sacs - - 226 
 
 Ecdysis - - 223 
 
 Echinaster, Reproduction 84 
 
 Echinodermata - - 84, 163 
 
 Tabular view - . 267 
 
 Echinococcus, Development 132 
 
 PuUulation - - 147, 153 
 
 Ectozoa - - 95 
 
 Edward's, Milne, Experiments 
 
 on Spontaneous Generation 3 
 
 Gemmation of Myriam.idu] 101 
 
 Page. 
 Egg-cases or sacs - 226 
 
 Egg-coverings, Rupture - 107 
 
 Egger Moth, Parthenogenesis 208 
 Egg and Seed Structures 235 
 
 Embryo of Plants - 63, 182 
 
 Embryogeny, Phenomena of 18 
 
 Representative of one form 
 
 of Alternation - 156, 164 
 
 Embryonal vesicles of ovule 62 
 
 Embryonic gemmation - 160 
 
 Endochrome - - 20, 23 
 
 Endothalloid germination 183 
 
 Endosperm - - 65, 260 
 
 Entochoncha, Germinal vesicle ^ 
 
 of 
 
 72 
 
 70 
 
 94 
 
 79 n 
 
 160 
 
 194 
 
 Entozoa, Impregnation - 
 
 Reproduction - 
 
 Conjugation - 
 Eolis, Embryonic division 
 Ephippial ova 
 Epochal acts in Reproduc- 
 tion - - 107 
 Equisetacese, Reproduction 55 
 Ergot, Development - 44 
 Eschricht, Prof., Development 
 
 of Entozoa - - 97 
 
 Esothalloid germination 183 
 
 Explanation of Tables - 253, 260 
 Extrusion of ova - 107 
 
 Exuviation - - 223 
 
 Fabre, Development of Scuti- 
 
 gera - - 102 
 
 Farre, Dr. A., Penetration of 
 
 Spermatozoa - 69 
 
 Development of the Ovary 245 
 Ferns, Reproduction - 52 
 
 Contrast with Mosses 52, 142, 187 
 Filaria, Origin - - 7 
 
 Reproduction - - 99 
 
 Filippi, Alternation in Ptero- 
 
 malus - • 113 
 
INDEX 
 Page 
 
 289 
 
 Fission, as contrasted with 
 
 gemmation - . 7G n 
 
 Concentric - - 223 
 
 Florideae, Eeproduction - 32, 36 
 
 Fluke- worm, Development 111 
 
 Focke, Germination of Clos- 
 
 terium - - 27 
 
 Food-yolk - . 74 
 
 Foraminifera - - 77 
 
 Formula) of Genetic Cycle 216 
 
 Frog, Penetration of Sperma- 
 tozoa - - 69 
 Fucoidese, Eeproduction 32, 36 
 Fucus, Impregnation - 37 
 Incipient Germination of 
 
 Unimpregnated Spores 202 
 Fungi, Reproduction - 40 
 
 Germination . - 44 
 
 Conjugation - - 47 
 
 Furcation of Embiyo - 159 
 
 GamomorpMc Stage - 14, 239 
 Alternation - - 111, 117 
 
 Pullulation - - 147 
 
 Gartner's Canal - 244 
 
 Gasteromycetes, Reproduc- 
 tion - - 42,45 
 Gemmae, adherent and deci- 
 duous - - 157 
 Relation to Ova - 190 
 Bearing on Alternation 200 
 Gemmation - - 9 
 Relation to Fission - 76 n 
 In the higher species - 167 
 Alternation of - 221 
 Table of interpolation of 256 
 Generation, Spontaneous 2 
 
 See Alternation. 
 
 Genetic Cycle, Formula 216, 218 
 
 Relation to affinity - 219 
 
 Tabular views 254, et seq. 
 
 Qeophihis, Spermatophore 226 n 
 
 Germinal olementa 
 
 
 Vesicle of 0\ti1o 
 
 62 
 
 Vesicle of Ovum 
 
 68 
 
 Gemaination of Algaj 
 
 27,30 
 
 Of Fungi - 
 
 4ri 
 
 Giraldes, " Corps Innomine" 
 
 of 245 
 
 Globule of Chara 
 
 38 
 
 Gouidium 
 
 49 
 
 Gonophore 
 
 125 
 
 Goodsir, H. D., Organization 
 
 
 of Male Cirripedes - 1' 
 
 "6, 230 
 
 Spermatozoa of Crustacea 177, 208 
 
 Gosso, Organization of As- 
 
 
 plauchna 
 
 176 
 
 Gradation of Sex Organs into 
 
 
 Zooids 
 
 173 
 
 Greene, Prof., Protozoa - 
 
 76 
 
 GregaHna, Conjugation - 
 
 79 
 
 Griffiths, Conjugation of Dia- 
 
 
 tomaceaa 
 
 28 
 
 Guinea-worm, Origin 
 
 98 
 
 Gymnosperms, see Coniferae. 
 
