THE LIBRARY 
 
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 GIFT OF 
 
 HASKELL F. NORMAN 
 
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 BIOLOGICAL LECTURES ""'•'" 
 
 DELIVERED AT 
 
 THE MARINE BIOLOGICAL LABORATORY 
 OF WOOD'S HOLL 
 
 In the Summer Session of 189? 
 
 A 
 
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 •^'• 
 
 
 >^" 
 
 BOSfip^, U.S.A. 
 
 
 PUBLISHED BY GINN & 
 
 COMPANY 
 
 1894 
 
 
By GINN & COMPANY. 
 
 ALL RIGHTS RESERVED. 
 
PREFACE. 
 
 In offering the second volume of these lectures,^ it may be 
 well to remind the reader who may not be acquainted with the 
 Laboratory, that only one side of our work is here represented. 
 Such a series of lectures on special problems in biology is 
 offered every summer; but the main body of our lectures 
 is of quite a different type, having direct reference to the 
 instruction going on in the laboratories. As a rule, these 
 special lectures are given by investigators, who undertake not 
 only to review the field, but also to set forth the results of their 
 own work. While these lectures may show the general drift 
 of the authors' investigations, they cannot, of course, be ex- 
 pected to give a complete account of the facts on which the 
 conclusions are based. In lectures of this kind due allowance 
 must be made for the authors' limitations in time, as the sub- 
 ject is often one which would require a dozen or more lectures 
 for its complete elaboration. Somewhat greater freedom in the 
 expression of opinion than might be expected in strictly scientific 
 communications, must also be permitted. In fact, it is one of 
 the leading objects of this course of lectures to bring forward the 
 unsettled problems of the day, and to discuss them freely. It is 
 to be expected, of course, that now and then opposed stand- 
 points will be developed, as has happened this time; but these 
 differences exist, and will continue to exist, as long as anything 
 remains for investigation, and the scientific reader will not be 
 surprised to find them here. It may be hardly necessary to 
 add that the authors are severally responsible for the method 
 and form of their lectures. A brief account of the work and 
 aims of the Laboratory will be found in the appendix. 
 
 C. O. Whitman. 
 
 1 The first volume appeared in 1890. 
 
 
CONTENTS. 
 
 LECTURE PAGE 
 
 I. The Mosaic Theory of Development. E.B.Wilson. i 
 
 II. TJie Fertilization of the Ovum. E. G. Conklin . 15 
 
 III. Oil Soine Facts and Principles of Physiological 
 
 Morphology. J. Loeb 37 
 
 IV. Dynamics in Evolution. J. A. Ryder .... 63 
 
 V. On the Nature of Cell Organization. S. Watase . 83 
 
 VI. TJie Inadequacy of the Cell- Theory of Development. 
 
 C. O. Whitman 105 
 
 VII. Bdellostoma Dombeyi, Lac. Howard Ayers . . 125 
 
 VIII. The hifltcence of External Coiiditions on Plant 
 
 Life. W. P. Wilson 163 
 
 IX. Irrito-Contractility in Plaiits. J. Muirhead Mac- 
 
 FARLANE 1 85 
 
 X. The Marine Biological Stations of Europe. Bash- 
 ford Dean 211 
 
 Appendix — TJie Work and the Aims of the Ma- 
 rine Biological Laboratory . CO. Whitman. 235 
 
FIRST LECTURE. 
 
 THE MOSAIC THEORY OF DEVELOPMENT. 
 
 EDMUND B. WILSON. 
 
 A REMARKABLE awakening of interest and change of opinion 
 has of late taken place among working embryologists in regard 
 to the cleavage of the ovum. So long as the study of embry- 
 ology was dominated by the so-called biogenetic law, so long 
 as the main motive of investigation was the search for phyletic 
 relationships and the construction of systems of classification, 
 the earlier stages of development were little heeded. The 
 two-layered gastrula was for the most part taken as the real 
 starting-point for research, and the segmentation stages were 
 briefly dismissed as having little purport for the more serious 
 problems involved in the investigation of later stages. The 
 cleavage is equal or unequal, total or partial, regular or irregular; 
 the diblastic condition attained by delamination, migration or 
 invagination ; the gastrulation embolic or epibolic : — such 
 were the general conclusions announced regarding the prae- 
 gastrular stages in a large proportion of the embryological 
 papers published down to the time of Balfour and even later. 
 The last decade has, however, witnessed so extraordinary a 
 change of front on this subject that it will not be out of place 
 to review briefly the three leading causes by which it has been 
 brought to pass. 
 
 First, it has become more and more clear that the germ-layer 
 theory is, to a certain extent, inadequate and misleading, and 
 that even the primary layers of the "gastrula" cannot be 
 regarded as strictly homologous throughout the animal kingdom. 
 To assume that they are so involves us in inextricable difficul- 
 ties — such as those for instance encountered in the comparison 
 of the annelid gastrula with that of the chordates, or the com- 
 
2 BIOLOGICAL LECTURES. 
 
 parison of the sexual and asexual modes of development in 
 tunicates, bryozoa, worms and coelenterates. This considera- 
 tion led some morphologists to insist on the need of a more 
 precise investigation of the prae-gastrular stages, and the desi- 
 rability of taking as a starting-point not the two-layered gastrula 
 but the undivided ovum. ''The 'gastrula' cannot be taken as 
 a starting-point for the investigation of comparative organo- 
 geny unless we are certain that the two layers are everywhere 
 homologous. Simply to assume this homology is simply to 
 beg the question. The relationsJiip of the inner and outer 
 layei^s in the variojis forms of gastrnlas nmst be investigated 
 not only by determining their relationsJiip to the adult body, but 
 also by tracing out the cell-lineage or cytogeny of the individttal 
 blastomcres from the begifuiing of development .'' 
 
 The second of the causes referred to was the discovery of the 
 so-called pro-morphological relations of the segmenting ovum. 
 It is now just ten years since Roux and Pfliiger independently 
 announced the discovery that the first plane of cleavage in the 
 frog's Qgg coincides with the median plane of the adult body 
 (a fact announced many years earlier by Newport, whose obser- 
 vation fell, however, into oblivion). The same result was soon 
 afterwards reached in the case of the cephalopod (Watase) and 
 tunicate (Van Benden and Julin), and for a time it seemed not 
 improbable that a general law had been determined. Later 
 researches disappointed this expectation ; for it was demon- 
 strated that the first cleavage plane may be transverse to the 
 body (annelids, gasteropods, urodeles), or even in some cases 
 show a purely variable and inconstant relation (teleosts). 
 The fact remained, however, that in the greater number of 
 known cases definite relations of symmetry can be made out 
 between the early cleavage stages and the adult body ; and 
 this fact invested these stages with a new and captivating 
 interest. 
 
 The third and most important cause lay in the new and 
 startling results attained by the application of experimental 
 methods to embryological study, and especially to the investi- 
 gation of cleavage. The initial impulse in this direction was 
 given in 1883 by the investigations of Pfliiger upon the influ- 
 
THE MOSAIC THEORY OF DEVELOPMENT. 3 
 
 ence of gravity and mechanical pressure upon the segmenting 
 ova of the frog. These pioneer studies formed the starting- 
 point for a series of remarkable researches by Roux, Driesch, 
 Born and others, that have absorbed a large share of interest 
 on the part of morphologists and physiologists alike ; and it 
 is perhaps not too much to say that at the present day the 
 questions raised by these experimental researches on cleavage 
 stand foremost in the arena of biological discussion, and have 
 for the time being thrown into the background many problems 
 which were but yesterday generally regarded as the burning 
 questions of the time. It is the purpose of this lecture to 
 consider, briefly, the most central and fundamental subject of 
 the current controversy. 
 
 It is an interesting illustration of how even scientific history 
 repeats itself that the leading issue of to-day has many points 
 of similarity to that raised two hundred years ago between the 
 prae-formationists and the epigenesists. Many leading biolo- 
 gical thinkers now find themselves compelled to accept a view 
 that has somewhat in common with the theory of prse-forma- 
 tion, though differing radically from its early form as held by 
 Bonnet and other evolutionists of the eighteenth century. No 
 one would now maintain the archaic view that the embryo 
 prae-exists as such in the ovum. Every one of its hereditary 
 characters is, however, believed to be represented by definite 
 structural units in the idioplasm of the germ-cell, which is 
 therefore conceived as a kind of microcosm, not similar to, 
 but a perfect symbol of, the macrocosm to which it gives rise 
 (Hertwig). In its modern form this doctrine was first clearly 
 set forth by Darwin in the theory of Pangenesis ('68). Twenty 
 years later ('89) it was remodeled and given new life by Hugo 
 de Vries, in a profoundly interesting treatise entitled Intra- 
 celhdar Pangenesis and in its new form was accepted by 
 Oscar Hertwig, and pushed to its uttermost logical limit by 
 Weismann. Kindred theories have been maintained by many 
 other leading naturalists. 
 
 The considerations which have led to the rehabilitation of 
 4 the theory of pangenesis are based upon the facts of what 
 
2 BIOLOGICAL LECTURES. 
 
 parison of the sexual and asexual modes of development in 
 tunicates, bryozoa, worms and coelenterates. This considera- 
 tion led some morphologists to insist on the need of a more 
 precise investigation of the prae-gastrular stages, and the desi- 
 rability of taking as a starting-point not the two-layered gastrula 
 but the undivided ovum. ''The 'gastrula' cannot be taken as 
 a starting-point for the investigation of comparative organo- 
 geny unless we are certain that the two layers are everywhere 
 homologous. Simply to assume this homology is simply to 
 beg the question. The relationship of the i^itier and onter 
 layers in the various forms of gastridas must be investigated 
 not only by determining their relationship to the adult body, but 
 also by tracing out the cell-lineage or cytogeny of the individual 
 blastomeres from the begijiniftg of development.'' 
 
 The second of the causes referred to was the discovery of the 
 so-called pro-morphological relations of the segmenting ovum. 
 It is now just ten years since Roux and Pfliiger independently 
 announced the discovery that the first plane of cleavage in the 
 frog's Qgg coincides with the median plane of the adult body 
 (a fact announced many years earlier by Newport, whose obser- 
 vation fell, however, into oblivion). The same result was soon 
 afterwards reached in the case of the cephalopod (Watase) and 
 tunicate (Van Benden and Julin), and for a time it seemed not 
 improbable that a general law had been determined. Later 
 researches disappointed this expectation; for it was demon- 
 strated that the first cleavage plane may be transverse to the 
 body (annelids, gasteropods, urodeles), or even in some cases 
 show a purely variable and inconstant relation (teleosts). 
 The fact remained, however, that in the greater number of 
 known cases definite relations of symmetry can be made out 
 between the early cleavage stages and the adult body ; and 
 this fact invested these stages with a new and captivating 
 interest. 
 
 The third and most important cause lay in the new and 
 startling results attained by the application of experimental 
 methods to embryological study, and especially to the investi- 
 gation of cleavage. The initial impulse in this direction was 
 given in 1883 by the investigations of Pfluger upon the influ- 
 
THE MOSAIC THEORY OF DEVELOPMENT 3 
 
 ence of gravity and mechanical pressure upon the segmenting 
 ova of the frog. These pioneer studies formed the starting- 
 point for a series of remarkable researches by Roux, Driesch, 
 Born and others, that have absorbed a large share of interest 
 on the part of morphologists and physiologists alike ; and it 
 is perhaps not too much to say that at the present day the 
 questions raised by these experimental researches on cleavage 
 stand foremost in the arena of biological discussion, and have 
 for the time being thrown into the background many problems 
 which were but yesterday generally regarded as the burning 
 questions of the time. It is the purpose of this lecture to 
 consider, briefly, the most central and fundamental subject of 
 the current controversy. 
 
 It is an interesting illustration of how even scientific history 
 repeats itself that the leading issue of to-day has many points 
 of similarity to that raised two hundred years ago between the 
 prae-formationists and the epigenesists. Many leading biolo- 
 gical thinkers now find themselves compelled to accept a view 
 that has somewhat in common with the theory of prse-forma- 
 tion, though differing radically from its early form as held by 
 Bonnet and other evolutionists of the eighteenth century. No 
 one would now maintain the archaic view that the embryo 
 prae-exists as stick in the ovum. Every one of its hereditary 
 characters is, however, believed to be represented by definite 
 structural units in the idioplasm of the germ-cell, which is 
 therefore conceived as a kind of microcosm, not similar to, 
 but a perfect symbol of, the macrocosm to which it gives rise 
 (Hertwig). In its modern form this doctrine was first clearly 
 set forth by Darwin in the theory of Pangenesis ('68). Twenty 
 years later ('89) it was remodeled and given new life by Hugo 
 de Vries, in a profoundly interesting treatise entitled Iiitra- 
 celhdar Pangenesis and in its new form was accepted by 
 Oscar Hertwig, and pushed to its uttermost logical limit by 
 Weismann. Kindred theories have been maintained by many 
 other leading naturalists. 
 
 The considerations which have led to the rehabilitation of 
 4 the theory of pangenesis are based upon the facts of what 
 
4 BIOLOGICAL LECTURES. 
 
 Gallon has called particulate inheritance. The phenomena of 
 atavism, the characters of hybrids, the facts of spontaneous 
 variation, all show that even the most minute characteristics 
 may independently appear or disappear, may independently 
 vary, and may independently be inherited from either parent 
 without in any way disturbing the equilibrium of the organ- 
 ism, or showing any correlation with other variations. These 
 facts, it is argued, compel the belief that hereditary character- 
 istics are represented in the idioplasm by distinct and definite 
 germs ( " pangens," ** idioblasts," ''biophores," etc), which 
 may vary, appear or disappear, become active or latent, without 
 affecting the general architecture of the substance of which 
 they form a part. Under any other theory we must suppose 
 variations to be caused by changes in the molecular composi- 
 tion of the idioplasm as a whole, and no writer has shown, 
 even in the most approximate manner, how inarticulate inheri- 
 tance can thus be conceived. 
 
 Based upon this conception two radically different theories 
 of development have recently been propounded. The first of 
 these — the so-called mosaic theory of Roux and Weismann, 
 which forms the subject of this lecture — is based upon the 
 assumption that the cause of differentiation lies in the nature 
 of cell-division. Karyokinesis is conceived as qualitative in 
 character in such wise that the idioplasmic germs are sifted 
 apart, and cells of different prospective values receive their 
 appropriate specific germs at the moment of their forma- 
 tion. The idioplasm therefore becomes progressively simpler 
 as the ontogeny goes forward, except in the case of the germ- 
 cells ; these retain a store of the original mixture (''germ- 
 plasm" of Weismann). Every cell must therefore possess an 
 independent power of self-determination inherent in the specific 
 structure of its idioplasm, and the entire ontogeny is aptly 
 compared by Roux to a mosaic-work ; it is essentially a whole 
 arising from a number of independent self-determining parts, 
 though Roux qualifies this conception by the admission that 
 the self-determining power of the cell is capable in some 
 measure, of modification, through interaction with its fellows 
 ( " correlative differentiation " ). 
 
THE MOSAIC THEORY OF DEVELOPMENT 5 
 
 In the hands of Weismann this theory attains truly colossal 
 proportions. The primary germs or units (which he calls 
 '* biophores " ) are aggregated to form ''determinants," the 
 determinants to form "ids," and the ids to form "idants," 
 which are identified with the chromosomes of the ordinary 
 karyokinetic figure. Upon this basis is reared a stately group 
 of theories relating to reproduction, variation, inheritance and 
 regeneration, which are boldly pushed to their utmost logical 
 limit. These theories await the judgment of the future. 
 Brilliantly elaborated and persuasively presented as they are, 
 they do not at present, I believe, carry conviction to the minds 
 of most naturalists, but arouse a feeling of scepticism and 
 uncertainty; for the fine-spun thread of theory leads us little 
 by little into an unknown region, so remote from the terra firma 
 of observed fact that verification and disproof are alike impos- 
 sible. 
 
 In its original form the mosaic theory has, I believe, received 
 its death-blow from the facts of experimental embryology, 
 though both Roux and Weismann still endeavor to maintain 
 their position. It is rather curious that the very line of 
 research struck out by Roux, by which he was led to the 
 mosaic theory, should in later years have ended in a view dia- 
 metrically opposed to his own. In 1888 Roux succeeded in 
 killing (by puncture with a heated needle) one of the first two 
 blastomeres of the segmenting frog's ^^g. The uninjured 
 blastomere continued its development as if still forming a part 
 of an entire embryo, giving rise successively to a half-blastula, 
 half-gastrula, and half-tadpole embryo, with a single medullary 
 fold. Analogous results were reached by operation upon four- 
 celled stages. It was this result that led Roux to compare the 
 development to a mosaic-work, asserting that '' the development 
 of the frog-gastrula, and of the embryo immediately derived 
 from it is, from the second cleavage onward, a mosaic-work, 
 consisting of at least four vertical independently developing 
 pieces." Roux himself, however, showed that in later stages 
 the missing half (or fourth) is perfectly restored by a process 
 of ''post-generation," which begins about the time of the 
 formation of the medullary folds — a result which, in itself, 
 
6 BIOLOGICAL LECTURES. 
 
 really contradicts the mosaic hypothesis ; for the course of 
 events in the uninjured blastomere, or its products, is radically 
 altered by changes on the other side of the embryo. 
 
 A more decisive result was reached in 1891 by Driesch, who 
 succeeded, in the case of EcJiinns, in effecting a complete sepa- 
 ration of the blastomeres by shaking them apart. A blastomere 
 of the 2-celled stage, thus isolated, gave rise to a perfect but 
 half-sized blastula, gastrula, and Pluteus larva ; an isolated 
 blastomere of the 4-celled stage produced a perfect dwarf gas- 
 trula one-fourth the normal size. Even in this case, however, 
 the earliest stages of development (cleavage) showed traces of 
 the normal development, the isolated blastomere segmenting, 
 as if it were a half-embryo, and only becoming a perfect whole 
 in the blastula stage. In the following year, however, the 
 writer repeated Driesch's experiments in the case of AinpJii- 
 oxtis (the Qgg of which is extremely favorable for experiment), 
 and found that in this case there is, as a rule, no preliminary 
 half-development whatever. The isolated blastomere behaves 
 from the beginning like an entire ovum of one-half or one- 
 fourth the normal size. 
 
 It is quite clear that in Amphioxus the first two divisions of 
 the ovum are not qualitative, as the mosaic theory assumes, 
 but purely quantitative ; for the fact that each of the two or 
 four blastomeres may give rise to a perfect gastrula proves that 
 all contain the same materials. Nevertheless, in the normal 
 development, these cells give rise to different structures — i. e., 
 they have a different prospective value — from which it follows 
 that, in this case at least, differentiation is not caused by quali- 
 tative cell-division, but by the conditions under which the cell 
 develops. 
 
 These facts are obviously a serious blow to the mosaic 
 theory, and the efforts of Roux and Weismann to sustain their 
 hypothesis in the face of such evidence only serve to emphasize 
 the weakness of their case. In order to explain the facts of 
 post-generation — i.e., the capability of isolated blastomeres 
 to produce complete embryos — both Roux and Weismann are 
 compelled to set up a subsidiary hypothesis, assuming that 
 during cell-division each cell may receive, in addition to its 
 
THE MOSAIC THEORY OF DEVELOPMENT. 7 
 
 specific form of idioplasm, a portion of unmodified idioplasm 
 afforded by purely quantitative division. This unmodified 
 idioplasm ("accessory idioplasm" of Weismann, or in some 
 cases "germ-plasm"; "post-generation or regeneration idio- 
 plasm " of Roux) remains latent in normal development which 
 is controlled by the active specific idioplasm. Injury to the 
 ovum — e. g.y mechanical separation of the blastomeres — acts 
 as a stimulus to the latent idioplasm, which thereupon becomes 
 active, and causes a repetition of the original development. 
 By assuming a variable latent period following the stimulus, 
 Roux is able to explain the fact that regeneration takes place 
 at different periods in different animals. 
 
 Considered as a purely formal explanation this subsidiary 
 hypothesis is perfectly logical and complete. A little reflection 
 will show, however, that it really abandons the entire mosaic 
 position, by rendering the assumption of qualitative division 
 superfluous; and, aside from this, its forced and artificial char- 
 acter, places a strain upon the mosaic theory under which it 
 breaks down. Both of the two fundamental postulates of the 
 modified theory — viz.^ qualitative nuclear division, and accessory 
 latent idioplasm — are purely imaginary. They are complicated 
 assumptions in regard to phenomena of which we are really 
 quite ignorant, and they lie at present beyond the reach of 
 investigation. The "explanation" is, therefore, unreal; it 
 carries no conviction, and no real explanation will be possible 
 until we possess more certain knowledge regarding the seat of 
 the idioplasm (which is entirely an open question), and its 
 internal composition and mode of action (which is wholly 
 unknown). In the meantime we certainly are not bound to 
 accept an artificial explanation like that of Roux, however 
 logical and complete, unless it can be shown that the phenomena 
 are not conceivable in any other way. 
 
 We turn now to a brief consideration of opposing views, 
 among which I ask attention especially to those of Driesch and 
 Hertwig. In common with Kolliker and many other eminent 
 authorities, these authors insist that cell division is not quali- 
 tative but quantitative only, and hence is not, /rr sc, a cause 
 
lO BIOLOGICAL LECTURES. 
 
 we find, for example, among the annelids; and I would ask 
 attention for a moment to the case of Nereis, which is, at 
 present, the best known form. Differentiation here begins at 
 the very first cleavage (which is conspicuously unequal), and 
 it becomes more pronounced with every succeeding division. 
 The median plane is marked out at the second cleavage ; at 
 the third the entire ectoblast of the trochal and prse-trochal 
 regions is formed ; at the fourth the material for the entire 
 ''ventral plate " (including the ventral nerve-cord and the seta- 
 sacs) is segregated in a single cell, that for the stomodaeum in 
 three cells*; the fifth cleavage completes the ectoblast, and by 
 the 38-celled stage the germ-layers are completely segregated 
 (the mesoblast in a single cell) and the architecture of the 
 embryo is fully outlined in the arrangement of the parent 
 blastomeres, or protoblasts. 
 
 We do not know whether, in this case, the first two blasto- 
 meres are qualitatively different, though there may be some 
 ground for holding that they are, from the fact that the larger 
 of the two contains a relatively larger proportion of protoplasm 
 than the smaller.^ But in any case their difference in size 
 renders it impossible that they should play interchangeable 
 parts in the cleavage. The entire later development is, how- 
 ever, moulded upon the 2-celled stage, every blastomere having 
 a definite relation to it and a definite morphological value. The 
 development is a visible mosaic-work, not one ideally conceived 
 by a mental projection of the adult characteristics back upon 
 the cleavage stages. The principle of ''organbildende Keim- 
 bezirke " has here a real meaning and value, and this would 
 remain true even if it should hereafter be shown that both of 
 the first two blastomeres of Nereis, if isolated, could produce a 
 perfect embryo. 
 
 It is clear, from such a case, that the more extreme views 
 of Driesch and Hertwig cannot be accepted without consider- 
 able modification. It seems to me, however, that they may be 
 modified in such a way as, without sacrificing the principle of 
 epigenesis for which they contend, to recognize certain ele- 
 
 1 All my attempts to separate these blastomeres by shaking have thus far been 
 unsuccessful. 
 
THE MOSAIC THEORY OF DEVELOPMENT. \\ 
 
 ments of truth in the mosaic hypothesis ; and I will attempt 
 to indicate this modification by a comparison between Amphi- 
 oxtis and Nereis. In the case of AinpJiioxiis we have the clear- 
 est evidence that differentiation is, in a measure, dependent 
 upon the relation of the cell to the whole of which it forms a 
 part. The first visible differentiation in this case is at the 
 third cleavage, which consists in an unequal division of each 
 of the four blastomeres, so as to give rise to four micromeres 
 and four macromeres, the former giving rise to ectoblast only, 
 while the latter give rise to entoblast 
 and mesoblast as well {Diagravi I). 
 If, however, the blastomeres of the 
 4-celled stage be separated (shaken 
 apart) the course of events is entirely 
 changed ; for in this case each divides 
 equally, not unequally, and ultimately 
 gives rise to a complete quarter-sized "" dlIgram I. 
 
 dwarf, instead of one-quarter of a 
 
 normal embryo, as it would have done under ordinary cir- 
 cumstances. The character of the fourth cleavage is here 
 directly or indirectly determined in each cell by the relation 
 of the cell to its fellows ; and if this is true of any one 
 stage of the ontogeny, a very strong presumption is created 
 that it is true of all — that, in the process of progressive 
 differentiation occurring in the course of every animal on- 
 togeny, the character of each step is determined by the 
 condition of the entire organism. The ontogeny is, in other 
 words, a connected series of interactions between the 
 various parts of the embryo, in which each step estab- 
 lishes new relations, through which the following step is 
 determined. The character of the series, as a whole, depends 
 upon the first step, and this in turn upon the constitution of the 
 original ovum. In Aniphioxiis differentiation proceeds slowly, 
 the earlier blastomeres show no appreciable divergence, and the 
 first stages show no trace of a mosaic work. In Nereis, on the 
 other hand, a mosaic-like character appears from the begin- 
 ning, because of the inequality of the first cleavage, which 
 conditions the entire subsequent development through the 
 
12 
 
 BIOLOGICAL LECTURES. 
 
 peculiar relations established by it. The cause of the inequa- 
 lity must lie in the undivided ovum, and a study of the first 
 cleavage-spindle shows that the inequality is unmistakably 
 foreshadowed before the least outward sign of division appears ; 
 for the asters at the spindle-poles are conspicuously unequal 
 in size, the larger aster corresponding with tho future larger 
 cell (Diagram II). This difference is not conn.cted with any 
 
 determinable Mechanical 
 conditions ; foi the centro- 
 somes lie nearl}/ equidistant 
 from the membrane (the 
 ^g<g is spherical), and the 
 deutoplasm shows no per- 
 ceptible inequality in hori- 
 zontal distribution. The 
 conclusion seems unavoid- 
 able that the differentiation 
 in size is caused by a specific 
 form of activity in the 
 cytoplasm (or archoplasm), 
 occurring prior to cell-division. But if a differentiation in 
 size may have such an origin, we may fairly argue that other 
 differentiations may likewise precede cell-division, and that 
 in such cases the division may be, in a sense, qualitative. 
 
 It seems to me, that in these considerations we may find, in 
 some measure, a reconciliation between the extremes of both 
 the rival theories under discussion — that we may consistently 
 hold with Driesch that the prospective value of a cell may be 
 a function of its location, and at the same time hold with Roux 
 that the cell has, in some measure, an independent power of 
 self-determination due to its inherent specific structure. Such 
 a view is only possible, however, if we regard the specific struc- 
 ture of the cell to have arisen not through the segregation and 
 isolation within its boundaries of special idioblasts or germ- 
 substances, that have been sifted out by qualitative division, 
 but through a physiological specialization (as de Vries and 
 Hertwig insist) that may have taken place before, during, or 
 after cell-division, according to circumstances. If differentia- 
 
 DlAGRAM II. 
 
THE MOSAIC THEORY OE DEVELOPMENT. \x 
 
 tion precedes or accompanies division, the latter process may 
 be in a sense qualitative. If it follows, division will be purely 
 quantitative, and in such a case we may rightly speak of differ- 
 entiation as a result of cellular interaction. The segmentation 
 of the Qgg presents more or less of a mosaic-like character, 
 according to the period at which differentiation appears, and 
 the rate at which it proceeds, as expressed in limitations of 
 the power of development in the individual blastomeres, and 
 their differences in size and structure. 
 
 The general interpretation of development which I have thus 
 endeavored to sketch will be found to differ widely in some 
 respects from that set forth in one of the subsequent lectures 
 of this volume, from which, through Professor Whitman's 
 courtesy, I am enabled to quote. Whitman argues that 
 "cell-orientation may enable us to infer organization, but to 
 regard it as a measure of organization is a serious error." 
 "The question as to the presence of organization," he says, 
 " is not settled by the form of cleavage. Eggs that admit of 
 complete orientation at the first or second cleavage, or even 
 before cleavage begins, are commonly supposed to reflect 
 precociously the later organization, while eggs in which such 
 early orientation is impossible are supposed to be more or less 
 completely isotropic and destitute of organization. When the 
 region of apical growth is represented by conspicuous telo- 
 blasts, the fate of which is seen to be definitely fixed from 
 the moment of their appearance, we find it impossible to doubt 
 the evidence of organization, or ' precocious differentiation ' as 
 it is conventionally called. When the same region is composed 
 of more numerous cells, among which we are unable to distin- 
 guish special proliferating cells, we lapse into the irrational 
 conviction that the absence of definitely orientable cells means 
 just so much less organization." 
 
 It would be manifestly out of place to enter here upon any 
 of the interesting discussions suggested by the passage just 
 quoted, and I will therefore only add that Professor Whitman's 
 position seems to me to rest upon a special and peculiar use 
 of the word "organization," and that his view leads to a denial 
 of the principle of epigenesis. No one would maintain that 
 
14 BIOLOGICAL LECTURES. 
 
 the living ^gg is 'destitute of organization," but neither can 
 any one maintain that the egg-organization is identical with 
 that of the adult. Development is essentially a transformation 
 of one form of organization into another along the path of 
 cell-division and cell-differentiation ; and it is undeniable that 
 the adult form of organization is thus expressed earlier in some 
 cases than in others — for example, in the segregation of the 
 germ-layers in the polyclade, as compared with the annelid or 
 gasteropod. We are still profoundly ignorant of the nature 
 and causes of differentiation, and of its precise relation to 
 cell-formation ; and the question is probably not yet ripe for 
 discussion. It is, however, impossible to maintain that differ- 
 entiation in the Metazoa is entirely independent of cell-forma- 
 tion, when we recall the multitude of cases in which the lines 
 of differentiation coincide with cell-boundaries. 
 
SECOND LECTURE. 
 
 THE FERTILIZATION OF THE OVUM. 
 
 E. G. CONKLIN. 
 
 In the history of the biological sciences perhaps no problem 
 has received more attention than the fertilization of the ovum. 
 The first important advance in our knowledge of this phe- 
 nomenon within recent years was made by O. Hertwig^ about 
 twenty years ago. He showed that after a period of prepara- 
 tion in which the Qgg cell extrudes two small corpuscles, the 
 polar bodies, the nuclei of the male and female cells fuse to 
 form the first or segmentation nucleus of the new organism. 
 He therefore held that the process of fertilization consisted 
 essentially in the fusion of two nuclei coming from different 
 individuals. 
 
 This idea has dominated biology for the past decade, and it 
 is the generally accepted view to-day. In his recent work, Die 
 Zelle tmd die Gewebe, Hertwig says (p. 220), ''The nuclear sub- 
 stances which are derived in equal quantities from two different 
 individuals, are the only essential substances upon whose union 
 the act of fertilization depends ; they are the real fertilization 
 materials. All other substances, such as protoplasm, yolk, 
 nuclear sap, etc., have nothing to do with fertilization as such." 
 It is well known that Weismann in his various essays and 
 works upon heredity has expressed himself as fully satisfied 
 that the essence of fertilization consists in the fusion of the 
 nuclei of the ovum and spermatozoon. In fact his whole 
 theory is to a very large extent founded upon this fundamental 
 assumption that fertilization is essentially a nuclear process. 
 And quite recently Boveri,^ after a full discussion of the ques- 
 
 1 O. Hertwig, Beitrage zur Kenntniss der Bildung, Befruchtung und Theilung 
 des thierischen Eies. Morphol. Jahrbi'icher, 1875, 1877, 1878. 
 
 2 Boveri, Befruchtung. Ergebnisse der Anatomie u. Entiuick., 1892. 
 
1 6 BIOLOGICAL LECTURES. 
 
 tion, concludes with these words :^ "Their union [that of the 
 Qgg and sperm nucleus] is not the condition but the goal of 
 fertilization, and in this sense the statement is true to-day in 
 which O. Hertwig summed up the results of his first funda- 
 mental investigations, that ' the essential thing in fertilization is 
 the union of egg and spejin nucleus! " 
 
 It is only within the most recent times that a different view 
 has arisen, and for the sake of clearness I will sketch briefly 
 the rise of the idea that fertilization is not a purely nuclear 
 phenomenon, that it does not consist simply in a union of 
 nuclei coming from different individuals, but rather, as it seems 
 to me, in a union of all the essential parts of the reproductive 
 cells, cytoplasm as well as nuclei. 
 
 In 1873 Hermann Fol ^ described in the eggs of a jelly-fish 
 two star-shaped figures or asters at the two poles of the 
 nucleus, and one year later E. Van Beneden ^ described a 
 polar corpuscle as present in the cytoplasm during the karyoki- 
 netic division of the nucleus in some small parasitic organisms, 
 the Dicyemidae ; but it was certainly not until a much later 
 date that anything satisfactory was known of these bodies. 
 
 In 1887, only six years ago. Van Beneden^ in his work on 
 the fertilization of the ^gg of Ascaris, a thread-worm inhabit- 
 ing the intestine of the horse, gave a very minute account 
 of two granular bodies, the spJihes attractives which he 
 believed to be present at all times in the cytoplasm of the cell. 
 He described -each sphere as consisting of a central refractive 
 body, the central corpuscle, around which was a clear space, the 
 medullary zone, which in turn was surrounded by a deeply 
 staining granular area, the cortical zone, Fig. i, A and C. 
 Although he regarded these spheres as permanent organs of 
 the cell, he did not know how they originated in the Qgg under- 
 going fertilization, but he thought that the two spheres appeared 
 simultaneously in the Qgg as newly formed structures, and he 
 
 1 Loc. cit., p. 433. 
 
 2 Hermann Fol, Die erste Entwicklung des Geryonideneies. Jenaische Zeit- 
 schrift, 1873. 
 
 3 E. Van Beneden, Recherches sur les Dicyemides. Bull. Acad. roy. Belg., 1874. 
 * Van Beneden et Neyt, Nouvelles Recherches sur la Fecondation et la Division 
 
 mitosique chez I'Ascaride megalocephale. 
 
THE FERTILIZATION OF THE OVUM. \J 
 
 believed that they were derived "■ from the division of the Qgg 
 nucleus after it had given rise to the second polar body" (p. 60). 
 As described by Van Beneden, the position of the attraction 
 spheres at their earliest appearance, is shown in Fig. i A. 
 They appear together in close proximity to the female pro- 
 nucleus and at a considerable distance from the male pro- 
 nucleus. Van Beneden therefore supposed that the male 
 pronucleus had nothing to do with their formation. In later 
 stages, Fig. i, B and C, the two spheres begin to separate, 
 the spindle fibres appearing between their central corpuscles 
 and at the same time the two pronuclei approach each other 
 and the first cleavage spindle is formed, in large part at least, 
 from the two attraction spheres. 
 
 One year later, 1888, Boveri ^ described these bodies in 
 the same Qgg, that of Ascaris ; the central corpuscle of Van 
 Beneden he called the ccjitrosoine, and the dark granular sub- 
 stance surrounding this, which probably corresponds to the 
 cortical zone of Van Beneden, he named the archoplasm. The 
 relation of these parts to each other, and to the pronuclei, is 
 shown in Fig. i, D, E and F, which are taken from Boveri. 
 When first seen in the ovum, the male pronucleus lies in the 
 midst of a mass of granular material, the archoplasm. Later 
 it moves out of this, and in the place where it first lay a single 
 highly refractive body, the centrosome, appears. The centro- 
 some is at first single but later it divides, as shown in E, and 
 then around each of the centrosomes the archoplasm aggregates 
 to form two granular spheres. Meanwhile the two pronuclei 
 enlarge greatly and approach each other while the spindle 
 fibres are formed from the two spheres of archoplasm. With 
 regard to the origin of the constituents of the archoplasmic 
 system, Boveri believed that the centrosome was derived from 
 the spermatozoon, since it first appears in the archoplasm at 
 the very place previously occupied by the male pronucleus, 
 while the archoplasm itself, he supposed, came entirely or at 
 least in large part from the ^gg cell.^ 
 
 ^ Boveri, Zellen-Studien, Heft 2, Die I]efruchtung und Theilung des Eies von 
 Ascaris megalocephala, 1888. 
 - Loc. cit., p. 167. 
 
1 8 BIOLOGICAL LECTURES. 
 
 Two years ago Hermann Fol ^ published a preliminary account 
 of the fertilization of the ^g^ of a sea-urchin, in which he com- 
 municated the new and remarkable fact that each of the sexual 
 cells, ovum as well as spermatozoon, contains a kinetic center 
 or centrosome, which he called respectively the ovocenter and 
 the spcrmocentcr. When the spermatozoon enters the ovum 
 the spermocenter precedes the nucleus of the male cell, 
 Fig. I G, and finally reaches a point on the surface of the 
 female pronucleus opposite the ovocenter ; then the male pro- 
 nucleus comes to lie closely against the surface of the female 
 pronucleus, though it does not intimately fuse with it. The 
 two centers then divide. Fig. i H, and the half-centers push- 
 ing apart move in opposite directions around the cleavage 
 nucleus until one half of the ovocenter meets half of the 
 spermocenter at a point about 90° from that originally occu- 
 pied by the centers. Fig. i I. By the fusion of these half- 
 centres, one derived from the ovocenter the other from the 
 spermocenter, the astrocenters are formed. Around each of 
 these astrocenters there is formed a clear space, the astrocoel, 
 which probably corresponds to the medullary zone of Van 
 Beneden, as the astrocenter corresponds to the central cor- 
 puscle, while the astrocoel is surrounded by a zone of astral 
 radiaiionSj which is probably the cortical zone of Van Beneden 
 and the archoplasm of Boveri. From these facts regarding 
 the formation of the astrocenters, Fol concluded that ''fertiliza- 
 tion consists not only in the adding together of two pronuclei 
 derived from individuals of different sexes, but also in the 
 fusion of four half-centers derived from the father and the 
 mother into two new bodies, the astrocenters." ^ 
 
 In November of the same year, 1891, Guignard^ published 
 a most admirable account of the process of fertilization in some 
 of the flowering plants. He showed that the male pronucleus, 
 which is brought into close proximity to the female pronucleus 
 by the growth of the pollen tube, is always preceded by two 
 
 1 Hermann Fol, Die Centrenquadrille eine neue Episode aus der Befruchtungs- 
 geschichte. Anat. Anzeiger, May, 1891. 
 
 2 Loc. cit., p. 274. 
 
 3 Guignard, Nouvelles Etudes sur la Fecondation. Anuales des sciences natter. 
 Tom. 14, Botanique, 1891. 
 
THE FERTILIZATION OF THE OVUM. 
 
 19 
 
 Fig. 1. — Diagrams showing the process of fertilization according to different 
 authors. The first row (A, B and C), for Ascaris, according to Van Beneden ; 
 the second row, the same form, according to Boveri ; the third row for an Echinid, 
 according to Fol ; the fourth for Lilium, according to Guignard. 
 
20 BIOLOGICAL LECTURES. 
 
 bodies, the spJibres directrices, which are the equivalents of 
 Van Beneden's spheres attractives and Fol's asters ; two of 
 these spheres are also found in . contact with the female pro- 
 nucleus, Fig. I K. The two spheres which precede the male 
 pronucleus join those which surmount the female pronucleus 
 in such a way as to form two couples, each of which is com- 
 posed of one element derived from the male cell, the other 
 from the female cell. When the pronuclei come in contact, 
 the two couples diverge until they come to lie at opposite poles 
 of the nuclei. Fig. i L. Then the elements of each couple 
 fuse together into a single sphere with a single central cor- 
 puscle, Fig. I M, and from these spheres the first cleavage 
 spindle is formed. Guignard concludes, therefore, that fertili- 
 zation is not a purely nuclear phenomenon. "■ It consists not 
 only in the union of two nuclei of different sexual origin, but 
 also in the fusion of two protoplasmic bodies whose essential 
 elements are the sphtres directrices of the male cell and of the 
 female cell. Even if the nuclei are of great importance in the 
 transmission of hereditary properties, the permanent presence 
 of spheres directrices in the sexual and somatic cells, and above 
 all their fusion at the moment of fecundation, oblige us to 
 assign to the protoplasm the primordial role in the accom- 
 plishment of this phenomenon. This fusion appertains to 
 the very essence of fertilization ; it is necessary for the 
 formation and subsequent evolution of the Qgg'' ^ 
 
 More than a year ago (July, 1892), I found that the eggs of 
 one of our marine Gasteropods, Crepidiila plana, offered excep- 
 tional advantages for the study of the phenomena of fertiliza- 
 tion. In this ^gg, and that of other species of the same genus, 
 I had been able to trace the cell-lineage to more than one hun- 
 dred cells, and last summer, with more favorable material and 
 better methods, I was able to follow in surface preparations, as 
 well as in sections, the movements of the male and female pro- 
 nuclei, and what is much more important, the whole history of 
 the asters ^ from the time the first polar body is formed and the 
 
 1 Loc. cit., p. 276. 
 
 2 For these permanent organs of the cell, known by various authors as the 
 '■^ spheres attractives^^'' '^ spheres directrices,'" " archoplasmic bodies," "periplasts," 
 
THE FERTILIZATION OF THE OVUM. 
 
 21 
 
 spermatozoon enters the ^gg until a late stage in the cleavage 
 of the fertilized ovum. In the main, my observations on the 
 fertilization confirm those of Fol, concerning which a good 
 deal of doubt has been expressed by some authorities, though 
 in some respects they differ from these and resemble more 
 closely the results obtained by Guignard. 
 
 Since the aster plays so important a part in the process of 
 fertilization, it will be well to begin with a description of this 
 structure. Every aster undergoes periodical changes in form 
 and size as well as constitution. When it has reached its 
 largest size, which is just before it divides, it is a spherical or 
 ellipsoidal body, almost as large as the nucleus. Fig. 2. It 
 has a very definite out- 
 
 line from which radiating 
 rows of granules or micro- 
 somes ca,n be traced to all 
 parts of the cell. The 
 sphere itself consists of 
 an outer, darkly granular 
 zone and of a central clear 
 area. The granules of 
 the outer zone can in no 
 way be distinguished from 
 the microsomes scattered „ ^, . , r . . ^ 
 
 t IG. 2. — Section of one of the first four 
 throughout the cell ; their micromeres of C. plana showing the structure 
 general appearance is very o^ the aster and its relations to other parts of 
 
 similar and they stain in ^^^ ^^"• 
 
 the same way. Moreover, at certain stages in the history 
 of the aster it loses its definite outline, astral radiations 
 proceed from it in every direction, and the granules of 
 which it is composed become confluent with the microsomes 
 
 "para-nuclei," etc., I have decided to employ the name "aster," first used by 
 Fol, I believe. This name has the advantage of brevity, simplicity and accuracy, 
 which cannot be said of the others. Some of these names are not only unwieldy, 
 but absolutely misleading. For example, the spheres attractives have the function 
 of repulsion as well as attraction ; the spheres directrices do not, in all cases at least, 
 direct the nuclear division, and the same may be said of the archoplasm or "con- 
 trolling" plasm. The exact connotation of the words "periplast" and "para- 
 nucleus" is so doubtful that they cannot safely be used. 
 
22 BIOLOGICAL LECTURES. 
 
 of the cell ; at the same time the central clear area disappears. 
 This occurs in the formation of every nuclear spindle ; in the 
 later stages of the nuclear division, when the central portion 
 of the spindle begins to disappear, the granules which were 
 distributed along the radiating fibres are gathered together 
 in such a way that one or more rows of them are pressed 
 closely together to form the definite boundary of the aster, 
 while within this boundary the granules are less compactly 
 arranged. This graiiidar zone, with its radiations, corres- 
 ponds, I believe, to the cortical zone of Van Beneden and 
 the archoplasm of Boveri. 
 
 The central clear area probably corresponds to the medullary 
 zone of Van Beneden and the astrocoel of Fol, and in speaking 
 of it hereafter I shall employ the latter name. The astrocoel 
 always contains a large number of irregularly scattered granules, 
 which are considerably larger than those of the outer zone but 
 are not peculiar in any other respect. They show the same 
 micro-chemical reactions as the microsomes, and at an early 
 stage in the history of each aster they are closely connected 
 with the granules of the outer zone. After the nuclear spindle 
 has been formed these granules disappear, and in their 
 place is found, at each pole of the spindle, a darkly staining 
 body much larger than any one of the central granules. 
 This is doubtless the central corpuscle of Van Beneden or 
 centrosome of Boveri, and I cannot doubt that the numerous 
 central granules represent a fragmented or scattered centiv- 
 some. 
 
 The structure of the outer granular zone of the aster, its 
 micro-chemical reactions, and particularly its method of growth, 
 seem to me to indicate plainly that this portion of the aster 
 is merely a part of the general cytoplasm temporarily modified 
 or differentiated for a particular function. Regarding the 
 astrocoel and centrosomes there is more doubt, but I believe 
 that the evidence is clearly in favor of the view recently 
 expressed by Watase,^ that these structures are also a part 
 of the cytoplasm. Whatever the ultimate origin of the 
 centrosomes may be, there is no doubt that in Crepidula they" 
 
 1 Watase, Homology of the Centrosome. Jotu\ Morph., Vol. 8, No. 2. 
 
THE FERTILIZATION OF THE OVUM. 
 
 23 
 
 do not go back into the nucleus after every division, as 
 Brauer^ asserts is the case in Ascaris. It therefore seems 
 highly probable that the entire aster is a cytoplasmic struc- 
 ture, temporarily modified or differentiated for the purpose 
 of contraction and expansion, whose chief function in the 
 reproductive cells is to bring the pro-nuclei together, accom- 
 plish nuclear division, and move the nuclei from place to place 
 in the resulting cells. 
 