 
 Hair, Life of 
 
 178 
 
 Hectocotylus - 179 ?», 
 
 225 H 
 
 Helmintha, Reproduction 94, 112, 
 
 131, 153, 161 
 
 Tabular views 
 
 268 
 
 Henfrey, Prof., Germination 
 
 
 of Spirogyra 
 
 27 
 
 Polyembryony 
 
 184 
 
 Hepatica?, Reproduction 
 
 49 
 
 Hermaphroditism, normal 
 
 241 
 
 In Mollusca • 
 
 94 
 
 In Helmintha 
 
 94 
 
 In Annelida - 
 
 101 
 
 In Articulata - 
 
 106 
 
 Abnormal 
 
 2J2 
 
 Functional 
 
 2U5 
 
 Hermclla, Incipient develop- 
 
 
 ment of Unimpregnatod 
 
 
 Ova 
 
 202 
 
290 
 
 INDEX. 
 
 Page. 
 
 Heteroeyst - - 29 
 
 Heterogenesis - - 9 
 
 Heterosporous, Cryptogams 186 
 
 Hive Bee, Reproduction 196 
 Hofmeister, Germination of 
 
 Costnarin/m - 27 
 Reproduction of Mosses 
 
 and Ferns - - 52 
 
 Reproduction of Coniferse 57 
 
 Holothuridse, Reproduction 85 
 
 Homogenesis - - 9 
 
 Homoiosporous, Cryptogams 186 
 Homology of the reproduc- 
 tive structures in gene- 
 ral - - - 229,248 
 Special do. - - 237,244 
 
 Honey Bee, Reproduction 196 
 Huxley, Prof., Ovum of Pyro- 
 
 soma • - 72 n 
 
 Spermatozoa of Tethya 77 
 
 Zoological Individuality 110 
 
 Medusoids of Polypifera 125, 174 
 
 Gonophores of Polypifera 126 
 
 Reproduction of Salpa 141 
 
 Homology of Medusae 147 n 
 
 Germs of Aphis - 192 
 
 Hydra, Reproduction - 120 
 
 Hydra Tuba, Reproduction 120 
 
 Hydractinia, Composite 
 
 Structure - - 179 
 Hydrozoa, see Polypifera. 
 Hygrocrocis - - 47 
 Hymenium of Fungus - 49 
 Hymenomycetes, Reproduc- 
 tion - - 42,45 
 Hypliomycetes, Reproduction 41, 46 
 Hypottallus of Lichen - 49 
 Hypothesis, use in Science 17 
 Ihla, Defective Organization 176 
 Identity of Ova and Gemmae 205 
 Imago of Insect - 103 
 
 Page. 
 
 Impregnation, Modifications of 70 w, 
 
 246 n 
 Theory - . - 204,231 
 
 Incipient development of Un- 
 
 impregnated Ova - 202 
 
 Incompatibility of Ova and 
 
 Gemmae - 205 
 
 Individuality - . 109,165 
 
 Inessential Sprouts - 155 
 
 Infusoria - - 77 
 
 Ink Movdd - - 47 
 
 Insects, Metamorphosis 102 
 
 Insemination, Relation to 
 
 other epochal acts - 107 
 
 Interpolation of Geramation, 
 
 Table of - - 256 
 
 Isoetes, Reproduction - 55 
 
 Isophytoids - - 152 
 
 Isozooids " - 152 
 
 Itzigsohn, Development of 
 
 Oscillatoria - 29 
 
 Jelly-fishes, Reproduction 117 
 
 Jenner, Germination of Clos- 
 
 terium - 27 
 
 Analogy of Ferns and 
 
 Mosses - 53, 143, 183 
 
 Jungerma7inia, Reproduction 49 
 Fructification - - 188 n 
 
 Karsten, Conjugation of Si- 
 
 phoneae - - 35 
 
 Keber, Penetration of Sper- 
 matozoa - - 69 u 
 Eang's yellow^ worms • 115 
 Knox, Dr., Development of 
 
 Sex 242, 245 
 
 Kobelt, Wolffian Bodies - 244 
 
 Koren on Development of 
 
 Gasteropoda - 91 
 
 Kiichenmeister, Origin of 
 
 Parasites - - 8, 99 
 
 Determination of drone ova 197 
 
INDEX. 
 
 201 
 
 Page. 
 
 80 
 
 Lachmann, Reproduction of 
 
 Infusoria 
 Lankester, Nomenclature of 
 
 Gemmae 152 
 
 Larvae - - 73,103,238 
 
 Larval Gemmation - 13G 
 
 Late Development of Sex 168 
 
 Laycock, Prof., Diffusion of 
 
 Vitality - 179 n 
 
 Leect, Multiple Embryos 226 n 
 Lereboullet, Double Monsters 
 
 in Pike - 159 
 
 Lemeans, Retrograde Meta- 
 morphosis - 106, 172 
 Leveille, Development of Ergot 45 
 Lewis, Gemmation in An- 
 nelida - - 139 n 
 Heterogony - 130 u 
 Leuckart, Development of 
 
 Trichina - 99 n 
 
 Reproduction of Chermes 134 n, 
 
 136 11 
 Reproduction of A^ihis 193 
 
 Spermatopbores of Odoinis 225 n 
 Development of Sperma- 
 tozoa - - 204, 230 n 
 Homology of tlie Prostate 
 
 Vesicle - 244 n 
 
 Leydig, Prof., Germs of Aphis 192 
 Lichens, Reproduction 
 Life, Somatic and topical 
 Limnadia, Absence of Males 
 Lindsay, Dr. L., Reproduction 
 
 of Lichens 
 Links, Variable number in 
 
 the Genetic Cycle 
 Liquor Seminis 
 Lizzia, Pullulation 
 Lolligo, Spermatopbores 
 Lubbock, Zoological Indivi- 
 duality 
 
 4« 
 177 
 206 
 
 4« 
 
 153 
 231 
 117 
 
 225 71 
 
 110 
 
 
 r«<f* 
 
 Lubbock, Germs of Aphis 
 
 192 
 
 Ova of Daphnia 
 
 191 
 
 Lucemariadifi, Reproduction 83 
 
 ,120, 
 
 
 127 
 
 Liinfbricus, Multiple embryos 
 
 C'Jn 
 
 Lycopodiacea;, Rej^roduction 
 
 55 
 
 Macrospore 
 
 55 
 
 Maggot 
 
 104 
 
 Males, Coraplementwry 176, 216 
 
 Absence of 
 
 206 
 
 Malformation of duplicity 
 
 158 
 
 Mammalia, Penetration of 
 
 
 Spermatozoa 
 
 70 n 
 
 Reproduction 
 
 1(>7 
 
 Mangrove, Germination 
 
 64 
 
 Manubrium 
 
 122 
 
 MarcJuxntia, Fructification 
 
 188 
 
 Marsileaceffi, Reproduction 
 
 56 
 
 Marsupium 
 
 122 
 
 Maturation of Sex - 1 
 
 5, 167 
 
 Meconidium 
 
 123 
 
 Medusa?, Origin and Relations 
 
 117 
 
 Direct development 
 
 129 n 
 
 Pullulation 
 
 U7 
 
 Morphology - 126, 
 
 117 n 
 
 Medusoids • - 83,117 
 
 Meissner, Penetration of Sper- 
 
 
 matozoa 
 
 69 n 
 
 Meloseira, Conjugation 
 
 27 
 
 Mesocarpu^, Conjugation 
 
 26,27 
 
 Metagenesis 
 
 * 109 
 
 Metamorphosis - 73, 102, 223 
 
 Microgouidium 
 
 33 
 
 Micropyle of Algiu 
 
 32 
 
 Of Rhizocarpeas 
 
 57 
 
 Of Phauerogamia 
 
 58 
 
 Of the Animal Ovum 
 
 70 
 
 General Homology - 
 
 234 
 
 Microspore 
 
 55 
 
 Mildew 
 
 k5 
 
 MoUusca, Reproduction 
 
 91 
 
292 
 
 INDEX. 
 