 To return to the process of fertilization : the spermatozoon 
 usually, though not invariably, enters the ovum near the vege- 
 tal pole. I have not observed it in the actual process of enter- 
 ing, though I have seen it immediately afterward. In such 
 cases it consists of a small conical or sometimes fusiform 
 nucleus, surrounded by a clear non-granular area. Fig. 3. At 
 this stage the sperm nucleus 
 consists entirely of chromatin 
 closely packed together; there 
 is no nuclear sap and no aster 
 is visible, though, perhaps, the 
 clear area surrounding the 
 nucleus may be taken as an 
 indication of the presence of 
 such a body. In Fig. 3 the 
 Q^^ nucleus is shown in the 
 process of division preparatory 
 to the formation of the first 
 polar body. There are two 
 centrosomes at the upper pole 
 of the spindle, though but one is to be seen at the lower pole. 
 The centrosome at the upper pole has divided thus early, 
 preparatory to the division of the chromatin of the first 
 polar body. This division occurs soon after the polar body 
 is formed. The surface of the ^gg is indented over the 
 upper pole of the spindle, thus indicating, as it seems to me, 
 that the astral fibres are here attached to the surface and are 
 drawing it in by their contraction. 
 
 1 Brauer, Zur Kenntniss der llerkunft des Centrosomes. Biol. Ccntralblatt, 
 13d. 13, Nos. 9 and to. 
 
 Fig. 3. — C. plana ; formation of the 
 first polar body ; at the left the sperma- 
 tozoon has just entered the ovum. 
 
24 
 
 BIOLOGICAL LECTURES. 
 
 The spermatozoon usually enters the ovum at about the same 
 time that the first polar body is being formed, though in a con- 
 siderable number of eggs it does not enter until after both 
 polar bodies have been extruded. Soon after its entrance, the 
 sperm nucleus begins to move toward the ^g'g nucleus. This 
 motion is quite slow, several hours (four to eight) being neces- 
 sary to bring the two nuclei together ; it is, therefore, possible 
 to find almost every stage in this process in eggs which have 
 been fixed and stained. During the whole of this journey 
 toward the ^gg nucleus, the sperm nucleus continually increases 
 in size ; but before this nucleus shows any appreciable enlarge- 
 ment, and when it is removed from the Qg<g nucleus by almost 
 the whole diameter of the ovum, the sperm aster appears as a 
 granular sphere, considerably larger than the sperm nucleus, 
 and lying immediately in advance of it, Fig. 4. Throughout 
 the approach of the two pronuclei, the sperm aster precedes 
 the sperm nucleus, and, as I believe, actually leads it to the 
 ^g'g nucleus. 
 
 As already explained, Boveri believes that the centrosome 
 of the new organism is derived exclusively from the sperma- 
 tozoon. In his latest work (already referred to) he says that, 
 in the case of Ascaris, there is neither centrosome nor aster 
 present in the formation of the two polar bodies, although 
 they were present at an earlier stage in the oogenesis ; he 
 therefore concludes that in this case the centrosomes of the 
 segmentation spindle, which forms later, must be derived 
 exclusively from the sperm centrosome. Vejdovsky^ has 
 reached the same conclusion with regard to one of the anne- 
 lids, Rhinchelmis. He says, regarding Fol's communication 
 relative to the ovocenter, that no one has hitherto seen such 
 a body in connection with the female pronucleus, and that he 
 conceives it to be the scarcely functional remnant of the 
 Eikei'nperiplaste, or ^gg aster. *' It is therefore," he says, 
 '* questionable to assume the presence of an ovocenter in 
 order to make a general law that in fertilization not only the 
 pronuclei, but also the halves of the ovocenter and spermo- 
 
 ^ Vejdovsky. Bemerkungen zur Mitteilung H. Fol's "Contribution a I'histoire 
 de la fecondation." Anat. Anzeiger, Bd. 6, No. 13. 
 
THE FERTILIZATION OF THE OVUM. 25 
 
 center unite. The facts observed in the case of Rhinchelmis 
 speak against Fol's theory." 
 
 In the face of the conclusions of these well-known investi- 
 gators, it is interesting to find, in the case of the Crepidula 
 ^g^, a well marked centrosome and surrounding parts of the 
 aster present at each pole of the spindle in the formation of 
 each of the polar bodies ; and immediately after the second 
 polar body has been extruded, and while the sperm nucleus 
 and aster are still far removed from the ^g<g nucleus, a large 
 and distinct aster can be seen in contact with this nucleus. 
 This Qgg aster lies below the ^gg nucleus, and usually slightly 
 to one side of the chief axis of the ovum, as shown in Fig. 4. 
 
 Fig. 4. — Ovum of C. plana, side view; FiG. 5. — Ovum of C. plana seen from 
 the asters are shown in dotted outline, upper pole ; in this and the following 
 the clear spheres with dark centers, at figures the male aster and nucleus lie to 
 the upper pole, are the two polar bodies, the left, the female to the right. First 
 
 contact of the two asters. 
 
 It is at first much larger than the sperm aster, and in fact 
 remains larger until it enters upon ^'ia MaixJie dc la Quadrille T 
 The sperm nucleus always approaches the ^gg nucleus from 
 below and in such a way that the sperm aster is directed 
 toward the egg aster. Fig. 4. The force which draws the two 
 pronuclei together seems to exist between the two asters rather 
 than between the pronuclei. Accordingly, in the progress of 
 the sperm nucleus toward the ^gg nucleus, the asters first 
 come in contact, Fig. 5. In all movements of the nucleus, the 
 latter appears to be passive while the asters are active. This 
 
26 BIOLOGICAL LECTURES. 
 
 principle is illustrated throughout the whole history of the 
 cleavage ; whenever the nucleus is moved from one position to 
 another in the cell it is preceded by its aster. The method by 
 which the asters draw the two pronuclei together is, I believe, 
 by the formation, attachment and contraction of the astral or 
 archoplasmic fibrils. In this connection it is interesting to 
 contrast the methods by which the male and female cells 
 approach each other before and after the spermatozoon has 
 reached the ovum. In the case of Crepidula, as in most 
 other forms, the spermatozoon moves toward the ovum by the 
 lashing from side to side of a long thread-like flagellum. As 
 soon, however, as the sperm enters the ovum this flagellum is 
 
 Fig. 6. — Ovum of C. plana from Fig. 7. — Separation of the two 
 
 upper pole ; first contact of the two asters; the polar bodies lie immediately 
 pronuclei. over the female pronucleus. 
 
 lost in most cases, and the rest of the progress toward the Q%g 
 nucleus and aster must be accomplished in some other way. 
 This, as just said, seems to be done by the formation and con- 
 traction of astral fibers. This movement of the sperm cell 
 within the ovum is the result of protoplasmic contractility 
 no less than is the movement of the spermatozoon outside of 
 of the nucleus, operating, however, in a slightly different way. 
 After the two asters have come in contact, they move slightly 
 to one side, remaining however connected, though individually 
 distinct, and the two pronuclei then come together, Fig. 6. 
 Even at this time, the sperm aster and nucleus are usually a 
 
THE FERTILIZATION OF THE OVUM. 27 
 
 little smaller than those of the ^gg cell, and they frequently 
 remain slightly smaller as long as they can be distinguished. 
 In cases where there is no appreciable difference in size 
 between the two pronuclei, the one may be distinguished from 
 the other, as long as they remain distinct, by the position of 
 the polar bodies which lie directly over the female pronucleus. 
 After the two pronuclei have met, the two asters begin to 
 move apart. They continue to separate, moving around the 
 appressed nuclei, until they lie at opposite poles. Fig. 7. The 
 sperm aster now lies on the outer side of the sperm nucleus, 
 and the ^gg aster on the outer side of the ^gg nucleus ; it is 
 thus seen that the position which the asters occupy relative to 
 
 Fig. 8. — The halves of the male and Fig. 9. — The halves of the female 
 female asters about to unite at the aster at the poles of the pronuclei ; the 
 poles of the pronuclei. male aster still undivided. 
 
 the pronuclei, is just the reverse of that which obtained previ- 
 ous to the meeting of the two pronuclei. It must also be 
 allowed, I think, that the function now exercised by the asters 
 must be the reverse of that which prevailed before the pro- 
 nuclei met. Then, by active contraction, they drew the two 
 pronuclei together; now, by active expansion, they diverge, move 
 to opposite poles, and press the pronuclei together. This func- 
 tional alternation of contraction and expansion, or perhaps 
 better, attraction and repulsion, is manifest not only during 
 fertilization, but throughout the entire process of cleavage. 
 The contraction can be seen in the way in which the asters 
 
28 
 
 BIOLOGICAL LECTURES. 
 
 draw the nuclei from one place to another in the cell, as well 
 as in the pulling asunder of the chromatic elements of the 
 nucleus, the expansion in the division of the asters and the 
 subsequent divergence of the resulting daughter asters, as well 
 as in the formation of the karyokinetic spindle and the pushing 
 together of the chromatic elements into the equatorial plate. 
 
 After the asters have reached the outer sides of the two pro- 
 nuclei, each divides into two half-asters, which diverge from 
 each other until they come to lie at opposite poles of the 
 nuclei and in the plane of contact between the two. At this 
 stage, therefore, there is found at each pole of the two pro- 
 nuclei one-half of the sperm aster and one-half of the ^gg aster, 
 Fig. 8. Each of these couples soon fuses into a single aster, 
 and the two asters thus formed lie at opposite poles of the 
 first cleavage-spindle-, Fig. lo, and from them all the other 
 asters of the developing ovum are derived. 
 
 As an interesting variation of this more usual behavior of 
 the asters, it should be mentioned that in cases where the 
 sperm nucleus and aster meet the corresponding parts of the 
 
 ^gg cell, while there is yet 
 considerable disparity in size 
 between the two, the ^gg 
 aster after having reached its 
 full size divides, and the two 
 half-asters pass to the two 
 poles of the nuclei, while the 
 sperm aster, during all this 
 time, remains undivided until 
 it has reached its full size, 
 when it divides, and its halves 
 move around to meet the 
 waiting halves of the ^g'g 
 aster, Fig. 9. 
 
 With the fusion of the half- 
 asters, one part of the fecunda- 
 tion, and that a very important one, is completed, although the 
 two pronuclei may still be recognized as such. In fact, the 
 boundary line between the ^gg and the sperm nucleus can be 
 
 Fig. 10. — Formation of the first 
 cleavage-spindle. The half-asters have 
 fused, but a trace of the nuclear mem- 
 brane remains between the two pro- 
 nuclei. 
 
THE FERTILIZATION OF THE OVUM. 29 
 
 distinguished even after the first cleavage spindle begins to 
 form, and their chromatin masses remain distinct, Fig. 10, 
 until the equatorial plate stage. 
 
 After the chromatin of the two pronuclei has assumed the 
 shape of distinct rods, the chromosomes, and before these rods 
 have been pressed together into the equatorial plate, it is 
 possible to determine that each pronucleus contains twelve of 
 these elements. Since these elements are doubled at every 
 division of the .nucleus, it follows that each of the first two 
 nuclei contains twenty-four chromosomes, twelve derived from 
 the sperm nucleus and twelve from the ^^^ nucleus, and this 
 number is probably constant for all the nuclei of this species. 
 
 It is difficult to define exactly the time at which the two 
 pronuclei have sufficiently united to be considered a single 
 element, but perhaps this can be most conveniently located at 
 the time when the boundary wall between the two vesicular 
 nuclei disappears, although, as just said, the two masses of 
 chromatin remain distinct until a somewhat later period. Cer- 
 tain it is that a fusion of the pronuclei to form a resting seg- 
 maitation micletis, as described by Hertwig, does not take 
 place. 
 
 With the union of the pronuclei, the entire process of 
 fecundation may be considered as ended. So far from being 
 a purely nuclear phenomenon, it must be evident to any one 
 who follows the history of the asters that they take an 
 extremely important part in this process. If we are amazed 
 at the precision with which the chromatic elements of the 
 nucleus are divided and distributed, we can be no less astonished 
 at the wonderful directive influence exercised by the asters 
 upon the nuclei ; and if it is justifiable to conclude that the 
 chromosomes have an extremely important function in the 
 building of the new organism because of the way in which 
 they are distributed, how is it possible to avoid the same con- 
 clusion with regard to the asters, which, as we have seen, are 
 equally divided in a manner not clearly understood into half- 
 asters, which then fuse in such a way that one-half of each 
 aster of the new organism comes from the paternal and one- 
 half from the maternal organism } 
 
30 BIOLOGICAL LECTURES. 
 
 Hertwig, Boveri and Weismann, as well as a number of other 
 well-known investigators, assert that the hereditary substance, 
 by means of which heritable qualities are transmitted from one 
 generation to another, is contained wholly within the nucleus, 
 and, speaking more strictly still, within that part of the nucleus 
 called the chromatin. Since, however, many of the characters 
 of the cytoplasm are heritable, and in fact are generally the 
 only characters which are known by observation to be herit- 
 able, these authorities are compelled to assume that the control 
 of the cell, if not the actual genesis of all its constituents, is 
 located wholly within the chromatin. As a matter of fact, it 
 must be acknowledged that this assumption that the chromatin 
 makes the cell-body just what it is in point of structure, func- 
 tion, shape, position and size, does not rest upon observation 
 but upon supposed theoretical necessities. All these necessi- 
 ties find their source in the assumption that the nucleus, and 
 especially the chromatin, is the only bearer of heredity, an 
 assumption which was wholly justified so long as it was sup- 
 posed that fertilization consisted merely in the fusion of the 
 two pronuclei ; but now since it is known that the cytoplasm, 
 and especially the male and female asters, take a very import- 
 ant part in the process of fertilization, it seems to me that 
 such an assumption is wholly unwarrantable. 
 
 The spermatozoon does not cease to be a cell the moment it 
 has entered the ovum. Both its cytoplasm (in the form of an 
 aster) and its nucleus are represented, and they grow just as a 
 cleavage or tissue cell does by the assimilation of food material, 
 which in this case is contained within the o^gg cell. Although 
 within the ovum the spermatozoon must be considered a dis- 
 tinct cell, preserving all its fundamental peculiarities, until that 
 time when its various constituents lose their identity by fusion 
 with corresponding parts of the ^gg cell. While it is known 
 in several cases that the spermatozoon introduces a nucleus 
 and an aster, which then fuse with similar parts of the ovum, 
 it is not known, with one or two exceptions, that any portion 
 of the general cytoplasm of the male cell is carried into the 
 ovum. In the case of Ascaris, both Van Beneden and Boveri 
 agree that a certain part of the cytoplasm of the spermatozoon 
 
THE FERTILIZATION OF THE OVUM. 
 
 31 
 
 is carried into the ^ggy and is there absorbed, used as food, by 
 the cytoplasm of the ovum. On the ground of direct observa- 
 tion, the fusion of the general cytoplasm of the sperm with 
 that of the ovum can neither be affirmed nor denied in most 
 cases ; but it is a matter of observation that there is a union 
 of those portions of the cytoplasm which can be followed, viz., 
 the asters, and in view of what we know of conjugation among 
 the simplest animals and plants, where there is a fusion of 
 the cell-bodies as well as of the nuclei, I question whether 
 the cytoplasm which the sperm carries into the ovum, in the 
 case of Ascaris, merely degenerates and serves as food for the 
 ^gg cytoplasm. It seems to me more probable that this sperm 
 cytoplasm does not act as so much dead matter, but that it also 
 takes part in this union of the essential constituents of the two 
 cells. 
 
 On a priori ground, I think we ought to expect that in fer- 
 tilization all the essential parts of one cell would unite with 
 corresponding parts of another cell. In fact, the form of 
 fertilization characteristic of the higher animals and plants 
 is generally supposed to have been derived from a condition 
 similar to that which at present obtains among the lower 
 animals and plants in which there is a fusion of two entire 
 cells. Most persons would probably agree that fertilization 
 consists in the union of the essential parts of two cells ; the 
 question is, ''What are essential parts .^ " It is known that if 
 some of the Infusoria are cut to pieces so that some of the 
 pieces contain portions of the nucleus, while others do not, the 
 nucleated portions will regenerate all the lost parts, while those 
 pieces which contain no part of the nucleus do not regenerate 
 but sooner or later perish. It is, therefore, certain that the 
 cytoplasm cannot perform the normal funtions of growth and 
 regeneration apart from the nucleus. It seems equally certain, 
 although much more difficult of demonstration, that the nucleus 
 cannot perform all its normal functions apart from the cyto- 
 plasm. Both nucleus and cytoplasm are essential constituents 
 of the cell, and one cannot be said to be more important than 
 the other. In spite of the assumption of smaller structural 
 units within the cell (such as the biophors of Weismann, the 
 
32 BIOLOGICAL LECTURES. 
 
 pangenes of De Vries, the plasomcs of Wiesner, which assump- 
 tion, in one form or another, seems to me a necessity), the 
 independent unit of structure is still the entire cell, not cyto- 
 plasm alone, nor nucleus alone, but the two together. So far 
 as we know, the cytoplasm of every cell comes from the cyto- 
 plasm of some parental cell, just as certainly as the nucleus 
 comes from a preceding nucleus. Until, therefore, it can be 
 shown that the nucleus can exist independently of the cyto- 
 plasm, it is unsound to assert that the cytoplasm is not an 
 essential constituent of the cell. And until some one has 
 shown that cytoplasm is not derived from pre-existing cyto- 
 plasm, but is the product of the nucleus,^ it is too soon 
 to assert that the control of the entire cell lies in the 
 nucleus, and hence that the nucleus is the sole bearer of 
 heredity. 
 
 In seeking to show that the nucleus is not the sole bearer 
 of heredity, we are not confined entirely to the a priori argu- 
 ment ; aside from the important evidence already adduced in 
 the presence and function of the asters observations are not 
 altogether wanting to show that the cytoplasm, in many 
 respects at least, is not controlled by the nucleus. In the 
 early cleavage stages of Crepidula pla^ia, it can be shown beyond 
 question that the direction of the cleavage, the size of the cells 
 formed, and the shape of those cells is the result of cytoplasmic 
 activity rather than of nuclear.^ It is generally believed that 
 
 1 This is, I know, what Weismann asserts (The Germ Plasm, p. 50), and he 
 urges in proof the observations of Riickert on the alteration in size of the 
 chromosomes of the nucleus during the growth of the ovum ot the dogfish. 
 These chromosomes first enlarge greatly, and afterward diminish in size until 
 they are not much larger than at first. Riickert, therefore, believes that the 
 chromosomes give off a large amount of substance to the cytoplasm, and this 
 conclusion is probably correct. It does not follow, however, that this material 
 controls the cytoplasm, as Weismann assumes, any more than the fact that the 
 cytoplasm supplies the nucleus with a large amount of nuclear sap in its pre- 
 division stages, argues that the cytoplasm controls the nucleus. It is probable 
 that each supplies substances to the other, and it is interesting to note that at 
 the very stage described by Riickert (the pre-division stage), in which the chro- 
 mosomes are giving off substances to the cytoplasm, the nucleus, in many 
 forms at least, is receiving a large amount of material in the form of nuclear 
 sap from the cytoplasm. 
 
 2 Since this lecture was given, I have found that Boveri, in his recent work on 
 
THE FERTILIZATION OF THE OVUM. 33 
 
 the nuclear spindle predetermines the direction of the cleavage, 
 yet, in this case, the spindle may be formed in any possible 
 direction, and yet the cleavage invariably takes place in the 
 same direction. It is frequently asserted that the division-wall 
 between the daughter-cells appears at right angles to the 
 spindle, and yet, in this case, it may form at a greater or a 
 smaller angle than 90°. The direction of the cleavage is pre- 
 determined not only before the nucleus divides, but long before 
 the asters divide. Certain oscillatory movements of the cyto- 
 plasm, which begin with the first division of the ovum and can 
 be observed throughout a large part of the cleavage, determine 
 with absolute certainty the direction of the cleavage before any 
 indication of division can be found within the cell. Since. the 
 direction of the cleavage is not determined by the nucleus, it 
 follows that the rotation of the cells and the position which 
 they take, with reference to each other, are not determined by 
 the nucleus ; and since it can be shown that the shape of the 
 cleavage cells is very largely the result of intercellular rela- 
 tions, it follows that in this case, at least, the shape of the 
 cell is not determined by the nucleus. 
 
 Still farther, the size of the cell seems to be determined by 
 the cytoplasm rather than by the nucleus. The indirect or 
 karyokenetic division of the nucleus results in an equal division 
 of the chromatic substance. After the division has taken 
 place, the two-daughter nuclei are for a considerable period 
 equal in size, though the cell-bodies in which they lie may be 
 very unequal. Likewise, the division of the asters is always 
 an equal division, and in the early stages of karyokinesis the 
 two asters are always equal in size. Yet in these very stages 
 in which the nuclei and the asters are equal in size, the lobing 
 of the cytoplasm may show beyond doubt that the division of 
 the cell-body is to be very unequal. I believe, therefore, that 
 neither the nuclei nor the asters determine the initial size of 
 
 fertilization (" l^efruchtung," p. 469), mentions the fact that he fertilized ova of 
 one genus of sea-urchin with the sperm of another, from which cross a larval 
 form developed which was intermediate in character bet\yeen the two genera. 
 The cleavage, however, was purely maternal, thus indicating that it was not 
 influenced by the sperm nucleus. He, therefore, concludes that the process of 
 cleavage, to all appearances at least, is not directed by the nucleus. 
 
34 BIOLOGICAL LECTURES. 
 
 the cells which are formed by division ; it is determined rather 
 by the general cytoplasm. In the later stages of karyokinesis, 
 after the lobing of the cytoplasm has indicated the size of the 
 daughter cells, but sometime before the division-wall is formed, 
 the asters become unequal in size if the division is to be an 
 unequal one, and by the time that the division-wall is formed 
 the asters are proportional in size to the daughter cells in 
 which they lie. At a considerably later period the nuclei 
 become proportional in size to the cells in which they are 
 found. 
 
 In Crepidula, therefore, I believe it is certain that the direc- 
 tion of the cleavage, as also the position, the shape and the 
 size of the resulting cells are not directly governed by the 
 nucleus. These definite forms of cleavage which are so 
 excellently exemplified in Crepidula are inherited as certainly 
 as any definite adult structures are, and if they are not 
 under nuclear control, these hereditary tendencies must be 
 transmitted through the cytoplasm. 
 
 Of course, it may be urged that there is some unknown and 
 invisible influence emanating from the nucleus which controls 
 all the processes of cell life. In the nature of the case such 
 an assertion cannot be affirmed nor denied on the ground of 
 observation, and it seems to me sufficient to urge in reply that 
 we should believe things are what they seem unless we are 
 compelled to believe differently. Many of the processes of 
 cell life seem to be controlled by the cytoplasm more inti- 
 mately than by the nucleus ; so far as we can observe, all 
 cytoplasm comes from pre-existing cytoplasm, just as all 
 nuclei come from previous nuclei. We know that the cyto- 
 plasm from both the father and mother are represented in 
 every stage of fertilization, and it is unnecessary and therefore 
 unscientific to assume that the nucleus controls all the 
 processes of cell life, and that the heritable characters of the 
 cytoplasm are transmitted only through the nucleus. 
 
 If, in stating my objections to the view held by the vast 
 majority of the biologists of the present day, I may seem to 
 have denied the importance of the nucleus while empha^zing 
 the importance of the cytoplasm, I would wish to say, in con- 
 
THE FERTILIZATION OF THE OVUM. 35 
 
 elusion, what has been said several times already, that I con- 
 sider both cytoplasm and nucleus essential constituents of the 
 cell, and therefore one cannot be said to be more important 
 than the other. In all the phenomena of cell life, — growth, 
 regeneration, fertilization, division, the building of the organ- 
 ism, the transmission of heritable characters, — both nucleus 
 and cytoplasm take part, though probably not always an equal 
 part. The entire cell is still the ultimate independent unit of 
 organic structure and function. 
 
THIRD LECTURE. 
 
 ON SOME FACTS AND PRINCIPLES OF PHYSIO^ 
 LOGICAL MORPHOLOGY. 
 
 JACQUES LOEB. 
 
 In this address I shall give a short account of a series of 
 experiments which were undertaken in order to 
 determine the causes of animal forms. Some of 
 the results of these investigations have already 
 been published. ^ Among others, which are new, 
 are experiments upon the artificial production of 
 double and multiple monstrosities from one ovum ; 
 in the sea-urchin. 
 
 I. Heteromorphosis. 
 
 If we look at an animal we perceive that its 
 various organs are arranged in a definite way. 
 From our shoulders originate arms, and from our 
 hips legs, but we never see that legs grow out 
 from the shoulders or arms from the hips. In 
 the lower animals there exists the same definite [ 
 arrangement of parts. 
 
 Fig. I is a diagram of a hydroid Antennularia, 
 which is pretty common at Naples. From a 
 bundle of roots or stolons a perfectly straight 
 stem arises to a height of six inches or more. 
 From this main stem originate, in regular suc- 
 cession, very short and slender branches, which 
 carry polyps on their upper sides. 
 
 In this case we never find that a root originates 
 at the apex, or in the place of a branch, or that 
 polyps originate at the lower side of a branch 
 
 1 Untersuchiingen ziir physiologischen Morphologie der Thiere. I, Heteromor- 
 phosis, WUrzburg, 1891. II, Organbildung und Wachsthum, Wiirzburg, 1892. 
 
38 BIOLOGICAL LECTURES. 
 
 physiologist the question arises : What are the circumstances 
 
 which determine that only one kind of organs originate at 
 
 certain places in the body ? I conceived that the answer to 
 
 this question might be obtained by finding out 
 
 whether or not it was possible to make any 
 
 desired organ of an animal grow at any desired 
 
 place. In case of success, the question to be 
 
 decided was whether the same circumstances by 
 
 which we can change the arrangement of organs 
 
 experimentally determine also the arrangement 
 
 of organs in the natural development. 
 
 If we cut out a piece (Fig. 2) of an Antennu- 
 
 laria, and hang it up vertically in the water, the 
 
 apical end b above and the root end a below, we 
 
 find that after a few days the root end a forms 
 
 little roots, r, which grow downward, 
 
 and the apical end, b, forms a new 
 
 apex, c. 
 
 If we cut out a similar piece and 
 
 hang it upside down (Fig. 3), the 
 
 root end ^, which now is above, 
 
 forms a new apex, ac, and the apical 
 
 end by which is below, forms roots. 
 Fig. 2. ^ , , 
 
 In such an apex the arrangement 
 
 of organs is just the same as in the normal 
 animal, namely, branches growing obliquely 
 upward bearing polyps on their upper sides. We 
 are, therefore, able to substitute a root for an 
 apex and an apex for a root. I have called this 
 substitution of one organ for another hetero- 
 morphosis. If we place the cut-out piece of 
 Antennularia horizontally instead of vertically, 
 something still more remarkable happens, namely, 
 the branches on the lower side suddenly begin to 
 grow vertically downward, and the outgrowing ^^" ^' 
 
 parts are no longer branches but roots, rr, Fig. 4. This we can 
 prove by their physiological reactions, for the roots fix them- 
 selves to the surface of solid bodies, for instance, the glass of 
 
ON PHYSIOLOGICAL MORPHOLOGY. 
 
 39 
 
 the aquarium, while the stems never show any reaction of this 
 kind. These new parts growing out from the branches of 
 the under side of the stem attach themselves to solid bodies, 
 if we bring them in 
 contact with the same. 
 Moreover, they are pos- 
 itively geotropic (that 
 is, they grow toward 
 the centreof theearth), 
 while the branches 
 never show any pos- 
 itive geotropism. The 
 branches on the upper 
 side are not trans- 
 formed into roots. 
 They either perish or give rise to very long, slender, perfectly 
 straight stems (b, Fig. 4), which grow vertically upward. 
 These stems, as a rule, are too slender to bear branches, 
 but at parts of the upper surface of the main stem there 
 originate new stems (<:, Fig. 4) which grow vertically upward 
 and produce the typical little branches with polyps. 
 
 If we bring the stem into an oblique position (Fig 5), with 
 the apex b upward, from every element of the main stem new 
 
 Fig. 4. 
 
 Stems and roots may originate, but with this difference, stems 
 always originate from the upper side of an element and roots 
 from its lower side. But if we place the stem in an oblique 
 
40 
 
 BIOLOGICAL LECTURES. 
 
 position (Fig. 6), with the root end above, the branches on the 
 under side grow out as roots and at the upper end, a stem 
 arises as usual. 
 
 What circumstances have all these experiments in common ? 
 These two : stems always originate from the upper end or side 
 of an element, and roots always originate from the lower side 
 or end of the same element. These facts can be explained 
 only through the assumption that gravitation, in this case, 
 determines the place of origin of organs. 
 
 Now we may ask whether the 
 action of this force, gravitation, 
 produces the natural arrangements 
 of parts, i. r., roots growing only at 
 the base of the stem and never at 
 the apex or in the place of a branch. 
 I think that it does. By reason of 
 its negative geotropism, the stem 
 grows vertically upwards. Gravita- 
 tion does not permit roots to arise 
 at any place except the under side 
 of the organs, and that, in the 
 normal position, is the base of the 
 stem. The same force determines 
 that polyps can originate only at 
 the upper side of branches, and so 
 the main arrangement of organs is 
 brought about by gravitation. But 
 how does gravitation determine that 
 roots grow at the upper and stems 
 at the under side t This is a question to which I shall return 
 later. 
 
 Fig. 7 is a drawing of a case of heteromorphosis in Margeliss, 
 a hydroid common at Woods Holl. 
 
 If we cut off a stem, or a small piece of a stem, and place it 
 in a dish containing sea water, and protect it carefully from 
 every motion, a curious change takes place in the organism. 
 Almost all, and in some cases all of the stems which touch 
 the glass begin to give rise to roots that spread out and very 
 
 Fig. 7. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 41 
 
 soon cover a large area of the glass. In this way the apical 
 end of a stem may continue to grow as a totally different 
 organ, namely, as a root. Every organ not in contact with 
 some solid body gives rise to polyps. Even the main root, if 
 not in contact with a solid body, no longer grows as a root, but 
 gives rise to a great number of small polyps which appear at 
 the end of long stems. Fig. 7, which Mr. Tower was kind 
 enough to draw for me, shows a branch which formed roots 
 at its apex and polyps at its roots in this way. The stem 
 touched the bottom of the dish with the apical ends, a, b, c and d. 
 All these ends gave rise to roots. From the upper side of the 
 original root, r, which was not in contact with the glass, later 
 on small polyps, //, grew out. Every place which was in con- 
 tact with solid bodies gave rise to roots, and every place which 
 was in contact with sea water gave rise to polyps. 
 
 This is not the only species of hydroid found at Woods Holl 
 in which such forms of Heteromorphosis can be produced. 
 Another form, Pennaria, is just as favorable. In Pennaria I 
 succeeded repeatedly in producing roots at both ends of a 
 small stem that bore no polyps.^ 
 
 What circumstances are common in these experiments on 
 Margelis and Pennaria } Organs brought into contact with 
 solid bodies continue to grow as roots, if they grow at all. 
 Organs surrounded on all sides by water continue to grow in 
 the form of polyps, if they grow at all. In Margelis, contact 
 
 1 In a Tubularian I was able to produce the opposite case, namely, to get an 
 animal that ended at both ends in a polyp and had no root. Weismann seems 
 to assume, in his " Germ Plasm," that the latter result is to be explained by the 
 principle of natural selection, inasmuch as an animal without polyps could not 
 continue to live, and hence it would be impossible to produce roots at both ends. 
 In Pennaria this supposed impossibility was realized. One may say that these 
 roots in Pennaria may give rise later on to polyps. In the special case that I 
 observed they did not, although as a rule they do. But the same is the case in 
 Tubularia, in which polyps also arise from the roots. It might be said, perhaps, 
 that the formation of roots in Pennaria is, for some reason, absolutely necessary. 
 But it is just as easy to produce polyps at both ends. Even if it were possible to 
 reconcile these facts with the principles of natural selection, causal or physio- 
 logical morphology would not gain thereby, as the circumstances that determine 
 the forms of animals and plants are only the different forms of energy in the 
 sense in which this word is used by the physicist, and have nothing to do with 
 natural selection. 
 
42 BIOLOGICAL LECTURES. 
 
 with a solid body plays the same role as did gravitation in the 
 case of Antennularia. In what way the contact may have an 
 influence shall be mentioned later. We may add, however, 
 one more point. In Antennularia, gravitation not only deter- 
 mines the place of origin of the various organs, but also the 
 direction of their growth ; the stem, growing upward, is nega- 
 tively geotropic, the root, growing downward, is positively 
 geotropic. In Pennaria, the nature of the contact not only 
 determines the place of origin of the various organs, but also 
 the direction of their growth. If we bring an outgrowing 
 polyp of Pennaria into contact with a solid body, the polyp 
 begins to grow away from the body, and the new stem is very 
 soon nearly perpendicular to the part of the surface with which 
 it came into contact. 
 
 I have called this form of irritability Stereotropism. We 
 may speak of positive Stereotropism in the case of the root, 
 and of negative Stereotropism in the case of the polyp. 
 
 Here, too, it may be asked whether contact with foreign 
 bodies, which in these experiments determined the arrange- 
 ment of the various organs, may not have the same effect in 
 the natural development of the organism. I believe that such 
 is the case. Negative Stereotropism forces the polyps to grow 
 away from the ground into the water, and so parts surrounded 
 by water form polyps only. Positive Stereotropism forces roots 
 in contact with the ground to grow toward it, so parts in con- 
 tact with the ground give rise to roots only. Thus it happens 
 that, under ordinary circumstances, in the animal we find roots 
 only at the base where it touches the ground. In other hydroids 
 the place of origin of the different organs is determined by 
 light, and in others we find more complicated relations. 
 
 It may appear from the foregoing 
 
 that such cases of heteromorphosis are 
 
 confined to hydroids, but such is not 
 
 the case. We find similar cases in 
 
 Timicates. Ciona intestinalis (Fig. 8), 
 
 a solitary ascidian, has eye-spots around the two openings 
 
 into the pharyngeal cavity, a and b. If we make an incision 
 
 at c, eye-spots are formed on both sides of the incision. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 
 
 43 
 
 While 
 observed 
 any kind 
 
 a 
 
 II. Polarization. 
 
 the foregoing experiments were in progress, I 
 that in many animals I was unable to produce 
 of heteromorphism. These animals showed, in 
 regard to the formation of organs, a 
 phenomenon with which we are familiar in 
 a magnet. If we break a magnet into 
 pieces, every piece has its north pole on 
 that side which in the unbroken magnet 
 was directed toward the north. Likewise, 
 there are animals every piece 
 of which produces, at either \\\\\|///Y 
 
 Fig. 9. 
 
 end, that organ toward which ^ 
 it was directed in the normal 
 condition. We may speak in 
 such cases of polarization. 
 The clearest example of this 
 I found in an actinian, Ceri- 
 anthus membranacetis. 
 
 Fig. 10. 
 
 If we cut a rectangular piece, abed, out of the body- wall 
 of Cerianthus (Fig. 9), very soon new tentacles begin to grow 
 
 out of this piece, but only from the side 
 V\\\llMf ab (Fig. 10), which was directed toward ^ 
 WWU///// the oral end of the animal. Nothing of 
 the sort occurs in the side, c d, or ac, 
 or b d. The production of tentacles 
 takes place before any other regeneration 
 begins. The same polarization is shown 
 in the following variation of the preceding 
 experiment : If we make an incision, 
 abc (Fig. 11), into the body- wall of the / 
 actinian, only the lower lip, be, produces 
 tentacles, while the upper lip, a e, pro- 
 duces none. The two ends heal together 
 in such a way that one-half of a mouth, 
 with its surrounding tentacles, a (Fig. 12), 
 is formed. It is curious to see how these tentacles behave if 
 
 J 
 
 Fig. II. 
 
 Fig. 12. 
 
44 BIOLOGICAL LECTURES. 
 
 we offer them bits of meat. They endeavor to force it into 
 the new oral disc, where the mouth ought to be, but where no 
 mouth exists, and only after a struggle of some minutes give up 
 the hopeless attempt. I tried in every possible way to produce 
 tentacles in the aboral end of a piece which had been cut out, 
 but without success. 
 
 Hydra behaves, as regards polarization, a little differently 
 from Cerianthus. If we make an incision in the stem, a 
 whole new oral pole grows out, but otherwise it, too, shows 
 polarization. 
 
 A good many animals, so far as is yet known, reproduce 
 only the lost organ, but never show any heteromorphism. We 
 see, therefore, that while in some animals we are able to pro- 
 duce heteromorphosis, in others the most definite polarization 
 exists, and we are able to produce regeneration of lost parts 
 only in the arrangement which exists in the normal animal. 
 In this case we must assume that unknown internal conditions 
 determine the arrangement of limbs. 
 
 In addition to examples of heteromorphosis or polarization 
 occurring separately, we find cases in which both phenomena 
 are exhibited by the same animal. If we cut out a sufficiently 
 large piece of the stem of Tubularia mesembryanthemum, and 
 place it in the bottom of a dish of water, carefully protected 
 from jarring, the anterior end of the piece gives rise to a new 
 polyp, the posterior end to a root ; but if we hang up the stem 
 in such a way that the posterior end does not touch the surface 
 of the glass, and is sufficiently provided with oxygen, this end, 
 too, produces a polyp, and we have a true case of heteromor- 
 phosis. In all cases the polyp at the oral end is formed first, 
 and a relatively long time (one or more weeks) elapses before 
 the aboral polyp is formed. But under one condition I could 
 cause the stem to form a polyp at the aboral as quickly as at 
 the oral end, namely, by inhibiting or retarding the formation 
 of the oral polyp. This could be done readily by diminishing 
 the supply of oxygen at the oral end. In such cases the 
 aboral polyps were produced nearly as quickly as the oral 
 polyps. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 45 
 
 III. The Mechanics of Growth in Animals. 
 
 In order to get an explanation of the phenomena of organiza- 
 tion we must ask, What are the physical forces that determine 
 the formation of a new organ t We know that the ultimate 
 sources of energy for all the functions of living bodies are 
 chemical processes. The question is, How can these chemical 
 forces be brought into relation with the visible changes which 
 take place in the formation of a new organ .-* The answer to 
 this question is to be obtained by a knowledge of the mechanics 
 of growth. It is very remarkable that the mechanics of growth 
 forms almost an empty page in the history of animal morphol- 
 ogy and physiology. I can refer here only to the few experi- 
 ments that I have made on this subject ; but fortunately the 
 subject has been worked out very carefully in plants, and as 
 my experiments show that the conditions for growth in animals 
 are, to a certain extent at least, the same as the conditions for 
 growth in plants, we have the beginning of a basis for work. 
 
 A brief outline of the manner of growth in plants is as fol- 
 lows : Before the cell grows it forms substances which attract 
 water from the surroundings, or, as the physicist expresses it, 
 it forms substances which determine a higher osmotic pressure 
 within the cell than did the substances from which they origi- 
 nate. The walls of the cell, or rather the protoplasmic layer 
 that lines the cell wall, possesses peculiar osmotic properties, 
 in consequence of which it allows molecules of water to pass 
 through freely while remaining resistant to the passing through 
 of the molecules of many salts dissolved in the water. The 
 result is that when substances of higher osmotic pressure are 
 formed inside the cell, water from the outside passes in 
 until the pressure within again equals the pressure without. 
 The cell-wall becomes stretched and, according to Traube, 
 new material is precipitated in the enlarged interstices, 
 thus rendering growth permanent. This method of growth is 
 most conspicuous, perhaps, in the germinating, seed. The rising 
 temperature in spring produces in the seed substances of higher 
 osmotic pressure (with greater attraction for water) than the 
 substances from which they originate. The result is that 
 
46 BIOLOGICAL LECTURES. 
 
 water enters the seed ; by the pressure of the water within the 
 cells their walls are stretched out and the seed grows. The 
 chemical and osmotic changes are the sources for the energy 
 which is needed to overcome the resistance to growth. 
 
 To see whether I could determine what are the mechanical 
 causes of growth in animals, I began at Naples some experi- 
 ments on Tubularia mesembryanthemum. I chose long stems 
 belonging to the same colony and distributed them in a series 
 of dishes containing sea-water of different concentrations. In 
 some of the dishes the concentration had been raised by adding 
 sodium chloride, and in others it had been lowered by adding 
 distilled water. According to the laws of osmosis the amount 
 of water contained in the cells of these tubularians differed 
 with the concentration of the sea-water, the amount being 
 greatest in the most diluted solution and least in the most 
 concentrated solution. If now in reality the mechanics of 
 
 / 1 3 
 
 DiL ifjed S^A - ¥fAr£P 
 
 Fig. n. 
 
 growth are the same for animals as for plants, it must result 
 that the more diluted the sea-water the more rapid would be 
 the growth in the tubularian stem. Of course, at last, a limit 
 is reached where the water begins to have a poisonous effect. 
 It was found, indeed, that within certain limits of concentra- 
 tion the increase in the length of the stems during the same 
 period was greatest in the most diluted and least in the most 
 concentrated sea-water. It is remarkable that the maximum of 
 growth took place not in sea-water of normal concentration, 
 but in more diluted sea-water, though that of course may not 
 be the case in all animals. The following curve (Fig. 13) will 
 give an idea of the dependence of growth upon the concentra- 
 tion of the sea-water in Tubularia. The values for the amount 
 
ON PHYSIOLOGICAL MORPHOLOGY. 47 
 
 of sodium chloride, in 100 cubic centimetres of sea- water, are 
 represented on the axis of the abscissa, the values for the 
 increase in growth on the ordinate axis. 
 
 These and similar experiments, which on account of lack of 
 time I cannot mention here, show that growth in animals is de- 
 termined by the same mechanical forces that determine growth 
 in plants. An obstacle to such a conclusion seems to lie in 
 the fact that many plant cells have solid walls, while such is 
 not the case in most animal cells. But the solid cell-wall does 
 not determine the peculiar character of growth. This charac- 
 ter is determined first, by chemical processes within the cell, 
 which result in a higher osmotic pressure, and, secondly, by 
 the osmotic qualities of the outer layer of protoplasm, which 
 allows water to pass through freely, but does not allow all salts 
 dissolved in it to do the same. Both these qualities are inde- 
 pendent of the solid cell-wall, and I see no reason why the 
 animal cell should not agree in these two salient features with 
 the plant cell. 
 
 In order that the foregoing explanation of the mechanism of 
 growth in the animal cell might be based only upon known 
 processes, it was necessary to find out whether, indeed, in case 
 of growth, chemical processes of such a character take place 
 that there are formed substances of higher osmotic pressure 
 than those from which they originate. Every one knows that 
 by practice our muscles increase in size. No satisfactory 
 explanation of this fact has been given. If my interpretation 
 of the method of growth was correct, I must expect that during 
 activity there are formed in the muscle substances which deter- 
 mine a higher osmotic pressure than those from which they 
 originate. This is exactly the case. Ranke had already shown 
 that the blood of a tetanized frog loses water and that this 
 water is taken up by the muscles. In experiments which were 
 carried on by Miss E. Cooke in my laboratory, we were able to 
 show directly that during activity the osmotic pressure inside 
 the cell-wall is raised. We determined the concentration of a 
 solution of Na CI, or rather of a so-called Ringers mixture, in 
 which the gastroconemius of a frog neither lost nor took up 
 water. We found that while this concentration for the resting 
 
48 BIOLOGICAL LECTURES. 
 
 gastroconemius was about 075 per cent, to 0.85 per cent., for 
 the gastroconemius that had been tetanized from 20 to 40 
 minutes it varied from 1.2 per cent, to 1.5 per cent. 
 
 This increase of osmotic pressure inside the muscle cell 
 leads, during normal activity, to a taking up of water from the 
 blood and lymph, and the consequence is an increase in volume. 
 The same muscle, as soon as it ceases to be exercised, begins 
 to decrease in size. Activity, therefore, plays the same role 
 in the growth of a muscle that the heat of spring plays in the 
 growth of the seed. 
 
 Upon endeavoring to determine whether the function of seg- 
 mentation, like other functions of growth, is influenced by 
 the amount of water contained in the cell, I found that by 
 decreasing the amount of water in the ovum of the sea-urchin 
 segmentation is retarded, and that by using a sufficiently high 
 concentration of sea-water it may be stopped entirely. There- 
 fore the amount of water contained in the cell plays still 
 another role in the process of organization and influences the 
 process of cell division. 
 
 IV. The Artificial Production of Double and Multiple 
 Monstrosities in Sea-Urchins. 
 
 The idea that the formation of the vertebrate embryo is a 
 function of growth has been made the basis of the embryo- 
 logical investigations of His. In a masterly way, His has 
 shown how inequality of growth determines the differentiation 
 of organs. In the blastoderm of a chick, for example, the first 
 step in the formation of the embryo is a process of folding. 
 There originates a head fold, a tail fold, a medullary groove 
 and the system of amniotic folds. According to His, all these 
 processes of folding are due simply to inequalities of growth, 
 the centre of the blastoderm growing more rapidly than the 
 periphery. It can be shown, very simply, that such a process 
 of unequal growth must, indeed, lead to the formation of exactly 
 such a system of folds as we find in the blastoderm of a chick. 
 If we take a thin, flat plate of elastic rubber, such as is used 
 for medical purposes, and lay it on a drawing-board, we can 
 
ON PHYSIOLOGICAL MORPHOLOGY. 49 
 
 imitate the stronger growth in the centre by sticking two tacks 
 into the middle of the rubber, a short distance apart, and 
 then pulling them in opposite directions. In this way we 
 imitate unequal growth, the centre growing faster than the 
 periphery. If we, then, fix the tacks in the drawing-board, 
 so that the rubber in the middle remains stretched, we 
 get the same system of folds shown by the embryo of a 
 chick. I mention this way of demonstrating the effects of 
 unequal growth as the ideas of His are still doubted by some 
 morphologists. 
 