 Page. 
 Mollusca, Germinal Segmen- 
 tation - - 159 
 Monoecious arrangement 247 
 Monogenesis - 9 
 Monsters, Double - '158 
 '\Lonostomum, Development 113 n 
 ilorphology of Chara - 39 
 Of Medusae - 126, 147 n 
 Of the Uterus - 244 
 Mosses, Reproduction - 49 
 Analogy with that of 
 
 Ferns - - 53,142 
 
 Mougeottia, Conjugation 26 
 
 Moulds - - 41,46 
 
 Mucor, Development - 47 
 
 Mulberry body - 157 
 
 Munter, Reproduction of 
 
 Ferns - - 57 n, 186 
 
 MiiUer, Johan, Embiyogeny 
 
 of Entochonclia - 72 
 
 Development of Echinoder- 
 
 mata - - 84 
 
 Otto, Fission of Annelida 101 
 Mullerian Cord - 244 
 
 Murray, Development of Insects 105 
 Mycelium of Fungi - 40, 49 
 
 Myrianida, Fission - 101, 138 
 Myriapoda, Reproduction 102 
 
 Nais, Fission - 101 
 
 Nautilus, Spermatophores 225 n 
 Needham, Filaments of 225 
 
 Nelson, Dr., Penetration of 
 
 Spermatozoa - 69 n 
 
 Nematoidea, Reproduction 70, 72 
 Nereis, Fission - 101 
 
 Neuters - - 161,241 
 
 Newport, Penetration of Sper- 
 matozoa - 69 n 
 Germinal Vesicle of Ba- 
 
 trachia - 71 
 
 Segmentation of Ovum 203, 205 
 
 Page 
 Nomenclature, Ambiguities 126 n, 
 
 132, 153 n, 163 n, 227 
 
 Non-sexual Reproduction 9 
 
 Nostochinese, Reproduction 31 
 
 Nucules of Chara - 38, 39 
 
 Octopus, Spermatophores 225 n 
 
 (Eginopsis, Direct development 130 n 
 
 CEdogonium, Reproduction 33, 34 
 
 Access of Antherozoids 63 n 
 
 Ophiuridae, Reproduction 85 
 
 Organic Bodies, Origin 2 
 
 Organization, Adventitious 175 
 
 Origin of Organisms - 1 
 
 Orthomorphic Stage - 14, 133, 238 
 
 Pullulation in - 149 
 
 Representationinthe higher 
 
 species - 166 
 
 Oscillatorieae, Reproduction 29, 31 
 Ova, in relation to Gemmae 190,et seq. 
 Bearing on Alternation 208 
 
 Development, without im- 
 pregnation - 191, 199 
 Ovary, Development - 245 
 Ovigeous, Capsules of Poly- 
 
 pifera - - 123 
 
 Ovisac - - 68 
 
 Ovules of Coniferae - 58, 186 
 
 Of Phanerogamia - 62, 181 
 
 Ovum . - 68 
 
 Of Bird - - ' 73 
 
 OiPyrosoma 73 
 
 Owen, Prof., Development of 
 
 Distoma - 113 
 
 Relations of MedusoB 121 
 
 Reproduction of Ap)his 152 
 
 Identity of Ova and Gemmae 205 
 
 Paget, Life of hairs, &c. 178 
 
 Palmelleae, Conjugation 23 
 
 Germination - 27, 28 
 
 Palmoglea, Conjugation 26 
 
 ParamoBcium, Reproduction 77 
 
Paraphyses of Lichens 
 Parasites, Origin 
 
 (See Cestoidea, Nematoidea, 
 Trematoda, &c.) 
 Parthenogenesis (True) 19 i 
 
 In Plants - 199 
 
 Pasteur, Spontaneous genera- 
 tion - - 4 
 Pectinibranchiata, Reproduction 92 
 Pelagia, Direct development 130 n 
 Pelodytes, Hermaphroditism 94 n 
 Penetration of Spermatozoa 70 
 
 Of Antherozoids 32, 34, 63 
 
 PentacrinuSy Development 87 
 
 Perichoetium of Moss 50 
 
 Periodicity of Sex - 107 
 
 Phanerogamia, Reproduction 29, 57 
 
 Analogies vsith Crytogamia 60, 65, 
 
 180 
 
 Tabular \^ew • 262 
 
 Physalia, Medusoids - 125 
 
 Physical Origin of Organic beings 2 
 Physosphoridae, Reproduction 83, 118 
 
 124 
 Phytoids - . 10, 110 
 
 Phytozoa, Phytozoaria, see 
 
 Antherozoids. 
 Pilularia, Reproduction 186 
 
 Pike, Duplex embryos 159 
 
 Pistillidium - 51 
 
 Placenta of Salpa • 90 
 
 Plants, see Vegetables. 
 Planaria, Multiple of embryos 227 
 Pluteus of Echinus - 85 
 
 PoUen - - 22 
 
 Polyembryony . 181 
 
 Polyphemus, Absence of Males 206 
 Polypifera, Reproduction 81, 117 
 
 Tabular view - 266 
 
 Gradation of organs into 
 
 zooids - - 124,174 
 
 INDEX. 
 