 His raised the question, Why is growth different in different 
 parts of the blastoderm } But instead of trying to answer it 
 from the physiological standpoint he answered it from the 
 anatomical standpoint. According to His, the different regions 
 of the unsegmented ovum correspond already to the different 
 regions of the differentiated embryo. But this so-called theory 
 of preformed germ-regions gives no answer to the question, 
 Why do some parts of the embryo grow faster than others } 
 Nevertheless, it is not necessarily in opposition to the theory 
 of growth that I offered in the preceding chapter. Starting 
 with the idea of His, we may well imagine that the different 
 regions of the ovum are somewhat different chemically, and 
 that these chemical differences of the different germ-regions 
 determine the differences of growth in the blastoderm. Thus 
 the phenomena of heteromorphosis would show that, in some 
 animals at least, the arrangement of preformed germ-regions 
 may be changed by gravitation, light, adhesion, etc. 
 
 But, from the standpoint of causal morphology, it must be 
 asked what determines the arrangement of the different germ- 
 regions in the ovum. If we answer ''heredity," causal mor- 
 phology can make no use of such an explanation. Our blood 
 has the temperature of about 37°, but although our parents had 
 the same temperature its heat is not inherited, but is the result 
 of certain chemical processes in our tissues. Still it may be 
 possible that the molecular forces of the chemically different 
 substances of the ovum determine a separation of these 
 substances and at the same time the chief directions of the 
 future embryo. 
 
50 BIOLOGICAL LECTURES. 
 
 Driesch has shown ^ that by shaking a sea-urchin's ^gg in the 
 four-celled stage the four cells may be separated, and each one 
 be capable of giving rise to a complete embryo, which is only 
 different in size from the normal em^bryo. If the theory of 
 preformed germ-regions with its later modifications were true, 
 we ought to expect that every one of the isolated cells would 
 give rise to one-fourth of an embryo. But it has been said 
 that the artificial isolation of one cleavage cell causes a process 
 of post generation or regeneration. Driesch, moreover, changed 
 the mode of the first cleavage by submitting the ovum to one- 
 sided pressure. In this way the nuclei were brought into 
 somewhat different places from those they would have held in 
 the case of normal segmentation. Still, normal embryos 
 resulted. One might object again that the preformation of 
 the germ-regions existed in the protoplasm, and not in the 
 nucleus. I have made a series of experiments to the results 
 of which these objections cannot be made. I shall describe 
 these experiments somewhat fully, as they have not yet 
 been published, though I cannot enter into details at this 
 place. 
 
 I brought eggs of a sea-urchin, within ten to twenty minutes 
 after impregnation, into sea-water that had been diluted by 
 
 the addition of about lOO per 
 cent, distilled water. In this 
 solution the eggs took up so 
 much water that the mem- 
 brane (;;/, Fig. 14) burst and 
 part of the protoplasm escaped 
 in the form of a drop {b, Fig. 
 14), which often, however, re- 
 mained in connection with the protoplasm inside the membrane 
 after the eggs were brought back into normal sea-water. 
 These eggs gave rise to adherent twins, the ejected part of the 
 protoplasm, b, as well as the part remaining inside the mem- 
 brane, developing into a normal and perfectly complete embryo. 
 The part of the protoplasm which at first had connected 
 the two drops, formed the part where the twins remained 
 
 '^ Zeitschrift f. luissensch. Zoologie, Vol. LI 1 1 and LV. 
 
 Fig. 14. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 51 
 
 grown together. Of course, it often happened that, by 
 accident or rapid movement, the twins were separated, and 
 they then developed into perfectly normal single embryos. 
 Since we cannot assume that in every case the same part 
 of the protoplasm escapes, we must conclude that every 
 part of the protoplasm may give 
 rise to fully developed embryos 
 without regard to preformed 
 germ-regions. In many eggs a 
 repeated outflow of the proto- 
 plasm takes place (Fig. 15). In 
 
 such cases each of the drops 
 
 • . Fig. 15. 
 
 of the protoplasm may give rise 
 
 to an embryo, and I obtained not only double embryos, 
 
 but triplets and quadruplets all grown together. 
 
 In order to understand these experiments more fully, let us 
 
 follow out the history of development in these double and 
 
 multiple monstrosities. The ova were put into the diluted 
 
 sea-water before any segmentation had taken place and while 
 
 they had still but one nucleus. When parts of the protoplasm 
 
 flowed out, the nucleus either remained in the protoplasm, 
 
 inside of the membrane, or passed out with the part that was 
 
 ejected. Therefore, at first, only one part of the protoplasm 
 
 contained a nucleus. The other part obtained its nucleus by 
 
 the cleavage which took place, as follows : In case the nucleus 
 
 had remained inside the membrane (Fig. 16), the first cleavage 
 
 took place inside the membrane, the 
 
 cleavage plane being always at right 
 
 angles to the common diameter of 
 
 the two protoplasmic drops (Fig. 16). 
 
 (Only when the nuclear-spindle had 
 
 already formed, at the time of the 
 
 bursting of the membrane, were 
 
 there exceptions to this rule.) A peculiarity of the first 
 
 cleavage was that the protoplasm was always divided into a 
 
 larger sphere (I, Fig. 16), and a smaller sphere (II) which was 
 
 connected with the extra-ovate. 
 
52 
 
 BIOLOGICAL LECTURES. 
 
 The next stage was a normal division of I (Fig. 17), and 
 then II, divided (Fig. 18), the cleavage plane, as a rule, lying 
 
 Fig. 18. 
 
 in the extra-ovate. In this way the extra-ovate obtained its 
 nucleus, receiving in this case but one-fourth of the whole. 
 It very often happens that the extra-ovate receives its nucleus 
 later, obtaining in that case a still smaller fragment, but, never- 
 theless, the outcome is a perfectly normal embryo. Later on 
 
 the division takes its regular course. Fig. 19 shows the morula 
 stage, and one recognizes already the double monster. Figs. 
 20, 21 and 22 show double, triple and quadruple gastrulae. 
 
 Fig. 21. 
 
 Fig. 22. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 
 
 53 
 
 Figs. 23 and 24 represent double Plutei and Fig. 25 a triple 
 Pluteus. 
 
 It is remarkable that the development of these monstrosities 
 goes on nearly at the same rate as that of the normal embryo, 
 provided they are equally well 
 supplied with oxygen and 
 equally protected from mi- 
 crobes and infusoria. If pre- 
 formed germ-regions deter- 
 mined the arrangements of 
 organs in the embryo, we 
 ought to expect that these 
 ruptured ova would give rise 
 to single embryos, with a 
 modified arrangement of 
 limbs, and not to several 
 embryos with normally ar- 
 ranged limbs. Nevertheless, 
 it remains true that the de- 
 velopment in most eggs takes 
 place in such a regular and 
 
 Fig. 23. 
 
 typical manner that it seems as if there were a pre-arrangement 
 of some kind. But it is perfectly well possible that this pre- 
 arrangement consists in a separation of different liquid sub- 
 stances in the ovum by the molecular qualities of these 
 liquids. Such a separation, of course, might be called a 
 preformation of germ-regions, but it would be something 
 totally different from what is now understood by that term. 
 
 V. Theoretical Remarks. 
 
 I. All life phenomena are determined by chemical processes. 
 This is equally the case whether we have to do with the 
 contraction of a muscle, with the process of secretion or with 
 the formation of an embryo or a single organ. One of the 
 steps that physiological morphology has to take is to show in 
 every case the connecting link between the chemical processes 
 and the formation of organs. I have tried to show that in a 
 
54 
 
 BIOLOGICAL LECTURES. 
 
 few cases at least this connecting link was to be sought in the 
 changes of osmotic pressure determined by the chemical changes 
 which take place in the growing organ. 
 
 But this fact alone does not explain why it is that we get 
 differences in the forms of organs. In order to understand 
 this we must bear in mind that the processes of growth must 
 necessarily be different for different organs, as for example in 
 the formation of a root, and the formation of a stem. As 
 
 Fig. 24. 
 
 growth is a process in which energy is used up in overcoming 
 the resistance to growth, differences of growth can only be 
 determined either by differences in the amount of energy set 
 free in the growing organ or by differences in resistance. Dif- 
 ferences in the energy must be the outcome of differences in the 
 chemical processes which determine growth. Therefore we 
 are led to the idea that differences in the forms of different 
 organs must be determined by differences in their chemical 
 
ON PHYSIOLOGICAL MORPHOLOGY. 
 
 55 
 
 constitution, or, if the chemical constitutions be similar, by 
 differences in resistance to growth. That organs which differ 
 in shape very often are chemically different is a well known 
 fact. The formation of urea in the liver and the synthesis of 
 hippuric acid by the kidneys are the consequences of chemical 
 differences. 
 
 In this way we are led through the mechanics of growth to 
 a conclusion which forms the nucleus of Sachs' theory of 
 
 Fig. 25. 
 
 organization, namely, " that differences in the form of organs 
 are accompanied by differences in their chemical constitution, 
 and that according to the principles of science we have to 
 derive the former from the latter." According to Sachs there 
 are as many " spezifische Bildungsstoffe " in a plant as there 
 are different organs. ^ 
 
 1 J. Sachs, Stoffund Form der PJlanzenorgane, Gesammelte Abhandlungen, Vol. 
 II, 1893. 
 
56 BIOLOGICAL LECTURES. 
 
 2. In adopting the theory of Sachs and applying it to 
 animal morphology, we must avoid a mistake very often made 
 even in the case of good theories, namely, the endeavor to 
 explain special cases which are complicated by unknown 
 conditions. Huyghens explained by his theory of light the 
 phenomena of refraction, but he could not and did not attempt 
 to explain the sensations of color. For these phenomena 
 the wave theory of light remains true, but color sensations 
 depend not only on the wave motion of the ether, but also 
 on the peculiar chemical and physical structure of the retina. 
 I think it perfectly safe to say that every animal has specific 
 germ substances, and that the germ substances of different 
 animals differ chemically. Its chemical qualities determine 
 that from a chick's Qgg only a chick can arise. But it would 
 be a mistake and a falling back into the German Natur- 
 philosophie to attempt at present an explanation of how the 
 unknown chemical nature of the germ determines all the 
 different organs and characters that belong to the species. 
 For instance, the yolk sac of the Fundulus embryo has a tiger- 
 like coloration. We might say that these markings may be 
 due to a certain arrangement of molecules or complexes of 
 molecules (determinants), which later on give rise to the colored 
 places of the yolk sac, but I found that this coloration 
 originates in a manner much more simple. The pigment cells 
 are formed irregularly on the surface of the yolk. The pigment 
 is chemically closely related to haemoglobin, and so its forma- 
 tion may from the first be connected with the formation of the 
 blood corpuscles. But the arrangement of the pigment cells 
 during the first days of development is not such as to produce 
 any definite markings. They lie upon the walls of the blood 
 vessels as well as in the spaces between the capillaries. Later 
 on, however, all of the pigment cells have crept upon the 
 surface of the neighboring blood vessels. I succeeded experi- 
 mentally in showing it to be probable that some of the 
 substances contained in the blood determine this reaction. 
 These substances, if they diffuse from the blood vessel and 
 touch the chromatophore, make, according to the laws of 
 surface tension, the protoplasm of the chromatophore flow 
 
ON PHYSIOLOGICAL MORPHOLOGY. 57 
 
 towards and at last over the blood vessel and form a sheath 
 around it, while the gaps between the blood vessels become 
 empty of chromatophores. In this way the chromatophores 
 are arranged in stripes, and changes in the surface tension, and 
 not a preformed arrangement of the germ, determine the 
 marking. We do not know what processes determine the 
 coloration of animals which owe their markings to interference 
 colors, but the task of deriving such a coloration in the adult 
 from a similar arrangement of molecules in the germ plasm 
 would prove too much even for a genius like Huyghens, and 
 without the possibility of such a derivation the theory is of 
 no use. 
 
 3. The reasons why roots grow on the under side of the 
 stem of Antennularia and stems on the upper side, can only be 
 given when the special physical and chemical conditions inside 
 the stem of Antennularia have been worked out. At present 
 we can only think of possibilities. It is possible that the 
 hypothetical root substances of Sachs may have a greater 
 specific gravity than the substances which form stems, and 
 therefore take the lowest position in the cell. Since outgrowth 
 can take place only at the free surface of a stem or branch, 
 roots could grow only at the under side and stems only at the 
 upper side of an element. But there are still other possibilities 
 which we must omit here. In the case of Margelis and other 
 hydroids, it might happen that contact with solid bodies 
 produced an increase of surface in the touched elements in 
 case they contained specific root substances, while the opposite 
 took place in the case of elements containing polyp substances. 
 The consequence would be an increase in the surface of the 
 roots if they came into contact with solid bodies, while polyps 
 only would grow out in the opposite direction. I found, indeed, 
 in some forms at Naples that roots of hydroids which grew free 
 in the water began to grow much faster and to branch off more 
 abundantly when brought into contact with solid bodies. But 
 in these cases we must wait with our attempts at explanation 
 until the physical and chemical conditions for the form are 
 worked out. For the same reasons I will not go into a discus- 
 sion of the question of what determines the polarization of 
 
58 BIOLOGICAL LECTURES. 
 
 animals like Cerianthus. It may suffice to suggest the possi- 
 bility that in polarized animals the tissues or cells may 
 have such a peculiar structure as to allow the specific 
 formative substances to migrate or arrange themselves only 
 in one direction, while in cases of heteromorphosis migra- 
 tion or arrangement in every or in several directions is 
 possible. 
 
 4. The ovum of a sea-urchin under normal conditions gives 
 rise to but one embryo. This circumstance is due simply to 
 the geometrical shape of the protoplasm, which, under normal 
 conditions, is that of a sphere. When we make the eggs 
 burst, the protoplasm outside the (t^g membrane and that 
 which remains within it assume spherical forms, by reason of 
 the surface tension of the protoplasm. When this happens, 
 as a rule, we get twins, if two separate segmentation cavities 
 are formed, and only one embryo, if both cavities communi- 
 cate with one another. Whether the first or the second case 
 will happen depends upon the molecular condition of the part 
 of the protoplasm connecting the two drops. Therefore, the 
 number of embryos which come from one ovum is not deter- 
 mined by the preformation of germ regions in the protoplasm, 
 or nucleus, but by the geometrical shape of the ovum and 
 the molecular condition of the protoplasm, in so far as these 
 circumstances determine the number of blastulae. In my 
 experiments, I got double or triple embryos when the ovum 
 formed a double or triple sphere, as every sphere determines 
 a blastula. In Driesch's experiments, one single cell of the 
 four-cell stage necessarily formed a whole embryo after it had 
 been isolated, as it assumed the shape of a single sphere or 
 ellipsoid. Of course, there must be a limit to the number of 
 embryos that can arise from one ^%g\ but the limit is not due 
 to any preformation, but to other circumstances, the chief 
 one being that with too small an amount of protoplasm the 
 formation of a blastula — from merely geometrical reasons, 
 as there must be a minimum size for the cleavage cells, — 
 becomes impossible. Without the formation of the blastula, 
 of course it is not possible to get the later stages which 
 are determined by the blastula. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 59 
 
 5. The formation of the embryo begins with the formation 
 of the gastrula. The hollow sphere (the blastula, Fig. 26) 
 begins to fold at one place {ciy c, b, Fig. 26), and an invagina- 
 tion takes place (Fig. 27). The formation of the fold {ciy c, b, 
 Fig. 27) is due, undoubtedly, to unequal growth. The fact 
 that invagination, and not evagination (Fig. 28), takes place 
 
 Fig. 27. 
 
 depends upon other conditions. So far as the first phenom- 
 enon is concerned, there are different possibilities by which 
 unequal growth may lead to a process of invagination. It is 
 possible, for instance, that the part c (Fig. 26), between a and 
 bf may begin to grow more rapidly than the rest. But such 
 an unequal growth can only be the outcome of a chemical 
 difference between the parts a, c, b, and the rest. Such a 
 distribution of chemically different material exists in the 
 blastula which originates from the extra ovate, as well as in 
 the one which develops within the membrane. In the normal 
 ovum this distribution of material finds, perhaps, its first mor- 
 phological expression in the formation of micromeres. But 
 Driesch has shown that all possible variations in the formation 
 of micromeres may occur without affecting the formation of 
 the embryo. A necessary condition for the formation of the 
 embryo is the chemical differentiation which leads to unequal 
 growth; but whether this differentiation exists from the first, 
 or whether it takes place in the eight or the sixteen or the 
 sixty-four-cell stage is of minor importance. In order to 
 demonstrate this I made eggs burst in the two, four, sixteen, 
 and sixty-cell stages. In all cases except the sixty-cell stage 
 I produced the doublets, triplets, etc. The only condition 
 
6o BIOLOGICAL LECTURES. 
 
 necessary was that one part of the protoplasm should flow out. 
 The chief facts for causal morphology are the chemical differ- 
 ences and the local distribution of the chemically different 
 material by molecular forces. 
 
 In regard to the question why under normal conditions 
 the entoderm is pushed inside the segmentation-cavity 
 I wish to direct attention to a point that, as far as I 
 know, has not yet been considered. The sea-urchin's ^z%y 
 during the first stages of development, has a higher specific 
 gravity than the sea-water. In the blastula stage, however, 
 its specific gravity decreases and the ^gg begins to float and 
 comes at last to the surface of the water. This is possible 
 only through the eggs taking up substances which have a 
 lower specific gravity than the sea-water, and the only sub- 
 stance that could, in this case, be taken up is water. As the 
 cells themselves do not become larger, we must assume that 
 by a process of secretion the segmentation-cavity is filled with 
 a liquid of lower specific gravity than sea-water. In this way 
 the cells of the blastula come to have their peripheral surfaces 
 in contact with sea-water while their central surfaces are in 
 contact with a fluid containing less salts. This might result 
 in such differences of tension, between the inner and outer 
 walls of the blastula as to determine invagination. I found, 
 last year, that when I raised the eggs in diluted sea-water, 
 evagination (Fig. 28), instead of invagination, took place. 
 Herbst got the same result by using solutions of lithium salts. ^ 
 It is possible, too, that in these cases the hydrostatic pressure 
 within the segmentation-cavity is increased, and this increase 
 of pressure may have a direct or an indirect effect upon 
 growth. 
 
 It is for further investigation, and not for speculation, to 
 settle all these questions in detail. I only wish to point out 
 where, and how far, there exists a relation between substance 
 and form in the early stages of the development of the sea- 
 urchin. 
 
 I have chosen the name Physiological Morphology for these 
 investigations, inasmuch as their object has been to derive the 
 
 1 Herbst, Zeitschr. f. wissensch. Zool., Bd. 55. 
 
ON PHYSIOLOGICAL MORPHOLOGY. 6 1 
 
 laws of organization from the common source of all life phe- 
 nomena, i. e., the chemical activity of the cell. In what way 
 this is to be done is indicated in the chapter on the mechanics 
 of growth. 
 
 But the aim of Physiological Morphology is not alone an 
 analytical one. It has another and higher aim, which is 
 synthetical or constructive, that is, to form new combina- 
 tions from the elements of living nature, just as the physicist 
 and chemist form new combinations from the elements of 
 non-living nature. 
 
FOURTH LECTURE. 
 
 DYNAMICS IN EVOLUTION. 
 
 JOHN A. RYDER. 
 
 The statement that energy, in its kinetic and static forms, 
 has been a factor in the production of the shapes of organisms, 
 does not admit of question at the present time. In order that 
 the data in support of this statement may be presented in their 
 simplest forms, it is necessary to begin with the consideration of 
 the physical causes of the configuration of some of the simplest 
 unicellular organisms. In this way it will eventually be pos- 
 sible to pass from the consideration of the unicellular to that 
 of the multicellular type, viewed from the same standpoint. 
 It requires but little familiarity with the principles of physical 
 science to discover that similar laws hold with respect to the 
 behavior of fluid and semi-fluid bodies, notwithstanding the 
 fact that we may have before us, in one case, a so-called 
 "dead" fluid body, and in the other, a fluid ox fluent ** living " 
 chemical compound or mixture of compounds. Though the one 
 presents the phenomena of 'dead,' and the other of living, 
 matter, both exhibit the similar and common properties of 
 fluids, namely, those of surface-tension, viscosity and adhesion 
 to the surfaces of other bodies, with which they are brought 
 into contact. Under certain conditions, also, the semi-fluid 
 cells of living bodies undergo reciprocal deformation or altera- 
 tion in configuration, as a result of the interaction of the 
 inherent forces above specified, in ways so precisely similar to 
 those seen when a number of semi-fluid, or fluid dead masses, 
 are juxtaposed or brought into contact, that the resemblances 
 are seen to be due to the cooperation of closely similar, if not 
 identical, forces and properties. 
 
64 BIOLOGICAL LECTURES. 
 
 This remarkable resemblance of the physical behavior of 
 semi-fluid living protoplasm to that of semi-fluid dead matter 
 of certain kinds, such as the oils, has led me to apply the term 
 cytophysics to the study of the physical properties of the 
 substance of the cell. The convenient terms cytostatics and 
 cytokinctics very naturally follow from a consideration of 
 the contrasted states of rest and activity presented by the 
 ^'living" cellular unit of organization. The cytostatic state 
 will be one in which no visible physical activity, other than 
 its secular metabolism, will characterize the cell, during which 
 time, also, the parts of its substance will be in a condition of 
 statical equilibrium in respect to each other, and the cell will, 
 so long as this equilibrium lasts, maintain a constant configu- 
 ration. The cytokinetic state, on the other hand, is one in 
 which the visible or invisible parts of the cell are undergoing 
 a displacement in respect to each other, as a consequence of 
 which the cell as a whole will manifest changes of configuration. 
 
 Free and interfacial surface-tension is probably the most 
 important factor in determining the shapes of cells, since 
 there is associated with it, in multicellular organisms, a com- 
 plicated series of definite and constant space relations and 
 reciprocal interactions, as respects the cells of definite tissue- 
 tracts, that grow out of the very conditions of combination of 
 those tracts. Still more important, perhaps, are the incessant 
 unequal disturbances of surface-tension, due to metabolic 
 changes, at different points on the surfaces of cellular masses 
 of plasma — a fact beautifully illustrated by the proteus ani- 
 malcule, Amoeba pivtens. Differences of surface-tension are 
 thus developed at different points and times coexistently and 
 consecutively which lead to the assumption of the most diverse 
 and inconstant shapes by the bodies of these lowly organisms. 
 Such differences of surface-tension are, however, themselves 
 caused by chemical and molecular transformations at definite, 
 but previously unspecifiable, points at or near the surface of 
 the mass of plasma. These processes are, therefore, ultimately 
 to be associated with molecular or chemical transformations, 
 the production of heat, the disintegration and integration of 
 living matter. 
 
DYNAMICS IN EVOLUTION. 65 
 
 But, it will be asked, what is surface-tension ? If a drop of 
 water falls through a vacuum, as long as it is falling in space 
 it will present very nearly the form of a sphere. This is due 
 to the fact that the very outermost layers of molecules which 
 lie at insensible distances apart, attract each other with a force 
 that is apparently very much greater than that developed by 
 the action of gravitation. It results from this that the remain- 
 ing molecules contained within this outer molecular film are 
 held as within an elastic bag, the walls of which are of exactly 
 the same strength at every point. This exactly equal strength 
 and elasticity of the outer molecular film at every point on the 
 surface also causes it to fall into a condition of spherical^ 
 statical equilibrium. This is true because the molecules at 
 every point on the surface of the drop are of exactly the same 
 size, therefore every one attracts its fellows that are in contact 
 with it, with exactly the same force at every point on that 
 surface. Now, let any change in the dimensions of these 
 molecules occur at any point on the surface of such a fluid 
 sphere, such as may be accomplished by chemical transforma- 
 tions and recombinations, such as oxidation or decomposition, 
 and it must follow that the surface-tension or reciprocal pull 
 of the molecules upon each other, adjacent to the point of 
 such disturbance, must be increased or diminished. The 
 inevitable result of this will be that the form of the drop must 
 instantly change in order that a new condition of statical 
 equilibrium may be attained. The surface of the drop is 
 finite and returns in every direction upon itself since it is 
 approximately spherical. Any deformation of the drop due to 
 surface-tensional disturbances will therefore affect the shape and 
 curvature of some or all of the surface of the drop so that its 
 shape may become very irregular, provided its surface-tension 
 be disturbed at a number of irregularly distributed points 
 simultaneously ; but, since the drop is a finite mass made up 
 of solid particles moving freely among themselves, no matter 
 how much the drop may be deformed or how irregular it may 
 become, its most superficial layer of molecules will always form 
 a closed surface. This fact is important, since, no matter how 
 irregular in shape an Amoeba may become, its outermost stratum 
 
66 BIOLOGICAL LECTURES. 
 
 of molecules always form a closed surface and a molecular 
 envelope for the organism. 
 
 Since the molecules within a semi-fluid mass also move freely 
 over one another there is friction developed between them. 
 This friction is known as viscosity, and differs in fluids of 
 differing densities and chemical compositions, just as, in fact, 
 the surface-tension of a unit- surface, formed of different fluids, 
 differs, owing to the differing dimensions and properties of the 
 superficial layer of molecules of each fluid. The specific 
 viscosities and surface-tensions manifested by any given fluid 
 are therefore correlated, so that we may infer that these two 
 properties of fluent living matter are also correlated. Since, 
 again, living matter, as found in the cell, is not a homogeneous 
 body or compound, it will be plain that the correlative disturb- 
 ances in viscosity and surface-tension, due to the processes of 
 metabolism and the associated interplay of osmotic changes, 
 are so complex, when considered together with still other facts, 
 that it will be difficult, if not impossible, in the present state 
 of our knowledge, to trace all the steps of their interrelations 
 and interdependences in any given case. 
 
 The recent progress in the study of the process of fertiliza- 
 tion or conjugation shows that dynamical considerations must 
 here also be taken into account. As is well known, the nucleus 
 and archoplasm undergo alternate expansion and contraction 
 in linear dimensions. The male and female pronuclei increase 
 greatly in size during the phases just before conjugation. In the 
 ^'g^ oi Ascaris, for example, I have noticed that the pronuclei 
 soon assume a globular form and rapidly grow into large 
 spherical bodies by absorbing substance from the surrounding 
 cytoplasm. This rapid growth and spherical form show that 
 surface-tension is being disturbed uniformly over the whole 
 surface of the nucleus, otherwise its form could not re^nain 
 spherical. The remarkable growth of the rays of the asters 
 has the same meaning and must also be interpreted, in part, as 
 a physical process involving radial interdiffusion of heteroge- 
 neous molecules to and from the centrosomes into the nucleus 
 and cytoplasm, consequent osmotic disturbances, metabolism 
 and changes of surface-tension. The comparison of the astral 
 
DYNAMICS IN EVOLUTION. 67 
 
 figures, with their rays extending in every direction from the 
 archoplasm, with the rays developed on the surface of a fluid 
 when another fluid of definite properties is dropped upon the 
 former, leading instantly to the production of a " cohesion 
 figure" with rays extending out in every direction, is no mere 
 analogy. In the case of the archoplasm, the rays with their 
 lines of microsomes are probably the effects of diffusion of 
 one kind of plasma, the archoplasm, through another, the 
 cytoplasm, and is therefore not necessarily a phenomenon of 
 contractility, but simply an interdiffusion of the unlike sub- 
 stances produced by the metabolism of growth, which tends to 
 reestablish statical equilibrium among the parts of the molecular 
 system represented by the cell. This diffusion or osmotic 
 redistribution is conditioned at every step by surface-tension in 
 precisely the same way that the rays of many Heliozoa and 
 Radiolarians are conditioned in water by states of unequal 
 surface-tension at very close but nearly equal intervals over a 
 spherical surface, so that a summation of these uniformly 
 distributed and seemingly conflicting surface tensional forces 
 does not interfere with the maintenance of the spherical figure 
 by the body of the organism. The alternate inflation and col- 
 lapse of the nucleus during fertilization, and growth during 
 indirect cell-division, is a rhythmical process, and we may char- 
 acterize it as the diastole and systole of the nucleus. The alter- 
 nate extension and retraction of the rays of the archoplasm, as 
 I have observed in the Q.^g of Ascaris, is similarly an osmotic or 
 metabolic diastole and systole of the radial figures formed by it, 
 which is intimately associated with and absolutely conditioned 
 by metabolism and osmosis, as the direct experimental researches 
 of Prof. Jacques Loeb have rendered exceedingly probable. 
 Unless the processes of karyokinesis are traced with the 
 utmost caution in the light of dynamical and physiological 
 considerations, there is great danger of our misinterpreting the 
 facts and of assuming that certain of the phenomena guide 
 and control others. It may indeed be possible that embryolo- 
 gists have been until now steadily confounding ontogenetic 
 effects due to the physical processes of growth, as visualized 
 in karyokinesis, with their causes. I anticipate that this 
 
68 BIOLOGICAL LECTURES. 
 
 remark will meet with a decided denial from most morpholo- 
 gists ; nevertheless it seems opportune to warn them that the 
 problems they have before them can never be settled by purely 
 morphological methods. If my contention that all ontogenetic 
 problems must be approached by a most intimate combination 
 of the methods of physical, physiological and morphological 
 research is true, we are still far from having anywhere an 
 ideal biological investigator. If it is true that "we have been 
 mistaking ontogenetic effects for ontogenetic causes, what a 
 mass of speculation must probably be set aside. All that will 
 remain, in fact, will be the many most valuable and beautiful 
 results of observation made by our foremost morphologists. 
 
 It is not intended to thus minimize in any way the great 
 and increasing value of morphological research ; what is really 
 meant is, that there is danger of overrating the importance of 
 morphology to the injury or exclusion of other disciplines of 
 paramount importance. If, as we must suppose, there is such 
 a perpetual flux and interflux of particles and molecules going 
 on throughout the plasma of an ^g^, owing to the metabolism 
 due to respiration and the consequent surface-tensional and 
 osmotic disturbances during the earliest steps of development, 
 it becomes inconceivable that any such morphologically con- 
 ceived and entirely hypothetical bodies as *Mds," "idants," 
 "determinates," etc., can have a stable existence. The exist- 
 ence of such bodies as fixed entities of finite complexity is 
 absolutely disproved by experiments of the most varied charac- 
 ter in separating the first two or four blastomeres of the ^gg, 
 since it is then found that, in each of these blastomeres, there 
 still inheres the power to produce a perfect embryo. The 
 hypothetical ids, determinants, biophores, gemimiles, etc., must, 
 therefore, be supposed to be capable of being halved and then 
 quartered without destroying their potentialities. These and 
 numerous other difficulties that cannot be discussed here, 
 render it exceedingly probable that we must look in altogether 
 another direction for an explanation of the processes of 
 ontogeny, viz., to a study of the modes and conditions of the 
 manifestations of the energies that constitute the 'Mife" of 
 the simplest organized forms. 
 
DYNAMICS IN EVOLUTION. 69 
 
 In the very simplest unicellular organisms we have also 
 unicellular molecular mechanisms of a most peculiar kind. 
 The fearfully complex molecular structure of these mechan- 
 isms conditions their actions, their forms and powers, no less 
 than does the nature of the watery media, in which these first- 
 lings of life, as well as the germs of higher organisms, must 
 in common develop. In the belief that the study of the 
 ''living" mechanism of some of the lowest types of organized 
 existence, in relation to and as affected by their not-living sur- 
 roundings, might throw some light upon the origin of their 
 forms, the writer has here, in the main, taken up the problems 
 thus raised as physical ones. In the belief, also, that these 
 studies have not been entirely fruitless, the following evidence 
 is offered. 
 
 An Amoeba proieits may be compared to a smoke- or vortex- 
 ring of particles that has been greatly modified, owing to the 
 very complex interaction of disturbances of the surface-tension 
 of its outer enveloping film of molecules, the viscosity of its 
 own plasma, its gravity and power of adhesion to other bodies. 
 If we conceive a smoke-ring to have become a viscous semi- 
 fluid body with an outer film of molecules, and that this ring 
 has contracted until the central opening in it has completely 
 closed, we shall have a mechanism which may be compared in 
 detail with an Amoeba in motion, provided only that we modify 
 it still further and in such ways as we are obliged to suppose 
 that the combination of the four forces above specified cooper- 
 ate in order to produce and maintain the form of an amoeboid 
 organism. Verworn^ has already referred to the flux of the 
 particles of the Amoeba through itself, in discussing the 
 general subject of contraction, but as he has not understood 
 the complexity of the process, we need not here concern 
 ourselves further than to say that he has failed to correctly 
 interpret this vortical flux of amoeboid organisms. There 
 is, however, such a central flux of particles through the centre 
 of the body of an amoeboid, as any one can soon convince 
 himself by carefully observing the behavior of a large living 
 proteus animalcule. The chemical transformations that go on 
 
 1 Bewegung der lebendigen Substanz. Jena, 1892. 
 
70 
 
 BIOLOGICAL LECTURES. 
 
 within the body of an amoeboid, amongst its molecules, are 
 responsible for disturbances of the surface-tension at one or 
 more points over its surface. It is certain that the chemo- 
 tropism, or affinity for oxygen of its surface molecules, as Ver- 
 worn holds, is essential to this; but we must remember that in 
 order to call forth local disturbances of surface-tension in this 
 way, there must also be a locally exaggerated chemotropism, or 
 affinity for oxygen, at some one point on the surface of the 
 organism. This point has apparently not been made clear by 
 Verworn, but it is essential to a clear understanding of the 
 processes presently to be described. How the positions of 
 such local disturbances of the chemical complexity of the sur- 
 face-layer of molecules of an amoeboid arc determined, we do 
 not know. That they are definitely determined, according to 
 some definite law, we may be certain. 
 
 As every one knows who has ever watched a proteus animal- 
 cule under the microscope, the "anterior" pole of the creature, 
 for the time being, is tensely filled with its own substance, so 
 as to present a rounded, full ''anterior" extremity while in 
 motion. ''Posteriorly," on the other hand, the creature is 
 found to present a wrinkled, partially collapsed appearance. 
 A study of the motions of the organism discloses the fact that 
 its substance is flowing through itself. The central part of 
 this current is moving most rapidly along the middle of the 
 body, while toward the sides it is observed to become progress- 
 ively slower until the outer layers of its substance, along the 
 sides of the creature, are seen to come to rest. It thus results 
 that the outer layers of molecules, along the sides, form a sort 
 of shell or tunnel through which the central current flows. 
 This flux, however, means that there must be a continual or 
 fitful rupture of the "anterior" end of the organism in order 
 to let some of itself escape out of itself in front, in order to let 
 some of itself flow into itself behind, in order that some of 
 itself may thus continuously flow through itself in order to 
 make the progressive forward motion of itself possible. In 
 this way the substance of the "posterior" part of the organism 
 can be picked up and carried through the tunnel-like physical 
 shell, formed of the outer layers of molecules of the organism, 
 
DYNAMICS IN EVOLUTION. 71 
 
 and thus be transported forwards and poured out ''anteriorly." 
 It will readily be seen that, in order to do this, work must be 
 performed, energy dissipated. This energy is dissipated in 
 reestablishing a dynamical balance between the parts of the dy- 
 namical system represented by the molecular aggregate that we 
 behold in the body of the Amoeba. We have here before us a 
 finite molecular mechanism, or dynamical system, every part of 
 the surface of which returns upon itself. Any disturbance of 
 the equilibrium of the molecules at the surface of that system 
 will provoke a deformation of the whole. If the disturbance 
 is great enough at any one point, there will inevitably be 
 developed a vortex-ring motion of the particles amongst them- 
 selves, due to the friction of the constituent molecules. If 
 this vortical motion of the particles of an amoeboid mass of 
 ** living" matter be due to a preponderating superficial dis- 
 turbance of the equilibrium of the system at one point on the 
 surface, that alone will suffice to determine the direction of 
 the motion of the whole. For this reason the proteus animal- 
 cule has no fixed ''head" or "tail" end. "Head" and "tail" 
 seems to be entirely a matter of the combination of inner and 
 outer conditions that determine the point on the surface of the 
 organism, at which the maximum chemical and physical dis- 
 turbance of surface-tension will occur. These are absolutely 
 determined by the physical processes of the readjustment of 
 the equilibrium of its molecules, in respect to outer conditions, 
 during every consecutive moment of its motions. It is pos- 
 sible, in fact, to show that every change of the shape of this 
 interesting organism is the result of energies inter-acting in a 
 very complex way. 
 
 If an Amoeba is allowed to fall through the water, its 
 surface-tensions are apparently disturbed with great uniformity 
 over its whole surface, and at nearly equal distances apart. 
 It results from this that short, blunt pseudopodia are pushed 
 out in every direction, as in Fig. i and it becomes nearly 
 globular in outline. The moment, however, that the organ- 
 ism touches a plane surface, as in Fig. 2, it flattens out 
 into the form of a biscuit-shaped mass. It now behaves 
 like a mass of dough, and falls into a new condition of 
 
72 
 
 BIOLOGICAL LECTURES. 
 
 equilibrium, due to its own gravity, its viscosity, and the 
 force with which the particles on its under side tend to adhere 
 to the fixed solid surface upon which it rests. The upper part 
 of the mass now falls into an equilibrium determined by the 
 surface-tension of its superficial molecules and the viscosity or 
 reciprocal friction of the latter upon each other. Gravity, 
 viscosity, surface-tension, and adhesion are the four cooper- 
 ating agents that now determine its figure. So long as it was 
 floating or suspended in the water, the influence of gravity 
 and adhesion operating in relation to a fixed surface were 
 excluded. We thus see how completely this organism is 
 the creature or subject of energy-conditions in this state. 
 
 In the next phase of its motions this is still further 
 illustrated. In Figs, i and 2, short, blunt pseudopodia are 
 being protruded in all directions; but in Fig. 3, the sequence 
 of events changes, and the organism begins to take up its 
 march by means of a vortical flux of its substance across the 
 surface upon which it rests, and in the direction of the arrow. 
 Surface-tensional disturbances of greater magnitude have evi- 
 dently affected the right side of the mass, and one or more of 
 the small original blunt pseudopodia at this point have been 
 merged into a strong, single ''anterior," pseudopodal current, 
 in which a maximum flux of molecules is taking place in the 
 
DYNAMICS IN EVOLUTION, 73 
 
 direction of the motion of the whole organism. This maximum 
 vortical flux of the material particles of the amoeboid in this 
 new direction will result in elongating the organism in th 
 direction of the motion thus set up. The elongation of the 
 organism is, therefore, due to the flow of its own particles 
 amongst and through themselves. We are thus made aware 
 of the fact that this simplest organism is elongated in the 
 direction of its own motions, as a consequence of the continuous 
 readjustment of the internal equilibrium of its parts in respect 
 to influences affecting it from without. The shape of this 
 organism, at every instant of its motions, is, therefore, 
 mechanically caused. 
 
 We may pursue our analyses still further. If we now look 
 down upon such an amoeboid organism from above, when 
 moving upon a plane surface, as in Fig. 4, we find that it is 
 not only elongated in the direction of its motion, but that its 
 anterior end is tensely filled with substance; its outer layer of 
 molecules at the "anterior" end is tensely stretched. At the 
 tail end the organism is wrinkled or papillated; this wrinkled 
 or papillated appearance of the posterior end of the organism 
 is due to physical causes, as the following observation proves: 
 In Fig. 4 there are two anterior pseudopodia, — b and c, — 
 through which there are fluxes of particles in progress at 
 about the same rate. The vortical current is seen to divide 
 and to flow into both these pseudopodia, thus keeping the 
 outer molecular film over both tense and rounded. Let, 
 however, a disturbance of the surface-tension occur at the 
 end of b, while at the end of c^ this disturbance subsides, as 
 in Fig. 5 and there will be a flux of particles out of r' — in 
 the direction of the arrow — into /;, and r' will lose its tense, 
 full outline, and its surface will become wrinkled or papillated, 
 just as appears at the "tail" end of the organism at a. In 
 every detail of the morphology of this organism, we therefore 
 discover that physical or " physiological " agencies are 
 operative in determining its figure. We are, therefore, in a 
 position to afiirm, with positive certainty, that the morphology 
 of this organism has little significance until its actions and 
 their physical causes have been studied. This is only one of 
 
74 BIOLOGICAL LECTURES. 
 
 many reasons why the present speaker holds that all purely 
 morphological work is one-sided, and incapable of dealing with 
 the deeper problems of biology. In the same way, physiology 
 alone is equally incapable of dealing with the great general 
 problems in biology. Neither of the two disciplines alone can 
 ever, by any stretch of imagination, command the power to 
 produce a theory of life. Such an expectation is simply 
 fatuous. 
 
 The many other dynamical phenomena, especially the singular 
 manner in which the nucleus of an Amoeba proteiis is caused 
 to oscillate back and forth within its body within certain limits, 
 all take place in accord with the views above developed. For 
 example, the curious lateral flow of the plasma of Ama;ba proieiis 
 when in a fully extended condition, along the sides of the 
 body on either side of its posterior and middle thirds, may be 
 explained by the physical tendency of this part of the organism 
 to adhere to the substratum upon which it is moving. This 
 lateral spreading does not take place at its *' anterior " end 
 because here the influx of molecules from behind is taking 
 place so rapidly that this spreading due to adhesion has not 
 yet had time to take place. This spreading due to adhesion 
 causes the central current to be narrowed and elevated so that 
 the discoidal nucleus is lifted and rolled along on its edge in 
 this narrow elevated part of the body of the organism as if 
 passing through a tunnel with its sides wider than its floor. 
 Rolled along in this way through this narrow passage by the 
 vortical current of plasma, the nucleus is finally arrested by 
 contact of its edge with the molecular boundary wall of the 
 organism, and is thus automatically kept from being bodily 
 rolled to the outside of the plasma of the organism. Reaching 
 a certain point at the ''anterior" end of the mass of plasma, 
 it also falls over on its side, wedged between the roof and floor 
 of the mass of plasma of which it forms a part. It is thus 
 prevented from passing out of the organism with the vortical 
 current that must now flow past it and on forward to continually 
 form anew the ''anterior" end of this singular being that is 
 thus continually turning itself inside outward in front and 
 outside inward behind. 
 
DYNAMICS IN EVOLUTION. 75 
 
 The manner in which the successive rents in the outer 
 molecular skin of the organism are produced is such that a 
 sudden rupture occurs through which a fresh outpour of 
 substance happens over which a new molecular skin is instantly 
 formed continuous with the ruptured edge of the old. These 
 rents do not take place in relatively the same place in succession. 
 For example, rents may occur in the outer film one after the 
 other at points a little off of the extreme central point of the 
 '' anterior '* end, and alternately a little to the right and left side 
 of the latter. The vortical flux is thus thrown slightly aside 
 alternately to the right and then to the left, then to the right, 
 then to the left again, and so on, indefinitely. It thus results, 
 however, that the summation of these alternating outbursts of 
 substance become the components of the aggregate motion of 
 the whole organism in one general direction. 
 
 If a rent occurs at one side of the organism, due to a 
 disturbance of surface-tension at an anterior lateral point, a 
 lateral flux of particles may thus be set up, as a result of 
 which the entire contents of the organism may be sucked up 
 ''anteriorly" and ''posteriorly" to the point where the new 
 outflow has taken place. In other words, the "head" and 
 " tail " ends of the organism may be thus caused to flow in 
 opposite directions into the lateral outburst and the whole 
 organism take a new direction of motion with all its parts 
 oriented in respect thereto. Amceba protciis, therefore, cannot 
 move except by developing a vortical flux of particles, and 
 it therefore is a "living" vortex-ring of particles. These 
 outbursts, in large individuals, occur successively at short 
 intervals of time, so that the motion of the creature is 
 fitful. In young protcus animalcules the bursting out or 
 pouring forth of the plasma at the "anterior" end maybe 
 continuous, so that the motion is uniform and an ideally perfect 
 type of the "living" vortex-ring of particles is realized. 
 
 Every pseudopodium is, however, so long as it is being 
 protruded, a vortex-current in which the motion of the particles 
 is swiftest at its center and at its tip, while at the sides the 
 particles are quiescent and form a shell through which the 
 central ones are moving. The pseudopodia, therefore, divide 
 
76 BIOLOGICAL LECTURES. 
 
 the vortex-current of particles into diverging currents, the 
 summation of the motions of which may, when the organism 
 is moving on a plane surface, become resolved mechanically 
 into a single motion of translation in one direction. 
 
 When the organism is freely suspended in water it protrudes 
 pseudopodia equally in every direction and assumes a globular 
 figure, somewhat like a Heliozoan or Radiolarian, because 
 its surface-tension is now being disturbed at nearly equally 
 separated points over its whole surface. It therefore falls into 
 a condition of spherical equilibrium, since the components of 
 all the surface-tensions are resolved at the centre of the 
 organism. The moment it touches a fixed surface, distortion of 
 the formerly globular organism takes place under the influence 
 of gravity and adhesion, and the vortical flux of particles that 
 is now set up is different in nature from that which took place 
 in every direction when it was in the suspended globular con- 
 dition. There is at once a maximum flux of particles in the 
 direction of the point at which the most active disturbance of 
 surface-tension occurred, and the resulting current becomes very 
 massive so that the whole contents of the organism, except the 
 nucleus and water vacuole, flow forward as a massive pseudopod, 
 that is somewhat flattened or depressed by the action of gravity 
 and adhesion, but which is much larger than any of those 
 produced while in the spherical condition. How little Verworn 
 has appreciated and understood these complex processes may 
 be judged by any one who has read his work on the motion of 
 living substance. He has affirmed what does not exist in 
 regard to small Amoeba proteus, where the flux is continuous 
 and where no retreat of particles to the nucleus, such as he 
 postulates, can take place for hours together. In short, 
 Verworn has totally failed to understand the real significance 
 of these complex phenomena. Greef, also, has made assump- 
 tions with regard to amoeboid motion, especially the existence 
 of muscular fibrils, which by no stretch of the imagination can 
 be conceived to hold of the proteus animalcule. 
 
 Verworn has also failed to understand the physical reasons 
 why small blebs or pseudopodial warts were produced along the 
 sides of a retracting pseudopod. He speaks of " stimulation " 
 
DYNAMICS IN EVOLUTION J J 
 
 {Reiz), a word which to me has a very indefinite meaning. 
 The production of these blebs or incipient pseudopodia, which 
 I have often observed, and in a great variety of forms, may be 
 equally well explained by surface-tensional disturbance, the 
 viscosity of the plasma, etc., and not necessarily as caused by 
 a retreat of the substance toward the nucleus, as claimed 
 by Verworn, in order to receive a reinforcement or accession 
 of new nuclear molecules. 
 
 The differentiation of the substance of an amoeboid, such as 
 A. protcus, into an outer hyaline layer and a central or medul- 
 lary part, — the so-called *'endosarc" and ''ectosarc," — is 
 again a purely physical phenomenon. The surface-tensional 
 forces rniLst be exerted, for physical reasons, between molecules 
 of approximately the same dimensions, otherwise there could 
 be no tolerably coherent and stable outer stratum formed. 
 In other words, the molecules of the outer layers are recipro- 
 cally attracted to each other with a greater force at insensible 
 distances apart, than the larger and coarser particles are 
 attracted by the small uniform molecules at the same intervals 
 apart. The materials of an amoeboid are thus dynamically 
 sorted into two kinds, in virtue of their differences of attrac- 
 tion for one another. It thus comes about that ''endosarc" 
 and "ectosarc" are merely names for the results of a 
 dynamical process that, so to speak, sorts the particles of 
 a living amoeboid into two kinds. The small surface-particles 
 or molecules necessarily attract each other under such condi- 
 tions of dynamical advantage over and above their attraction 
 for the larger particles, that the latter are constantly driven 
 inward and kept there for this reason. ^ In this case, again, a 
 morphological fact is only understood when subjected to 
 dynamical analysis. 
 
 In this way one might go on and subject every detail of the 
 organization of an amoeboid to physical scrutiny, and show 
 that complex energy-combinations determined every detail of 
 its structure. Not a single amoeboid form that I have 
 yet encountered has failed to disclose this mechanical 
 and dynamical complex of agencies as factors competent to 
 
 ^ A geometrical diagram would be nee:!ed to make this statement perfectly clear. 
 
yS BIOLOGICAL LECTURES. 
 
 determine its figure at every instant of its existence. There 
 may be those, however, who will find fault with my identifi- 
 cation of the motions of an amoeboid with that of a whirl- or 
 vortex-ring of particles. It may be well, also, to explain here 
 that this notion has nothing to do with the physical con- 
 ception of Lord Kelvin respecting the existence of vortex 
 atoms. The identification of amoeboid motion with a vortex- 
 ring of particles is perfect, provided certain reservations are 
 made that grow out of the very nature of the conditions and 
 nature of amoeboid motion. In a typical smoke- or vortex- 
 ring the impulse of rotation that impels all its particles is 
 imparted from without; in the living vortex-ring secular 
 changes in the nature of its constituent particles condition 
 its motions and provoke them. And, while it is true that the 
 energy that drives the living vortex-ring is primarily derived 
 from without, it is not set free until the constituent particles 
 have changed their dimensions, affinities, and reciprocal attrac- 
 tions within the ring, due to causes acting antecedently from 
 without. The living vortex-ring is a constantly changing, 
 closed, and regenerative dynamical system; the other is a 
 dynamical system that derives all its energy from without in 
 the form of a single impulse, and comes to rest after a time, 
 owing to the friction of its superficial particles with their 
 surroundings. 
 
 It may be objected, also, that there is only a remote resem- 
 blance of a smoke-ring to that of the flux of living particles 
 through an amoeboid organism. This objection may be met 
 by the statement, that not only do I suppose the living vortex- 
 ring to be flattened by its gravity, but I also suppose it to 
 have no central opening, and that the median longitudinal 
 stream of particles represents the point where the opening 
 would be in a smoke-ring — now a line in Amoeba — along 
 which the central "living" vortex current is flowing. I 
 moreover suppose that the ring is greatly elongated, owing 
 to the viscosity of its substance and the adhesion of the 
 surface of the living amoeboid to the substratum upon which 
 it moves. I would not have any one suppose that I imagined 
 that amoeboids ever existed that had a central opening in them 
 
DYNAMICS IN EVOLUTION. 79 
 
 like a smoke-ring. I have only used this comparison because 
 of the obvious identity of the living and dead vortices, when 
 proper allowance is made for the physical conditions under 
 which both subsist on account of the different nature of their 
 constituent substances. The outer molecular shell, for example, 
 of a living vortex-ring is fixed to its substratum, and is only 
 involuted ''posteriorly," and evoluted ''anteriorly" as it moves 
 over a fixed surface. These ideas once clearly grasped, will 
 enable any one to see that, underlying the apparent unlikeness 
 of the smoke-ring to a living amoeboid vortex, there is in reality 
 a fundamental similarity. The kind of "contractility" which is 
 exhibited by an amoeboid is thus also seen to be fundamentally 
 different in nature from that presented by a muscle, in which 
 contraction is conditioned by a vastly more complex structure. 
 When an Amoeba passes into the resting stage its plasma is 
 very apt to assume an almost perfectly globular form. Its 
 pseudopodia are retracted ; its surface becomes smooth, and 
 the whole organism passes into the almost homogeneous, 
 quiescent or lethargic condition of a ball of protoplasm that no 
 longer manifests its characteristic types of motion and irrita- 
 bility, at least externally. Unequal surface-tensional disturb- 
 ances no longer affect it ; it is now under the domination of 
 the same physical influences that determine the globular form 
 of a sphere of oil in a mixture of alcohol and water of the same 
 specific gravity as itself. Its cytoplasmic substance is nearly 
 or quite homogeneous, and the excessively slow and torpid meta- 
 bolic processes, within the protoplasmic mass of the Amoeba, 
 now secrete or pour out a cuticle or envelope over its surface 
 and in which the organism is said to be "encysted." All of 
 these processes are purely dynamical, just as were all of those 
 associated with the motion of the organism. Not only are all 
 of these processes dynamical, but all are also directly "adap- 
 tive," in virtue of the fact that the equilibria successively 
 attained are merely a quantitative dynamical response from 
 within a "living " molecular mechanism to a change in external 
 energy-conditions. All " adaptation " is to be so interpreted, 
 so that "natural selection" may be at last resolved into pure 
 energy-factors, and thus brought into coordination with the 
 
8o BIOLOGICAL LECTURES. 
 
 rest of the forces of the cosmical universe. The mischievous 
 metaphor, '' natural selection," has blinded many naturahsts to 
 the real meaning of this expression. 
 
 In the same way we may discuss the characters of other 
 amoeboids. Each is found to have its own kind of plasma, 
 that behaves differently in each species. Some move more 
 rapidly than others, some have blunt, others long, slender or 
 attenuated pseudopodia ; some may have bent pseudopodia, or 
 have the axes of their straight pseudopodia normal to the sur- 
 face of the spherical body of the organism ; others obey a 
 different rule in this respect. In some the plasma is clear, 
 in others more opaque ; in some the nucleus is globular, in 
 others flattened. Thus one might go on and show that the 
 different proportions and behaviors of the same parts, in dif- 
 ferent species, was evidence that totally different molecular 
 mechanisms were simply making their necessarily different 
 responses to the same environment, because of differences 
 in the physical and chemical properties of their constituent 
 plasma. Herein, probably, also lies the whole secret of the dif- 
 ference of power presented by the germs of different creatures. 
 They develop as they do in the case of each species, because 
 of their specific chemical constitutions, and not because there 
 are a lot of ''biophores," '^gemmules," etc., ''superintending" 
 the business of development in a particular way during the 
 evolution of the ^gg of each form. The preposterous assump- 
 tion that enough energy can be squeezed into an ^^g poten- 
 tially to carry the materials into place that are assimilated during 
 development in order to build an elephant, for example, is 
 worthy of mediaeval philosophers, but not of those of the close 
 of the nineteenth century. Every form of energy, including 
 that of "life," is correlated, and is amenable to the same laws. 
 Full knowledge of the mode of operation of the material 
 energy-complexes that we call ''living," will disclose the true 
 theory of morphology and the true meaning of life as well. 
 
 These, here incompletely reported, observations make it toler- 
 ably clear that amoeboid motion is worth studying, in order to 
 get clear notions of how living motions and energies are oper- 
 ative in one of the simplest organisms known to the zoologist. 
 
DYNAMICS IN EVOLUTION. 8 1 
 
 They also make it very evident that observers have hitherto 
 allowed purely morphological considerations to becloud their 
 vision. In order to discover the meaning of the morphology 
 of the simplest organisms, their actions must be subjected to 
 the most searching analysis. These observations have proved 
 that the functions of an organism are also functions of its form. 
 It has been pretty clearly established, by what has been said 
 above, that every action of the Amoeba was followed by a mor- 
 phological change. In the belief that this same thing holds 
 good throughout the whole animal and vegetable world under 
 most complexly interacting energy-conditions, I will predict 
 what I believe will yet be possible, viz., the discovery of the 
 true causes, in detail, of the forms of all organized existences. 
 In order, however, to accomplish this end, the following will 
 first have to happen, namely, an abandonment of all hitherto 
 accepted hypotheses of inheritance, a new conception of the 
 nature of life, new views of the nature of the process of natural 
 selection, and, above all, the abandonment of all such concep- 
 tions as gemmules, biophores, pangenes, plastidules, plassomes, 
 etc., and the admission that the phenomena of life are ulti- 
 mately physical in their nature and are to be treated in detail 
 as physical problems. 
 
 It is now my firm conviction, also, that experimental investi- 
 gation in embryology will make no solid progress until the 
 foregoing prepossessions are abandoned, or until the mischiev- 
 ous influence of such speculations and their kindred, as those 
 regarding a *' germ-plasm," etc., have been entirely eradicated 
 from the minds of the present generation. In conclusion, 
 let me remark that five sciences are indissolubly connected 
 together in the study of the fundamental problems of life; 
 these are : physics, chemistry, physiology, morphology, and 
 psychology. When each of these sciences shall have been 
 given its due weight and place in the conduct of the study of 
 life-forms, we shall begin to know what the latter really mean, 
 but not until then. 
 
FIFTH LECTURE. 
 
 ON THE NATURE OE CELL-ORGANIZATION.i 
 
 S. WATASE. 
 I. 
 
 If the true nature of a higher organism cannot be 
 understood without considering the structure and the function 
 of its component organs, it is equally certain that the nature 
 of an individual cell cannot be made intelligible without a 
 comprehensive study of the different organs of which it is 
 composed. 
 
 At the present time, when morphologists are explaining 
 the origin and development of the different structures in an 
 organism in terms of cell-growth and of cell-metamorphosis, 
 and when physiologists are referring the activities of the whole 
 organism back to the functions of its component cells, it is 
 natural that considerable attention should now be directed 
 toward the solution of more elementary problems concerning 
 the nature of the cell-organism. The cell-theory, while it 
 explains the structure and functions of a tissue on a cellular 
 basis, leaves the real nature of the cell itself unexplained. 
 
 The vital properties of a nucleated cell manifest themselves 
 in various ways, but they may be broadly classified under two 
 categories, viz., (i), those tending to the preservation of the 
 individual cell, and (2), those tending to the maintenance of 
 the species. Under the first are included the general phe- 
 nomena of cell-metabolism and different forms of irritability, 
 and under the second those of cell-division and cell-fusion. 
 
 Diverse as are these special cell-phenomena which tend 
 directly or indirectly to the preservation of the cell, it must 
 
 1 Lecture given before the Biological Club of the University of Chicago, 
 February 7, 1893, ^^^^ afterward written out in the present form. 
 
84 BIOLOGICAL LECTURES. 
 
 be admitted that their real significance can only be under- 
 stood when each is taken in connection with the others, 
 the tout e7isemble of which form the life of the nucleated 
 cell. If any explanation of special phenomena be attempted, 
 it should be in the light of what we know of the whole. 
 
 We do not gain much, however, by so saying, as long as 
 this knowledge of the whole is merely a name for the sum 
 total of incoherent observations on diverse cell-phenomena. 
 Beneath and beyond all vital manifestations of a cell, there 
 must exist a primary physiological condition, on which the 
 details of secondary cell-phenomena depend. Just what con- 
 stitutes the primary physiological phenomenon of the cell, 
 is the point that I wish to discuss in the present paper, 
 believing, as I do, that such a problem as that of cell-organ- 
 ization, can be approached from the functional side with 
 better effect than has thus far been attained from the side of 
 pure morphology. 
 
 Before we proceed further, it may not be out of place here 
 to introduce a general schematic description of a nucleated 
 cell.i 
 
 Excluding the centrosome and chromatophore for the present, 
 an animal cell may be described as composed of two sharply 
 distinct organs : the cell-body {cytosoinc), and the nucleus 
 {caryosoine). 
 
 The nucleus, in its ''resting stage," has a definite membrane ^ 
 around it, called the nuclear membrane or caryothcca. The 
 cell-body consists of a net- work of cytoplasm. This net-work 
 contains within its own substance small bodies of varying 
 sizes, which are known as the microsonics or, more strictly, 
 the cytomici'osonics. Surrounding the cytosome, there is a 
 membrane known as the cell-membrane or cytotheca. It may 
 exist as a thickened border of the cytosome or as a distinct 
 membrane separated from the cytosome. 
 
 1 The descriptive cytological terms adopted here have merely an anatomical 
 significance, and do not refer to the chemical or functional properties of the struc- 
 ture. Several terms recently used by Haeckel [Anthropogeiiie, 4th edition, Leipzig, 
 1891), have therefore been found most convenient. Only the more salient features 
 of the cell will be emphasized in this place, that being sufficient for our present 
 purpose. 
 
ON THE NATURE OE CELL-ORGANIZATfON. 85 
 
 The meshes of the cytoplasm are filled with a fluid sub- 
 stance, commonly called the cytoplasmic fluid, or to use 
 Haeckel's term, the cytolympJi. 
 
 The cytoplasm is, however, the only living portion of the 
 cell-body, and hence properly belongs to the category of 
 protoplasm in the more strict technical sense of the term. The 
 cytolymph is the inert, passive, non-living portion of the 
 cell-body. Besides the cytolymph, there usually exist a number 
 of non-living bodies in the cell-body, as yolk-granules, oil drops, 
 debris of food, zymogen granules, etc., according to the nature 
 of different cells. These non-living substances altogether 
 belong to the group known as victaplasin or paraplasm^ in 
 contradistinction to the substance which is the real living 
 element of the cell — the protoplasm. 
 
 The contents of the nucleus {caryosome) may be arranged 
 also into two .similar groups of living and non-living elements. 
 The cJiromosome is distinctly protoplasmic in character, and so 
 is the fine net-work of the ''achromatic" thread-like substance 
 which is often found traversing the nuclear cavity. In several 
 cases, if not in all, these filaments are the actual continuation 
 of the cytoplasmic net-work existing around the nuclear 
 membrane. 
 
 The fluid substance which bathes these semi-solid living 
 constituents of the nucleus is known as nuclear fluid or caryo- 
 lympJi. In the caryolymph there exists a body known as the 
 nucleolus. In certain cases, the filaments of the chromosome 
 have been found passing through the substance of the nucleolus 
 or directly ending in it. Sometimes only one nucleolus exists 
 in each nucleus, while in other cases over .one hundred nucleoli 
 may be found in one nucleus. The number of nucleoli is quite 
 variable in different cells, but fairly constant in a given species 
 of cell. The nucleolus is not a permanent body in the nucleus. 
 It may exist at one stage of the cell, and may disappear at the 
 next. The micro-chemical reaction of the nucleolus is entirely 
 different from that of the chromosome. It appears probable 
 that three or more different bodies are included under the 
 same name of nucleolus. Indeed, one sees no reason why the 
 inside of the nuclear membrane may not be used as a deposi- 
 
86 BIOLOGICAL LECTURES, 
 
 tory for some solid products of cell-metabolism, under certain 
 circumstances, just as the spaces in the cell-body are used for 
 such a purpose. And thus some of the bodies included under 
 the generic name of nucleolus, may belong to the group of 
 metaplasm. It is, however, difificult to pass any definite 
 opinion on the nature of the nucleolus at the present stage 
 of our knowledge on the subject. 
 
 To recapitulate briefly, then, the chromosome and cyptoplasm 
 are the two active, living constituents of the cell. The rest of 
 the bulk of a cell consists of non-living substances, which have 
 yet to be converted into vital elements, or are the products of 
 metabolism which have now lost the distinctive characteristic 
 of a living substance. 
 
 The behavior of the cytoplasmic thread or network suggests 
 that it is formed of a group of small, living particles, each 
 with the power to assimilate, to grow and multiply by division. 
 The chromosome, in the .same way, is itself a colony of 
 minute organisms of another kind, each endowed with similar 
 attributes of vitality. The media, in which they live, — the 
 cytolymph and caryolymph — are the media in which they 
 breathe, from which they derive their nourishment, or within 
 which they deposit the products of their metabolism. The 
 reason why the cell as a whole assimilates, grows and divides, 
 is ultimately due to the fact that the minute particles whiA 
 compose the cytoplasm and chromosome are endowed with 
 these functions. 
 
 Keeping in mind then such a simple nucleated cell like 
 an amoeba or an animal ovum, as a type, let us ask ourselves 
 the following questions : What is the relation of nucleus^ to 
 cytoplasm, and of cytoplasm to nucleus in a cell .'' What is 
 the significance of this duplex morphological organization } 
 Through what process may such an organization as the 
 nucleated cell be considered to have come into existence.? 
 
 The biogenetic law as applied to the study of metazoan 
 organisms, has been an important instrument of research in the 
 field of comparative anatomy and embryology, but it is hard to 
 
 1 In the following, the word " nucleus " is used, unless otherwise stated, 
 synonymous with its essential constituent, the " chromosome." 
 
ON THE NATURE OE CELL-ORGAN/ZATfy>^j ^r yi^j 
 
 use it as a working theory in the explanation of cellular 
 phenomena such as I have already indicated. For it is possible 
 that the law followed by the cell-aggregate in the course of its 
 development, may not have been followed in the formation of 
 the individual cell. 
 
 It is perfectly conceivable that the process by which the cell 
 was first formed may have been due to causes of special 
 character, while the conversion of the cell thus formed, into an 
 organism of higher complexity, may have been due to causes 
 entirely different from those that operated in the production of 
 the nucleated cell. 
 
 There is no necessary reason to conclude, as has been done 
 by several naturalists, that because the complex organism 
 develops by a process of differentiation of the homogeneous 
 germ, the duplex structure of the cellular units which compose 
 the organism, must have also had a parallel course of develop- 
 ment from its antecedent germ. 
 
 It is this point that I wish to discuss more in detail in the 
 following. 
 
 II. 
 
 The parts of a living organism commonly termed its organs 
 may be studied from three points of view : — 
 
 1. How far are these parts adapted, by their form and 
 structure, to perform their physiological work } This mode of 
 studying the organs belongs to physiology. 
 
 2. Where and how do they arise in a given organism ? This 
 field of study is a branch of morphology. 
 
 3. If the morphological study of the organ be extended 
 through organisms of different grades of complexity, it may 
 enable us to infer the probable steps through which the given 
 organ may have passed in the course of its phylogenetic history. 
 
 When these three modes of study as pursued by naturalists 
 at the present day, are applied to the study of organs of an 
 individual cell, it resolves itself into three problems : — 
 
 I. How far are nucleus and cytoplasm adapted by their form 
 and structure, to perform their physiological work in a given 
 cell } 
 
8i8| ^^v- BIOLOGICAL LECTURES. 
 
 2. In what manner do they originate in a given cell ? This 
 ultimately resolves itself into the problem of cell-division 
 {Cytomci')') on the one hand and cell-fusion on the other. 
 
 3. What are the probable steps in the ancestral history, by 
 which these structures came into existence ? This belongs to 
 the broad question of Cytogciiy as understood in its phylogenetic 
 sense. 
 
 In following out these questions more in detail, it is 
 important to bear in mind at the outset, some vital distinctions 
 involved in the use of the term oj'gaii, whether we understand 
 it in a \>\\YQ\y physiological, or in a morphological sense. From 
 the purely physiological standpoint, any structure or member 
 which, by its activity, contributes to the general welfare of the 
 whole organism is an organ, whether that structure may have 
 originated primarily in the organism, 'or may have been derived 
 secondarily from an external source. Thus, the chromatophores ^ 
 in the leaves of a plant are the organs of assimilation in that 
 plant ; the '* gonidia " in the thallus of a lichen are the organs 
 of a lichen, in a physiological sense as the heart or lung is the 
 organ in the body of a higher organism. 
 
 But from the morphological side of the case it is different. 
 According to the morphological view, every diffcreiitiatfd 
 orgajiisvi, every organism composed of orgajis, can only have 
 originated from a homogeneous stage by the differentiation of 
 its parts. To state this in another way, "however complicated 
 one of the higher animals and plants may be, it begins its 
 separate existence under the form of a nucleated cell. This, 
 by division, becomes converted into an aggregate of nucleated 
 cells : the parts of this aggregate,, following, different laws of 
 growth and multiplication, give rise to the rudiments of the 
 organs ; and the parts of these rudiments again take those 
 modes of growth and multiplication and metamorphosis which 
 are needful to convert the rudiment into the perfect structure." ^ 
 
 1 The term chroniatophore (Schmitz) is here used in a broad sense, including 
 leucoplasts and the various coloring substances in the flower and the fruit, as well 
 as the chrophyll granules in the leaves of a green plant. The term is synonymous 
 with Arthur Meyer's trophoplast and Schimper's plastid. 
 
 2 T. H. Huxley : Article Biology, Encyclopaedia Britannica, 9th edition, Vol. Til, 
 p. 682, 1878. 
 
ON THE NATURE OF CELL^ORGANIZ AT/ON 89 
 
 Now, this morphological criterion of an organ, which 
 necessarily relates to the history and mode of its origin wit/iiti 
 the orgaiiisDi, by the differentiation of its parts, does not apply 
 to the chromatophore in a green plant, nor to the "gonidia" 
 in a lichen thallus, although there can be no doubt whatever 
 that these structures serve as organs in the physiological sense, 
 in the respective organisms. The chromatophores are not 
 the products of differentiation of an homogeneous germ of 
 the plant. They can only originate by the division of pre- 
 existing chromatophores, if we follow such botanists as Schmitz, 
 Schimper and Meyer. ^ The colorless protoplasm of the plant 
 and the chromatophores are the coexistent but independent 
 structures, with no genetic connection between them. 
 
 In the organization of a lichen, the case is clearer and more 
 to the point of our inquiry. As is well known, the "gonidia" 
 and their supporting meshwork are derived from two different 
 groups of plants, viz., Algce and Fungi, respectively, although 
 their physiological adaptation to each other is so perfect, so 
 much so, in fact, that in several lichens the hyphae of the 
 fungus cannot live when separated from the algal portion, the 
 "gonidia." Here, again, it is needless to say that these two 
 organs are not the products of differentiation from some homo- 
 geneous an/age as different organs are in one of the complex 
 animals.^ On the other hand, the *'gonidia" of one individual 
 lichen are genetically related to the "gonidia" of another, and 
 not at all to the hyphae of the thallus. In a similar way the 
 hyphae of one individual lichen are genetically related to the 
 hyphae of another lichen of the same species, and not to 
 
 1 Schmitz : Die Ckromatophoren Jer Algen, Bonn, 1882. Schimper : Ueher die 
 Entwickelung der Chlorophyllkoriier und Far/>korfer, Bot. Zeit., 1883, 41. Jahrg. 
 Meyer : Ueber Krystalloide der Trophoplaslen iind i'tber die Chromoplasten der 
 Angiospermeu, Bot. Zeit., 1883, 41. Jahrg. 
 
 2 Before the discovery of the true nature of lichens, it was thought that both 
 " gonidia " and supporting fungal hyphae were the products of development of a 
 single germinating spore. " Gonidia," which are the symbiotic algal cells, were 
 supposed to be, as the term indicates, asexual organs of reproduction produced 
 from the hyphae and capable of development into a new and perfect lichen-thallus. 
 The view that hyphae might also be produced from the "gonidia" was often 
 expressed. De Bary, Historical Notice of the Lichens. Comp. Morphology and 
 Biology of Fungi, etc., p. 416. 
 
90 BIOLOGICAL LECTURES. 
 
 the "gonidia," with which they live in close symbiotic rela- 
 tions.^ 
 
 Thus the morphological and physiological consideration of 
 an organ, such as we have just given, leads us to conclude that 
 when we find two structures in an individual organism most 
 intimately associated in their physiological relationship, it does 
 not necessarily follow that they are organs in the morphological 
 sense also. The history of the lichen clearly shows that an 
 independent organism, composed of organs^ can be created by the 
 union of tivo dissimilar organisms by the establishment of an 
 intimate physiological relationship between them. In fact, a 
 certain number of species of lichens have been actually pro- 
 duced by bringing fungi and algae together in a synthetic way.^ 
 The fungus and alga, by the interchange of their metabolic 
 products, supply the nutritive wants of each, and thus produce 
 the autonomous whole which can exist in places where neither 
 the alga nor the fungus would be able to exist separately. 
 
 In dealing with the structures in an organism commonly 
 called organs, I repeat, we must clearly bear in mind whether 
 the structure in question is an organ in the physiological and 
 morphological senses, or whether it is an organ simply in ^he 
 physiological sense. If the structure is an organ in the mor- 
 phological sense, the study of the development of the whole 
 organism will show that it is a part of the products of differ- 
 entiation of some preexisting germ from which the entire 
 organism was derived ; if it be an organ in a purely physio- 
 logical sense alone, there will be no genetic connection between 
 the different structures, although each is indispensable to the 
 existence of the other. In short, the perfection to ivJiicJi the 
 physiological adaptation of different orgaits is canned out in a 
 given organism, is, in itself, no proof that they ivei'e derived 
 by the diffeirntiation of some common germ ; but, on the con- 
 trary, tivo dissimilar organisms may, by mutual adaptation, 
 
 1 In using the term " symbiotic," to express the relation between the alga and 
 fungus in the organism of a lichen, I simply follow such botanists as De Bary 
 (Z>?> Erscheinung der Symbiose, Strassburg, 1879, p. 15, et seq.), Frank {Sytnbiose, 
 Lehrbiich der Botanik, Bd. I, 1892, Leipzig), and others. 
 
 - See, for example, the recent work by Bonnier, Recherches sur la syiithese des 
 lichens. Ann. des sc. nat., 7^2 serie, IX, Botanique, 1889. 
 
ON THE NATURE OF CELL-ORGANIZATION 91 
 
 give rise to a third organism in wJiich eaeh of them serves as 
 an organ to the luhole. 
 
 It is needless to say that almost all structures in higher 
 organisms ^ are derived by the differentiation of some pre- 
 existing germ, but at the same time it is important to bear in 
 mind that this is not always the case, particularly in the lower 
 forms. It is this consideration which interests us particularly, 
 as it may be the key to the interpretation of the organization 
 represented by the single nucleated cell. 
 
 III. 
 
 The permanent organs of the cell are, following the recent 
 exposition of Strasburger,^ considered to be (i) Cytoplasm, 
 (2) Nucleus, (3) Centrosome, (4) Chromatophore. 
 
 The last named structure occurs normally in the cells of 
 green plants, and sometimes in those of animals.^ Following 
 
 1 If Riickert's observation {(Jber physiologische Polyspermie bei vieroblastischen 
 Wirbeltiereiern, Anat. Anzeiger, Bd. VII, 1892) that in a certain vertebrate the 
 merocyte-nuclei come from the nuclei of the supernumerary sperm-cells which 
 enter the ovum, be confirmed, it would seem that a part of one important 
 embryonic organ, in an organism like Torpedo, is bodily derived from the outside 
 source. 
 
 2 E. Strasburger : Das Protoplasmaiind die Reizbarkeit, 1891, Jena. 
 
 3 See in this connection, Lankester's article Animal Chlorophyll (Nature, vol. 44, 
 1 891) which is the review of G. Haberlandt's paper Ueber den Ban und die Bedeu- 
 tung der Chlorophyllzellen von Convoluta Roscoffensis, in von Graff's Die Organi- 
 sation der Turbellaria accela, 1891, Leipzig. I have not been able to see 
 Haberlandt's original paper. Haberlandt suggests, to quote Prof. Lankester, 
 "that while phylogenetically they [chlorophyll-cells in Convoluta^ must be regarded 
 as Algae (that is to say, have descended from Algae) yet at the present time they 
 have by profound adaptation to life in and with the Convoluta^ altogether lost 
 their character as algal organisms, and have become an integral histological 
 element of the worm, and in fact constitute its assimilation tissue. . . . Haber- 
 landt is inclined to place his theory as to the green cells of Convoluta alongside 
 the suggestion of Schimper as to the origin of the chlorophyll corpuscles of higher 
 plant — namely, that these are due to the union in the remote past of a green 
 colored with a colorless organism." 
 
 .Schimper has shown that the chromatophores (Schimper's plastids) are formed 
 by the division of the preexisting chromatophores, and not by the differentiation 
 of the cell-protoplasm. Schimper's view referred to above on the origin of the 
 chlorophyll bodies in the plant cells may be gathered from the following quota- 
 tions : " Sollte es sich definitiv bestatigen," says Schimper, " dass die Plastiden in 
 den Eizellen nicht neu gebildet werden, so wiirde ihre lleziehung zu dem sie 
 enthaltenden Organismus einigermassen an eine Symbiose erinnern. Moglicher- 
 
92 BIOLOGICAL LECTURES. 
 
 the views held by Schmitz, Schimper and others, we have 
 already regarded this structure as an organ totally independent 
 of the colorless protoplasm of the green plant. In regard to 
 the centrosome, aside from its apparent function during the 
 division of the nucleus, we know very little to justify our 
 discussion in the present connection. Personally, I cannot 
 agree with those who place the centrosome in the same category 
 of the permanent cell-organs as the nucleus. On the other 
 hand, I believe that the centrosome is a special form of the 
 cytomicrosome, which exists almost in every part of the cell. 
 For the reason of this homology of the centrosome, I may 
 refer the reader to my former paper. ^ 
 
 weise verdanken die griinen Pflaiizen wirklich einer Vereinigung eines farblosen 
 Organismus mit einem von Chlorophyll gleichmassig tingirten ihren Ursprung." 
 (Schimper : Ueber die Eutwickcliing der Chlorophyllkorucr und Farbkorper, Bot. 
 Zeit., 41. Jahrg., 1883, pp. 111-112.) Schimper supports this statement by quoting 
 Reinke (Allg. Botanik, p. 62), who states that the chlorophyll bodies in the 
 decomposing cells of a cucumber attacked by a certain fungus, still continued to 
 grow and multiply. 
 
 In view of the fact that there exists a close analogy between the nucleus 
 and the chromatophore (see Schmitz, Die Chrofnatop/wren da^Algcn, Bonn, 1882, 
 p. 167), the observations by Metschnikoff and Soudakewitch {La phagocytose 
 musculaire ; contribution a V etude de V injiamviation parenchyjnateiise. Annales de 
 rinstitut Pasteur, 6me Annee, No. i, Janvier, 1892, pp. 1-20, Pis. I-III), on the 
 repeated division of the muscle nuclei in the debris of degenerating muscle fibres 
 which originally constititted a part of their cytoplasm, in the course of muscle 
 degeneration, may be interpreted in the same way as Schimper did of Reinke's 
 observation on the behavior of the chlorophyll bodies in the decomposing vegetable 
 tissue referred to above. 
 
 For the view that considers the animal chlorophylls as the veritable Algae, see 
 the well-known papers by Gesa-Entz and K. Brandt. Felix le Dantec, in his 
 recent paper, Kecherches sur la symbiose des algues et des protozoaires ( Annales de 
 I'Institut Pasteur, t. VI, No. 3, 1892), has brought further experimental evidence 
 in support of the view that the chlorophyll corpuscles in an animal organism as 
 Paramcecium, are the symbiotic Algae. I mention these simply to call attention 
 once more to the fact that certain parts of an organism, which were originally 
 considered to be integral elements of the organism, derived by the differentiation 
 of the germ, have been shown to be due, in reality, to a secondary association of 
 two or more different orga^iisms, originally separate and independent, and what 
 we call organs from the physiological side, in such an organism, are in reality 
 organisms by themselves. 
 
 1 S. Watase : Homology of the Centroso?ne, Journal of Morphology, Vol. VIII, 
 Pt. 2, 1893. A. Brauer {Zur Kentitniss der Herkunft des Centrosomas, Biol. Central- 
 blatt, Bd. XIII, Nr. 9 u. 10, May, 1893), ^^^ recently come to the conclusion that 
 in the spermatocyte of A scar is megalocephala, variety univalens, the centrosome 
 
ON THE NATURE OF CELL-ORGANIZATION. 93 
 
 If, therefore, I omit from consideration the chromatophore 
 and the centrosome in the following, it is because the former 
 has been fully treated by able botanists, and the latter is 
 not sufficiently known, to my knowledge, to admit of useful 
 discussion in connection with our subject. If, however, the 
 centrosome be shown to be an organ of the cell, contrary to 
 my former conclusion above alluded to, with a morphological 
 significance comparable to that of the nucleus or the cyto- 
 plasm, the inference I advance in regard to the nature of the 
 latter organs will apply equally well to the former. 
 
 Confining our remarks, then, to the nucleus and the cyto- 
 plasm, we may first ask whether the nucleus is to be regarded 
 as an organ in a morphological sense, or only in a physiological 
 one. Are nucleus and cytoplasm products of differentiation 
 from some homogeneous milage in the sense that all morpho- 
 logical organs are, or may not their constant occurrence in 
 the cell rather be regarded as the result of a union formed in 
 the remote past, between two organisms originally independent 
 and dissimilar — a union of such a kind that ages of mutual 
 adaptations have rendered their independent existence no longer 
 possible } Is it not possible to regard the cell as a symbiotic 
 community, in which the cytoplasm represents one group of 
 
 originates in the inside of the nuclear membrane, Brauer's view, however, does 
 not militate against my statement that the centrosome is the cyto-microsome of a 
 gigantic size, and that wherever cytoplasmic net-work exists there is a possibility 
 of developing a microsome. When the centrosome originates inside of the 
 nuclear membrane, it may be said, for a descriptive purpose, that it is derived 
 from the nucleus ; when it originates outside of the nuclear membrane, such 
 a centrosome may be said to be cytoplasmic in its origin. Such a distinction is 
 purely a nominal one, however, from my standpoint, and I believe the general 
 statement that all centrosomes are cytoplasmic in their origin is fundamentally a 
 correct one. Confusion only arises when we do not keep in mind the fact that 
 the cytoplasmic net-work, in the substance of which the microsome and centrosome 
 arise, exists on both sides' of the nnclear membrane, and the structure kncnun as 
 nucleus, contains a great deal of cytoplasmic substance in it. 
 
 As is beautifully shown in Brauer's tnore recent paper {Zur Kcuntniss der Sper- 
 matogenese non Ascaris megaloeepAala^ Arc\\. f. mikr. Anat., Bd; 42, 1893, August, 
 p. 1S5), the fact that in one variety of Ascaris megaloccphala, namely, univalens^ 
 the centrosome lies- inside, and in another variety, bivaloi^, outside of the nuclear 
 membrane, is enough, to my mind, to show that it is the substance which gives 
 rise to the centrosome, and not the position where the centrosome makes its first 
 appearance, which we must consider in the determination of its honxoJogy. 
 
94 BIOLOGICAL LECTURES. 
 
 extremely minute organisms, each with a power of growing, 
 assimilating, and dividing ; and the nucleus, or, more strictly, 
 the chromosomes, a colony of still different forms, each with 
 the same powers, — the whole making an organization compar- 
 able to that of the lichen, which is composed of two totally 
 dissimilar organisms ? 
 
 If this be so, then, there are two possible ways of explaining 
 the nature of a nucleated cell ; viz., the T/icojy of Differen- 
 tiation, such as was held by Haeckel, Auerbach, and several 
 others, and more recently by Verworn ^ and Wiesner,^ and the 
 Theory of Symbiosis, as I have briefly suggested. 
 
 Let us examine the fundamental phenomena of the nucle- 
 ated cell from the standpoint of the symbiotic theory, and, 
 incidentally, point out the inadequacy of the differentiation 
 hypothesis as an explanation of the cell phenomena in general. 
 
 IV. 
 
 Two important activities in the developmental phases of 
 protoplasmic life^ ^.xq cell-division, e.g., caryokinesis, and cell- 
 fusion, e.g., fecundation. In both cases, the identity of the 
 nucleus and of the cytoplasm is never once lost during the 
 whole series of remarkable changes. There is a continuity of 
 nuclear matter from one phase to another, just as there is a 
 continuity of the cytoplasm through the successive j^eriods in 
 the history of the cell. In other words, the nucleus always 
 originates from a preceding nucleus, and the cytoplasm from a 
 preceding cytoplasm. There is no evidence proving that the 
 nucleus is formed by the process of differentiation from the 
 cytoplasm, nor that the cytoplasm is formed by the differen- 
 
 1 Max Verworn: Die J)hysiologische Bedejitiing des Zell-kerns, Bonn, 189 1, 
 p. 115. 
 
 2 J. Wiesner: Die Elementarstructur tind das IVachsthiim der lebenden Siibstaiiz, 
 Wien, 1892, p. 266. 
 
 3 Following the suggestion brought out by Professor Burdon Sanderson in his 
 discourse on the elementary problems in physiology {Nature, Vol. XI, Sept. 26, 
 1889), it is convenient to divide the protoplasmic activities into two main groups 
 — the developmental and the non-developmental. The former refers to those 
 phenomena of the cell which are more especially connected with the development 
 or unfolding of latent character of the germ, and the latter to such functions as 
 respiration, secretion, excretion, etc. 
 
ON THE NATURE OE CELL-ORGANIZATION 95 
 
 tiation of nuclear substance. The developmental history of 
 these two substances naturally leads us to regard them as 
 independent structures, although each is necessary to the 
 physiological existence of the other. They are not, therefore, 
 morphological organs of the cell in the sense of the term as 
 we have explained it. Furthermore, the phenomena of division 
 in the nucleus and cytoplasm remind us forcibly of the mode 
 of origin of the soredia in the lichen ; nor is this remarkable, if 
 a nucleated cell is, like the lichen, a symbiotic community of 
 two dissimilar organisms. The single soredium is a miniature 
 lichen, consisting of one or more algal cells with a weft of 
 fungal tissue around them. The algal and fungal elements in 
 a single soredium are derived from the corresponding elements 
 in the mother lichen-thallus, just as the daughter cell derives 
 its nucleus and cytoplasm from the corresponding elements in 
 the mother cell. 
 
 The most convincing argument proving the symbiotic 
 character of a lichen consists in the synthetic production of 
 certain species of lichens, by bringing algal and fungal 
 elements together. If, therefore, the morphological rela- 
 tionship between nucleus and cytoplasm in a cell is that of 
 a symbiotic community, the fact analogous to the artificial 
 synthesis of lichens must be found in the cell. I venture to 
 suggest that such a synthesis of a living cell has been accom- 
 plished. I refer to Verworn's ^ experiment on the Radiolarian, 
 Thalassicolla. Verworn took three vessels of equal size, and 
 in the first he put a number of normal TJialassicolla ; in the 
 second, he put one which had its central capsule with its 
 nucleus removed ; in the third, he placed an individual whose 
 central capsule had been removed and replaced by the trans- 
 plantation of the central capsule of another individual of the 
 same species. The Radiolarian in the third vessel was, 
 therefore, a synthetic one, the extra capsular protoplasm lying 
 outside of the central capsule, being derived from one indi- 
 vidual, and the central capsule itself, with its nucleus, being 
 derived from another. In the course of time, the Thalassi- 
 colla which had lost its nucleus by the removal of its central 
 
 1 Verworn, loc. cit., p. 42. 
 
96 BIOLOGICAL LECTURES. 
 
 capsule died, while the other Radiolarian which had lost its 
 nucleus and then regained it, by the acquisition of a central 
 capsule of another individual, throve well, and could not be 
 distinguished from the normal Thalassicolla in the first vessel, 
 upon which no operation had been performed. 
 
 This is, in my judgment, a genuine case of synthesis of a 
 living nucleated cell, by bringing, from two dissimilar sources, 
 the cytoplasmic and nuclear elements together. If Stahl's and 
 Bonnier's results, on the synthesis of lichens are the conclusive 
 evidence of their symbiotic character, may not the Verworn's 
 experiments on Thalassicolla be interpreted as equally conclu- 
 sive evidence of the symbiotic origin of the nucleated cell .^ 
 In fact, the process of fecundation is nothing more than a 
 synthetic production of one nucleated cell from two nucleated 
 cells that are derived from independent sources. And, further, 
 there is good ground, as the phenomena of heredity show, for 
 believing that each germ substance retains the individual 
 qualities characteristic of its origin, throughout all stages of 
 later development of the organism. 
 
 It is true that, in the case of a lichen, the algal and the 
 fungal elements may exist independently, while in case of the 
 nucleated cell, all investigation leads to the conclusion that 
 when the nucleus is separated permanently from the cytoplasm 
 or the cytoplasm separated from the nucleus, they invariably 
 die, sooner or later.^ 
 
 This is, however, no objection to the idea of the symbiotic 
 origin of the nucleated cell, as a moment's reflection will 
 show, for the more perfect the symbiotic adaptation of two 
 organisms, the greater is their inability to live independently, 
 until at last the symbiotic existence between the two organisms 
 becomes imperative, if they are to continue to exist. Remove 
 
 1 For recent contributions and a general summary of our knowledge on the 
 relation between nucleus and cytoplasm, see O. Ilertwig : Die Zelle und die 
 Gewebe, Jena, 1893 '■> E. G. Balbiani : N'ouvelles recherches experinientales sur la 
 merotomie des infusoires cilies. Annales de micrographie, Nos. 8, 9 and 10, t. IV, 
 1892, Paris; Verworn : ■ Die physiologische Bedeiitufig des Zell kerns, Bonn, 1891 ; 
 Korschelt : Beitrdge zur Morphologie und Physiologie des Zellkernes, Jena, 1889 ; 
 Whitman : The Seat of Formative and Regenerative Energy, Journal of Mor- 
 phology Vol. II, 1888, Boston. 
 
ON THE NATURE OF CELL-ORGANIZATION 97 
 
 that opportunity, by one means or another, of their combining 
 thus and death is the result, somewhat in the same way as in 
 the case of an obligatory parasite, which though descended 
 from a free-living ancestor, dies if deprived of its appropriate 
 host. 
 
 The minute organisms which we assume to make up the 
 cytoplasm on the one hand and nucleus on the other, probably 
 once were free and lived independently, but if so, it is plain 
 they have since lost their power by the acquisition of sym- 
 biotic habits. By adopting symbiotic habits, however, they 
 acquired the ability to adapt themselves to surroundings so 
 different from the normal habitat of each that neither symbiont 
 alone could have lived in them, and thus possibilities each was 
 incapable of accomplishing alone, are performed successfully 
 by the composite organism.^ We can reasonably suppose, 
 therefore, that tJiose cell- forming organisms y which entered into 
 the symbiotic relation in the past, with others, have survived in 
 a modified foj'in, in the body of the nucleated cell, while those 
 organisms which did not, have perished owing to their ijiability 
 to adapt themselves to the vicissitudes of circumstances. The 
 nucleated cell, then, is a colony of heterogeneous organisms, 
 which maintains a complete autonomy and behaves as if it were 
 an independent organic being, subject to the law of growth and 
 development peculiar to itself. 
 
 It is perhaps needless to point out, after we have dwelt so 
 much on the subject, that the fundamental assumption of our 
 theory is that at least some of the earliest living beings that 
 ever existed were not in the form of a cell, but a great deal 
 simpler, somezvhat like those individual physiological units 
 whicJi constitute the cytoplasm and the nucleus of the cell. The 
 cell itself was formed later out of these still smaller organisms 
 which already existed. It is not our purpose, in this place, to 
 enter into an extensive examination of the different views that 
 have been brought forward to explain what these cell-forming 
 units are. All that is essential for our present purpose is the 
 existence, as all writers unanimously agree, of such units in 
 
 1 See important remarks on the result of commensalism between two organisms. 
 Sachs : Physiology of Plants, pp. 391-394. 
 
98 BIOLOGICAL LECTURES. 
 
 the cell, each with the power of assimilating, of growing and 
 of multiplying by division.^ 
 
 Perhaps the easiest way of arriving at the conception of 
 the existence of such ultra-microscopic organisms in the cell is 
 attained by separating the cytoplasm from the nucleus in a 
 given cell, say an Amoeba, and dividing each of them into 
 smaller and smaller pieces, as far as our imagination can carry 
 us. *' Just as in division of the chemical mass we come to the 
 chemical molecule, the further division of which changes the 
 properties of the substance, so in the continual division of the 
 Amoeba we should come to a stage in which farther division 
 interfered with the physiological action ; we should come to a 
 physiological unit, corresponding to, but greatly more complex 
 than the chemical molecule." ^ Such a physiological unit, 
 Foster suggests, might be called a Somacide. This physiologi- 
 cal unit is what Weismann calls the ''bearer of vitality," or 
 Biopho7% because it is the smallest unit which exhibits the 
 primary vital forces., viz, assiinila9ion and metabolism, growtJi, 
 and multiplication by fission? This unit is not the chemical 
 molecule, hence it has all the essential characteristics of living 
 organisms, such as assimilation and division, and mere 
 molecules can neither assimilate nor multiply. It is, in fact, 
 the organism itself, with all fundamental attributes of the 
 higher organism; indeed, the reason why a higher organism 
 exhibits these fundamental properties, is, as has already been 
 mentioned, because its component units are endowed with such 
 properties. 
 