 Pago. 
 
 4« 
 
 7 
 
 Polypifera, Piillulation 
 Polypidom, Composite nature 
 
 293 
 117 
 
 of 
 
 Polyzoa, Reproduction 
 
 Tabular view 
 
 Embryonic gemmation 
 
 Gamomorf>hic do. 
 Pouchet, Experiments on 
 Spontaneous Generation 
 Proglottis 
 
 Prostate Gland, Homology 
 Prostate Vesicle 
 ProthalUum 
 Protomorjihic Stage 
 
 Alternation 
 
 Pullulation 
 
 Representation 
 Protonema of Moss 
 
 110,119 
 87 
 
 2G7 
 IGO 
 170 
 
 3 
 
 132 
 
 245 
 
 24t 
 
 52, 182 
 
 14, 237 
 
 111 
 
 1 17 
 
 15(> 
 
 50, 154, 188 n 
 
 2<> 
 31 
 
 76 
 
 Protoph}^^, Reproduction 
 
 Tabular view- 
 Protozoa, Distinction from 
 
 Protoph}'ta 
 Reproduction 
 Protracted fertility of Queen bee 2C^l 
 Priugsheim, Reproduction of 
 
 Algfo . 27, et scq. 
 
 Pteromalus, Supposed Alter- 
 nation - - 136 
 Puccinia, Development 42 
 Pullulation, - - IkJ 
 
 Formula - 218 
 
 Pupae - . 105 
 
 Pycnidium of Lichen - 4S 
 
 Pyrosoma, Development of Ovmn 72 
 Quatrefages, Fission of Sijllis Id 
 Incipient development of 
 
 unimpregnatod Ova 
 Rabbit, Penetration of Sj>er 
 
 matozoa 
 Radlkofer, Reproduction of 
 
 Fungi - - 43 n, 45 r» 
 
 202 
 
 69 n 
 
294. 
 
 INDEX. 
 
 Page. 
 Radlkofer, Genetic Cycle of 
 
 Cryptogamia . 53, 143 n 
 Vegetable Partlieiiogenesis 200 
 Ralfs, Gemmation of Closterium 27 
 Redia of Trematoda - 113 
 Kegel, Denial of True Par- 
 thenogenesis in Plants 200 n 
 Regional Life - 177 
 Reissek, Germination of Pollen 203 n 
 Reid, Gemmation of Hydra 
 
 Tiiha . - 120 
 Representation of Alternation 
 
 in tlie higlier species 15 
 
 Protomorpliic - 156 
 
 Gamomorphic - 166 
 Reproduction, Sexual and 
 
 Non-sexual - 9 
 
 In tlie Vegetable Kingdom 17 
 
 In the Animal Kingdom 68 
 
 Homologies - 229 
 
 Resting-spores - 28 
 
 Resting-periods, Table of 257 
 
 Rhizocarpese, Reproduction 56 
 
 Robin, Antberozoids of Viva 29 
 
 Defective Organization of 
 
 Males - - 175 
 Rosenmuller, Development of 
 
 tbe Ovary - 245 
 Rotifera, Ova - 195 
 Rye, Spurred (Ergot), De- 
 velopment - 44 
 Salix, Cbange of Sex - 207 n 
 Salpa, Reproduction - 90 
 Alternation - 140 
 Tabular view - 268 
 Sarsia, Pullulation - 147 
 Sanderson, Dr., Genetic Cycle 
 
 of Mosses and Ferns 53, 57 
 
 Analogies of Coniferae 186 
 
 Table (modified) - 258 
 
 Saprolegnia, Development 35 
 
 Page. 
 