 Although it is difficult to define the exact nature and morpho- 
 logical character of the physiological units individually, we can 
 study them collectively in the phenomena of their groiLpings. 
 
 1 The following are the examples of names recently proposed for the cell-form- 
 ing units, by different writers: Bioblasts (Altmann, 1887); Pangenes (Hugo de 
 Vries, 1889); Somaades (M. Foster, 1888); Plasomes (J. AViesner, 1892); Biophors 
 (Weismann, 1893); Idioblasts (O. Hertwig, 1893). Darwin's Genunules, Nageli's 
 Micellcp, Spencer's Physiological units, Elsberg-Haeckel's Plastidiiles, Bechamp- 
 Estor's Microzymas are already well known, It is important, however, to bear in 
 mind that these names are not always synonymous. 
 
 2 M. Foster: A Text-Book of Physiology, 5th edition, pp. 5-6. 
 8 A. Weismann: The Germ-plasma, pp. 39-40. 
 
ON THE NATURE OF CELL-ORGANIZATION 99 
 
 Take chromosomes of the nucleus, for example. In some cells 
 the physiological units of the chromosome arrange themselves 
 in a series of short rods — chromatomeres — at a certain period 
 of their existence, while in others they arrange themselves in 
 a series of elongated filaments at the corresponding period. 
 What, therefore, we see in the grouping of micro-organisms 
 such as bacteria, exactly applies to those units which form the 
 chromosomes. As De Bary ^ says of bacteria, so we may say 
 here, that it is precisely in the phenomena of grouping that 
 specific peculiarities of conformation of such physiological 
 units best display themselves, being collected together, as it 
 were, in large quantity. These groupings are forms of vegeta- 
 tive development, growtJi-forms of the minute organism which 
 constitutes the physiological unit of the chromosome. 
 
 The growth-forms of the physiological unit forming the 
 cytoplasm of the cell are equally characteristic, as is plainly 
 shown in the reticular, striated, or fibrillar arrangements of 
 the. cytoplasm in different kinds of cells. 
 
 V. 
 
 To re-state the problem, then, we may say that there 
 exist two easily recognizable elements in every cell, viz., 
 {a) the nucleus, or more strictly the chromosome, and {b) 
 the cytoplasm. 
 
 It has been conclusively settled by a number of investigators 
 that the presence of both is essential for the continued 
 manifestation of life activity in a given cell. A piece of 
 cytoplasm or nucleus may continue to maintain a certain activity 
 after it has been detached from the cell, but it perishes, sooner 
 or later, if left alone by itself. 
 
 So much is certain, but how and why each is essential to the 
 other are quite other questions, and have received different 
 answers from different investigators. Some claim that the 
 nucleus influences the cytoplasm by some dynamical action ; 
 others hold that some invisible living particles of the nuclear 
 matter diffuse through the nuclear membrane, and become 
 converted into the substance of the cytoplasm ; while still 
 
 1 De r>ary : Lectures: on Bacteria, Oxford. 1SS7. 
 
lOO BIOLOGICAL LECTURES. 
 
 Others believe that the influence of the nucleus upon the 
 cytoplasm is that of a fermentative action. To a fourth group 
 of investigators, {e.g., Verworn), again, the action of nucleus 
 and of cytoplasm is a reciprocal one, the nucleus influencing 
 the cytoplasm, and the cytoplasm influencing the nucleus in 
 return, by the interchange of the metabolic products. This 
 last view is adopted in the present paper. The results of 
 operations performed on the nucleated cell seem best to 
 support this view. 
 
 All of these explanations are finally reduceable to two funda- 
 mentally different views one may take in regard to the nature 
 of chromosome and cytoplasm in each cell. Some hold ia) that 
 the nucleus and cytoplasm are essentially one and the same 
 substance, and that they only differ from each other, in so 
 far as their stages of development are concerned. Hence the 
 difference between the nucleus and the cytoplasm is merely 
 that of degree. Others, on^he other hand, maintain ib) that 
 the difference between the nucleus and the cytoplasm is not 
 that of a degree of development of one and the same substance, 
 but of the kind of material of which each is composed. 
 
 So far as we can judge from the micro-chemical reactions 
 of nucleus and cytoplasm, they must be regarded as belonging 
 to two substances entirely different from each other. There 
 is no evidence to show that one is actually produced from the 
 other, but the cytoplasm always originates from the preced- 
 ing cytoplasm, and the nucleus always from the preceding 
 nucleus. 
 
 There are, then, four well ascertained facts, in regard to 
 the nature of nucleus and cytoplasm ; viz., 
 
 1. The two elements in each cell — the chromosome and 
 the cytoplasm — have the capacity for assimilation, growth and 
 multiplication by division. 
 
 2. Each is essential to the physiological existence of the 
 other. 
 
 3. The chromosome always originates from the preceding 
 chromosome, and the cytoplasm from the preceding cytoplasm. 
 
 4. Each has a definite micro-chemical reaction, different 
 from the other, and is composed of different chemical substance. 
 
ON THE NATURE OF CELL-ORGANIZATION loi 
 
 Any theory that explains the nature of a nucleated cell 
 must explain all of these, and hold them under one common 
 point of view. Such a theory must, in short, recognize 7iot only 
 the profound pJiysiological interdcpeiidence between nucleus and 
 cytoplasm, but it must also recognize tJieir nattcral morphological 
 independence. 
 
 The doctrine of symbiosis, first propounded by De Bary,^ 
 just fulfils these requirements, inasmuch as it means now, in a 
 more restricted sense, tJie normal fellowship or the consortial 
 union of two or more organisms of dissimilar origin, each of 
 wJiicJi acts as the physiological compliment to the other in the 
 struggle for existence. 
 
 Under the assumption of such a principle as that of 
 mutualistic symbiosis, the fact of natural anatomical difference 
 between the chromosome and the cytoplasm can only be har- 
 monized with the fact of their complimentary physiological 
 adaptation. Only on the assumption that the chromosome and 
 cytoplasm had dissimilar oi-igin, can we understand their 
 constant difference in optical, microchemical and anatomical 
 characters, through all phases of their activity. 
 
 To summarize for the sake of clearness, then, the general 
 consequence of the symbiotic existence to its participants, we 
 may say, that, (i) inasmuch as one organic being comes in 
 connection with another in order to be nourished and nourish 
 the other in return, they obtain a freedom in the choice of 
 dwelling place, which is not enjoyed by them otherwise; (2) 
 symbiosis of twt) dissimilar organisms induces certain modifi- 
 cation in each symbiont, by the suppression of certain 
 characters originally present in each, or by the acquisition of 
 others, which were formerly absent; (3) when the adaptation 
 of one symbiont to the other becomes perfect, the whole 
 community behaves like a new organism, subject to new laws 
 of growth and of development, and is no longer subjected to 
 those relating to each symbiont separately, and thus, (4) a 
 power of adaptation to the external world which each symbiont 
 did not possess individually, in the struggle for existence, may 
 be acquired indirectly, by the combined efforts of the two. (5) 
 
 ^ De l^ary : Die Erscheiming der Symhiost\ Strassburg, 1S79. 
 
I02 BIOLOGICAL LECTURES. 
 
 In proportion as the symbiotic adaptation of two or more 
 organisms becomes more and more perfect, each symbiont 
 loses the power of living independently which it originally 
 possessed. 
 
 The view that ascribes a symbiotic significance to the 
 association of these two different kinds of cell-forming 
 organisms in each cell, explains the following points, viz., (I) 
 the constant difference in anatomical, optical and micro-chemi- 
 cal characteristics between the chromosome and the cytoplasm; 
 (II) the maintenance of their specific identity through all 
 phases of developviental changes, as caryokinesis and fecunda- 
 tion; (III) the participation of both nucleus and cytoplasm in 
 the manifestation of non-dcvelopmcntal phenomena of cell- 
 life, such as secretion, excretion, etc. ; (IV) the interchange of 
 metabolic products between nucleus and cytoplasm as the 
 necessary outcome of a symbiotic mode of existence; (V) the 
 reason why the cytoplasm separated from the nucleus, or the 
 nucleus isolated from the cytoplasm invariably perishes; and, 
 therefore, (VI) why the nucleus and cytoplasm are the physio- 
 logical organs of a cell, and yet they are not organs from a 
 morphological or developmental standpoint. 
 
 The nuclear substance must not be considered, in any sense, 
 as inactive, which becomes only active when it migrates into 
 the cytoplasm as Hugo de Vries ^ maintains in his well-known 
 work. The nuclear substance of a cell is just as much active 
 as the cytoplasm, according to the present view, but in an 
 entirely different manner, somewhat in the same way as the 
 chlorophyll-bearing algal cells and the colorless fungal elements 
 in a lichen are active at the same time, but each in its own way. 
 
 The vital properties of a cell do not reside in the nucleus 
 alone, nor in the cytoplasm which surrounds it, but in the two 
 together. The cell maybe destitute of a cell-wall — cytotheca 
 — or each may be enclosed within its own cell-membrane, or a 
 cell may exist side by side without any visible boundary 
 between them — the syncytium. The division of an organism 
 into distinct cell -entities in a multicellular organism is a 
 phenomenon widely distributed, it is true, but still of secondary 
 
 1 Hugo de Vries: Ijitracelhdare Pangenesis^ Jena, 1889. 
 
ON THE NATURE OF CELL-ORGANIZATION. 1 03 
 
 significance,^ due to physiological causes, I believe, emanating 
 from the fundamental difference existing between the chromo- 
 some and the cytoplasm, — the difference between the two 
 being of such a character that makes their mutual association 
 necessary for the existence of each. The chromosome 
 cannot grow beyond a certain bulk, nor is the cytoplasm 
 capable of unlimited growth, without each meeting with 
 restraining influence from the other, if one may express it in 
 a metaphorical way. The formation of a nucleated cell is, 
 in other words, a secondary adaptation to keep the nuclear and 
 cytoplasmic material within the reach of reciprocal physiologi- 
 cal influence of each. The division of the cell, when such exists, 
 is the result incidental to the increase in the number of two 
 kinds of cell-forming organisms existing in each nucleated cell. 
 
 The sphere within which the symbiotic reciprocal influence of 
 these two cell-forming organisms is felt, corresponds to what 
 Sachs 2 calls the eiiergid. The term C7iergid as a substitute for 
 the modern idea of the nucleated cell, aptly expresses one 
 aspect of the cell-organism, namely, its physiological side. 
 From the genetic standpoint, as given in the present paper, 
 this single energid is already a complex of at least two kinds 
 of organisms, different in their anatomical character, in their 
 function, and in their origin. 
 
 Stated in this way, the view is not a new one, but agrees, in 
 its broadest feature, with the idea of a cell expressed by 
 Darwin in his theory of Pangenesis,^ and in its special aspect 
 which considers mutualistic symbiosis as the basis of cellular 
 organization, may perhaps add a more concrete meaning to his 
 well-known passage, without necessarily adopting his further 
 inference from it, when he said that **an orofanic being: is a 
 microcosm— a little universe, formed of a host of self-propa- 
 gating organisms inconceivably minute and numerous as the 
 stars in the heavens." 
 
 1 Sachs: Lectures on the Physiology of Plants, p. "jt^. 
 
 2 Julius V. Sachs: Physiologische Notizen II. Beitrdge zur Zellentheorie. Flora: 
 Jahrg. 75, 1892. Reprinted in his Gesamnielte Abhandlungen, 11.^ 1893, pp. 1 1 so- 
 il 55- 
 
 ® Darwin: Proz'isional Hypothesis of Pangenesis {Animals and Plants under 
 Domestication, vol. ii.); The Descent of Man, Appleton, p. 22S. 
 
SIXTH LECTURE. 
 
 THE INADE:QUACY of the CELL-THEORY OF 
 DEVELOPMENT.! 
 
 C. O. WHITMAN. 
 
 The doctrine of Schleiden and Schwann that in cell-formation 
 lies the whole secret of organic development, has held the place 
 of a central axiom in biological work and speculation for over 
 half a century. All this time the cell has been, as it were, the 
 alpha and omega of both morphological and physiological 
 research. Regarded as a primary element of structure, it has 
 come to signify in the organic world what the atom and mole- 
 cule signify in the physical world. 
 
 The traditional cell-staitdpoint has been most exactly defined 
 by Schleiden and Schwann. In his celebrated '' Beitrage zur 
 Phytogenesis " (Miiller's Archiv, 1838), Schleiden sets forth 
 the cell-doctrine, which he limited to plants, in the following 
 words : ''Each cell leads a dojible life ; an independent 07ie, 
 pertaining to its oivn development alojte ; and a?iot/ier inci- 
 dental, in so far as it has become an integral part of a plant '^ 
 
 Schwann, in his classical Researches of 1839, extends the 
 same view to the entire organic world. 
 
 ''Each cell,'' he affirms, "is, witJiin certain limits, an individ- 
 ual, an independent zuhole. The vital phefiomena of one are 
 repeated, entirely or in part, in all the rest. These individuals, 
 however, are not ranged side by side as a mere aggregate, but 
 so operate together, in a manner imknown to ns, as to prodtice 
 an Jiarmonious ivJiole'' (Introduction, p. 2.) 
 
 " The whole organism subsists only by means of the recipro- 
 cal action of the single elementary parts!' 
 
 The method of reasoning is precisely the same as we have 
 seen in some of the latest experimental studies on cleavage. 
 Witness the following : " If we find that some of these 
 
 1 Read Aug. 31, at the Zoological Congress of the World's rolumbian Kxposition. 
 
I06 BIOLOGICAL LECTURES. 
 
 elementary parts, not differing from the others, are capable of 
 separating themselves from the organism, and pursuing an 
 independent growth, we may thence conclude that each of the 
 other elementary parts, each cell, is already possessed of power 
 to take up fresh molecules and grow ; and that, therefore, 
 every elementary part possesses a power of its ozvn, aji inde- 
 pendent life, by means of ivhich it would be enabled to develop 
 independently, if the relations which it bore to external 
 
 PARTS were but SIMILAR TO THOSE IN WHICH IT STANDS IN 
 
 THE ORGANISM. The ova of animals afford us examples of 
 such independent cells, growing apart from the organism." 
 {I.e. p. 192). 
 
 In these words of Schleiden and Schwann we see no vague 
 anticipation, but a clear statement, of the cell-standpoint of 
 to-day. The organism consists, morphologically, of cells, and 
 subsists, physiologically, by means of the "reciprocal action" 
 of the cells. Organizatioji means cellular structure, and 
 ontogeny means cell-formationib '^ Der gleiche Elementarorganis- 
 mus ist es, der Thiere nnd Pflanzen znsammensetzt.'' (Schwann.) 
 
 In this ''double life," this ''harmonious whole," this "recip- 
 rocal action" of "elementary organisms," this "operating 
 together in an unknown manner," we see the "cell-state" 
 theory, the "unknown principle of correlation," the "correlative 
 differentiation," the "cellular interaction " of current literature. 
 
 Much as we have enlarged our knowledge of the cell, we 
 are still looking at the problems of life from the point of 
 view occupied by the founder of the cell-doctrine. The most 
 notable advances in cytology have but tended to define and 
 emphasize the cell-standpoint. The discovery that all cells 
 arise by division of preexisting cells, neatly embodied in Vir- 
 chow's maxim, ^^ omnis cellula e cellnla'' ; the extension and 
 verification of this maxim furnished by Gegenbaur in 1861, 
 in demonstrating tJie vertebrate egg to be a single cell ; and the 
 proof obtained during the last twenty years that the internal 
 processes of cell-division are fimdamentally the same in both 
 plants and animals, — all these capital steps forward have 
 tended to magnify the importance of the cell as a universal 
 unit of structure. 
 
THE INADEQUACY OF THE CELL-THEORY. lOJ 
 
 All higher organization is supposed to begin with cell-forma- 
 tion, and to reach its fullest expression in the mutuality of the 
 constituent cells. Whether the cytoplasm be regarded as 
 isotropic or as definitely organized, whether the hereditary 
 substance be identified with the egg as a whole, or with the 
 nuclear chromosomes alone, the cell-dogma is still supreme. 
 
 Our microscopes resolve the organism into cells, and onto- 
 geny shows that the many cells arise from one cell ; hence, 
 the organism seems to be the product of cell-formation, and 
 the cleavage of the germ seems to be a bicilding process. 
 The cell-theory points us to very definite units, as the ele- 
 ments of organization, and thus offers what has for a long time 
 appeared to be a rational basis for the investigation of life- 
 phenomena. All the search-lights of the biological sciences 
 have been turned upon the cell ; it has been hunted up and 
 down through every grade of organization ; it has been 
 searched inside and out, experimented upon, and studied in its 
 manifold relations as a i^nit of form and function. It has been 
 taken as the key to ontogeny and phylogeny, and on it theories 
 of heredity and variation have been built. For a long time it 
 has been regarded as a decisive test of homology in germ- 
 layers, tissues, and organs. Fundamental distinctions have 
 been made between ////r^^-cellular and mter-ce\\u]d.r organiza- 
 tion, between unicellular and multicellular organisms and 
 organs, between cellular and acellular growth and develop- 
 ment, between the processes of fission and regeneration in the 
 protozoan and the metazoan, between differentiation witJiin 
 the cell and dmoiig cells, between the formative forces which 
 shape the infusorian and those which act in a many-celled 
 organism. 
 
 An organism of many cells is supposed to differ from one of 
 one cell, somewhat as a complex molecule differs from a simple 
 one. The complex unit bears not only the structure of its in- 
 dividual parts, but also a totally new structure formed by the 
 union of these parts. In like manner the organism is fancied 
 to carry at least two distinct organizations, the organization of 
 the separate cells and that of the cells united. The higher 
 organization thus differs, qualitatively, from the lower, so that 
 
I08 BIOLOGICAL LECTURES. 
 
 we may have analogies, but no homology of organs between 
 unicellular and multicellular organisms. 
 
 How sharply the line is drawn in this regard is shown in 
 the scrupulous care with which authors avoid the suggestion 
 of anything comparable to muscle or nerve in the infusorian. 
 The Ehrenberg view of infusorian organization demanded 
 altogether too much, and we have swung to the opposite 
 extreme of thinking that the very idea of such comparison is 
 forbidden by the cell-doctrine. Any suggestion of a possible 
 community of origin between an organ — say the viouth — of 
 such an animal and the corresponding structure of a cellular 
 organism, would be quickly relegated to the livibiis fatiiorum. 
 Who dares question the proposition that there can be no 
 morphological identity between an organ formed without cells 
 and one formed with cells t No matter how complete the 
 physiological correspondence, the two things must be assumed 
 to differ toto coelo, as mcc^ured by the cell-rule. That is the 
 cell-standpoint. 
 
 While the cell-doctrine has been carried steadily forward, 
 confidence in its all-sufficiency has been somewhat shaken from 
 time to time, and a few cautious protests have been ventured 
 against the complete ascendancy of the cell as a unit of organ- 
 ization. Botanists, among whom in this particular the name 
 of Sachs stands foremost, have led the way to another stand- 
 point, which, in contradistinction to the prevailing one, may 
 be called the o^'ganism-standpoifit. Among zoologists, Rauber 
 has most boldly and ably defended this point of view; and 
 more recently Wilson has expressed similar views, but with 
 reservations that still uphold the cell-standpoint. Driesch, 
 too, obtains experimental proof that " the mode of cleavage is 
 something unessential to the future animal," but still he feels 
 compelled to explain the organism from the cell-standpoint, — 
 that is, he supposes that the organism is determined by 
 correlative differentiation of homodynamous ("omnipotent") 
 cells or nuclei. The position is altogether similar to that of 
 Oscar Hertwig and Wilson. Wilson, however, holds that the 
 cleavage may secondarily acquire a "mosaic" significance, and 
 herein makes a decided advance towards a pre-organization 
 
THE INADEQUACY OF THE CELL-THEORY. 109 
 
 theory. A certain grade of organization as the result of 
 heredity rather than of cleavage is conceded for annelid 
 development, and for all forms, in so far as future characters 
 are foreshadowed in cleavage stages. This is a limited appli- 
 cation of the view which I believe holds true of all eggs, even 
 before cleavage begins. It will be easy to show that the very 
 facts generally relied upon to disprove the existence of organi- 
 zation in the G.gg furnish very strong evidence in support of it. 
 
 The question as to the presence of organization is not set- 
 tled by the form of cleavage. Eggs that admit of complete 
 orientation at the first or second cleavage, or even before cleav- 
 age begins, are commonly supposed to reflect precociously 
 the later organization, while eggs, in which such early orien- 
 tation is impossible, are supposed to be more or less completely 
 isotropic and destitute of organization. When the region of 
 apical growth is represented by conspicuous teloblasts, the 
 fate of which is seen to be definitely fixed from the moment of 
 their appearance, we find it impossible to doubt the evidence 
 of organization, or ** precocious differentiation," as it is con- 
 ventionally called. When the same region is composed of 
 more numerous cells, among which we are unable to distin- 
 guish special proliferating cells, we lapse into the irrational 
 conviction that the absence of definitely orientable cells means 
 just so much less organization. 
 
 Cell-orientation may enable us to infer organization, but to 
 regard it as a measure of organization is a serious error. The 
 organization of a vertebrate embryo cannot be said to be 
 less advanced than that of an annelid embryo, because it 
 lacks the unicellular teloblasts which the latter may possess. 
 The regular holoblastic cleavage of the mammalian ^gg is 
 evidently no index to its grade of organization. The more 
 carefully we compare the cleavage in different eggs, the more 
 clear it becomes that the test of organization in the ^gg does 
 not lie in its mode of cleavage, but in subtile formative pro- 
 cesses. We find the most unlike forms of cleavage issuing in 
 the same remarkable form-phases ; for example, the primitive 
 streak of mammalian and avian eggs ; and conversely, we find 
 identical forms of cleavage leading to fundamentally different 
 
no BIOLOGICAL LECTURES. 
 
 results ; for example, in the ^gg of the polyclad as compared 
 with that of the mollusc or the annelid, where '' cells having 
 precisely the same origin in the cleavage, occupying the same 
 position in the embryo, and placed tinder the same mechanical 
 conditions, may nevertheless differ fundamentally in morpJio- 
 logical significance. ' ' (Wilson .) 
 
 The most remarkable feature of avian development is the 
 primitive streak. The presence of this feature in typical form, 
 in such an ^gg as that of the mammal, is certainly one of the 
 most significant facts in embryology. The conclusion is here 
 forced upon us — and I see no escape from it — that the forma- 
 tion of the embryo is not controlled by the form of cleavage. 
 The plastic forces heed no cell-boundaries, but mould the 
 germ-mass regardless of the way it is cut up into cells. That 
 the forms assumed by the embryo in successive stages are not 
 dependent on cell-divisio#, may be demonstrated in almost any 
 Ggg- Watch the expansion of the blastoderm in the pelagic 
 teleost ^gg, the formation of the germ-ring, and especially 
 the axial concentration of material, which is so beautifully 
 illustrated in these eggs. Such developmental processes 
 are, if I mistake not, clearly indicative of some sort of organ- 
 ization. 
 
 The formation of the whole from a part, regarded by some 
 as conclusive evidence of isotropy and correlative tv/Z-differenti- 
 ation, no more disproves the existence of definite organization 
 in the case of the ^gg than in the case of hydra. A fragment 
 of a hydra may reproduce the whole organism ; and in so doing 
 act as a unit, not as a fraction of a unit. In the same way, 
 one of the first two or four blastomeres, when severed from 
 vital connection with its fellow or fellows, may develop as a 
 unit, not as a half-unit, precisely as Wilson insists is the case 
 in Amphioxus. 
 
 If the isolated blastomere continues for a while to form cells 
 as if it were a half-unit or a quarter-unit, and only later mani- 
 fests the whole unit-power of the organism, I see no reason to 
 conclude that the case is fundamentally different. In either 
 case the part has the power of reorganizing itself into the 
 whole, and it makes no essential difference whether the reor- 
 
THE INADEQUACY OF THE CELL-THEORY. I I I 
 
 ganization be accomplished at once, before cells are formed, or 
 gradually, while cell-formation is going on. 
 
 If we no longer hesitate to accept Briicke's view that the 
 functions of the cell are proof of organization, although our 
 best microscopes fail to give us any idea of what it consists in, 
 it certainly ought not to be difficult to regard the Qgg as a 
 young organism, and the developmental phenomena as proof of 
 organization. Such organization is, in fact, conceded when we 
 speak of the Qgg as the rudiment of an organism (''Anlage 
 eines Organismus," O. Hertwig), but, nevertheless, we go on 
 insisting that cellular structure is the essence of a higher 
 organization. 
 
 We are so captured with the personality of the cell that we 
 habitually draw a boundary-line around it, and question the 
 testimony of our microscopes when we fail to find such an 
 indication of isolation. We have so long insisted on these 
 boundary-lines as limiting homologies that we find it extremely 
 difficult to ignore them. How difficult it is, for example to 
 regard a multicellular nephridial funnel as the exact homologue 
 of the unicellular funnel. If the organ consist of one cell, the 
 tube is intm-cQ\\\\\2iY ; if of many cells, then it is inUr-cel\u\3.T. 
 But we have the ''tube" and the ''flame" just as perfect with 
 one cell as with many, as Vejdovsky's studies make very 
 certain. How idle, then, to deny homology between two 
 such organs merely because one is hi/ra- and the other iuUr- 
 cellular. And yet that is precisely what we have been accus- 
 tomed to do. 
 
 Now this one case illustrates, as I believe, a general truth of 
 no little importance. T/ie nepJirostome is a nephrostoine all the 
 same zvhethc}^ it consist of one cell, tzvo cells, or many cells. Its 
 form and fnnction are both independent of the number of com- 
 ponent cells. Cells multiply, but the organ retnains the same 
 throughout. So far as homology is concerned, the existence of 
 cells may be ignored. 
 
 May we not go further, and say that an organism is an organ- 
 ism from the oigg onward, quite independently of the number 
 of cells present "i In that case continuity of organization would 
 be the essential thing, while division into cell-territories might 
 
112 BIOLOGICAL LECTURES. 
 
 be a matter of quite secondary importance. As the nephro- 
 stome is not the result of cell-formation, but exists as such 
 before division into cells, so the organism exists before cleavage 
 sets in, and persists throughout every stage of cell-multipli- 
 cation. Continuity of organization does not of course mean 
 preformed organs, it means only that a definite structural 
 foundation must be taken as the starting-point of each organ- 
 ism, and that the organism is not multiplied by cell-division, 
 but rather continued as an individuality through all stages of 
 transformation and sub-division into cells. 
 
 We have long been aware that the cell could not be taken as 
 the ultimate unit of life, and every notable effort to account for 
 heredity has led to the postulation of primary elements in com- 
 parison with which tht^ cells appear as complex organisms. 
 Since Ernst Briicke first contended for the organization of the 
 cell in 1861, and the existence of "smallest parts" as the basis 
 of this organization, we have seen similar ideas reappear in the 
 ''physiological units" of Herbert Spencer, the ''gemmules" of 
 Darwin, the ''micellae " of Nageli, the "plastidules " of Elsberg 
 and Haeckel, the " inotagmata " of Th. Engelmann, the "pan- 
 gens" of de Vries, the "plasomes" of Wiesner, the "idioblasts" 
 of Oscar Hertwig, and the "biophores" of Weismann. 
 
 After the discovery of cell-division as the law of cell-forma- 
 tion, and after the scheme of the cell set up by Schleiden and 
 Schwann had been revised and reduced to essentialities by 
 Leydig, Max Schultze, and others, the next great step forward 
 in the cell-doctrine must be credited to Briicke, who, seeing that 
 the phenomena of life could not be referred to a striictiu'clcss 
 substance, declared for the orga7ii::;atio7i of the cell in words 
 that were scarcely less than revolutionary. 
 
 " We must therefore," says Briicke, ascribe to living cells, in addi- 
 tion to the molecular structure of the organic compounds which they 
 contain, still another, and otherwise complicated, structure ; and this 
 it is that we designate by the name organization." 
 
 Further, in his own words : " Wir miissen in dcr Zelle imtner cinen 
 kleinen Thierleib se/ien, und diirfen die Analogicn^ ivelche zivischeji ihr 
 und den kleinsten Thierforine?i exisfiren^ niemals aus de7i Augen lassen^ 
 (Elementarorganismen, p. 387.) 
 
THE INADEQUACY OF THE CELL-THEORY. II3 
 
 On the botanical side, Sachs has maintained since 1865 (" Experi- 
 mental-Physiologie ") that protoplasm is an ^''organized body^' {cf. 
 Lectures on Physiology, 1887, p. 206-7). While Briicke contended 
 for organization 7vithin the cell, and remained true to the cell-theory 
 of all higher organization, Sachs, Goebel and some other botanists 
 early challenged the doctrine of cell-hegemony. Sachs briefly indi- 
 cates his standpoint in the following words : 
 
 " To many, the cell is always an independent living being, which 
 sometimes exists for itself alone, and sometimes 'becomes joined with ' 
 others — millions of its like, in order to form a cell-colony, or, as 
 Haeckel has named it for the plant particularly, a cell-republic. To 
 others again, to whom the author of this book also belongs, cell- 
 formation is a phenomenon very general, it is true, in organic life, but 
 still only of secondary signijicance : at all events, it is merely one of 
 the numerous expressions of the formative forces which reside in all 
 matter, in the highest degree, however, in organic substance." (Lect- 
 ures, etc., p. 73.) 
 
 Briicke's great merit consists in this, that he taught us the 
 necessity of assuming stnicture as the basis of vital phenomena, 
 in spite of the negative testimony of our imperfect microscopes. 
 That function presupposes structure is now an accepted axiom, 
 and we need only extend Briicke's method of reasoning, from 
 the tissue-cell to the egg-cell, in order to see that there is no 
 escape from the conclusion that the whole course of develop- 
 mental jDhenomena must be referred to organization of some 
 sort. DevclopDicnt, no less tJian other vital p/ie?iomefta, is a 
 function of organi::ation. 
 
 Nageli followed the same method of reasoning when he con- 
 cluded that the organism was, in a certain sense, *' vorgebildet " 
 in the germ-cell (Beitrage zur wiss. Botanik, Heft IL i860). 
 This point of view is well expressed in his classical work, the 
 *' Theorie der Abstammungslehre," where he says: *' Organisms 
 differ from one another as egg-cells no less than in the adult 
 state. The species is contained in the ^gg of the hen as com- 
 pletely as in the hen, and the hen's egg differs from the frog's 
 ^gg just as widely as the hen from the frog." 
 
 While all will admit that the organization of the ^gg is such 
 as to predetermine the organism, few will be prepared to admit 
 that tJie adult onraiiization is identical in its individuality 
 
114 BIOLOGICAL LECTURES. 
 
 with that of the egg. The organism is regarded rather as a 
 community of such individualities, bound together by inter- 
 action and mutual dependence. According to this view, de- 
 velopment does not consist in carrying forward continuous 
 changes in the same individual organization, but in multiplying 
 individualities, the complex of which represents, at every 
 stage, not tJie organism, but one of an ascending series of 
 organisms, which is to terminate in the adult form. 
 
 In the egg-cell we are supposed to have an elementary organ- 
 ism ; in the two-cell stage, two elementary organisms, forming 
 together an organism of a totally different order, based on 
 a new scheme of organization. In the four-cell stage we 
 have another organism, in the eight-cell stage another, and 
 so on. 
 
 ** Physiological division of labor," as Milne-Edwards first 
 phrased it, is unquestionably a principle of wide application. 
 Given the cells as morphological units and this physiological 
 principle, the evolution of a cellular organism, may be con- 
 ceived of as a most simple affair. From a simple colony of 
 like cells, we pass to a commonwealth of differentiated and 
 mutually dependent cells. A multitude of independent cell- 
 organisms, adopting mutual service as the best economy, find 
 themselves in the end incapable of independent life, and so 
 firmly bound together in interdependence, that they constitute 
 a complex individual. The usual conception of this division 
 of labor is, as Herbert Spencer ^ has recently stated it, '* an 
 excJiaiige of services, — -^w arrangement under which, while one 
 part devotes itself to one kind of action, and yields benefits to 
 all the rest, all the rest, jointly and severally performing their 
 special actions, yield benefits to it in exchange. Otherwise 
 described, it is a system of mutual dependence." 
 
 We habitually apply this anthropomorphic conception to 
 every grade of organization. The higher organism is regarded 
 as a colony of cells ; the cell as a colony of simpler units, 
 nucleus, centrosome, and so on ; the nucleus as a colony of 
 chromosomes ; the chromosome, according to Weismann's ter- 
 minology, as a colony of "ids"; the ''id" as a colony of 
 
 1 The Contemporary Review, February, March, and May, 1893. 
 
THE INADEQUACY OE THE CELL-THEORY. I 15 
 
 "determinants"; the ''determinant" as a colony of " bio- 
 phores," and the ''biophore" as a colony of molecules. 
 
 In proportion as division of labor is carried out, inter- 
 dependence is increased, and the units become more and more 
 intimately associated. The struggle for existence is supposed 
 to extend to the cells, and even to the biophores. Symbiotic 
 relations are fought out, refined, and confirmed by natural 
 selection, and eventually reduced to a system of mutual adap- 
 tations which are fancied to be the basis of organic unity. 
 ' Whether organization is wholly a matter of acquisition, and 
 whether it became possible only as a result of symbiotic ad- 
 vantages accidentally discovered in the struggle for existence, 
 need not here be discussed. It is enough for present purposes 
 to know that organization exists, and that organic unity 
 depends on intrinsic properties no less than does molecular 
 unity. 
 
 It is not division of labor and mutual dependence that 
 control the union of the blastomeres. It is neither functional 
 economy nor social instinct that binds the two halves of an ^g'g 
 together, but the constitutional bond of individual oi'ganisa- 
 tion. It is not simple adhesion of independent cells, but 
 integral structural cohesion. 
 
 , That organization precedes cell-formation and regulates it, 
 rather than the reverse, is a conclusion that forces itself upon 
 us from many sides. In the infusoria we see most complex 
 organizations worked out within the limits of a single cell. 
 We often see the formative forces at work and structural 
 features established before fission is accomplished. Cell- 
 division is here plainly the result, not the cause, of structural 
 duplication. The multicellular Microstoma behaves essentially 
 in the same way as the unicellular Stentor, or the multinucleate 
 Opalinopsis of Sepia. The Microstoma organization duplicates 
 itself, and fission follows. The chain of buds thus formed 
 bears a most, striking resemblance to that of Opalinopsis, and 
 the resemblance must lie deeper in the organization than cell- 
 boundaries. 
 
 Compare the results obtained by artificial division in two 
 such forms as Stentor and Hydra. The two courses of regen- 
 
ii6 
 
 BIOLOGICAL LECTURES. 
 
 eratioR are so exactly parallel that one cannot fail to see at 
 once that the formative forces operate in essentially the same 
 manner with the one-celled as with the many-celled organism. 
 Gruber's experiment, as described in his recent article, '^Micro- 
 scopic Vivisection'' (Berichte der Naturforschenden Gesellschaft 
 zu Freiburg, Vol. VII, Part i, 1893), illustrates well this point. 
 A Stentor was cut into three pieces. A, B, C, each of which 
 regenerated the missing parts within 24 hours. The anterior 
 
 M\ 
 
 m 
 
 
 A ' 
 
 m\ 
 
 vc 
 
 Fig. I. — Regeneration of a vStentor cut into three parts, A, B, C. tr == pulsating 
 vacuole. S = regenerating frontal field. 
 
 end regenerated posterior end, and vice versa. The middle 
 piece regenerated both ends — the complicated frontal field 
 with its mouth, pharynx, long cilia, pulsating vesicle, etc., as 
 well as the simpler posterior region. 
 
 Treat a Hydra in the same way and similar results will follow. 
 In both cases the orientation of the parts will remain the same 
 as that of the whole. Gruber repeated the division of Stentor 
 four times in succession, getting perfect regeneration each 
 
THE INADEQUACY OF THE CELL-THEORY. 117 
 
 time, but smaller individuals, as no growth was possible. 
 The experiment reminds one of the half- or quarter-sized 
 embryos obtained by separating the first two or four blasto- 
 meres. 
 
 Gruber's highly interesting paper calls attention to the iden- 
 tity in form and structural detail of the ''membranellae " of 
 Stentor with the so-called '* corner-cells " (Eckzellen) of mol- 
 luscs {Cyclas cornea). The comparison is a most instructive 
 one, illustrating in the most conclusive manner that differenti- 
 ation of the parts of the soma depends, not on the interaction 
 of cells, but upon the elementary structure of the protoplasm. 
 
 Fig. 2. — A, three membranellae of Stentor, B, membranella in section. 
 C Section at the base of the two plates. Bl, Basal lamella. Ef, Terminal fibre. 
 Bf, l>asal fibril. A', Nucleus. 
 
 The membranellae of the frontal field of Stentor consist of two 
 thin, adherent plates, each of which represents a number of 
 coalesced cilia. The structure has a basal seam or ridge ^ 
 (Leiste), and a basal lamella which is continued into a termi- 
 nal fibre. All these fibres are connected by the basal fibril, 
 through which the movements of the membranellae are evi- 
 dently regulated. 
 
 Now this highly differentiated organ, the membranella, is 
 reproduced with most remarkable exactness in the " corner- 
 cell " of Cyclas. But here the organ represents an individual 
 
 ^ This seam consists of a series of microsomes, as Dr. Watase has discovered. 
 
ii8 
 
 BIOLOGICAL LECTURES. 
 
 cell, while in Stentor a whole crown of such organs is formed 
 without any division into cells. Could one ask for a clearer 
 demonstration ? Are we not forced to conclude with Gruber 
 that ^^ Jiowcver great tJic diffcrciicc bctivccii an infusoriiiDi and a 
 highly orga7iizcd a7iimal, it cannot be a qualitative one. We 
 can assume that the same vital elements serve in both as the 
 foundation, only in ever nezu combinations . This kinship 
 declares itself very clearly in the correspondejice of many organs 
 of the infusoria with those of the higher organisms'' [I.e. p. i6). 
 
 Fig. 3. — A, '-Corner cell" of Cyclas cornea. B, Section of three cells. Other 
 
 letters as in Fig. 2. 
 
 *' So finden wir," says Gruber, " in einem Thiere, das 
 schon hoch auf der Stufenleiter der vielzelligen Organismen 
 steht, dieselben Grundelemente wieder wie in dem einzelligen 
 Infusionsthierchen. . . . 
 
 ''Wieder und wieder der Beweis von dem gottlich einfachen 
 aber auch gottlich gewaltigen Gesetze der Einheit der Natur'' 
 
 (p. 18). 
 
 The entoderm of Dicyema illustrates one or two points of interest in this 
 connection. We have here an organ in which, as often happens, in parasitic 
 degradation, cell-formation has been dispensed with. The entoderm remains 
 throughout life as a single cell, and the whole process of reproduction, for ])oth 
 kinds of embryos, is carried on /;/ the body of this cell without any cellular organs 
 whatever. 
 
 In one respect this unicellular organ, which was undoubtedly once multicellular. 
 
THE IDADEQL/ACV OF THE CELL-THEORY. 119 
 
 What is the difference between an organization embracing 
 one cell and one embracing two or many cells ? Certainly the 
 essential difference cannot lie in the iiumber of cells. We must 
 look entirely behind the cellular structure for the basis of 
 organization. Even a highly differentiated organism may 
 reach a relatively late stage of development just as well without 
 cell-boundaries as with them, as we see so well illustrated in 
 the insect ^^^. If we fall back on the number of nuclei as the 
 essential thing, then we shall have to reckon with multinucleate 
 infusoria. In these forms do we not see that it is always the 
 same organism before us, as we follow its history through the 
 whole cycle of nuclear phases ? 
 
 The essence of organization can no more lie in the number 
 of nuclei than in the number of cells. The structure which we 
 see in a cell-mosaic is something superadded to organization, 
 not itself the foundation of organization. Comparative embry- 
 ology reminds us at every turn that the organism dominates 
 cell-formation, using for the same purpose one, several, or many 
 cells, massing its material and directing its mov^ements, and 
 shaping its organs, as if cells did not exist, or as if they existed 
 only in complete subordination to its will, if I may so speak. 
 
 In the phenomena of regeneration and embryogenesis we 
 find abundant evidence. For the present I must limit myself 
 to a few features of development. 
 
 Perhaps the peculiar formation of the embryo Toad-fish 
 (Batrachus) is as instructive a case as I am acquainted with. 
 
 is quite unique, for it may become the receptacle of nuclei Ijelonging originally 
 to other cells; in other words, it becomes multinucleate, not by the multiplication 
 of its own nucleus, but by the acquisition of exotic nuclei. 
 
 The acquired nuclei are what I have called elsewhere the "residual" nuclei, 
 which are left over when the formation of " infusoriform embryos " ceases. Each 
 of these nuclei enters into vital relations with the cell, and each undergoes the 
 differentiations characteristic of the true entoderm nucleus, so that in the end they 
 can only be distinguished by their positions. This seems to show that the differ- 
 entiation of nuclei may be controlled by the cell to which they are transplanted. 
 
 One of IJoveri's observations* shows that the same may be said of the chromo- 
 somes. One or more of the chromosomes, normally eliminated in the polar 
 globules, are sometimes carried into the cleavage-nucleus.. The supernumerary 
 chromosomes here undergo the regular transformations, quite unlike those which 
 they show when carried out in the polar globule. 
 
 * Zellen-Studien. Heft 2, pp. 171 - 175. 
 
I20 BIOLOGICAL LECTURES. 
 
 If one will take the trouble to compare this formation with the 
 ordinary type of teleostean development, he will not fail to see 
 that the organizing forces, whatever they may be, operate to 
 form an embryo under peculiar difificulties. It will be seen 
 towards the end of embryogenesis that the material of the 
 germ-ring, owing to the enormous size of the ^^g, has to travel 
 over quite a long distance, in order to reach the embryo. A 
 very thin bridge of cells connects the hind end of the embryo 
 with the closing germ-ring, and this bridge is formed by the 
 migrating cells of the germ-ring. What determines this 
 wholly exceptional rnovement of the cell-material required to 
 form the embryo 1 Is it possible that the cells move as so 
 many independent individualities } But they do move, and 
 no doubt in obedience to directing influences, acting, not in 
 the cells as individuals, but in and through the entire forma- 
 tive material, irrespective of cells. 
 
 Whoever doubts this would do well to study more faithfully 
 the living embryo during its formation. If the cell-ghost 
 should still haunt his vision, I would suggest still another field 
 for study. I would suggest first of all that he try to get as 
 clear a notion as possible of the formation of the archenteron 
 in Amphioxus, Petromzyon, and the Frog. The case of the 
 reptile might then be studied with profit. Next the '' chorda- 
 canal " of mammals, and finally Kupffer's vesicle in the 
 teleost. 
 
 There is no longer any doubt in my mind — and here 
 lam in accord with most authorities on this subject — that 
 this little vesicle is a reminiscence of the archenteron. The 
 development of Gecco, as traced by Ludwig Will, removes, as 
 I think, the last doubt on this point. 
 
 If the development of Kupffer's vesicle be studied in the 
 light of its phylogenetic significance, and studied in the living 
 as well as the dead ^gg, I cannot help thinking that candid 
 reflection on the facts will be sufficient to force conviction to 
 the standpoint here taken. 
 
 Having learned the meaning of the vesicle, one should trace 
 step by step its mode of origin in the pelagic fish-egg. Here 
 one may see this remnant of an archenteric cavity arise, not 
 
THE INADEQUACY OE THE CELL-THEORY. 121 
 
 inside the embryonic tissues as in the eggs of fresh-water 
 fishes, but actually outside the tissues on the inner face of the 
 embryo, near its posterior end. Its whole ventral and lateral 
 boundary is formed, not by archenteric cells, but by a periblastic 
 layer often as thin as the wall of a soap-bubble, and completely 
 free from all nuclei. It does not even arise as a single cavity, 
 but as numerous minute cavities that look like a cluster of 
 granules. These expand, flow together gradually, and finally 
 form one bubble-like vesicle projecting almost wholly into the 
 transparent yolk. Having attained a maximum size, its slightly 
 concave roof becomes more and more deeply hollowed out, and 
 thus it comes to inclose more and more the cavity, while the 
 latter gradually shrinks in size, and finally vanishes as the true 
 cell-walls close up. Such is briefly the history of this floor-less 
 form-reminiscence of what is a more substantial rudiment in 
 many other embryos. 
 
 This remarkable reproduction of a form-phase that is to last 
 only for a few hours and then pass away without leaving a 
 visible trace of its existence, cannot be explained as due to cell- 
 formation nor as the result of individual action or interaction 
 on the part of the cells. The embryonic mass acts rather as a 
 //;///, tending always to assume the form peculiar to the state of 
 development reached by its "■ essential architectonic elements " 
 (Briicke) — elements that are no less real because, like the atom 
 and molecule, they are too minute to be seen by the aid of our 
 present microscopes. 
 
 That cells as such do not participate in this fomiative act, is 
 shown by the mode of development of the vesicle and by the 
 absence of cells in its ventral and lateral walls. This fact, the 
 absence of cells, has actually been urged recently against the 
 identity of the structure with Kupffer's vesicle, — an error 
 which one is likely to fall into only while under the delusion 
 that acellular walls cannot be homologous with cellular walls. 
 
 The evidence furnished by Kupffer's vesicle will doubtless 
 lose much of its force with those who have not had an oppor- 
 tunity to study the subject sufficiently to form an independent 
 opinion about it. To some who are better acquainted with the 
 structure, its meaning may still appear to be somewhat prob- 
 
122 BIOLOGICAL LECTURES. 
 
 lematical, and the evidence drawn from it as therefore unsatis- 
 factory. It would be useless in such a case to urge the point, 
 and also wholly needless, as examples abound that are not open 
 to such objections. 
 