 Scalpellum, Defective Organ- 
 ization - 176 
 Scbacht, Development of Pol- 
 len-tube - 58, 62 
 Scbleiden, Vegetable Impreg- 
 nation - - 62 
 Scbneider, Hermaphroditism 
 
 of Peloclytes - 94 
 
 Schultze, Experiments on 
 
 Spontaneous Generation 2 
 
 Development of Nemertini 99 
 
 Scolex . . 132 
 
 Scutigera, Development 102 
 
 ScypMstoma, Development 120 
 
 Seeds and eggs. Analogies 235 
 
 Segmentation of Ovum 72 
 
 Selaginella, Reproduction 55, 186 
 
 Seminal Vesicles, Homology 245 n 
 
 Sex, Late development 168 
 
 Periodicity . 167 
 
 Theory of original conjunction 242 
 
 Gradation of Organs into 
 
 Zooids - 173 
 
 Ultimate Corpuscules 231 
 
 Disguise and Mixture 244 
 
 Sexes, Association in Plants 185 
 
 Distribution in Species 241, 247 
 
 Sexual reproduction - 7 
 
 Rudimentary manifestation 20 
 
 Siebold, Parasitic FilarioB 7 
 
 Penetration of Spermatozoa 69 
 
 Development of Distoma 113 
 
 Genetic Cycle of Polypifera 128 
 
 Development of Tcenia 161 
 
 Parthenogenesis of the Bee 
 
 and other Insects 196, 206 
 
 Spermatophores - 226 
 
 Silkworm Moth, Partheno- 
 genesis - 207 n 
 Simpson, Prof., on Hermaph- 
 roditism " 243 
 
INDEX. 
 
 295 
 
 rage. 
 31 
 
 Siphoneae, Reproduction 
 Simulation of Alternation 
 Smith, J., of Kew, Partheno- 
 genesis of Ceelobogyne 
 Smut, Development 
 Somatic and topical life 
 Soredium of Lichen 
 Special homology of reproduction 237 
 Spermagonium of Lichen 48 
 
 Spermatia of Fungi and Lichens 41 
 Spermatic Element - 10 
 
 Liquor - - 231 
 
 Ultimate Corpuscules 229 
 
 221 
 
 199 
 42 
 
 177 
 49 
 
 Homologies 
 
 235 
 
 Theory of Action - 203, 
 
 206 
 
 Spermatophores 
 
 225 
 
 Spermatozoa - 68,230; 
 
 177 
 
 Self-development 
 
 203 
 
 Sphceria, Reproduction 41, 46 
 
 Siyhceroplea, Reproduction 
 
 33 
 
 Spinula of Ascidia 
 
 91 
 
 Spirogyra, germination 
 
 25 
 
 Sponge, Spermatozoa - 
 
 77 
 
 Spontaneous Generation 
 
 2 
 
 Spores, Conjugate 
 
 27 
 
 Resting, or winter - 
 
 28 
 
 Of Fungi 
 
 41 
 
 Of the higher and lower 
 
 
 Cryptogamia 
 
 187 
 
 Sporocarp - 
 
 56 
 
 Sporocyst - 
 
 113 
 
 Sporophore . 
 
 225 
 
 Sporosac 
 
 122 
 
 Spurred Rye, Development 
 
 44 
 
 Star-fish do. 
 
 86 
 
 Statoblast of Polyzoa - 
 
 222 
 
 Steenstrup, Alternation of 
 
 
 Generations 
 
 109 
 
 Development of Distoma 
 
 112 
 
 Hectocotylus-arm of Cuttle- 
 
 
 fish - - 2 
 
 25 n 
 
 Stein, Motamoqihosis of Protozoa 80 
 Stolon of Tunica ta - 90 
 
 Strobila - - 126, 132 n 
 
 Stylospore of Lichen . -W 
 
 Suminski, Germination of Ferns 57 n 
 Summary of Conclusions 212 
 
 Survey of Vegetable reproduction 17 
 Survey of Animal reproduction 68 
 Suspensor of Emijryo 182, 188 
 