 The form-changes by which the fish blastodisc passes into 
 the germ-ring stage are examples of this kind. It is well 
 known that the transformation of the blastodisc just before 
 the appearance of the germ-ring is quite rapid, at least in the 
 pelagic fish-egg, and also qjiitc independent of cell-formation. 
 The discoidal germ-rilass suddenly thins out, but not uniformly 
 in all parts. The half of the disc in which the embryo is to 
 be formed remains thick, anticipating as it were the axial con- 
 centration which is to follow, while the half lying in front of 
 this is rapidly reduced to a thin epithelial membrane. This 
 r^'^/V?;/«/ differentiation of the outer layer and the concomitant 
 formation of the germ-ring, including the forward movement 
 of the embryonic plate (''head process"), which advances in 
 an axial direction to the very centre of the disc, are indubi- 
 tably accomplished, not by the aid of cell-formation, but by 
 formative processes of an unknown nature, but nevertheless 
 real and all-controlling. Cell-formation, to be sure, goes on, 
 but it seems to me certain that it has no directive influence 
 on the formative processes. The cleavage runs on from begin- 
 ning to end, regularly or irregularly, without modifying in 
 any essential way the form of the blastodisc. All at once, 
 when this segmentation has been carried to a certain point, 
 the transformation sets in and goes rapidly on, without inter- 
 rupting cell-formation, but to all appearance quite indepen- 
 dently of it. 
 
 In the axial concentration of the very broad embryonic plate 
 we see a formative process that can have nothing whatever to 
 do with cell-division. Again, in the establishment of the caudal 
 end of the embryo, long before that part of the germ-ring which 
 represents, historically at least, this end can be brought into 
 place, we have another decisive test of formative power assert- 
 ing itself, not only independently of cell-division, but also 
 against all the obstructions interposed by the yolk. This pre- 
 potency of the "plastic power" (Schwann) is seen to great 
 
THE INADEQUACY OF THE CELL-THEORY. 123 
 
 advantage in the pelagic fish-egg, but still better in the Toad- 
 fish-egg. It is needless to cite further examples of this sort, 
 for the embryology of every animal is full of them, and no one 
 can fail to find who looks for them. 
 
 If the formative processes cannot be referred to cell-division, 
 to what can they be referred t To cellular interaction } That 
 would only be offering a misleading name for what we cannot 
 explain ; and such an answer is not simply worthless, but posi- 
 tively mischievous, if it put us on the wrong track. Loeb's 
 experiments in heterogenesis furnish a refutation of the inter- 
 action theory. The answer to our question may be difficult to 
 find, but we may be quite certain that when found it will recog- 
 nize the regenerative and formative power as one and the same 
 thing throughout the organic world. It will find, as Wiesner 
 has so well insisted, a common basis for every grade of organi- 
 zation, and it will abolish those fictitious distinctions we are 
 accustomed to make between the formative processes of the 
 unicellular and multicellular organisms. It will find the secret 
 of organization, growth, development, not in cell-formation, but 
 in those ultimate elements of living matter, for which idiosomes 
 seems to me an appropriate name. 
 
 What these idiosomes are, and how they determine organi- 
 zation, form, and differentiation, is the problem of problems 
 on which we must wait for more light. All growth, assimi- 
 lation, reproduction, and regeneration may be supposed to have 
 their, seat in these fundamental elements. They make up all 
 living matter, are the bearers of heredity, and the real builders 
 of the organism. Their action and control are not limited by 
 cell-boundaries. As Heitzmann and others have long insisted, 
 the continuity of these elements is not broken by cell-walls. 
 The organization of the ^g^^ is carried forward to the adult as 
 an unbroken physiological unity, or individuality, through all 
 modifications and transformations. The remarkable inversions 
 of embryonic material in many eggs, all of which are ordci'ly 
 arranged in advance of cleavage,^ and the interesting pressure 
 experiments of Driesch by which a new distribution of nuclei 
 is forced upon the ^t'g'g, without any sensible modification of the 
 
 1 As will be shown later. 
 
124 BIOLOGICAL LECTURES. 
 
 embryo, furnish, as I believe, decisive proof of a definite 
 organization in the ^%g, prior to any cell-formation. The opinion 
 expressed by Huxley in his review of "The Cell-Theory," in 
 1853, forms a fitting conclusion to this introductory sketch. 
 
 "They [the cells] are no more the producers of the vital 
 phenomena than the shells scattered along the sea-beach are 
 the instruments by which the gravitative force of the moon 
 acts upon the ocean. Like these, the cells mark only where 
 the vital tides have ^een, and how they have acted. "^ 
 
 1 British and Foreign Medico-chirurgical Review, Vol. XTI, p. 314. Oct., 1853. 
 
SEVENTH LECTURE. 
 
 BDELLOSTOMA DOMBEYI, LAC. 
 
 A STUDY FROM THE HOPKINS MARINE LABORATORY. 
 
 Problems in Biology are inexhaustible, they renew them- 
 selves continually. They appear with kaleidoscopic changes 
 to successive generations of men, who receive them to study 
 in new light and from new standpoints. The results of these 
 studies are not all as stable as the problems themselves. 
 These results present themselves to us as facts, and as theories 
 based on facts. Although one well-established fact is worth 
 much speculation about its significance, yet, without the aid 
 of well-considered theories concerning the causes which lie 
 back of the facts and the meaning of the facts in themselves, 
 progress were well-nigh impossible. 
 
 These are trite sayings, but they have very appropriate 
 applications to the problems of the nature and functions of 
 the ear at the present time. The general problems of the 
 morphology and physiology of the vertebrate ear are much 
 the same as they were when first taken up, for the two ques- 
 tions, *'How is the vertebrate ear constructed.^" and "How 
 does it operate.-*" still express the aims of our researches in 
 this field as well as they did when man first began to study 
 into his auditory anatomy. But our conception of the manner 
 in which these problems are to be solved at the present day is 
 no longer what it was fifty years ago, or, indeed, ten years ago. 
 We now appreciate the full force of the requirements which the 
 present condition of morphological and physiological science 
 demands in the investigation of these problems. To know 
 the structure and function of our own ear, we find it not only 
 necessary to study the adult anatomy and function of the ear 
 in man, but also in cvcjy otJier vertebrate form as far as pos- 
 
126 BIOLOGICAL LECTURES. 
 
 sible. Nor can we stop here. We must trace out the ontogeny 
 of this organ in all those forms whose adult anatomy we 
 study, and in so doing apply the known laws of physics and of 
 chemistry to the development of their forms and contents. We 
 must trace out the phylogenetic development of the ear by the 
 comparative study of what we have gained from the above out- 
 lined investigations, combined with knowledge from two sources 
 yet untouched, viz., the morphology and physiology of those 
 sense-organs, genetically related to the ear sense-organs, and 
 the scanty store of facts pertaining to our problems which 
 palaeontology can give us. Investigations undertaken on a 
 basis less broad than this, or which do not fall within some 
 one of the categories above mentioned, are sure to fall far 
 short of the solution in the first case, and, in the second case, 
 to be of little or no service in the general progress toward the 
 final solution of these problems. 
 
 It is thus made apparent, I think, that although the physio- 
 logical problem is not as extensive as the morphological, it is 
 not for that reason less difficult or more likely of an early solu- 
 tion, for its final solution depends quite as much upon our 
 advances in a knowledge of the anatomy and physiology of 
 the central nervous system as upon experiments upon the ear 
 itself. With this prospect of long-postponed final solution, 
 facts which have direct bearing upon any of the fundamental 
 topics of ear physiology, are all the more valuable. One such 
 fact I wish to announce, viz., that there is at least one verte- 
 brate which does not depend upon its internal ears for the 
 equilibration of its body. I had previously concluded that the 
 semi-circular canals were not organs of equilibration, and inci- 
 dentally during my anatomical work I was able to determine 
 that the ear of this vertebrate is in no way more concerned in 
 maintaining the position of its body in space than are the other 
 sense organs. 
 
 In the lectures for 1891, I brought to your attention certain 
 facts and arguments to illustrate the gradations of structure 
 of the ear found among vertebrate animals, which have led up 
 to the production of the human ear. And I showed the man- 
 ner in which the ear of Marsipobranch fishes presents us with 
 
BDELLOSTOMA DOMBEYL LAC. 
 
 27 
 
 the simplest form of this organ now in existence. In continu- 
 ance of my investigations of this important organ, it became 
 necessary for me to study in the living condition some repre- 
 sentative of this group of fishes, of which we have only two 
 species in American waters, viz., the Myxine, or Hag-fish, of 
 our Atlantic coast, which is found from Greenland to Cape 
 Cod, and the Bdellostoma of the Pacific coast, which has been 
 found along nearly the whole Pacific coast-line of both North 
 and South America. In reply to a letter of inquiry addressed 
 to President Jordan, of Leland Stanford Jr. University, who is, 
 as you know, preeminent for his knowledge of American Ich- 
 thyology, I learned that Bdellostoma occurs in great abundance 
 in the Bay of Monterey and that it could be obtained there with 
 comparative ease. These two factors determined the direction 
 of my journey, and I accepted the kind invitation extended me 
 by Profs. C. H. Gilbert and O. S. Jenkins of Stanford Univer- 
 sity, placing the facilities of the Hopkins Seaside Laboratory at 
 my disposal. This marine station is an adjunct of Stanford 
 University and has just passed through its second season. 
 
 It is a great pleasure for me to be able to tell you of the 
 true scientific spirit in which the affairs of this rapidly growing 
 laboratory are conducted, and to acknowledge the generous 
 assistance accorded me by the directors, Drs. Gilbert and 
 Jenkins. In the interest of biology in America, it should be 
 made widely known that Mr. Timothy Hopkins of San Fran- 
 cisco, in whose honor the laboratory has been named, has alone 
 rendered it possible to found the institution, and he has pro- 
 vided it with the means of growth. With an insight into both 
 the great scientific and practical importance of the biological 
 researches rendered possible by such a station, an insight as 
 rare in a man of affairs as it is admirable, Mr. Hopkins has 
 supplied the indispensible funds for the undertaking, and has 
 assured the directors of his desire to have the station grow, 
 not by words alone, but by meeting the expenses of the 
 additions to the station buildings and equipment. In doing 
 this Mr. Hopkins has not been unmindful of the library which 
 is a fundamental need of all research work, for he proposes to 
 make and keep it the most complete collection of biological 
 
128 BIOLOGICAL LECTURES. 
 
 literature in connection with any biological laboratory in this 
 country. From this time on the station is to be kept in readi- 
 ness for the use of investigators at all seasons of the year. 
 
 Thus you see the needs of biological research at the sea- 
 shore are appreciated and provided for on the Pacific coast in 
 a manner worthy of emulation by men of means on this side 
 of the contii^nt. How long must we wait for the needed 
 financial support of our permanent station here } Our needs 
 areurgent, and they should be met at once. Here is a great 
 opportunity which will hardly recur in this generation. 
 
 The Hopkins Seaside Laboratory stands near the beach on 
 a rocky point forming part of the peninsula which constitutes 
 the southern boundary of the granite basin known as the Bay 
 of Monterey. It is in the town of Pacific Grove, two miles 
 distant, west from Monterey, and 128 miles south of San 
 Francisco. The station consists, at present, of a plain frame- 
 building, very similar to the original building of the Wood's 
 HoU Laboratory, though additions to it are to be made this 
 year. A pump and tank house is added to the east end of the 
 building for supplying the station with sea-water, which is 
 pumped up more than twenty-five feet above the sea level to 
 the supply tank, from which it flows through the various 
 aquaria in the building, and thence into the large, out-of-door 
 ground aquarium, in which large animals and class supplies of 
 the hardier small animals are kept. The fauna and flora of 
 the Bay of Monterey are very rich ; but, until they are more 
 thoroughly studied, we cannot accurately estimate the cer- 
 tainly very large number of forms, both rare and common, or 
 the abundance of the individuals of the species most valuable 
 for the work of the station. 
 
 In general, we may say that the fauna and flora is sub- 
 tropical, and it is rendered so by a very constant, almost 
 unvarying temperature, which averages 65^0 the year through, 
 and also by its nearness to the northern bounds of the tropical 
 seas of Central and South America. 
 
 One of the features of the station is its nearness to a 
 Chinese fishing village, from which much of the material for 
 work is obtained. Fish are caught almost entirely by means 
 
BDELLOSTOMA DOMBEVI, LAC. 129 
 
 of trawl lines ; and, while nets of several kinds are used from 
 boats, no pound nets, such as we find in the shallow waters 
 about here, are used, because of the depth of water and the 
 rocky character of the coast. 
 
 On arriving at the station, it became at once apparent that 
 I should have to depend upon the Chinese fishermen for the 
 collection of my material, Bdellostoma is so abundant as to 
 be pestiferous to the fishermen by clogging the lines with 
 their peculiar tenacious slime. 
 
 Bdellostoma, as you know, belongs to the so-called Myxinoid 
 fishes, this name having been applied to them on account of 
 their unusually slimy bodies. The first of these fishes to be 
 discovered was the European Hagfish, which is identical with 
 our Atlantic coast species, and it has been classed with the 
 Worms, Mollusks, Amphibia, and finally with the Fishes, 
 where it properly belongs. The great Linnaeus called it a 
 worm, even though his attention was called to its affinity with 
 the fishes. Bdellostoma lives on the bottom of the ocean, out 
 to the depth of one hundred fathoms and more, but seems 
 occasionally to ascend fresh-water streams for short distances. 
 It is supposed to be in its habits more or less parasitic on the 
 Halibut, agreeing in this respect with Myxine, which is para- 
 sitic on the Codfish. I have seen large skins of the Halibut 
 beautifully deprived of all contents save the skeleton, and with 
 but a single opening in the region of the gills to show where 
 the devastator had entered the body. Bdellostoma is about 
 twenty inches in length (an average size), but varies from 
 about fifteen inches to twenty-five inches in length. The 
 relative proportions of the body in the two sexes, as well as 
 in youth and age, are much the same. The body is cylin- 
 drical in shape, but flattened from side to side in the tail 
 region. In color it varies from light pink to a dark-purple 
 brown. The color has a pinkish tinge during life, owing to 
 the shining through of the red blood in the vessels of the 
 white skin below the surface coloration spoken of above. The 
 median ventral line remains uncolored from the region of 
 the yolk duct or umbilicus to the cloaca, and in old individuals 
 the snout and a broad stripe on the ventral surface of the body 
 
130 BIOLOGICAL LECTURES. 
 
 is white. In other words, as age increases, those parts of the 
 body which come into frequent contact with objects other 
 than water lose their purple color. The color grows gradually 
 darker from the ventral surface to the dorsum. The skin is 
 attached to the surface of the body of the animal by a thin 
 median dor^l ligament and by a broad median ventral area of 
 trabeculous processes. The gill holes show a narrow, whitish 
 border, which is especially well marked about the ductus 
 oesophago-cutaneus, or the tube which permits the water to 
 escape from the oesophagus without going through the gills 
 (Fig. 9, D). The cloacal opening is edged with white. Over 
 the region of the eyes the skin is pigmentless and transparent, 
 so that light penetrates freely to the eye below ; but this 
 corneal membrane is not in any way invaginated or fixed to 
 the surface of the eye, and, since the skin in this region is 
 very movable, the transparent area is very much enlarged 
 when compared with the size of the eyes (Figs, i and 5). The 
 latter are small and devoid of pigment in the retina, as far as 
 can be discerned from the exterior, and the whole bulb is 
 imbedded in a fat pad between the two diverging cutaneous 
 branches of the V nerve where they issue from the sides of the 
 head. The fish are very sensitive to light, and seek for cov- 
 ering until the head is shaded, when they come to rest, it may 
 be, with most of the body exposed. 
 
 Bdellostoma is not provided with appendages, i.e., pectoral 
 or pelvic fins, and depends for locomotion upon movements of 
 its body, eel-fashion. It is a graceful and rapid swimmer. In 
 the aquaria it remains most of the time quiet upon the bottom, 
 resting upon its ventral edge or side. In order to maintain an 
 upright position, i.e., back uppermost, it is necessary for it to 
 curve the body more or less, in order to provide a base of 
 support. Oftentimes the curve is slight, as is always the case 
 when the animal is in poor health. The normal position is 
 that of a right or left-handed coil ; and they coil both ways, 
 apparently to rest the muscles occasionally (Fig. 3, a to //). 
 Sometimes the whole body is taken up in the formation of 
 the coil ; again, often only the posterior part is used, thus the 
 head-end being reserved free, and held straight or bent into an 
 
BDELLOSTOMA DOMBEYI, LAC. 131 
 
 S-shaped figure. A slight disturbance or an internal irritation 
 will cause them to uncoil slightly, when, like a delicate watch- 
 spring, they recoil and vibrate for an instant before coming 
 back to rest (Fig. 3, a and b). This motion is one of the most 
 beautiful illustrations of muscular elasticity which I have ever 
 seen. As shown in the Fig. 3, Bdellostoma can curve its body 
 into very complicated figures, the most complex being the 
 double and triple knots into which the fish can quickly tie 
 itself for the purpose of removing anything attached to the 
 surface of its body. This it accomplishes by keeping its body 
 in motion through the knot, and tying up as fast as it comes 
 untied. When in a position of complete rest, the fish rests 
 equally well with only a slight bend in the head or the tail 
 region, though it is the tail that is normally used as a support 
 for the body to lean upon. When irritated the fish discharges 
 from a series of minute holes in the skin, running along either 
 
 o. o. o. 0.0.0,0,0.0.0,0.0 
 
 Tonque muscles 
 
 ^ Taiichiol l?e£) t on . 
 
 Fig. I. — The Cephalo-Branchial region of Bdellostoma dombeyi seen from 
 the left side to show the truncated anterior end of the body and its complement 
 of feelers. The position of the eye-spot and the mutual relations of the external 
 branchial pores and the thread gland pores is also given, ^ natural size. 
 
 side of the body, which project like minute nipples above the 
 surface of the skin, a milky-white fluid, which almost instantly 
 disappears from sight when the fish is in the water. These 
 holes are the openings into the so-called mucous sacs or, as 
 I shall designate them hereafter, the thread cell pockets or 
 nida7nental organs. These sacs are imbedded in the muscles 
 of the body, and not in the subcutaneous tissue, as Jackson 
 affirms in his recent edition of Rollcston. The discharge is in 
 the form of minute jets, and is caused for the most part by 
 the muscular contraction of the skin about the body. The 
 fluid is composed of minute bodies about the size and having 
 something of the appearance of starch grains. Each grain is 
 a thread cell, and was originally a columnar cell, derived from 
 
132 
 
 BIOLOGICAL LECTURES. 
 
 the skin lining the pocket, and which has been transformed 
 into one continuous thread in such a manner that when 
 brought into contact with water it unrolls itself in layers, 
 much like a spool of knitting-silk, when it comes to pieces in 
 layers, and straightens out in the water in an incredibly short 
 space of time. After such a discharge, if one attempt to take 
 the fish out of the water, one will notice that the fish is 
 pushed away from before the hand, and that it is impossible 
 to touch it ; and, further, that there is an invisible something 
 between one's hand and the fish. By pouring off the water, 
 or raising the fish above the surface, you find the creature 
 inclosed in a transparent, gelatinous mass of about the con- 
 sistency of thick Qgg albumen, which is extremely slippery, 
 and yet adhesive and, at the same time, not readily broken 
 into pieces, notwithstanding its apparent gelatinous nature. 
 
 A single fish will quickly fill a 
 bucket with this so-called slime ; 
 ikx. i.e., convert the water into such 
 fgjI.CJ a thick jelly. But the amount of 
 v";' solid substance, i.e., the mass of 
 the exploded thread cells required 
 ••.*v*^v;<.;..i,c- ^^ \\o\(\ the water together in this 
 
 Fig. 2. — To illustrate the way in vvay, is not equal to a piece of tis- 
 
 which Bdellostoma surrounds itself ^^^^ ^^^ ^^^^ ^^ ^^^ ^^^^^^ 
 
 with a mass of tangled threads, in 
 
 the meshes of which a great quan- ^^ ^'^^ DUCKet. 
 
 tity of water is held. The consist- You see from this short account 
 
 ency of the mass is that of egg ^^^^ Bdcllostoma is provided with 
 
 a simple but effective means of 
 protection from its enemies, and at the same time with a good 
 nest-building apparatus, for it can at a moment's notice secrete 
 a dwelling-place exactly fitted to its body without stirring out of 
 its place, no matter what position it may be in. Oftentimes these 
 nest-shaped masses are brought up with the fish from the bottom. 
 Bdellostoma is not so much of a parasite as it is commonly 
 reputed to be. It lives on or close to the bottom of the sea 
 and like its relative, Myxine, it seems to prefer mud-covered 
 surfaces in which it may partly conceal itself. It feeds upon 
 fishes of the Teleost group. It is not known that they ever 
 
BDELLOSTOMA DOMBEYI, LAC. 133 
 
 disturb Elasmobranchs, They devour their own eggs, and I 
 have frequently taken the remains of small squids from the 
 stomachs of these animals. It is certain that they do penetrate 
 the bodies of such fish as the Halibut, the Flounder, the Rock 
 Cod and Codfish, though there is not the slightest evidence 
 that they do so while the fish is in the living condition. They 
 might readily do so, however, and the fishermen all believe that 
 they do attack living fishes and bore their way into them. This 
 much is certain ; very frequently fish are taken in the trawl 
 nets from which one may see the Bdellostoma issuing in haste 
 to get into the water again. These fish hulks are found to be, 
 usually, thoroughly despoiled of all their soft parts. They 
 retain the fish form by means of the skeleton within an intact 
 skin — intact with the exception of the small hole in the region 
 of the gills through which the squirming fish was seen to come. 
 Since Bdellostoma bites the sardine-baited, trawl-line hooks of 
 the fishermen with extreme avidity,^ and is able to swallow 
 pieces of fish or other food nearly as large as its own ordinary 
 diameter, it does not seem to be entirely correct to designate it 
 a strictly parasitic animal. And if it is not parasitic, its sense 
 organs i:an hardly be said to have been degraded by parasitism. 
 If they are not degraded, they must represent primitive 
 conditions, and so far as the structure of the nose, eye and 
 ear are known to us, they contain absolutely no anatomical 
 characters which would justify the conclusion that they are 
 degraded from a more perfect ancestral condition. The eye 
 lies beneath the skin, it is true, but this is doubtless a stage in 
 the phylogenetic development of the eye, just as the existing 
 and very primitive condition of the nose is, without question, 
 a stage in the genesis of the nose of higher forms. 
 
 The head end of Bdellostoma is obliquely cut off from above, 
 downwards and backwards, in such a fashion as to bring the 
 anterior end of the long tubular nose at the extreme front 
 end of the body ; and since this anterior nasal aperture is 
 
 1 The trawl-lines are often brought up with as many Bdellostomas as other fishes, 
 and my Chinaman assured me that sometimes nearly all of the Jiooks were taken 
 by this Ilagfish; or, as he expressed it, " Evely ho6k — one Sliklostome." i.e. 
 Cyclostome — he having learned the scientific name of the creature from the 
 students of the Hopkins Laboratory. 
 
134 
 
 BIOLOGICAL LECTURES, 
 
 surrounded by four elongate conical feelers, and is further under 
 the control of a set of muscles which effect its movements in 
 all directions about the long axis of the body, we see that 
 Bdellostoma is provided with a very sensitive and effective 
 organ of touch, and as such it makes continual use of it. 
 Each of me feelers is erectile ; that is to say, it may be laid 
 back against the side of the head or thrust out in any given 
 direction at the will of the creature (Fig. 4). Each feeler is 
 richly supplied with nerves and blood vessels, and has a slender 
 and flexible, though very tough filament running through it 
 to give it strength and to help in keeping its form. These 
 
 Fig. 3. — Ten representations of the positions taken by Bdellostoma at rest 
 (a, b, c, dy e, /,) and in motion {g, h, i, J), a and b, right- and left-handed coils. 
 c, with bent tail to act as support for body, i and /, single and double bow-knots, 
 into which Bdellostoma ties itself in order to draw its body through the knot for 
 the purpose of removing the thread cells or other foreign substances from the 
 surface of the body. 
 
 sensitive feelers about the nostril give warning of the presence 
 of solid particles in the water which is being respired, for a 
 constant stream of water is drawn into the nose to pass into 
 the mouth through the hole in the roof of the palate and 
 thence onward to the gills. The genuine nasal nerve end-organ 
 is the simplest in structure of any presented to us by the 
 vertebrate series, and consist (Fig, 7) of seven semi-oval plates 
 of mucous membrane which hang from the roof of the nasal 
 cavity down into the stream of water as it turns downward 
 to pass into the mouth. These plates are bilaterally disposed 
 in sets of three, on either side of the median plate, which is 
 
BDELLOSTOMA DOMBEYI, LAC. 135 
 
 the largest of the seven. The others decrease in size from 
 within outwards. The median plate is characterized by its 
 larger size, and the possession of a terminal knob at its 
 anterior end. This knob is continued forward for some distance 
 along the roof of the nasal tube as a continually decreasing 
 ridge. So far as my investigations have gone, the olfactory 
 nerves end in Bdellostoma, as they do in Petromyzon, on 
 either side of this median raphe, so that we now know that all 
 Craniate vertebrates possess bilaterally symmetrical special 
 sense organs since neither group of the Cyclostome forms an 
 exception to the rule. 
 
 The eyes in Bdellostoma have been considered greatly 
 degenerated, and this view is still generally accepted on the 
 strength of Johannes Miiller's view of their condition. I feel 
 assured, from a preliminary examination of the eyes, — and 
 my examination is more extended than the one upon which 
 Miiller based his conclusion,^ — that the Bdellostoma eye really 
 represents a phylogenetic stage in the differentiation of the 
 vertebrate eye. Two striking features of this eye are the lack 
 of visible pigment in the retina when viewed from the outside, 
 and the absence of a genuine cornea. From a study of the 
 adult condition, it is highly probable that the skin of the body 
 is never drawn into the formation of the eye as we meet with 
 it in the fishes ; consequently, neither crystalline lens nor 
 cornea are present. The original optic cup budded out from 
 the growing brain wall forms all there is of this creature's 
 eyeball, and hence it stands as an important and extremely 
 interesting intermediate stage between the Branchiostoma 
 condition and that obtaining among the rest of the sub-kingdom. 
 The large transparent oval spot over each eye serves as a" 
 cornea, permitting the light to enter the eye no matter how 
 much the skin may be moved out of its ordinary position. 
 The eyes, along with the rest of the body beneath the skin, 
 are constantly bathed in the lymph which occupies the space 
 between the skin and the muscles. 
 
 1 Kohl (Zoolog. Beitrage) has given us an account of the histology of the eye in 
 Myxine glutinosa and he adheres still to the old view of the degeneracy of this 
 organ. 
 
136 
 
 BIOLOGICAL LECTURES. 
 
 The ear of Bdellostoma lies imbedded in the cartilage of the 
 base of the skull and below a thick layer of muscle. The 
 membranous portion is essentially like the ear of Myxine, 
 and the reader is referred to the previous volume of lectures 
 where I have described the Hagfish's ear in considerable detail. 
 
 Bdellostoma lacks all traces of the 
 system of lateral line organs so far 
 as is yet known, and it has no rep- 
 resentatives of the other specialized 
 sense organs of the skin, common 
 to most fishes. 
 
 Isolated sensory cells are the only 
 special sensory structures yet found 
 in this animal's skin. The absence 
 of these surface sense organs, to- 
 gether with the entire lack of 
 appendages, renders Bdellostoma an 
 extremely valuable animal with 
 which to perform ear-function ex- 
 periments ; this is due in great part, 
 of course, to the very simple condi- 
 tion of the ear itself. 
 
 Upon cutting through the scale- 
 less and relatively thin skin along 
 the ventral line, the body muscles 
 come to view. Of these, there are 
 two principal layers covering the 
 whole body. When they are cut through along the ventral 
 line, from the mouth to the cloaca, most of the viscera are 
 exposed. In the branchial region, as shown in Fig. 9, we find 
 the heart with its large ventral aorta running forwards, giving 
 off gill-arteries as it goes, in such a manner that either side 
 receives as many branches as there are gills on that side. The 
 gills themselves are compressed sacks, circular in outline, which 
 assume a sub-globular shape when they fill with water. The 
 current of water which we have traced from the nose into the 
 mouth, passes back through the oesophagus, and then out into 
 the gills by as many short tubes leading from the oesophagus 
 
 Fig. 4. — A full front view of 
 the face of Bdellostoma. n, nasal 
 aperture, i, 2, 3 and 4, the tenta- 
 cles or feelers. / and o, the inside 
 and outside rows of teeth, m, the 
 mouth. T, the tongue, which is 
 here thrust forwards out of the 
 mouth and nearly conceals the 
 opening. The tongue stands here 
 at right angles, in two directions, 
 to its usual position inside of the 
 head. nat. size. 
 
BDELLOSrOMA DOMBEYI, LAC. 1 37 
 
 as there are gills. After entering these sacks the water is 
 forced out through the sides of the body through other short 
 tubes which connect the gill-sacks with the surface of the skin. 
 Here they form the circular gill-holes to be seen on the side of 
 the head region of the animal. Two features in the arrange- 
 ment of the gills deserve attention. First, the large tongue- 
 muscle seen in Figs. 5, 9 extends backwards among the gills, in 
 this individual separating the anterior five pairs, effectually pre- 
 venting any contact between the gill-sacks of the opposite 
 sides and also bringing about a compression of the sacks in this 
 
 Fig. 5. — A side view of the cephalo-branchial region of Bdellostoma. Some 
 of the internal organs are drawn into the figure, the body walls being thought 
 transparent. The arrow shows the direction of the respiratory current of water 
 toward the nose. T \, 2, 3, and 4, the tentacles. 77/, the teeth, which here are 
 erected and thrown outwards by the unfolding of the tongue. y\', olfactory organ. 
 E, the ear. /, the eye. M, the club-shaped tongue-muscle. E, the external 
 branchial pores. Tr, the thread gland pores. S. C, the spinal cord. A', the 
 kidneys. //, the intestine. Z, liver. //, heart. Below and behind each gill 
 opening is seen the opening of a thread gland, a, above the figure, the single, 
 median, pharyngeal tooth. 
 
 region whenever the tongue-muscle is in action ; second, the 
 apparent relation of the point of bifurcation of the branchial 
 aorta to the posterior end of this tongue-muscle. The number 
 of gills varies to an astonishing degree, and the significance of 
 this variation has not heretofore been the subject of any serious 
 inquiry so far as I am aware. There are two series of facts 
 concerning this flexibility of the branchial .system which 
 deserve separate consideration. First, the number of gills of 
 individuals from different localities varies from 6 on either 
 side to 14 on either side, with the observed intermediate 
 stages as follows: 
 
138 
 
 BIOLOGICAL LECTURES. 
 
 Six gills on both sides, 6 on one, 7 on the other side, and 
 7 gills on both sides. This series is from the Cape of Good 
 Hope, i. c, practically Indian Ocean, and was discovered by 
 Johannes Miiller in 1834. Miiller originally 
 gave a separate specific n^me to each of these 
 varieties but later concluded that they formed 
 only a single species. No representatives of 
 the series with more than 7 gills on both sides 
 and less than 10 on both sides, have as yet 
 been recorded, or so far as I know, observed. 
 This leaves a gap of 2 gills. But from 10 
 gills on both sides, up to 14 gills on both 
 sides the series is complete and is as follows: 
 
 10 gills on both sides, 1 1 gills on both sides, 
 
 1 1 gills on one side, 12 on the other, 12 gills 
 on both sides, 1 2 on one side, 1 3 on the other, 
 13 gills on both sides and 14 gills on both 
 sides. It is interesting to note the fact 
 as first made out by Willey that during 
 its larval development, the number of 
 primary gills laid down in Branchiostoma ^ 
 varies from about 8 to 16, with an average 
 number of 14. This may be a mere coin- 
 cidence, but I am disposed to look upon 
 this as a fact of fundamental importance. 
 Kowalewsky first studied the growth of 
 the gills in Branchiostoma, and Willey has 
 greatly increased our knowledge of the 
 processes of differentiation met with in 
 
 these organs. Unlike other members of the vertebrate stock 
 this animal has the gills on one side laid down before those of 
 the opposite side make their appearance, but this is a mere 
 retardation and not an essential difference. The second gill- 
 slit is the first to appear and is soon followed by the first, after 
 which increase in number takes place, only from before back- 
 
 1 It is advisable on account of priority to use the term Branchiostoma in place 
 of the more familiar term Amphioxus, as Prof. E. A. Andrews has recently pointed 
 out in his paper on Aft Undescribed Acraniatc. Studies Biol. Lab. Johns Hopkins 
 Univ., V, no. 4, 1893. 
 
 Fig. 6. — Two thread- 
 cells. I, unexploded, 
 showing two crossing 
 layers of the threads. 2, 
 partly exploded and un- 
 ravelled thread-cell, a, 
 a portion of a coil which 
 has slipped off the cell. 
 b, the unravelled thread, 
 much magnified. 
 
BDELLOSTOMA DOMBEYI, LAC. 1 39 
 
 wards. These simple primitive slits increase in number until 
 about 14 of them are laid down, when a stage is reached during 
 which no more slits are formed in the antero-posterior series. 
 This stage has been designated the critical stage by Willey. 
 When the activities of growth again rhanifest themselves in 
 these organs it is an entirely new fashion and results in the 
 splitting of each primitive gill-slit into two by the downward 
 growth of a median gill-bar which thus separates an anterior 
 from a posterior portion of the original aperture. After this 
 process has begun, increase in the number of gills from before 
 backwards again takes place ; but is now evidently related to 
 the acquired habits of the animal, as I have already pointed 
 out in another place. ^ In the matter of gills, we see that 
 Bdellostoma approaches very close to Branchiostoma, and in 
 this sense the Myxinoid retains very primitive relations of its 
 gill-apparatus. To return to the question of the variability of 
 the gills in Bdellostoma, what can be its significance.-* Have 
 we to do with an increase or decrease in the number of gills of 
 this animal, seeing that by far the largest number of individuals 
 now existing have either 10 or 12 gills on both sides of the 
 body } I think there can be no doubt as to the answer. We 
 are here dealing with a reduction in the number of gills and in 
 no case with an increase. This conclusion is supported by the 
 fact that the more highly differentiated Marsipobranchs have a 
 smaller number of gills, and this is true not only of Myxine, 
 which belongs to the same group as Bdellostoma, but in a 
 greater degree of the Petromyzonts. In view of these facts it 
 is extremely probable that the ancestors of Bdellostoma were 
 provided with about 13 to 14 gills, and this number maybe 
 taken as representing the numerical relations of the branchial 
 apparatus of the primitive forms of the vertebrate stock 
 generally. The relation of the base of the tongue-muscle to 
 the gills is of interest, and here again we find great variability. 
 Miiller found it to lie entirely in front of the gills in the 6 and 
 7-gilled forms from the Cape of Good Hope, and this condition 
 obtains in Myxine so far as known. In Bdellostoma with 10 
 or 1 1 gills the base of this muscle may lie between the 6th and 
 
 ^ Concerning Vertebrate Cephalogenesis. — Journal of AForpholo}:^', TV, 1890. 
 
140 
 
 BIOLOGICAL LECTURES. 
 
 8th pairs of gills, according to Putnam. In the 12 and 13-gilled 
 forms I have found it between the 5th, or at most, the 6th pairs 
 of gill-sacks. 
 
 In the material which I was able to collect at Monterey the 
 following proportions of the several variations prevailed : 
 
 loi individuals had ir gills on both sides. 
 
 26 
 
 ' 
 
 " 1 1 
 and 12 
 
 « « 
 
 one side 
 
 the other side. 
 
 208 
 
 < 
 
 had 12 
 
 « << 
 
 both sides. 
 
 II 
 
 
 " 12 
 
 " " 
 
 one side 
 
 
 
 and 13 
 
 « « 
 
 the other side 
 
 8 
 
 ' 
 
 had 13 
 
 « (( 
 
 both sides. 
 
 354 
 
 total 
 
 number of individuals 
 
 counted. 
 
 Fig. 7. — The olfactory organ 
 seen from its ventral surface. A\ 
 nasal tube. Z, the nasal plates, 
 of which there are three on either 
 side of the median raphe. K. 
 X 2 diameters. 
 
 Fig. 8. — A transverse section of the 
 olfactory organ of Bdellostoma, showing 
 the nasal plates cut across C, and also 
 partly in surface view, S. R^ the raphe, 
 and Z, the lateral wall of the nasal cap- 
 sule. X 4 diameters. 
 
 Of the eight 1 1-12 variation, where the position of the gills 
 was noted, four had 11 gills on the right side and 12 on the 
 left, while the other four were just the reverse, with 12 gills 
 on the right side and 1 1 on the left. The same alternate vari- 
 ation holds true of the 12-13 variation. This fact of alternate 
 variation proves conclusively that the variability in number of 
 gills between the two sides is in no way connected with the 
 formation of the ductus oesophago-cutaneus, which is always 
 upon the left side. 
 
 The vascular system of Bdellostoma is being studied in 
 Prof. Gilbert's laboratory at Stanford University, and I need 
 not enter into the interesting relations which this system of 
 organs sustains to the general variability of this animal. 
 
BDELLOSTOMA DOME E VI, LAC. 
 
 141 
 
 especially with respect to the branchial 
 is shown in the cut. It is through the 
 that the blood is carried to the walls 
 of the gill sacks, by means of the 
 individual branches a, one of which 
 leaves the main trunk, so long as it 
 remains unpaired, for each gill. 
 
 Owing to the possibility of its play- 
 ing an important part in the develop- 
 ment of the variability of the gills, it 
 is desirable to examine the nature of 
 the so-called tongue and its muscles a 
 little more in detail than we have yet 
 done. In Figs. 9 and 5 these structures 
 are shown as they appear upon slitting 
 open the body muscles. The tongue 
 forms a somewhat heart-shaped plate, 
 when spread out flat as in Fig. 4, and 
 is composed of two symmetrical lateral 
 pieces. These halves each bear two 
 rows of teeth, and during life, while 
 in the mouth, they are inclined at an 
 angle to each other, thus forming a 
 trough, whose shape is maintained by 
 the sides of the mouth. When, during 
 life, the tongue is thrust out of the 
 body, it is flattened out upon the 
 anterior edge of the solid floor of the 
 mouth cavity, as shown in Fig. 5, 
 when it is in the best possible position 
 for the use to which it is put, viz.y the 
 rasping away of the flesh of the fish to 
 which Bdellostoma has fastened itself; 
 or, if it is a small bait, the rapid and 
 certain forcing of the bait into the 
 mouth cavity. The mechanism which 
 effects this end is quite complicated, 
 and I need not enter into a complete 
 
 arteries, whose position 
 large median vessel A, 
 
 Fig. 9. — A ventral view 
 of a dissection of the gills 
 of a Bdellostoma dombeyi, 
 with 12-13 gil^s, to show their 
 relations to each other, to 
 their blood supply, and to 
 the surface of the body. M, 
 the club-shaped tongue mus- 
 cle. Z, its tendon. ^. s., 
 branchial sack, f-rj, the ex- 
 ternal branchial pores or gill 
 holes. Tr., the pores of the 
 thread glands. A, the ven- 
 tral aorta, a, the branchial 
 arteries. D, the ductus oeso- 
 phago-cutaneus. br. /., the 
 internal branchial tube. H^ 
 the heart. 
 
142 BIOLOGICAL LECTURES. 
 
 description of it here. It will suffice if I confine my remarks 
 to the large club-shaped muscle which lies between the 
 anterior pairs of gills. In cross section the muscle is seen to 
 be composed of an outer thin ring — the section of the thin 
 cylindrical muscle, and an inner solid muscular disc — the sec- 
 tion of the solid, club-shaped muscle, which is made up of two 
 equal literal halves. Johannes Miiller has called the outer one 
 of these the hollow tongue muscle, and it certainly does at 
 first sight seem to deserve the name. 
 
 The long tendon into which the tongue muscles taper, runs 
 forward in a groove in the top of the cartilaginous floor of the 
 mouth until it reaches the posterior border of the tongue, when 
 it splits up into two unequal bundles of tendinous fibrillae, 
 which run forward and insert into the upper surface of the 
 tongue body. These slender tendinous slips are so arranged 
 that, when the tongue is drawn out of the mouth, the carti- 
 laginous bars carrying the teeth are turned, so as to throw 
 the teeth outwards and forwards in such a manner that their 
 points are erected, and catch readily the instant the club- 
 shaped muscle begins to draw it back into the mouth. The 
 teeth are corneous structures,^ borne upon the soft teeth 
 papillae, and the teeth of any one row are more or less fused 
 together at their bases, so that when separated from their 
 papillae, they hang together in a row or plate. (Figs. 4 and 5.) 
 Oftentimes, the inner tooth, which is also the larger, separates 
 from the others, and the outermost tooth of the row is not 
 always united with its fellow. Each tooth is an exceedingly 
 sharp-pointed, conical body, flattened from abov£ downwards, 
 and curved from without inwards. 
 
 1 I have made a special examination of the teeth of Bdellostoma dombeyi and 
 Myxine glutinosa, and although I was desirous of finding the enamel cap described 
 by Beard I was unable to do so. There is not the slightest trace oibone in any of 
 the teeth of these two forms, and what Beard has taken to be such is doubtless 
 much hardened horn, produced by the methods used by this author in preparing 
 sections of teeth for microscopic examination. I have cut a large number of the 
 teeth of Bdellostoma and of Myxine and have found no difficulty in sectioning 
 them in situ when imbedded in celloidin. The Myxinoid teeth are cornefied 
 sheaths of the epidermal elevations on the tongue plate, and in adult life show no 
 trace of dentine or enamel. 
 
BDELLOSTOMA DOMBEYI, LAC. 1 43 
 
 The number of teeth in Bdellostoma varies as much, if not 
 more, than the number of gills, so that the only two ''constant'' 
 characters which Muller could find upon which to base a classi- 
 fication are both of them extremely variable. The limits 
 of the variability of the teeth, so far as known, are as 
 follows : — 
 
 Bdellostoma from the Cape of Good Hope, 6-j gills, |||, 
 li 111 12 112 
 
 11 I 1 1' 11 I 12- 
 
 Bdellostoma from coast of Chili, 10 gills, ^ |^y (Lacepede), 
 
 11112 13 113 
 11 I 11' 12 1 12- 
 
 Bdellostoma from coast of California, 1 1-13 gills, -|||, \\ | W. 
 
 The California series which I have counted is the only one 
 extensive enough to give opportunity for the observation of 
 the variations, although Muller evidently had nearly extreme 
 forms in the three individuals whose dental formulae he re- 
 corded. 
 
 In 22 individuals with 11 gills I found the dental formulae to 
 
 Kf^ 1Q follows • 110 19 110 19 4 IJ). I IJ). 1 1_0_ 110 1 10 I 10 
 
 DC as lOllOWS . 1 -g- I 9, J- 10 I To» ^ 9 I 9 ' ^ 9 | 1 0' ^ 1 | 1 0» 
 
 1 10111 1 10111 1 10 111 3 11110 1 11110 5 11 11 
 
 -"- TO] 9' -■- "9 r9' ^ 10 I 10' ^10 I 10' ^ 11 I 10' ^ 10 I 10' 
 
 1 11 I 11 1 L2 I \\ 9 12 112 
 ^ 1 1 I 10' -^ "9 I "9 ■' *" 11 I 11- 
 
 In 61 individuals with 12 gills the following dental formulae 
 
 nrrnrred • 1 8- 1 lil 1 ^l& 8-9-11-0. 1 -9_ I IJ). 1 _9_ 1 10 O J-0- 1 ^ 
 
 occurrea . ± 9 | j^, l 9] 9, o 9] 9, x ^q] 9, x io|iO'^ 9 |9' 
 
 1 10 19 1 10 19 1 1 |j_o_ 4 1 jiJi 6 10 110 7 j_o. 1 1 
 
 -*■ To|9' -•- TO I TO' ^^ 9 19 ' ^ 10 19 ' " ITTI IT)' ' 9 I 10' 
 
 1 Ul I i_l 1 10 1 11 1 JJ. 1 1-0. 1 11 1 1-0- 10 11 1 10 3111 11 
 
 ^ 9 I 9 ' -^ 10|l0' ^ 9 I 9 ' -*■ 10| 9' ^^ 10|l0' ^ iTFIlO' 
 
 -^ ixrii'o' -^ if 111- These counts were made on consecutive 
 animals as they came from the trawl line, and must represent 
 fairly the dental conditions of Bdellostoma in the Bay of 
 Monterey. Two things are apparent. First, there is not the 
 least relation between the number of gills and the number of 
 teeth ; and, second, the teeth are subject to much greater 
 variation than the gills, notwithstanding they belong to the 
 so-called hard parts. Size and age do not affect the dental 
 formula. 
 
 On combining the dental formulae of the ii-gilled and 12- 
 gilled variations, we find the following numbers to obtain for 
 the '^6 individuals whose dental formulae I have carefully 
 counted on both sides of the dentiferous plate. 
 
144 
 
 BIOLOGICAL LECTURES. 
 
 No. of 
 Indivi- 
 duals. 
 
 1 
 
 8 
 1 
 1 
 3 
 1 
 2 
 14 
 
 4 
 
 7 
 1 
 2 
 
 1 
 2 
 1 
 1 
 13 
 1 
 8 
 1 
 1 
 1 
 3 
 
 Predomi- FroiTi this table we learn that more than 
 
 Dental nant Num- 
 
 Formuia. ber of sevcn-tcnths of the entire number of indi- 
 
 Teeth. 
 
 I viduals belong to three groups, and over 
 
 i_o 
 
 9 
 
 ^10 
 
 half of these belong to the group in which 
 lo teeth occur in both rows oftener than 
 any other number. We have to do with a 
 reduction in the primitive number of teeth. 
 So much for the California specimens. 
 