 SijlliSy Caudal gemmation 100, 138, 
 
 180 n 
 Synapta, Parasite of 92 
 
 Fission - . 87 
 
 Syngamus, Conjugation 79 
 
 Synoecious arrangement 2 17 
 
 Syzygites, Conjugation W 
 
 Table of the Modifications of 
 
 Conjugation - 26 
 
 Of the Protophyta - 31 
 
 Of the Modifications of Im- 
 pregnation - 71 
 Of Epochal acts - 107 
 Of the Structure of Eggs 
 
 and Seeds - 235 
 
 Of the Homolog}' of Repro- 
 duction - 236 
 Of the Protomorphic, Or- 
 thomorphic, and Gumo- 
 morphic Stages - 237, 2 k) 
 Of Sexual Arrangement 2 tS 
 Of the Genetic Cycle 254, et seq. 
 Explanations - 253, 260 
 Tocniay Origin and develoj)- 
 
 ment - - 96, 131, 161 
 
 Tankworra - - 98 
 
 Tapeworm, see Taniia. 
 Teeth, Proper Life - 178 
 
 TcrchcUa, Gemmation 139 n 
 
 Termites, Neuters 105, 168 
 
 Tcthya, Spermatozoa - 77 
 
 Tdrarhynchu^, Development 98 
 
296 
 
 INDEX. 
 
 Page. 
 
 Tetraspores . 36 
 
 TJiaumantias, Pullulation 147 
 
 Theca of Fungus and Lichen 42 
 
 Of Moss - - "50 
 
 Thecaspore - 42 
 
 Theory, Use in science 17 
 
 Thomson, Prof. A., Nomenclature 9 
 
 Genetic Cycle of Polypifera 128 
 
 Double embryos - 158 
 
 Prof. Wyville, Development 
 
 of Comattda - 87 
 
 J. v., Development of 
 
 Comatula - 87 
 
 Thuret, Antherozoids of Uiva 29 
 
 Reproduction of Nostochinese 29 
 
 Reproduction of Fucoids 37 
 
 Germination of unimpreg- 
 
 nated spores - 202 
 
 Thwaites, Germination of Palmella 28 
 Gemmae of Algse - 36 
 
 Topical and Somatic life 177 
 
 Trachynemaf Direct Develop- 
 ment - - 130 
 Trematoda, Reproduction 95, 112 
 Tabular View - 268 
 Analogies in Cestoidea 153 
 Tremellineae, Reproduction 45 , 
 Trichina^ Development 99 n 
 Tulasne, Reproduction of Fungi 41, 48 
 Vegetable Impregnation 62 
 Tunicata, Reproduction 89 
 Typical form of Polypifera 120, 128 
 XJdekem, Metamorphosis of 
 
 Infusoria - 80 
 
 Ulvaceae, Reproduction 29, 31 
 
 Unimpregnated ova, Develop- 
 ment - - 191, 199 
 Incipient - 202 
 Uredo, Development - 42, 43 
 Uterus, Homology - 244 
 Valentine, Furcation of Embryo 159 
 Variability of Pullulation 153 
 
 Page. 
 109 
 
 34 
 
 74 
 154 71, 201 
 
 Varieties of Alternation 
 Vancheria, Reproduction 
 Vegetables, Composite Cha- 
 racter - 14, 149 
 Reproduction - 17 
 Alternation - 142 
 Tabular View - 254, 264 
 PuUulation - 149 
 Velella - - 118, 124 
 Vertebrata, Reproduction 106 
 Vesicula Prostatica - 244 
 SerainaHs - 245 
 Vinegar Plant - 47 
 Viscum, Polyembryony 184 
 ViteUigenous cells of Insects 193 
 Vitelline, Membrane 
 Viviparous Plants 
 Volvox, Reproduction 28 
 Volvocinese, do. - 31 
 Vorticellay do. - 79 
 Vrolik, Double Monsters 158 
 Wagner, Developmentof Sper- 
 matozoa - 204 
 Weber, Development of Sex 244 
 Weepiug-wiUow, Change of sex 207 n 
 Winter eggs - 194 
 Winter spores - 28 
 WoLSian Bodies, Development 
 
 and Relations - 244 
 
 Worms, Intestinal . 94, 153 
 
 Annelidan - 99 
 
 Wright, Dr., Reproduction of 
 
 Polypifera - 83, 123 
 
 Organization - 147 n^ 180 
 
 Yolk, Cleavage - 71 
 
 Supplementary - 74 
 
 Zooids . - 10,13,109 
 
 Gradation into Organs 173 
 
 Adventitious Organization 175 
 
 Zoophytic Organization 14, 82, 149 
 
 Zoospores - - 28, 32, 37 
 
 Zygnema, Conjugation 25 
 
J^. BDEeO^WlsT & CO., J^ 
 
 ^■^r*.' 
 
 ;:■•; •■vi 
 
 1,' 
 
 1 
 
 
 \ 
 
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