 The Chilian specimens seem to average a 
 larger number of teeth, for Girard counted in 
 his type specimen of 14 gills y||yI, while 
 Putnam found i| 1 1| or \\ | W in the ma- 
 terial he studied from Talcahuano Bay, 
 brought to this country by the Hassler expe- 
 dition, which is reported as having 10 gills. 
 Lockington gives the formula as ^^ I Lo.^ 
 which harmonizes with what I find to be the 
 most abundant formula. Lacepede's example 
 from Chili had a dental formula of \^-|V, 
 which is quite unusual, and indicates what 
 we may expect from a careful study of a 
 large series from the South American coast. 
 I fear that the dental formulae published in 
 the systematic accounts of Bdellostoma are 
 based for the most part on counts of the 
 teeth of one side of the tongue only, and in 
 this way only can I account for the bilateral 
 symmetry which characterizes them. 
 The reproductive organs of Bdellostoma are extremely simple 
 in their structure, and are composed in both male and female 
 of a simple, double-layered plate of the peritoneum which 
 hangs down as a fold from the dorsal wall of the body cavity 
 on the right side of the median line (Fig. 12). The ovary 
 occupies nearly the whole extent of the body cavity in the 
 female. The testis occupies only the posterior part of this 
 long fold, and in the female no eggs are developed in this 
 region. In hermaphrodites the two divisions of this organ are 
 
 1 
 
 TO 
 
 10 
 1 
 
 10 
 
 10 
 
 "i_o 
 '9' 
 
 1 
 TO 
 
 1 1 
 
 t 1 
 
 ii 
 10 
 
 1 0. 
 
 \ Q. 
 
 10 
 10 
 
 10 
 
 10^ 
 
 10 I 
 
 11 111 
 
 10 r -^^ 
 
 ^ 1 i 
 
 TO J 
 
 12 
 
 TO 
 1 1 
 
 12 
 11 
 
BDELLOSTOMA DOMBEYI, LAC. 
 
 145 
 
 separated by a notch in the lower edge of the fold. The left 
 organ seems never to be developed in any of the Myxinoids. 
 In all cases, so far as my observation goes, each individual is 
 potentially bisexual, but Bdellostoma is not much like the 
 Myxine in changing its sex with increase of age ; certainly this 
 condition does not seem to be so clearly expressed in Bdellos- 
 toma as in Myxine. For whereas in Mixine only the young 
 animals seem to be males, in Bdellostoma large and presumably 
 old animals are found to be males as well as females, and both 
 
 Fig. 10. — A view 
 similar to that shown 
 in Fig. 9, but drawn 
 from a ']-'] gilled 
 Bdellostoma. Let- 
 tering the same. 
 
 formed by th 
 one side. 
 
 Fig. II. — The branchial 
 apparatus of Myxine, seen 
 from the ventral face, to 
 show what the changes are 
 which have made Myxine's 
 respiratory tract so differ- 
 ent from Kdellostoma's. It 
 is at once apparent that the 
 only structures in any way 
 chaftged are the external 
 branchial tubes, which, by 
 all uniting together, have 
 only to pierce the skin at 
 one place, ce., oesophagus, 
 1-6 and g. s., the branchial 
 sacks, br. t., the external 
 branchial tubes of the first 
 gill. Z>, the short duct 
 e union of all the gill tubes of 
 
 sexes are found among the smallest individuals taken. The 
 large anterior region of the peritoneal fold is always ovary, while 
 the much smaller posterior region of the fold is the testicular 
 region. The ovary is readily distinguished by the numerous 
 eggs in many stages of development, while the testicular part, 
 which is separated from the ovarian part by a notch or deep 
 scallop cut in the border of the fold, is to be distinguished by 
 its clear vesicles, grouped together like a bunch of grapes. 
 Of course a crucial test of the character of the small vesicles 
 is the presence of spermatozoa in the testicular part. Tested 
 in this way many individuals were found to be ripe, while 
 among the females very few were found to contain eggs in 
 
146 
 
 BIOLOGICAL LECTURES. 
 
 the last stages of ripening. The explanation for this scarcity 
 of ripe females which has been applied to the case of Myxine, 
 viz., that the pregnant females, when the egg-laying time 
 comes on, cease to eat, and consequently are not to be 
 taken either in baited pots or on trawl lines, must suffice 
 for Bdellostoma until we have a better one. Other causes 
 may be operative here, but nothing is known with certainty 
 of the ^nditions of life which surround the ^^'g laying and 
 embryology of Bdellostoma. 
 
 Fig. 12. — A side view of the sexual gland of an hermaphroditic Bdellostoma 
 dombeyi. a and b, cross-sections of the gland at the points indicated by the 
 arrows, v, the dorsal blood vessel, below which the gland is suspended as a 
 double fold of the peritoneum. /. ov, ovary, te^ testis. E, nearly ripe eggs. 
 e, very young ova. /, testicular follicles. 
 
 Some individuals of Bdellostoma are truly hermaphroditic, 
 having at the same time a genuine testis with ripe sperm and 
 an ovary with eggs nearly or quite ripe. These individuals are 
 rare, so far as my experience goes, but others with the two 
 organs in a more unequal state of development are more 
 numerous. However, by far, the largest number of individuals 
 are genuinely male or female. Males are much more numerous 
 than the females, but this statement applies only to the catches 
 which I had the opportunity of examining. It may be merely 
 a coincidence, or on the other hand it may faithfully represent 
 the true conditions of things in the Bay of Monterey. All 
 things considered, I believe a preponderance of males represents 
 the ordinary condition. 
 
 The sex of 209 out of 354 individuals was noted, and they 
 
BDELLOSTOMA DOMBEYI, LAC. 147 
 
 are distributed between the males, females and hermaphrodites 
 in the manner indicated by the following table : 
 
 Of loi individuals having 1 1 
 
 gills on both sides, . 61 were males, y] were females, and 3 hermaphrodites. 
 Of 26 individuals having 1 1 
 
 gills on one, 12 on the 
 
 other side, . . . 14 " " 12 '.^* " '* O " 
 
 Of 163 individuals having 12 
 
 gills on both sides, . 94 " " 66 " " " 3 " 
 
 Of II individuals having 12 
 
 gills on one side and 13 
 
 on the other, . . 8 " " 3 " " " o " 
 
 Of 8 individuals having 13 
 
 gills on both sides, • 5 " "' 3 " " " o " 
 
 Totals, 182 121 6 
 
 The sexuality of the Bdellostoma does not appear to depend 
 upon size or age, for of 10 small individuals (under 15 inches) 
 there were 7 males with gills, \\, 2 females with gills, i|, and 
 I female with gills, yy- 
 
 Of 1 5 large individuals (over 20 inches) there were 8 males 
 with gills, i|, I female with gills, l|, 5 males with gills, l-i, 
 and I male with gills, l|. 
 
 In 1875, Anton Dohrn, the founder and talented director 
 of the Zoological Station of Naples, first clearly defined the 
 hypothesis of degeneration, and fully illustrated its application 
 to the vertebrata in his famous paper, ''Origin of Vertebrates." 
 Dohrn corrected the then prevalent ideas, according to which 
 all the simpler forms of animals, anatomically considered, were 
 to be looked upon as more primitive and as representing 
 ancestral stages in the development of the groups to which 
 they belonged. He was not fortunate in his selections of 
 cases of degeneracy among vertebrates, as I hope to make 
 clear to you. As a typical case of true degeneracy we have 
 the well-known case of the Tunicate, which during its devel- 
 opment passes through a stage which, according to the 
 '' biogenetisches Griindgesetz'' must be considered to be strictly 
 vertebrate in its morphological characters. These vertebrate 
 characters are not retained by the Tunicate, however, but are 
 absolutely destroyed during the growth of the larval body, so 
 that in the adult condition there is nothing left to ever remind 
 
148 
 
 BIOLOGICAL LECTURES. 
 
 one of the vertebrate type of organization, and the body ever 
 after remains in this inferior condition of structure, though it 
 produces germs which in their development attain the higher 
 level of vertebrate organization, only to sink back to the lower 
 level of Tunicate structure. 
 
 Fig. 13. — A view of three ripe eggs of Bdellostoma dombeyi, showing their 
 natural size, the variations in shape, the manner in which they hold together by 
 means of their anchor hooks, and the position of the suture which allows of the 
 ready separation of the cap from the body of the egg membrane, a, an end view 
 of an egg cap. The anchor filaments have all been radially spread to show the 
 spiral arrangement of the filaments upon the cap surface, x, the anchor head, 
 y", the filament, b, a side view of another cap. st, the cap membrane, b, the 
 row of enlargements forming the bases of the filaments, / x, the anchor heads. 
 The central dot in a shows the position of the micropylar funnel which leads into 
 the micropylar canal. The egg membrane is composed of a thin genuine vitelline 
 membrane and a thick corneous follicular (granulosa) membrane, and the anchor 
 threads are hollow evaginations from the end parts of the latter. Natural size, 
 a and b Y. 2 diameters.^ 
 
 1 After a study of the development and the adult condition of the egg mem- 
 branes in Bdellostoma dombeyi I am certain that Cunningham is in error in calling 
 the egg membrane of the Myxinoids a vitelline membrane. The corneous part of 
 the egg shell is cellular in nature and the cell remnants are to be seen in the ripe 
 egg shell. The anchor hooks are formed by the evaginations of this granulosa 
 layer in late stages of egg life, due to the outgrowth of solid rods of the vitelline 
 membrane. These rods appear to be resorbed before the ripening of the egg and 
 thus the anchor filaments are left hollow. The Myxinoid egg is thus very much 
 like other fish eggs as regards its envelopes. An illustrated account of these 
 facts, among others is ready for the press. 
 
BDELLOSTOMA DOMBEYI, LAC. 149 
 
 Thus it is that the evidence in favor of progressive simplifi- 
 cation of structure (which is all that is meant by the term 
 degeneracy) depend upon two factors : 
 
 {a) The comparison of the anatomy of the fully developed 
 degenerate animal with that of its supposed congeners. In 
 this way we can often be sure that the less complex animal 
 does not represent any of the ancestral stages common to its 
 nearest relatives. This is the anatomical method, and {b) by 
 the study of the embryological development of the forms under 
 consideration. This is the embryological method, and it is very 
 generally admitted to be conclusive whenever it can be shown 
 that either the embryonic or larval stages of the animal 
 under consideration possess a higher degree of morphological 
 differentiation than is possessed by the adult form. e. g. 
 barnacles (Cirrhipedes), Tunicates. In many instances the 
 embryological history may be, and is, so shortened as to give no 
 trace of a higher stage of existence having ever been enjoyed. 
 e.g. many Tunicates. Even from this very short review of 
 the degeneration hypothesis, it is evident that we must 
 conclude that a pidori there is much reason to suppose that 
 any given animal form may have developed from a more highly 
 organized ancestor by a process of simplification as to assume 
 that it has developed from a relatively simpler form by an 
 unbroken process of complication, and that our only means 
 outside of morphological research is to be derived solely from 
 the life habits of the animal, i.e. whether they are such as to 
 favor degeneracy or not. In saying that there is much reason, 
 on a priori grounds, to assume that an animal has degenerated 
 or developed downward to its present condition as that it has 
 developed upward, I certainly cannot acquiese in the view 
 expressed by Dohrn and adopted by Lankester that there is as 
 much probability in favor of the one process as of the other, 
 for it is evident that cases of degeneracy must be much less 
 common than cases of progression, otherwise the Law of 
 Agassiz, fully established by Darwin, would not be so easy 
 of observation in embryology and palaeontology. The law of 
 progressive differentiation is so universal in its application that 
 we are on safe ground in always considering any existing form 
 
ISO 
 
 BIOLOGICAL LECTURES: 
 
 as the result of a series of progressive changes, or viewing 
 any fossil form as the highest of its kind up to the time of its 
 existence, unless in either case there is positive proof to the 
 contrary ; for the biogenetic law lays' the burden of proof 
 upon the degenerationist. Life habits, favoring simplification 
 or obliteration of structure, are parasitism, sessile or fixed 
 life, burrowing and hiding in crevices and holes, and indiscrim- 
 inate and#:liffuse food habits, while free and unrestricted motion 
 within the aqueous and aerial oceans upon and over their 
 bottoms, involving the pursuit of fleeing prey and the struggle 
 with other forms for its possession and for life itself, are highly 
 favorable to increasing complication of structure. It is at 
 once evident that we cannot take existing vertebrates and 
 group them either in an arbor-like or ladder-like geneological 
 arrangement, and at the same time express the true relation- 
 ships of the many modifications of structure which have been 
 produced. This brings us to the consideration of the question 
 of the classification of Bdellostoma, and to this I shall return 
 after throwing what light I can upon the conditions under 
 which Bdellostoma exists and the probable relations which this 
 fish bears to these conditions of its environments. 
 
 What evidence can we bring forward to show that '' the small 
 and degenerate group Cyclostomata'' as Lankester ^- calls them, 
 are not degcficrate Vcrtcbi'atcs ? In previous publications I have 
 pointed out some of the facts, and I am sorry to say they have 
 not been accorded that consideration which they merit as 
 anatomical facts. In 1889^ I showed that ''the higher sense 
 organs of the Cyclostomata are all paired^ since the nose [i.e., the 
 nasal or olf active epithelinni) exists in the efjtbryo as zvell as the 
 adult in tJic form of two circumscribed areas lying 07i either side 
 of the media7i line, each of zvhich receives the entire iierve supply 
 ajforded by the olfactoiy nei^^e of its side. I then ventured to 
 predict that the Myxinoids would show the bilaterally sym- 
 metrical or paired nasal areas as distinctly as Petromyzon does. 
 I can now state that my conclusion was well founded, for in 
 Bdellostoma we have the nose divided into right and left halves 
 
 1 Reprint Article, Vertebrates, Eitcy. Brit. ed. 1887. London, 1890. 
 
 2 Concerning Vertebrate Cephalogenesis, Journal Morphology, l'V,\'&go. 
 
BDELLOSTOMA DOMBEYI, LAC. 151 
 
 by a median plate which is the homologue of the median raphe 
 of Petromyzon. In Figs. 7, 8 is shown this important feature 
 as seen from the ventral surface (inner face) of the nasal organ. 
 As concerns Bdellostoma's eye, we know very little of its adult 
 structure and nothing of its development, and the conclusion 
 that it is a degenerate organ in lacking a lens, choroid, etc., 
 and being entirely below the surface of the body and under the 
 skin, is purely hypothetical, for it can just as well represent 
 a stage in the phylogenetic development of vertebrates. I 
 believe such to be the truth. The undegenerate nature of 
 the ear I have already established in another publication. ^ On 
 the basis of our knowledge of the higher sense organs we may 
 well ask: Why are the Myxinoids primitive fishes ? instead of 
 '' Why are they degenerate vertebrates } " The following con- 
 siderations enable us to understand why they are primitive and 
 not degenerate: 
 
 1 . Their unusually great geographical distribution indicates 
 that they are descendants of a very ancient stock. 
 
 2. They are in a morphologically undifferentiated condition, 
 as compared with all other groups of craniate vertebrates and 
 their several organs show no certain traces of degradation 
 of structure. In this regard I have examined the following 
 organs: skin (here the absence of surface sense organs, scales, 
 except the teeth, and a lateral line is noteworthy and entirely 
 unexplained; they are not degraded but Jiave entirely vanished 
 from adnlt life), muscular system, skeleton, vascular system, 
 alimentary system, urino-genital system and the higher sense 
 organs, eye, ear and nose. Of these latter the two last are 
 normal stages in the development of the vertebrate stock, 
 and so far as I have examined the structure of the eyeball, 
 its lack of lens and eye muscles and its small optic nerve, 
 I have found no conditions which are not harmonious with the 
 view that this eye has simply never been highly developed. 
 
 The degeneration hypothesis fails completely to account for 
 Myxinoid anatomy, and the habits of the animal give no 
 grounds for this assumption. Certainly the natural conditions 
 surrounding the life of the animal as far as we know them, are 
 
 1 Contributions to the Morphology of the Y.zx, Journ. Morphol. VII, 1892. 
 
152 BIOLOGICAL LECTURES. 
 
 not such as to cause the extensive retrogressive development 
 which they are supposed to have undergone and which it is 
 assumed has affected nearly all of the organs of the body. 
 
 It seems to have become a settled belief among the large 
 majority of zoologists of both morphological and systematic 
 proclivities that the number of gills found among vertebrates 
 never rises above eight pairs in existing forms. The few who 
 have recognized the true state of the case have had little to do 
 with the education of the younger men, and so the error has 
 continued to be taught. Lankester ^ wrote in 1 890 — regarding 
 the gills of vertebrates, ''The pharyngeal slits follow closely 
 upon the mouth, and in existing Craniata never number more 
 than eight pairs." Wiedersheim ^ gives seven pairs of gills as 
 the largest number occurring among craniate vertebrates, while 
 Claus, Huxley, Jackson-Rolleston, Hertwig and others give the 
 number varying from 5 to 8, but never greater than 8. They 
 evidently confine themselves to Miiller's statement concerning 
 the number of gills (6-7) in Myxinoids and to the known facts 
 concerning Petromyzoa (7) and the Notidanidae (^-y). In 
 1854 Charles Girard described a fish from the coast of Chili 
 which he called Bdellostoma polytrema, and which he found to 
 have 14 pairs of gills. In 1873 Putnam found that the 
 Bdellostomas of the Hassler expedition, collected off the coast 
 of Chili, had 10 pairs of gills. Later on Lockington (1878) 
 described a similar fish from San Francisco which had 1 1 pairs 
 of gills. These are the only original observations, with which I 
 am acquainted, which give the number of Myxinoid gills greater 
 than the accepted numbers (6-1). Yet these facts have been 
 many times confirmed by such men as Gunther, 1873, Gill, 
 1880, and Jordan and Gilbert, 1882, who gave the number of 
 gills of the Pacific Bdellostomid as 1 1-14. Notwithstanding all 
 these published accounts, morphologists have completely over- 
 looked these facts, and while speculating on the ancestral 
 number of gills of vertebrates, have depended for the most pari 
 upon the embryological stages of Elasmobranch and Teleost 
 fishes. 
 
 1 Ency. Brit. Article on vertebrates. 
 ^ Grundriss d. vergl. Anat. Jena, 1893. 
 
BDELLOSTOMA DOMBEYI, LAC. 153 
 
 I have already referred to this matter in connection with the 
 brief description of Bdellostoma's gills, but it is sufficiently 
 important to call for a more detailed account, in which I shall 
 try to bring the branchial arpparatus of Bdellostoma into 
 harmony with the primitive condition of the same organs in 
 Branschiostoma. 
 
 Having shown that there is a great degree of variability in 
 some of the organs of Bdellostoma, it will be in place to seek 
 for the conditions which keep up this variability, — for the 
 conditions must be present conditions and in no sense past 
 ones. Three conditions suggest themselves as probably con- 
 cerned in keeping up this variability among the Bdellostomas 
 as a group of animals of common descent and as families of 
 individuals living under common conditions in circumscribed 
 areas. These are Geographical Distribution, Panmixia and 
 Hermaproditism. 
 
 The geographical distribution of Bdellostoma cannot be 
 satisfactorily accounted for by assuming several separate crea- 
 tions of these animals, for though so widely distributed on the 
 floor of the Indo-Pacific oceanic depression, all its morphologi- 
 cal characters and its life habits point to its origin from a single 
 ancestor at some place in the South Pacific ocean. Admitting 
 the common descent of the varieties of Bdellostoma, the 
 phenomena connected with the geographical distribution of 
 animals in general lead us to conclude that Bdellostoma has 
 existed for a very long period of time and that it has been but 
 little modified during this long period. We do not know that 
 it has always been as variable as it is at present ; but if it has 
 been, it is a most remarkable case, since ordinary ajiimals 
 would have become well differentiated into distinct species during 
 the process of dispei'sion over such a great territory and the 
 consequent operating of more or less changed conditions in 
 different ways upon different parts of the variable organism 
 during the great period of time necessary to accomplish this 
 dispersion. Bdellostoma has been widely distributed, and 
 while the conditions in different parts of the territory which it 
 inhabits can hardly be held to be identical, still the sea bottom 
 is far more stable in its temperature and other features produc- 
 
154 BIOLOGICAL LECTURES. 
 
 tive of variation than the shallower waters of inland basins or 
 the surface of the land itself. Hence so far as the effects of 
 geographical distribution are concerned, they may be said to have 
 had very little or almost no effect npon the anatomical structui'e 
 of the animal. This conclusion is fully sustained by the fact 
 that in each locality Bdellostoma shows similar variability in 
 the same organs, while individuals from widely separated 
 localities show variations which are frequently numerically 
 identical. The variability is of the same kind and comparable in 
 degree ia individuals from all the localities yet studied. This 
 is by no means a satisfactory presentation of the effect of 
 geographical distribution, but it must suffice for the present, 
 and until our knowledge of the distribution of the animal has 
 been more fully elucidated. 
 
 What effect should these facts have upon our ideas of the 
 classification of Bdellostoma.'* Most authorities are inclined to 
 look upon the difference in the number of gills as a sufficient 
 ground for the establishment of distinct genera. That this 
 character has not a generic value it is needless to state, for 
 reasons already sufficiently repeated. But it would be conven- 
 ient to recognize these several varieties by some name, if 
 possible, and, according to the present system of nomenclature, 
 there are two opportunities, — one for a specific, the other 
 for a variety name. Is the gill variation a sufficient specific 
 character } I think not, for the reason that we have all 
 grades of the variations, and the further reason that they all 
 belong to one colony of freely intercrossing individuals. It 
 appears to me by far the best plan to recognize one genus 
 of Bdellostomids, with one species composed of the several 
 varieties, and I propose that we return to the first satisfactory 
 name that was applied to our animal. The first account of 
 this animal which we find in the literature is that of Lacepede, 
 who described it from a dried skin sent from the Chilian coast. 
 He named it le GastrobrancJie dombey} Later, in 1815, Home 
 described the gills of a Heptatrema which he obtained from 
 
 1 Gaetrobranchus is the old name applied to Myxine, and these forms were kept 
 with Myxine till Dumeril put them in the genus Heptatrema, which of course 
 gives this name priority over Miiller's Bdellostoma. 
 
BDELLOSTOMA DOMBEYI, LAC. 155 
 
 Banks' South Sea collection. Johannes Miiller published his 
 well-known monograph on these forms in 1834, and applied 
 the name Bdellostoma to the forms from the South Sea, 
 Cape of Good Hope, and Chilian coast, making species on 
 the basis of the number of gills. He called the Chilian form 
 B. dombeyi, and made five species in all. In 1854, C. Girard 
 described a fish from the Chilian coast with fourteen gills, and 
 called it Bdellostoma polytrema. 
 
 In 1878, Lockington described the form found in San 
 Francisco Bay as B. stouti, and Gill changed the name in 
 1880 to Polistotrema stouti, which has again been changed to 
 Polistotrema dombeyi. Retaining the name polytrema for the 
 Chilian form, he changed it over to his genus Polistotrema, 
 which he says is characterized by 1 1 to 14 gills. These 
 accounts all refer to the varieties of what I shall call Bdello- 
 stoma dombeyi, adopting Miiller's genus, on account of the 
 inapplicability of Lacepede's Gastrobranchus, and of the inap- 
 propriateness of Cuvier's Heptatremes, which could only be 
 used for the seven-gilled form or variety. Bdellostoma, the 
 generic name proposed by Miiller, is satisfactory in every way, 
 and we may well use it. 
 
 The specific name dombeyi, applied by Lacepede in 1798, is 
 satisfactory in that it avoids all difficulties of a morphological 
 kind, and perpetuates the name of the discoverer of this 
 remarkable animal. Bdellostoma dombeyi is the name under 
 which are gathered all the variations we know of in the 
 branchial and dental systems and the correlated organs. F'or 
 the purpose . of distinguishing these varieties, we may use 
 either Latin variety names or a simpler numerical termination. 
 If we choose the Latin names, we meet with difficulty in sup- 
 plying all of the Jictci'otrcmes with sufficiently exact names, for 
 some are 6-^, others 11-12, and still others 12-13-gilled, and 
 no one knows when or where more of these heterotrem.es may 
 be found. 
 
 Gastrobranchus dombeyi (Lacepede), 1798. 
 Heptatremes dombeyi (Cuvier), 1829. 
 Bdellostoma " (Miiller), 1834. 
 
 (Gray), 1851. 
 
156 BIOLOGICAL LECTURES. 
 
 Bdellostoma polytrema (Girard), 1854. 
 
 " " (Giinther), 1870. 
 
 " " (Putnam), 1874. 
 
 " Stoutii (Lockington), 1878. 
 
 Polistotrema dombeyi (Gill), 188 1. 
 
 (Jordan, Gilbert), 1882. 
 IMellostoma forsteri. / 
 
 " cirrhatus. * 
 
 " hexatrema. 
 
 •' heterotrema. 
 
 " heptatrema. 
 
 I shaU, for my own convenience, hereafter use the numerical 
 method of designating the varieties ; and, unless sufficient 
 reasons be brought against this style of name, I would urge 
 its adoption on the ground of convenience, to go no further. 
 
 Iklellostoma dombeyi, 6 gills. 
 
 " " 6-7. ) Indicating the sides of the body upon 
 
 " " ']-(i. S which the respective numbers occur. 
 
 7. 
 " 10. 
 
 " " II. 
 
 " " 11-12. 
 
 " " 12-11. 
 
 " " 12. 
 
 12-13. 
 
 13-12. 
 
 13- 
 
 14. 
 
 Physiological. 
 
 From previous experience it seemed to me very desirable 
 that physiological experiments should be tried upon the ear 
 of some vertebrate with the simplest existing type, and, if 
 possible, upon an animal which lacked fins, — /. ^., paired 
 appendages, which in all fishes are specially used in main- 
 taining the equilibrium of the body. I felt that by securing 
 these conditions, we should be able to get much cleaner 
 responses or, in any case, safer results from operations on 
 the ear, for the presence of the paired fins — especially the 
 pectoral fins — complicates the reaction to ear operations by 
 introducing into observable phenomena mechanical factors 
 whose influences have not been carefully enough studied and 
 
BDELLOSTOMA DOMBEV/, LAC. 157 
 
 allowed for. The desired vertebrate was found in Bdellostoma, 
 which thus presented me with material for both morphological 
 and physiological investigations. Physiological operations on 
 the ear of Cyclostomes have been tried on Petromyzon only, so 
 far as I know, and then they were abandoned without obtain- 
 ing results, on account of the difficulty of the operations. The 
 first operations I performed were on anaesthetized animals ; but 
 I soon abandoned the use of anaesthetics for several very 
 sufficient reasons. 
 
 My method of operation was the following : In order to 
 hold the extremely slimy and slippery animal, I used large 
 sheets of blotting-paper, such as botanists require for drying 
 plants. Bdellostoma was taken from the aquarium, and at 
 once rolled up in the sheet in such a fashion as to hold it 
 extended during the operation. One sheet makes a roll suffi- 
 ciently stiff to retain the fish perfectly. A stout needle was 
 thrust through the skin at the side of the mouth, and another 
 through the skin and muscles of the tail, and both forced into 
 the table at such a distance apart as to prevent the fish from 
 squirming or crawling out of the paper cylinder. The blotting- 
 paper was removed over the region of the ear, and an incision 
 made through skin and muscle, exposing the cartilaginous 
 ear capsule. The top of this was shaved off with a sharp 
 scalpel of suitable shape and size, and the auditory nerves 
 cut inside the ear capsule, either with a scalpel or scissors. 
 The columella was then cut, and the ear lifted out with 
 forceps or with a small bent needle. An examination was 
 made with a lens to see if any part of the ear or auditory 
 nerve had been left in the capsule, and any such fragments 
 were removed before the cut in the skin was sewed up. This 
 done the animal was unrolled into the aquarium, and its 
 motions watched. The whole operation does not require more 
 than two minutes, and the fish does not appear to suffer in the 
 least from suspended respiration, so far as I could make out. 
 
 A fish thus operated upon, with both cars removed, will 
 swim from the moment it is placed in the aquarium like a 
 normal fish. In some cases the creature will tie itself into 
 a knot, with the evident ]:)urpose of removing the irritation 
 
158 BIOLOGICAL LECTURES. 
 
 from the skin of the head, but it soon leaves off such attempts, 
 and settles down on the bottom of the aquarium, coiling up in 
 the normal fashion, or else it will continue to swim about the 
 tank for a time. In case only one ear is taken out, the animal 
 may (it does not always do so) swim with the injured side 
 lower than the other, or may even roll as it swims — especially 
 if it is excited to szoim rapidly ; but like others, it will settle 
 to the bottom, and rest normally in its coil, coiling either away 
 from or toward the injured side. I thought I could notice in 
 some cases a tendency to coil away from the injured side ; i.e., 
 the norn#il side did the work of coiling ; but the case is by no 
 means clear that this coil is done oftener than the other. 
 
 Fig. 14. — The right internal ear of the Hagfish 
 {Myxine gluiinosa), seen from the inside or cerebral 
 face. P^igure after G. Retzius. The figure represents 
 the ear somewhat enlarged, and does not show the 
 shape or exact positions of the contained sense- 
 organs. 
 
 a Anterior ampulla. d Ductus endolymphaticus. 
 
 ap Posterior ampulla. fnu Macula utriculi et sacculi. 
 
 c Anterior and posterior canals. ;/ Nerve branchlets. 
 
 ca ) . -.^ 1 r .1 " Utriculo-sacculus. 
 
 \ Ampullar ends of the same. 
 ^r ) s Sacculus endolymphaticus. 
 
 Now, on the hypothesis that the ear is the specific organ of 
 the equilibrative sense, it might be argued that the removal 
 of one ear does not necessarily so powerfully affect the equi- 
 librium of the body as to destroy even the control of the 
 injured side ; for the uninjured side is able to take upon itself 
 the functions of the injured organ in part at least. If that 
 were the case, when both ears were removed we should cer- 
 tainly expect to see the animal lose control of its body ; but, 
 as I have already said, the animal is even better off zvith both 
 ears removed than with one ear removed, for all traces of equi- 
 librative distiirbaiice disappear at once on the removal of the 
 second ear. 
 
 How can the semi-circular canal with its two ampullae be 
 the special organ of dynamical equilibrium and the utriculo 
 sacculus with its sense organs the special organ of statical 
 
BDELLOSTOMA BOMB E VI, LAC. I 59 
 
 equilibrium when the animal maintains its perfect equipoise 
 without them? If in higher forms each canal appreciates 
 movements in its own plane and by definite functional combi- 
 nations of two or more canals is able to mediate all possible 
 rotational movements, what function has the single canal in 
 Myxime, or the two canals in Petromyzon ? Both of these 
 creatures are subject to the same mechanical conditions in their 
 progress through the water that the higher vertebrates are. 
 The fact that they do not have the canals proves that vertebrates 
 can swim as admirably without this apparatus as with it, and 
 such being the case, what was the physiological incentive 
 which lead to the production of the other canals ? I have 
 elsewhere given a sufficient mechanical explanation of the 
 genesis of the canals, but I have yet to learn of a sufficient 
 physiological one. Who will add to our knowledge in this 
 particular? 
 
 It is said that the semi-circular canals in man, for example, 
 are delicate organs whose special function is to take cognizance 
 of all the motions of the body in their respective planes, and 
 that they thus control either singly or by various combinations 
 with the other canals of the opposite side of the body, all 
 possible movements of the body. 
 
 One may readily disprove this assumption by a very simple 
 experiment. Have some person with normal ears and normally 
 developed muscles swim for a distance on his back with closed 
 eyes — first with his hands and arms alone, keeping his legs 
 straight, and second with his feet alone, folding his arms on his 
 breast. The average man is stronger on the right side of his 
 body than on the left, and consequently when he pulls himself 
 through the water with his arms alone — eyes closed — he 
 unconsciously pulls himself to the right and swims in a circle 
 — {Rcitba/ui bcivcguiigcii of German pJiysiologists I) When he 
 swims with his feet alone he pushes himself through the water 
 and consequently pushes himself over to the left side and 
 swims in a circle in an opposite direction to what he did before 
 {fij'ciis i}iovci)icnt to tJic left!) and he is, so long as his eyes 
 remain closed, unconscious of the fact that he is moving to 
 one side i.e., diverging from a straight line — but he becomes 
 
l6o BIOLOGICAL LECTURES. 
 
 conscious of this fact the moment his eyes rest upon some- 
 thing which enables him to orient himself, and yet this normal 
 individual has six organs in his head which are there for 
 the special purpose of controlling of his movements in space, 
 so say the physiologists. His two eyes are of more service to 
 him than are his six canals.^ 
 
 It may be objected that the canals are not intended to take 
 cognizance of such minute changes in position in space as are 
 involved in swimming around in a circle; but if they cannot 
 perceive such changes of position when swimming, how can 
 they perceive them when on a rotating table {e.g., Crum. 
 Brown's experiment). It would be a great service to determine 
 the minimum amount of angular motion of which the canals 
 can take cognizance, in order that we may know how much to 
 expect of our ear canals in this way. 
 
 It may be objected that the man in the water on his back is 
 in an unusual position and consequently his canals do not work 
 with sufficient delicacy on account of the unaccustomed 
 pressure, etc. But it is a necessary consequence of the 
 assumption that the canals are special organs of equilibrium, 
 that they should work in any position; otherwise what were 
 the use of them } Other organs of specific function work in 
 all positions of the body. The eyes see, the nose smells, the 
 ears hear, the brain thinks, the heart beats, and so on ad 
 infinitum, all except the ear canals, whose special work is to 
 cognize just such unusual spatial conditions, and according to 
 the hypothesis, the only organs in the body having this 
 function, — they fail of their function when most needed. In 
 the experiment with the rotating table the canals are subject 
 to even a severer test of very small angular motion and are 
 supposed to be able to operate very precisely, in some cases. 
 
 1 Experimental rides on the great Ferris wheel at Chicago during the Columbian 
 Exposition proved that a perception of the direction of the motion of one's body 
 in space was impossible unless one made use of the eyes. I found that the 
 upward motion could not be detected by the ears alone. Without the evidence 
 of one's eyes one seemed to be standing still upon a trembling platform, and the 
 while was really making a great circle through the air in a geotropically oriented 
 position. It is notorious that balloonists have difficulty in determining whether 
 they are moving upward or in any other direction when sight is hindered, and 
 that it is impossible to detect motion in the midst of a cloud. 
 
BDELLOSTOMA DOMBEYI, LAC. i6l 
 
 I think this swimming experiment gives very satisfactory 
 evidence to the effect that the serni-circular canals in man do 
 not function as organs of dynamical equilibration. At the 
 opposite end of the scale — Bdellostoma is certainly not 
 dependent upon its ear for the equilibrium of its body. I may 
 say in conclusion that I think Professor Ewald has made a 
 great discovery in showing how intimately the auditory nerve 
 is related to the musculature of the body and in proving that 
 some of the complicated phenomena which follow section of 
 this nerve and of its branches are fully accounted for by the 
 fact of the lessened muscular tonicity of the injured side and 
 not on the ground that these phenomena indicate the special 
 functions of the several parts of the ear. 
 
EIGHTH LECTURE. 
 
 THE INFLUENCE OF EXTERNAL CONDITIONS 
 ON PLANT LIFE. 
 
 W. p. WILSON. 
 
 If you open your eyes and look carefully about, as you are 
 traveling from place to place, you will easily see that there 
 are very many differences between the plants of one region 
 and those of another. In the high mountains you will find 
 many thick -leaved plants, such as the Rhododendrons and 
 Sedums, and quite a number of peculiar forms not seen lower 
 down. Many of these may have a stunted, gnarly or dwarfed 
 look, quite strange to the vegetation at the sea level. In still 
 another region the plants may have lost much of their natural 
 grace and beauty of form. They may look rigid and stiff, with 
 small thickened leaves or none, with short thickened stems, or 
 round and consolidated forms such as we find in the Cacti or 
 Euphorbias. These are the tenants of desert regions. 
 
 Again, if you happen to go south into the tropics, sheltered 
 and shaded by immense thin-leaved trees, with the waving 
 green of the palm and the vine, you will find dense masses 
 and banks of dark green foliage belonging to Ferns and Sella- 
 ginellas, with climbing plants of various kinds intermingled. 
 
 About your own door may be quite as interesting forms as 
 in more remote districts, only you are accustomed to them and 
 do not see their peculiarities. You may look out on pines and 
 oaks, on a great diversity of small plants, with the Indian. pipe, 
 a partial parasite, and a few ferns which can bear more wind 
 and cold than most of their relatives, plenty of mosses and 
 lichens, and, in fact, representatives of all the great plant 
 families. 
 
1 64 BIOLOGICAL LECTURES. 
 
 The ancients looked upon the whole animate world as having 
 been directly created by some higher power, and believed that 
 each species indicated a distinct and individual creation. They 
 also observed #iese differences between the plants of different 
 regions, and, in fact, between those of the same region. They 
 thought that all living organisms were created to fit the 
 special location and conditions under which they existed. 
 They believed that water animals and water plants, for 
 example, had always been and would always remain such ; 
 that the desert region had always been a desert region, and 
 that the Cactus had been created to fit it. We are not 
 obliged to go very far back in the history of our own times 
 to find eminent naturalists who have strongly advocated this 
 view. No less a man than Louis Agassiz was one of the 
 most strenuous defenders of this theory. He believed that 
 species of both plants and animals were invariable, living 
 and dying in form and color and habit just as they were 
 created. And there were many other naturalists the world 
 over who held to this doctrine of special creation. It must 
 not be forgotten, however, that though their views attained 
 no prominence, such men as Lamarck had at different times 
 indicated a strong belief in the variability of forms. 
 
 During the last twenty years there has been a great revision 
 of thought in regard to these subjects. At present all 
 naturalists believe not only in the possibility of a continual 
 change in both plants and animals, to fit them for varying 
 conditions, but also in the gradual growth and development of 
 very diverse changes in climates, rendering equal modifications 
 in both fauna and flora absolutely essential to their continued 
 existence. Since great changes have always been slowly taking 
 place in the earth's surface and climate, and since present 
 vegetation has always been subject to these gradually varying 
 conditions, it must have adapted itself, with a slowness commen- 
 surate with the earth's changes, to the ever-appearing new 
 conditions. In this way, we think, can be solved the problem 
 of the infinite variety of vegetation. 
 
 By experiment we may determine the two factors underlying 
 plant variation. On the one hand the laws of inheritance are 
 
EXTERNAL CONDITIONS ON PLANT LIFE. 1 65 
 
 ever holding the plant invariable, while the external forces 
 are ever pushing it toward variation. In this lecture we 
 will disregard entirely the interesting phenomena which relate 
 to that internal force the manifestations of which we call 
 inheritance, and try to discover how much the plant world is 
 moulded and shaped by what is exterior to it. 
 
 If you are inclined to think about all these differences in 
 the vegetation of the many regions through which you have 
 travelled you will soon see that where there is great change 
 in the appearance of the plants, in passing from one place to 
 another, there is also an equally marked difference in the 
 surroundings or soil or climate. You will soon find yourself 
 always looking for the one when you have found an expression 
 of the other, i.e., if the plants give you a new flora, you seek 
 at once to find the cause in external conditions ; or, if you 
 have great external difference in surroundings and climate, you 
 expect this to be at once reflected in the varying vegetation 
 about you. 
 
 Let us study a few plants a little more closely, and see 
 if we are able to determine on what this variation depends 
 and how rapidly it may take place. I shall assume at the 
 outset two sets of causes, both of which may be active in 
 bringing about variations in plants, the one wholly external, 
 such as light, heat, moisture and the like, and the other 
 internal, and concerned with the laws of inheritance, about 
 which we know so very little. 
 
 Let us for our present purpose consider only the external 
 influencing conditions, for I believe that they are much more 
 potent and determinative than the laws of inheritance. They 
 may be enumerated as follows : 
 
 I. The Water Supply. — This is more important than any of 
 the following points, as it is intimately connected with the 
 very vital process of organizing materials for growth and 
 their transport throughout the plant. 
 
 If the water supply is cramped and too little, we have 
 immediately before our minds the desert plants. 
 
 If the water supply is too great, equally important changes 
 take place. 
 
1 66 BIOLOGICAL LECTURES, 
 
 2. The Light Supply — Here again we may have too much 
 
 or too little, either condition leaving its strong impress 
 on the plant. 
 
 3. Altitude i#a third factor in the growth of plants, which 
 
 strongly influences the light, the moisture and the tempera- 
 ture, as we shall see in a later discussion. 
 
 4. Temperattif-e. — Temperature and light, together, govern 
 
 largely the transpiration of water from the plant. 
 The character and position of the leaves are often wholly 
 adapted to both the conservation and the loss of water by 
 transpiration. 
 
 5. The Food Supply produces the most fundamental changes 
 
 in the life of the plant, strongly influencing not only the 
 production and character of the flower and the fruit, but 
 in all probability determining the sex itself. 
 
 6. The Lnfltience of the Sea upon Plant Forms. — It will be 
 
 seen that quite as remarkable changes come to the sea as 
 
 to the desert plants, and in truth based upon similar 
 
 reasons. 
 
 (i) Let us first consider the water supply. You will readily 
 
 bring before the mind's eye the picture of desert plants, which 
 
 represent in their modifications a lack of water. But you will 
 
 not so easily call to remembrance plants which have undergone 
 
 changes from an oversupply of water. Yet there are many of 
 
 them even in your own neighborhood. 
 
 The Bald Cypress {Taxodimn disticJinm) grew in the present 
 Arctic region before the Glacial Epoch, in company with oaks, 
 maples, willows, the Redwoods {Sequoia gigantea, S. semper- 
 virens), the Gingko tree (Salisdnria adianti/olia), Torreya, and 
 Glyptostrobns. During later changes in climate these trees 
 were driven from their home and travelled down widely different 
 lines into the South. For reasons which we are unable to 
 understand, the Sequoia, or Redwood, descended along the 
 California coast, the Glyptostrobns and the Salisburia or Gingko 
 tree, down the coasts of China and Japan, the Torreya and 
 Taxodimn, or Cypress, to the eastern and southern parts 
 of North America. At present the Bald Cypress, to which I 
 wish especially to call attention, grows only along the water- 
 
EXTERNAL CONDITIONS ON PLANT LIFE. 167 
 
 courses and in the swamps of the south-eastern part of the 
 United States. It seeds itself naturally nowhere outside of 
 areas which are for several months during the year under water. 
 This tree belongs to the Pine family, but has some very marked 
 peculiarities which make it differ strongly from any of its 
 relatives. 
 
 The tree shown in Plate No. i stands normally surrounded 
 by water. Many root-like projections are seen underneath and 
 around the tree, which are popularly known as cypress knees. 
 These are all connected with the root system below the water. 
 They have extended their growth upwards until they are sure 
 to remain in the air at the ordinary level of the water during 
 most of the year. They are in such numbers that wagon-loads 
 of them could be taken away from one tree. P'rom many 
 careful experiments made on the growing seedlings, it has been 
 determined without doubt that these knees are organs of 
 respiration. All dry-land trees secure free oxygen from the soil 
 to carry on the oxidations needed in root growth. This tree 
 growing in water, which holds much less oxygen than the soil, 
 is unable to draw its full supply from the medium surrounding 
 the roots. To fill this want, these knees are pushed up out of 
 the water into the air as aerating organs. Although the plant 
 does not now grow normally on dry land, yet when planted 
 there it thrives as it once did in previous geologic ages in the 
 Arctic regions. Plant two sets of seedlings, the one in dry 
 soil, the other in soil flooded with water ; the first will show no 
 signs of the root-aerating organs, while the second will develop 
 them in abundance, as small vertical roots pushed above the 
 surface of the water. 
 
 In the water growth, the branches of the Cypress are 
 spreading and the top flattened, a marked departure from the 
 most striking characteristic of the Pine family, to which it 
 belongs. When grown, however, in dry soil, in our parks 
 and public grounds, it reverts to the normal type. The 
 branches are short and make a sharp angle with the main 
 stem, and its cone-like form is as pointed as in any of 
 the tall conifers. This will be seen in Plate No. 2, photo- 
 graphed from a tree planted in Fairmount Park, Philadelphia. 
 
1 68 BIOLOGICAL LECTURES. 
 
 It will be observed, too, that there are no signs of knees 
 underneath. 
 
 Plate No. I represents a water form from the James River. 
 The ba^, in this form, is always very much enlarged. This 
 enlargement is a part of the aerating system needed to secure 
 the necessary oxygen, and is, of course, entirely absent from 
 the land form. 
 
 The departure from the sharp, cone-like form natural to the 
 conifers, is due to the difficulty in obtaining both air and food 
 from the water. This lack of nourishment shows itself in the 
 dwindling, depauperate and dying branches of the upper part, 
 since that part is most remote from the food supply. 
 
 In some of the lakes of Southern Florida it now and then 
 happens that a cypress tree has obtained a foothold in much 
 deeper water than is its normal habit. Here all of these water 
 peculiarities are greatly exaggerated. The trunk of the tree 
 produces an immense cone, the top of which points up to the 
 surface of the water and ends with a few flat sprayey branches. 
 The base of the cone may be forty or fifty times the diameter 
 of the top, from which come the few straggling branches which 
 project above the surface of the water. There are at its base 
 innumerable knees. In a tree having the height of twenty- 
 five or thirty feet, the cone below the water will represent a 
 little over one-half, and the branches above the other half of its 
 altitude. Plate No. 3 represents such a tree in South Florida 
 after the waters of the lake had been drained away. The 
 knees, being of no further use, quickly rotted .and disappeared 
 and are not shown in the photograph. Originally the water 
 was high enough to touch the lower branches, and the tree 
 eked out a miserable existence, struggling hard in the deep 
 water for both air and food. The difficulties under which 
 it labored developed it into a great monstrosity. It is an 
 extreme expression of excessive water supply. Compare its 
 short, cone-like trunk, entirely immersed in water, with what 
 may be called the normal development now found only in 
 our parks (Plate No. 2). In this form the trunk is tall and 
 slender, with branches towering to a very sharp point. The 
 water form has acquired its knees and greatly enlarged 
 
No. 1. — TAXODIUM DISTICHUM RICH.— JAMES RlVER, V'A. 
 
NO. 2.— TAXODIUM DISTICHUM RICH. — FAIRMOUNT PARK, PHILA. 
 
EXTERNAL CONDITIONS ON PLANT LIFE. 169 
 
 base for jxirposes of respiration. Its flattened cone is the 
 result of the bad nutrition. The land form, dropping into its 
 native dry earth habitat, does not develop the knees and 
 enlargement, because its oxygen supply is ample. Its nourish- 
 ment, too, is sufficient, so that it will have as a result of these 
 normal, favorable conditions, the tall, sharp, cone-like form 
 natural to the pine family. Doubtless the cypress has been 
 millions of years adapting itself from its dry land conditions 
 to its watery surroundings, and the most interesting fact in this 
 connection is its readiness to fall back into its old habit of 
 growth, and even in the first generation on land to lose every 
 trace of these wonderful acquisitions. 
 
 The^e are many other plants which have acquired equally 
 remarkable organs in the same way. Some of the mangroves 
 of the Florida coast such as Aviccnnia iiitida and Laguncularia 
 raccnwsa, growing in the ooze between tide- waters, have developed 
 vertical roots which project out of the mud by hundreds under 
 each tree and are exposed to the air at every low tide. These 
 organs aerate the plant as the knees aerated the cypress. 
 They are much more highly organized, being covered on the 
 parts above the mud with great numbers of large, open 
 lenticels. 
 
 It is not necessary for us to go so far from home to find 
 numbers of plants which have adapted themselves, through 
 special aerating organs, to a change from dry land to water 
 growth. One of the most common is Dccodon vcrticiiiatiiSy 
 which develops over the surface of all its roots an extremely 
 thickened, corky, air-holding layer. A similar development 
 covers the branches when they happen to drop into the water. 
 
 Let us now see how plants are modified when they lack 
 water. If the supply is inadequate, the plant makes an 
 attempt to conserve the little that it has. As the surface of 
 ordinary plants allows large quantities of water to escape by 
 transpiration, and as this loss is largely proportioned to the 
 amount of surface exposed, such plants usually lessen this 
 surface by making the leaves smaller and thicker, or by losing 
 them entirely, by shortening the branches and by consolida- 
 tion generally. As the light and the heat of the sun increase 
 
170 
 
 EIOLOGICAL LECTURES, 
 
 transpiration, the surface of the plant may become for protec- 
 tive purposes hairy; the cuticular and epidermal layers may 
 be thickened; the interior air passages in the leaf which 
 communicate with the surface may become obliterated through 
 consolidation of the cellular structure; and, in certain cases, 
 the leaf may have added to it definite kinds of tissue for 
 storing water to be used in time of need. 
 
 (2) That light readily causes various reactions in many of 
 our ordinary plants, every one knows. Watch the folding of the 
 
 
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 Plate No. 
 
 I'late No. 5. 
 
 Clover leaves as daylight decreases, and you will see them go 
 into their sleeping position, while in the morning they open 
 their faces and present them to the sky. Look at the Wistaria 
 vine by the aid of a lamp, late at night, and you will see that 
 the little leaflets have dropped down and closed together. If 
 the morning is bright and warm, they will rise early and by 
 nine o'clock every young tender leaflet will point its tip directly 
 at the sun, in a direction parallel with both the light and heat 
 rays. As the heat of the sun increases toward noon and during 
 
EXTERNAL CONDITIONS ON PLANT LITE. 
 
 171 
 
 the hotter part of the day, you will find these leaflets constantly 
 rotating, maintaining their parallelism to the sun's rays. If the 
 day is cloudy and the heat of the sun obscured, these same 
 movable sensitive leaflets may remain in a stationary position 
 so as to receive the most direct light possible during the whole 
 day. If you choose to wander in your nearest woods, many 
 similarly-acting plants cannot fail to escape your notice, such 
 
 Plate N<3. 6. Plate No. 7. 
 
 as the Desmodiumy the Lespedcza, the Melilotns, and, among 
 the tree-like forms, Afuorpka, and Robinia, or the Locust. 
 
 Plate No. 4 shows the Melilotiis, or Sweet Clover, on a cool, 
 moist, somewhat cloudy morning, when the leaves are spread 
 out fully, striving to receive all the light and warmth possible. 
 The direction of the light is generally at right angles to the 
 surface of the foliage. 
 
 Plate No. 5 represents another plant on an extremely hot, 
 dry morning in midsummer, photographed at nine o'clock. 
 
172 
 
 BIOLOGICAL LECTURES. 
 
 The photograph was taken from the south. It will be seen 
 that the three leaflets, elevated on their sensitive petioles, are 
 all pointing directly at the sun in the south-east. The leaflets 
 being parallel to the heat and light rays, escape much of the 
 consequent transpiration of water which would occur were they 
 thrown down to the sun's rays as in Plate No. 4. 
 
 Another plant, Plate No. 6, photographed under similar 
 conditions of dryness and hot sun at twelve o'clock in the 
 
 morning, shows the leaves 
 pointing directly to the 
 zenith, thus again parallel 
 to the sun's rays and for 
 similar reasons. 
 
 Plate No. 7 shows still 
 another plant taken on the 
 same hot and dry day, 
 with the leaves pointing 
 directly toward the sun. 
 This photograph was taken 
 at 2 p. M. in the afternoon 
 from a position 15° north 
 of west, at right angles to 
 a profile view of the leaves. 
 It will be seen from 
 these illustrations that 
 when the conditions are 
 ripe for rapid loss of moist- 
 ure, that these sensitive 
 leaves continually keep 
 themselves parallel with the sun's rays during the day. As 
 the leaves in the morning are first influenced by heat and 
 light, they elevate themselves and point toward the eastern 
 sun. They continue to rotate during the day, so that at noon 
 they are erect, slightly inclined to the south, and at night are 
 directed to the west. 
 
 Plate No. 8 shows a cluster of these plants photographed 
 from the north at six o'clock in the afternoon after a compara- 
 tively warm, dry day. The leaves are mainly pointing to the 
 
 Plate No. 8. 
 
EXTERNAL CONDITIONS ON PLANT LIFE. 
 
 173 
 
 right toward the western sun which is still quite high. At 
 sundown, after the influence of the falling dew has been slightly 
 felt, the leaves will begin to assume the position seen in 
 Plate No. 4. 
 
 If we continue to watch this plant as darkness comes on, 
 we shall find all these leaflets dropping down slightly, each 
 turning itself one-fourth around on its petiole until the three 
 present their edges up- 
 permost. The two outer 
 leaflets, having their faces 
 toward each other, move 
 slightly toward the cen- 
 tral one until they touch 
 it. It will be seen that 
 the three little leaflets 
 have thus placed them- 
 selves together in such a 
 way as to reduce their 
 surface to nearly one- 
 third of the original area. 
 This protects them from 
 radiation and the loss of 
 much heat during the 
 night. Plate No. 9 shows 
 a plant while sleeping, 
 the photograph having 
 been taken at twelve 
 o'clock midnight. 
 
 But there are other 
 effects of light more 
 marked than these re- 
 actionary movements. In ordinary plant assimilation, which 
 takes place only under the influence of light, the leaves are 
 generally the active organs. It sometimes happens that when 
 the light becomes insufficient for assimilative purposes, certain 
 parts of the organ itself — the leaf — become quickly atrophied 
 or disappear entirely. Thus the form of the elm leaf has 
 gradually become oblique on account of the shading of one 
 
 Plate No. 9. 
 
174 
 
 BIOLOGICAL LECTURES. 
 
 of its sides. This is true, too, of the house begonia and many 
 others of our common plants. 
 
 At high altitudes, where the differences of light and shade 
 are much more intense, these changes are correspondingly 
 more quickly brought about. With these external changes of 
 form there are microscopic differences which are even more 
 striking. In Plate No. lo are shown two cross-sections of 
 leaves taken from the Mountain Balsam (Abies frascrt)^ a from 
 a sunny exposure and b from the more densely shaded part of 
 the tree. In Fig. a we have on the upper part of the leaf the 
 palisade cells above, and the more loosely arranged tissues,. 
 
 Fig. b. 
 
 Plate No. io. 
 
 for assimilation, below. About the middle of the leaf is a 
 large resin duct. Fig. b is the cross-section of a similar 
 leaf from the same tree, carefully selected from a point 
 underneath the heavy branches which the direct sunlight never 
 reached. Above the resin duct, on the upper side of the leaf, 
 are the palisade cells, much as in a \ but the loosely arranged 
 assimilating tissue beneath the resin duct is seen to be absent 
 in b. In other words, the light was not strong enough in the 
 lower shaded parts of this tree for assimilative purposes, and 
 in consequence these tissues have been dispensed with. 
 
 (3) And here let me speak of the influence of altitude, which 
 affects not only the light but also the temperature and the air 
 
EXTERNAL CONDITIONS ON PLANT LIFE. 175 
 
 supply. It will be readily understood that at any very high alti- 
 tude the amount of dust in the air is at a minimum; also, that 
 the greater the altitude the less dense the atmosphere, which 
 will, consequently, contain less moisture. But as the illumina- 
 tion of general space depends wholly upon the refraction of 
 light from the dust and particles of moisture in the air, it will 
 be seen that refraction at high altitudes must be at a minimum, 
 and that air spaces outside of the direct line of the rays of 
 light will be much darker than at lower altitudes. The light 
 given to shaded leaves, then, at these high altitudes through 
 refraction, often proves too little for the purposes of assimi- 
 lation, and the assimilating tissue consequently disappears. 
 
 This shows the relation of altitude to light and assimilation. 
 But altitude is many-sided in its influences. Because we have 
 here less dust and less moisture in the air, the sun's rays, not 
 being refracted out of their course, are much more direct. In 
 the shade, at an elevation of seven thousand feet, you are too 
 cool, but step into the sunlight and your upturned face will be 
 quickly burned by its strong, direct rays. These, same rays 
 burn the moisture rapidly out of mountain leaves. To avoid 
 this as much as possible, they become thickened in many ways, 
 often decrease in size, and travel along the same lines 
 generally for water retention as have the desert plants. High 
 altitudes, then, will produce desert-like plants, as seen in the 
 Live-for-evers, or Sediirns. Not only are the leaves found 
 decreasing in size and becoming thickened, but in all sensitive 
 plants the movements are much more rapid. 
 
 Many plants which do not have daily movements of leaves 
 to accommodate themselves to the light, still put their young 
 leaves, when thoroughly exposed to the sun, parallel to its rays 
 in the hottest part of the day. Later in the season, when the 
 epidermal tissues are more thoroughly developed and the cuticle 
 has been fully thickened, the leaves, thus becoming better able 
 to resist the heat rays, drop down to a position more or less at 
 right angles to the approaching light. Select another plant of 
 the same species, which is thoroughly shaded during the whole 
 day — it may not be twenty feet from the first — and we shall 
 find that the young leaves, as they develop themselves, at once 
 
176 
 
 BIOLOGICAL LECTURES. 
 
 drop down to a position in which the approaching light will be 
 at right angles to their surfaces. Plate No. 1 1 is a photograph 
 of Rhododendron maximum taken at an altitude of over 4000 
 feet. It developed itself entirely in the sunshine. It shows 
 the upper, or young leaves, erected vertically upward until 
 they are nearly parallel with the sun's rays during the hotter 
 portion of the day. The leaves below, which are more or less 
 horizontal, are more than one year old. At the end of the 
 
 Plate No. ii. 
 
 first year, the upper leaves, having become tough and coria- 
 ceous, will assume a position parallel to the older ones below. 
 
 In Plate No. 12 is shown a photograph of Rhododendron 
 catawbiense at the same altitude, but standing in a thoroughly 
 shaded spot. Although a different species, the action of the 
 leaves is the same. It will be seen that the young and growing 
 leaves above put themselves quickly in a position parallel with 
 the leaves below during development. 
 
 The differences between the microscopic structures of the 
 leaves exposed to direct sunlight and of those wholly shaded 
 
EXTERNAL CONDITIONS ON PLANT LIFE, 
 
 177 
 
 are even more marked than the corresponding differences in 
 position. Plate No. 13 shows two sections of leaves from 
 Rhododendron maximum, the one from the sunlight, the other 
 from the shade. Section a, from the sun, shows four super- 
 imposed rows of palisade cells, extremely long and narrow, 
 arranged with their long diameters pointing to the surface of 
 the leaf in a way to afford the best protection from the heat 
 rays. Section b, from the shade, has no very well marked 
 palisade system, for no such protection is needed. The section 
 
 Plate No. 12. 
 
 from the sun is much thicker than that from the shade, but 
 while the loosely arranged mesophyll in the under part of the 
 leaf, where assimilation is most active, occupies in the sun 
 section only one-half of the space of the whole leaf, yet in the 
 shade section it includes more than two-thirds. The explana- 
 tion is simple. The exposed leaf requires less space for the 
 work of assimilation on account of the strong light. The shaded 
 leaf, on the contrary, as much less light reaches it, must have a 
 greater number of cells in which to do a given amount of work. 
 (4) The food supply of the plant may exert a very strong 
 influence upon its development and life. It is a well-known 
 
178 
 
 BIOLOGICAL LECTLJRES. 
 
 fact among gardeners that over-fed plants will often produce no 
 fruit. When pear-trees refuse to bear fruit, they can often be 
 made prolific by cutting away the central root, thus lessening 
 the supply of nourishment. As a rule, when plants are poorly 
 fed, they put forth blossoms and ripen their fruit earlier, 
 although it may. be smaller and of poorer quality. 
 
 (5) The influence of the sea upon plants is quite remark- 
 able. We have seen that in desert regions, and to some extent 
 in high altitudes, plants have greater or less tendencies to take 
 on consolidated forms. This is also true of seashore plants. 
 
 caOPQO 
 
 Section a. 
 
 Plate No. 13. 
 
 Section b. 
 
 The cause in both desert and mountain regions was a lack of 
 moisture. On the seashore, at the water's edge, and even 
 with many plants standing in the water, we find these thick- 
 ened leaves and leafless forms. Hence we must look for 
 another cause for this than lack of water. 
 
 Ordinary land plants secure the water which they need 
 mostly through their roots. Although the soil may be appar- 
 ently dry, yet the plant has no difficulty in supplying its 
 necessities, for every particle of the soil is surrounded by a 
 
EXTERNAL CONDITIONS ON PLANT LIFE. 179 
 
 film of water, which is forcibly taken from it by the osmotic 
 action of the root hairs. Each hair is an elongation of a 
 single epidermal cell. Its external wall is composed of porous 
 cellulose. Besides the ordinary cell contents, such as nucleus, 
 masses of living protoplasm, vacuoles, microsomata, and the 
 like, there is a thin semi-fluid layer of protoplasm, closely 
 appressed to the whole interior of this porous cellulose wall. 
 This forms, with its cellulose support, an osmometer, and 
 when the root hair is tightly crowded in its growth against 
 the surrounding particles of earth, thus coming in contact 
 with the water film, there is at once set up, with great force, 
 a current from the thin fluid surrounding the particles 
 through the walls to the more or less thickened one within. 
 Under a pressure often of nearly an atmosphere, this water 
 is forced from the exterior cells of the root to the interior 
 conducting fibro-vascular bundles, through which it finds its 
 way to every part of the plant. It will be seen that the 
 condition of this forcible absorption is the interposition of 
 a protoplasmic membrane between two fluids of different 
 densities, the more dense, toward which the current always 
 tends, being within the cell. It is only necessary to state 
 that in sea-water we have a fluid of even greater density 
 than is usually found within the cells of plants, and that 
 this would tend at once to make it either very difficult or 
 utterly impossible for the plant to secure its water. Plants 
 which have adapted themselves to the influence of sea- water 
 have done it in a number of ways — sometimes by taking large 
 quantities of salt into the cells, which balances much of the 
 salt without. In this way the density of the fluid within is 
 made greater than that of the water without, and absorption 
 takes place to a limited extent. But since it is still very 
 difficult for the plant to secure a large amount of water, 
 although it may stand in it, — " Water, water everywhere, and 
 not a drop to drink," like Coleridge's shipwrecked mariner, — 
 all the other methods of retaining its scanty supply, usually 
 found in desert plants, are here also exemplified. Thus, the 
 leaves may become smaller or thickened or disappear alto- 
 gether, in order to lessen the transpiring surface. If the 
 
i8o 
 
 BIOLOGICAL LECTURES. 
 
 plant can get but little moisture, it also retains that little, or 
 lets it go with great difficulty. Hence, we have on the sea- 
 shore a vegetation corresponding in some respects to that in 
 high altitudes, or to that in desert regions, although the 
 apparent conditions are radically different from either. 
 
 Hydrocotyle iimbellata is a plant common in moist or watery 
 places from Maine to Florida. In the semi-tropical fresh-water 
 marshes of Florida, it places its slightly thickened, rounded 
 leaves at right angles to the sun's rays, parallel to the surface 
 of the water in which it grows. When it happens to encroach 
 upon the salt-water marshes of this same region the difficulty 
 of water supply is so heightened that the slender petioles 
 all make a right-angled turn at their upper end and put 
 
 Fig. a 
 
 Plate No. 14. 
 
 the now thickened leaves in a vertical position, in order to 
 avoid the direct rays of the sun, thus lessening the loss of 
 water. 
 
 Plate No. 14. fig. a, shows a sketch of this little plant, taken 
 from a fresh-water stream in South Florida. Fig. b on the 
 same plate shows another plant taken from a salt marsh near 
 by. All of its leaves are rendered vertical by this turn in their 
 petioles. The microscopic differences are much greater than 
 this relative difference in position. The leaves of the one in 
 the salt marsh have become much thicker, the epidermal tissues 
 much heavier, the number of the palisade cells has increased, 
 the intercellular spaces have nearly disappeared, and the 
 
EXTERNAL CONDITIONS OF PLANT LIFE. i8l 
 
 openings into the stomata have been transformed, through 
 thickening of the cuticle, into narrower, deeper channels. 
 These differences are common to many other plants which 
 inhabit indifferently fresh and salt water locations. 
 
 The plants which grow many miles from the sea-shore are 
 also more or less influenced by the salt in the spray which 
 is mechanically lifted by the winds and carried long distances 
 inland. Lighting on the leaves, it has a tendency to draw out 
 the moisture from within and in this way very materially 
 increases the normal transpiration. To guard against this 
 many plants near the sea-shore thicken up both the cuticular 
 and epidermal layers. Where the wind blows somewhat 
 constantly from the sea over the land, these effects may be 
 seen in plants extending from the shore sometimes as far 
 as twenty miles. 
 
 Many strand plants exhibit the same peculiarities as those 
 of the Rhododendrons of the mountains, i. e.^ they erect their 
 leaves parallel with the rays of the mid-day sun to avoid loss of 
 moisture. This is especially marked in the Mangroves of our 
 Southern coast, which, for a greater part of the day, stand 
 directly in the water. The plants on our New Jersey shore 
 illustrate many of these facts and are quite as interesting for 
 study as those of South Florida. A half-dozen plants of one 
 of our pigweeds {Atriplex litt oralis) taken from a salt marsh, 
 potted, and carried to a greenhouse in the city, exhibited the 
 following interesting characteristics: On the salt marshes from 
 which they were taken, all the leaves were rigidly erect, making 
 no shadow with the mid-day sun. But after being watered with 
 fresh water for five or six days in the greenhouse, all of the 
 leaves dropped down to a normal position, presenting their 
 faces to the direct rays of the sun. Upon watering them for 
 several days following with a strong salt solution, the leaves 
 again erected themselves, assuming the precise position in 
 which they had grown on the salt marshes. 
 
 It has long been known, through physiological experimen- 
 tation, that almost any salt or alkaline solution decreases 
 transpiration, because it at once lessens the water supply. The 
 converse is true of acid solutions. This law may be taken as 
 
1 82 BIOLOGICAL LECTURES. 
 
 a partial explanation of the conduct of the little New Jersey 
 Pigweed. 
 
 Perhaps enough has been already said to convince anyone 
 that the almost infinite variety of plant forms may have some 
 fairly direct connection with their environment. The cypress 
 tree produces its needful aerating organs when grown in the 
 water, but no sign of them in dry soil. It may be a matter 
 of wonderment, however, why these characteristic organs are 
 so quickly and readily lost. They are an acquired character to 
 fill a definite want — when this want no longer exists, they dis- 
 appear. Perhaps this character, which we know was acquired 
 since the Eocene period, has endured for too short a time 
 for permanent inheritance. Many other plant characteristics 
 acquired on physiological grounds, but regarding the duration 
 of which we have no record, although we have reason to 
 believe that they have been serving their purpose for an 
 immense period of time, are perfectly permanent, and inherited 
 by their offspring long after the developing cause has disap- 
 peared. We have in Australia a large number of trees which 
 have adapted themselves to a hot and dry climate by various 
 manipulations of the leaves. In some Acacias, for example, 
 the leaf-blade has entirely disappeared, and the wing growth 
 on the upper and under sides of the petiole is an apparently 
 vertical leaf. Other members of the same family make 
 the true leaf vertical by a twist of the petiole. Although 
 accomplished in two very different ways, the object in each 
 case is plainly to lessen the tranpiration. Apparently, this is 
 a much more trivial change than the acquirement of knees by 
 the Cypress. Both fulfil a physiological necessity ; but while 
 the knees of the Cypress are lost in succeeding generations 
 if the developing cause is removed, the Acacias may be 
 cultivated for generation after generation, entirely removed 
 from the climatic conditions which produced the changes, yet 
 they will be as permanently inherited as in their own native 
 land. 
 
 Avicennia nitida, the so-called Black Mangrove of our 
 Florida and West Indies coast, of which I have already spoken, 
 ^belongs to the Verbena family. Normally a dry land form, it 
 
EXTERNAL CONDITIONS OF PLANT LIFE. 183 
 
 has adapted itself to a growth between tide waters. In so 
 doing it not only produces the remarkable, vertical, negatively 
 geotropic roots, which grow up out of the salt mud, so that 
 at low tide they remain each day several hours in the air for 
 oxygen absorption, without which it could not live, but it has 
 also remarkably thickened its leaves and appressed them 
 vertically against the stems in order to protect itself from loss 
 of water, for reasons which have been already stated. 
 
 From the history and general relation of this mangroove 
 to the Verbena family, we judge that this adaptation is of 
 comparatively recent date. When removed to dry cultivation 
 it loses all these characteristics in the first offspring. In the 
 case of the Cypress we have not merely theoretical reasoning 
 from family relationship, but also definite data from fossil 
 remains, which prove that it was a dry land form in a very 
 recent geologic age, and that its aquatic habits are modern. 
 It is certainly curious, and you may interpret it as you please, 
 that both these plants, when subjected to opposite conditions, 
 immediately lose their acquired characters. In the Australian 
 plants, on the contrary, similarly acquired characteristics under 
 opposite conditions are perfectly permanent. That they have 
 been in this condition for an immensely longer period of time, 
 and that in consequence this development is so stamped upon 
 their parent stock that it reappears generation after generation, 
 even when withdrawn from their causal surroundings, is, 
 perhaps, the key to this riddle. 
 
 Let me, then, remind you once more of the almost infinite 
 variety and diversity of plant forms, and that, as seen in 
 nature, we can generally trace the relationship between the 
 peculiarities of the plant and its surroundings ; also, that in 
 general, these peculiarities, no matter what they may be, 
 reproduce themselves in the offspring. Let me state once 
 more that any plant which we may select as an example, no 
 matter how peculiar in form or habit of growth, gives us an 
 expression in this peculiar form and special habit of the forces 
 which have surrounded it and touched it all the way down its 
 long line of descent, from its earliest more simple and primary 
 condition to its present more complete expression of plant life. 
 
NINTH LECTURE. 
 
 IRRITO-CONTRACTILITY IN PLANTS. 
 
 Prof. J. IVIUIRHEAD MACFARLANE, D. Sc. 
 
 In a paper published by me about nine months ago, I 
 showed that the generally accepted view that the leaf of 
 Dioiicea contracted after one stimulus of the irritable hairs was 
 incorrect, and that two stimuli were necessary to cause contrac- 
 tion. The other phenomena connected with leaf-closure, and 
 described in the paper, were so remarkable as to cause me to 
 inquire whether these phenomena were unique in the vegetable 
 kingdom, or whether conditions could be traced that connected 
 Dioncea with other sensitive plants. 
 
 The behavior of the leaf of Dioncea to mechanical stimuli 
 given at varying intervals of time was such as to suggest a 
 very definite and exact contraction of the protoplasm of certain 
 cells. The outcome of the inquiries which are epitomized in 
 the present lecture, and which I hope in time to bring forward 
 in extended form, proves that in the vegetable as in the 
 animal kingdom, we have to do with a true contractile 
 tissue. Further, among those higher plants that we are now 
 to study, this tissue is made up of cells, each consisting of an 
 irrito-contractile protoplasmic sac enclosing a quantity of sap, 
 and each cell is joined to neighboring cells by protoplasmic 
 processes that pass through minute pores in the common 
 cellulose membranes. 
 
 In order to make clear the relation that is shown by many 
 sensitive leaves to environmental stimuli, it may not be inap- 
 propriate to indicate first the possible movements that such 
 leaves can perform, as generally stated in memoirs and text- 
 books on the subject. A plant of the common yellow sorrel 
 
1 86 BIOLOGICAL LECTURES. 
 
 {Oxalis strictd)^ if examined on a quiet and moderately cool 
 day when the temperature is 25° C, will show the trifoliate leaf 
 fully expanded, and the three leaflets so placed on their stalks 
 that their surfaces lie at right angles to the sun's rays ; i.e ., 
 they are not only heliotropic in that they grow toward the 
 light, but they are diaheliotropic in that they can, if need be, 
 so place their surfaces to the light as to receive the rays 
 at right angles. But if the temperature rise to 29°- 30° 
 C. in the shade, the leaflets will begin to fall down ; and if 
 a steady increase in temperature goes on, they will continue 
 to fall till at 33° C. they will incline downwards back to back. 
 This day-movement has long been known to occur in many 
 plants, and was regarded as a means by which the leaves 
 were screened from intense illumination ; but my colleague. 
 Prof. W. P. Wilson, considers it to be a heat-movement, or an 
 attempt on the part of the plant to screen itself from 
 intense solar thermal action. As connected with the varying 
 results of stimulation on different species afterward to be 
 described, it may here be noted that Oxalis stricta shows 
 distinct heat-movement at 29° C. ; Oxalis Deppei at 31° C; 
 Oxalis dendroides at 33°-34° C. ; while the common sensitive 
 plant {Mimosa pudica) that has thin and apparently delicate 
 leaflets only becomes affected when the shade temperature 
 rises to 37° C. This movement, described by Darwin as a 
 paraheliotropic one, I propose to term 'parathermotropic' 
 
 But as the sun's rays become tempered in the afternoon, or 
 as plants formerly exposed to the full heat of the rays get 
 sheltered by foliage, the flat, expanded condition is resumed. 
 Toward the approach of evening the leaflets again begin to 
 fall, and by 8.15 or 8.30 during midsummer have taken up the 
 same position that they had during the heat of the day. This 
 night-sleep, or nyctitropism, has, with every show of reason, 
 been viewed by Darwin and others as a protection against too 
 rapid radiation of heat and reduction of temperature in the 
 tissues. We would emphasize it, then, that alike during the 
 parathermotropic and nyctitropic states the leaflets of Oxalis 
 stricta are similarly placed. The nyctitropic position is 
 retained till the following morning, and in some plants, at 
 
IRRITO-CONTRACTILITY IN PLANTS. 187 
 
 least, we have evidence for believing that the effects of it are 
 not fully overcome till 7 or 7.30 a.m., in June or July. 
 
 The movements now described are characteristic of a large 
 series of plants belonging to many natural orders, but the 
 group Oxalidcce of the order Geraniacece, and the order 
 LeguminoscB probably include between them about three- 
 fourths of the entire number. 
 
 You are doubtless all aware, however, that leaves or leaf- 
 parts may exhibit movements which serve a different purpose 
 in the economy of the plants that bear them. The leaves of 
 Dioncea and Drosera, as well as tendriliform leaves and leaflets, 
 are examples in point ; and the question naturally presents itself, 
 — How are these movements effected } Before attempting an 
 answer, we propose to lay before you the results of observa- 
 tions and experiments which may aid in the solution of 
 the question. 
 
 Naturally, in the vegetable as in the animal world, irrito- 
 contractility can only be started by stimuli of a mechanical, 
 chemical, thermal, luminous, or electrical nature. For several 
 reasons, I can only treat briefly here the effect of thq first three 
 forms of energy, and I will select plants for illustration in the 
 order that seems most suited for elucidating the subject. 
 First, we may recapitulate regarding Dioncea. As my published 
 researches show,^ a summation of two mechanical stimuli is 
 ordinarily necessary to start contraction. Further, these must 
 be applied with a time interval between of at least \ second ; 
 for if two stimuli are given in rapid succession, both are propa- 
 gated through the protoplasm as one wave, so far, at least, as 
 motion of contraction is the visible outcome. But though one 
 stimulus or two rapidly applied stimuli are insufficient to start 
 contraction of the leaf-halves, we know that active molecular 
 changes are in process, for the leaf-halves exhibit delicate but 
 visible wave impulses passing along them from base to apex, 
 while Burdon Sanderson has demonstrated that active elec- 
 trical changes are going on. After a second mechanical 
 stimulus, or three, if two are rapidly applied, the leaf closes 
 partially, — i. ^., the marginal bristles loosely interlock. If 
 
 1 Bot. Cont. Univ. Penn., Vol. I, No. i, 1892. 
 
1 88 BIOLOGICAL LECTURES. 
 
 the leaf be not further irritated by some instrument, or by a 
 caught animal, it slowly relaxes after 12-15 hours; but if 
 additional stimuli are given, the leaf gradually and firmly 
 tightens up till its margins become recurved. Prolonged 
 stimuli, either of a mechanical, chemical, or electrical nature, 
 start eventually (after 8-10 hours usually) the flow of an acid 
 secretion from glands that cover both halves of the leaf. It is 
 clear, therefore, that complete contraction of DioncBa leaf can 
 only be effected by a summation of stimuli ; and such stimuli 
 may either be partially or entirely mechanical, chemical, or 
 electrical. I have further shown, contrary to prevailing 
 opinions, that not merely the three hairs of each leaf -half, but 
 the entire surface is irrito-contractile. Thus, a minute bit of 
 ice or a drop of hot water placed on any part of the leaf away 
 from the hairs, also a forceps' pinch, a mechanical shock, and 
 many chemical agents, excite to closure. 
 
 We have already said that the time-interval between two 
 shocks may be too short to start contraction, but it is equally 
 true that too great a time interval is attended with no visible 
 change ; in other words, the piling on of the second stimulus 
 to the first, if too long delayed, is insufficient to effect closure. 
 With an interval between of 50-60 seconds, at a temperature 
 of I4°-2I° C, contraction takes place after a second excitation; 
 and I stated that if the interval were increased to 90-120 
 seconds, the strength of the two was almost entirely cancelled. 
 Through the kindness, however, of my friend Mr. Aldrich 
 Pennock, I have studied plants in his hot-houses at high tem- 
 peratures (35^-40° C), and find that the effects of previous 
 stimuli can be retained for 4 minutes at least. But a 
 second stimulus applied 4 minutes after the first causes no 
 visible movement of closure ; a third, 4 minutes after the 
 second is similar ; and not till the sixth stimulus does an 
 almost inappreciable contraction of the halves take place. 
 Summation of successive stimuli from the eighth to the 
 twelfth gives added force — sufficient to bring the halves 
 together. Here, then, is an irritable tissue that steadily 
 contracts, or prepares for contraction, through a period of 
 from 30-45 minutes. 
 
IRRITO-CONTRACTILITY IN PLANTS. 1 89 
 
 The conditions thus revealed by Dioncea were so arresting 
 as to cause me to inquire whether similar phenomena might 
 not be demonstrated in other sensitive plants. Botanists 
 have long been acquainted with certain species which from 
 their contractile movements were aptly designated '' sensitive 
 plants." These included species of Oxalis, Averrhoa, Mimosa^ 
 Cassia, ScJirarikia, etc., some of which were considered to be 
 highly irritable, others less so, and others, again, scarcely 
 deserving the name. The best account hitherto given of the 
 action of some of these when affected by mechanical stimuli 
 is to be found in Pfeffer's PJianzeiiphysiologic (pp. 224-254), 
 where Mimosa pudica and Oxalis acetosclla are chiefly dealt 
 with. 
 
 Now I hope not only to show you that various transition 
 types exist between such roughly classified groups as are 
 expressed in the descriptions "very sensitive," "slightly sensi- 
 tive," " scarcely sensitive," but that under given environmental 
 conditions all exhibit a definite irrito-contractility, characterized 
 by varying degrees of latent period, of contraction period, of 
 expansion period, and of summation effects, or, to put it in a 
 broader sense, that tJie same pJienomcna of irrito-contractility 
 are encountered in the vegetable as in the animal kingdo^n. 
 The optimum temperature for most of the plants now to be 
 mentioned is an average of 26° C, exposure for a short time or 
 for a prolonged period to low temperatures (8°-i5° C) causing 
 an extension of the latent period, slower rate of contraction, 
 and a reduced power of conducting stimuli. 
 
 As being both a common plant and a central type in its 
 physiological behavior, we may now take the field and wayside 
 weed Oxalis stricta, the yellow sorrel. When plants are grown 
 in a rather shady situation and exposed to a temperature of 
 i8°-24° C, the leaves have a rich green color, and the three 
 leaflets together form a triradiate rosette. We need not now 
 refer to structural details further than to say that at the base 
 of each leaflet is a little cushion composed chiefly of small, 
 densely aggregated, and vacuolated cells forming a typical 
 sensitive pulvinus. After a sharp but delicate mechanical 
 stimulus applied with a pencil or other instrument to a terminal 
 
I90 BIOLOGICAL LECTURES. 
 
 leaflet, a latent period oi i\ seconds elapses, followed by a 
 period of slow but gradually accelerating contraction during 
 the next 4 seconds. From the seventh to the twentieth 
 second the motion is rapid, but thereafter slows down gradually 
 to the thirtieth second, and then becomes increasingly slow till 
 the forty-fifth second when the contraction ceases. After 
 15-18 minutes expansion begins, and a very slow rise can be 
 traced till the leaf regains its expanded state in 45-50 minutes. 
 The angle through which such a leaf falls is on the average 
 37°, but varies with the daily periodicity of cell tension, as well 
 as the temperature and moisture of the air and soil. 
 
 It should be stated that young, active — not necessarily 
 growing — leaves are to be preferred for experiment, but even 
 the oldest and fully matured leaves are sensitive to a definite 
 degree, though less so than those younger. Some interesting 
 statistics will be adduced later in this connection. 
 
 When the three leaflets of a leaf are simultaneously excited, 
 all contract, and the movement shown is as follows: The 
 terminal leaflet simply drops and folds its halves together 
 more or less toward their upper faces, but the two side leaflets 
 move forward and downward so that each describes a segment of 
 an ellipse. If care be taken, however, to stimulate the terminal 
 one of the three, it alone will contract, or, at most, the side 
 leaflets will move to a small extent. This, among other things, 
 proves that the capability of conducting a stimulus through its 
 tissues is comparatively feeble in this species. 
 
 In no case have I found that a single shock is sufficient to 
 produce a contraction approaching in amount to the nyctitropic 
 or the most pronounced parathermotropic states. The angle 
 fallen through varies from 25° to 48°. A summation of 
 stimuli, however, produces very different results. If an excited 
 leaflet be left till the downward movement has ceased, and 
 a second stimulus be applied, it will fall still further, but 
 through a less angle than before, and its motion will cease 
 sooner ; if a third stimulus be then applied there will be an 
 additional fall less in extent than the second, and greatly 
 less than the first, the time of motion being correspondingly 
 shortened. A fourth stimulus will give a slight but appreciable 
 
IRRITO-CONTRACTILITY IN PLANTS. 191 
 
 additional contraction. I may best illustrate by a concrete 
 example selected at random from many others. A leaflet 
 stimulated fell through 42° in 45 seconds, a second stimulus 
 increased the angle to 69° within 38 seconds after rest, a third 
 stimulus increased it to 81° after 33 seconds, and a fourth to 
 84° after 27 seconds. 
 
 Thus, by four successive stimuli applied during a period of 
 143 seconds, the leaf described an angular movement of 84°. 
 But, as I have already stated, the period of maximal movement 
 after first excitation occurs between the seventh and twentieth 
 seconds. Taking advantage of this fact, by shortening the time 
 interval between the stimuli, the same amount of contraction 
 can be got in a much shorter time. A leaf was irritated and 
 allowed to contract for 22 seconds, when it had fallen through 
 38° ; it was again irritated, and allowed to contract for 20 
 seconds when it had fallen through 61°. Again irritated it 
 fell through an additional 15°, and after the fourth stimulus 
 had fallen through 81°. 
 
 The above time-intervals remain wonderfully constant in all 
 active leaves when the environmental conditions remain 
 constant, but a distinct shortening of the latent period by | 
 to \ second was noted on a moist, close and warm morning in 
 early July after a thunder-storm of the previous evening. It 
 should also be stated that when the plants are continuously 
 exposed to such high shade temperatures as 35^-40° C, they 
 become smaller in size and irregular in action. 
 
 We now turn to thermal stimuli, and I may at once state 
 that ice particles produce a very marked effect on this and all 
 other sensitive plants. When a piece weighing \-\ grain is 
 placed at the junction of three leaflets a longer latent period 
 than for mechanical stimuli ensues, but when once started 
 contraction steadily proceeds till the ice has melted and the 
 resulting water has attained a temperature that fails to excite 
 the protoplasm. If by aid of a pipette or blotting paper the 
 water is sipped off and a fresh bit of ice is placed, contraction 
 will go on till the nyctitropic position has been reached. But 
 as in the case of mechanical stimuli more localized action can 
 be started, for if ice be placed not on the pulvini but near 
 
192 BIOLOGICAL LECTURES. 
 
 the base of the terminal leaflet, the latter will move through 
 a large angle, while the side leaflets will not at all or only 
 slightly participate. A bit laid similarly on one of the side 
 leaflets will make it move independently of the others. By 
 conducting control experiments with weights equal to the 
 particles of ice used, it can be proved that cold stimulus and 
 not weight of the particles is the determining factor. 
 
 As with Dioncea, so here a drop of hot water and the appli- 
 cation of a heated wire excite to contraction, but instead 
 of touching analytically on these I should prefer to dwell 
 on the question of parathermotropism. All my observations 
 go to, show that this is largely due to heat stimulation 
 of the irrito-contractile cells, acting steadily for some minutes 
 on these, and that the movements can be hastened or arrested 
 by a rise or fall of a few degrees of temperature. Moreover, 
 it seems undoubted that the soil temperature has much to do 
 with the amount of contraction that each leaf undergoes. It 
 is not difficult to understand why this should be. Given a soil 
 on which Oxalis is growing that is covered by a pretty close 
 herbage, above which the plant rears its tuft of leaves ; the 
 soil protected from the sun's rays, and retaining its moisture 
 by reason of the roots that spread through it, will furnish 
 currents of cool water that will constantly rise into the leaves 
 of the plant. Evaporation of the surplus moisture thus passed 
 into the leaves will further lessen the temperature of the 
 tissues. I may be allowed to quote only one set of statistics 
 in support. On a close, dull, but rather warm day, with 
 the temperature at 25° C. in the shade, several plants were 
 studied that grew under the shade of trees, and amid an 
 abundant herbage. The ground temperature was 23° C. All 
 the leaflets were either fully expanded or inclined slightly 
 upwards from their point of union. Another set grew on a 
 rather moist bank and were slightly overshadowed by a tree. 
 The thermometer placed alongside the plants, and like them 
 exposed to a slightly higher than the true shade heat, registered 
 27° C, while the surface of the soil below registered 25.5° C. 
 The leaflets were flat or faintly inclined downwards. Alongside 
 a third set, about two yards from the last, the thermometer 
 
IRRirO-CONTRACTILITY IN PLANTS. 1 93 
 
 registered 29.5° C. when exposed, and 27.5° C. on the ground. 
 Some plants that were exposed to the sun's heat grew on a 
 rather dry soil with scant herbage, and their leaflets were 
 deflected through an angle of 52° to 65°. Lastly, on a bit of 
 hard, dry, whitish soil, the exposed temperature alongside the 
 plants was 31° C, and on the soil 33° C. The leaflets of 
 the plants were as strongly deflected as during night-sleep. 
 
 The amount of moisture, therefore, that is drawn from a 
 cool shaded soil or from a hot, dry soil may largely determine, 
 by its temperature, the stimulus given to the protoplasm and 
 the position that the leaflets are to assume accordingly. A 
 cooperating factor in the parathermotropic movement may be 
 a lack of sufficient moisture, which, in all sensitive plants 
 studied, causes flaccidity and a want of tone in the tissues. 
 
 We shall have occasion in treating of other plants to speak 
 of the action of such chemicals as ammonia, carbonate of 
 ammonia, chloroform, ether, alcohol, etc., which all act as 
 excitants. 
 
 Oxalis Deppei is a large succulent species, commonly grown 
 now as an edging plant in herbaceous borders. Each leaf is 
 quadrifid, and examination of the base of the leaflets reveals 
 large reddish swellings or pulvini. Mechanical stimulus is 
 followed by a latent period of 3I seconds ; then slow but 
 accelerating contraction is observed for the next 4 seconds, 
 when rapid contraction follows for 22-23 seconds, and a very 
 gradual slowing down goes on till contraction ceases 80-90 
 seconds after stimulation. The striking and main difference 
 between this species and Oxalis stricta consists in the con- 
 traction period being about twice as prolonged. As with 
 Oxalis stricta, summation series can be obtained that vary 
 with the time-intervals between stimuli and the environmental 
 surroundings. 
 
 Observation of the contraction and expansion movements of 
 this and other sensitive plants shows that each is made up of 
 numerous minor contraction and expansion waves that cause 
 the leaf to move by minute jerks, each minor contraction phase 
 during the great period of contraction being much greater in 
 amount than the succeeding expansion phase. In all prob- 
 
194 BIOLOGICAL LECTURES. 
 
 ability this is due to the gradual passage of sap through the 
 contractile protoplasmic layer of each cell and the elastic recoil 
 of it and of the wall as additional liquid is extruded or absorbed. 
 
 I now pass to Oxalis dendroides, a plant eminently suited for 
 investigations like the present, and which has yielded results 
 as interesting as they were unexpected. For a supply of fine 
 specimens I am indebted to the kindness of Mr. G. Oliver of 
 the Washington Botanic Garden. It is an abundant weed in 
 Brazil and is often confounded with Oxalis sensitiva, that is 
 native from Persia to China. It is one of a series of nearly 
 related forms, some of which like the present have a simple 
 unbranched upright habit, while others incline to a proliferous 
 mode of growth. Though seldom seen outside botanic gardens, 
 it grows with the utmost readiness, fruits freely, and scatters its 
 seeds widely. Four noteworthy points can be readily demon- 
 strated on this species, though witnessed less perfectly in 
 others. These are : First, that the latent period varies accord- 
 ing to the age of the leaf; second, that a gradual propagation 
 of stimulus from base to apex or vice versa can be shown to 
 exist; third, that the rate of propagation of the contraction- 
 stimulus can be exactly measured ; and fourth, that the rate of 
 contraction and expansion of leaflets is quickest in young and 
 slowest in old leaves. 
 
 If the tip of the blade of a terminal leaflet be stimulated 
 by a forceps snip, in an atmosphere whose temperature 
 is 28° -32° C, it and the companion leaflet will fall 
 down through an angle of 40°-45° in about 20 seconds. 
 That irritation of a leaflet should excite to a rapid movement 
 not merely of one but of neighboring leaflets, suggests the idea 
 that at least some of the cells of every leaflet can conduct a 
 stinmlns. This idea is entirely confirmed by many other 
 experimental results. If the leaflet that has been irritated be 
 part of an old leaf, the succeeding pairs of leaflets will close in 
 regular succession from apex to base with a time interval 
 between each pair of 2\ seconds. By this we mean the time 
 required for propagation of the shock from one pair of pulvini 
 to another pair below, and succeeding contraction of the living 
 protoplasm of the different cells in the path of the stimulus. 
 
IRRITO-CONTRACTILITY IN PLANTS. 1 95 
 
 But as I shall point out later, it would be a mistake to suppose 
 that the actual rate of propagation of stimulus from apex to 
 base of the leaf is so slow as this. If the leaf operated on was 
 the fifteenth from the growing apex of the stem and the tenth 
 leaf be now chosen and similarly operated on, the time interval 
 between contraction of succeeding pairs of leaflets will be 
 1 1 -2 seconds; with the seventh leaf from the apex the interval 
 will be i^-if seconds; and finally a delicate light-green leaf, 
 such as the second or third from the apex, shows closure of 
 successive pairs with an interval between of i-i|- seconds. 
 The latent period shown after general stimulus in such a set 
 of leaves is equally variable, and under optimum surroundings 
 is only |-| of a second in young leaves such as the third from 
 the apex, |-i second in the seventh or eighth, i-ij in the 
 tenth or eleventh, and i j-i| in the fifteenth. 
 
 As mentioned above, the angle through which the leaflets 
 fall on excitation, is from 40° -45°. If a general shock 
 be given to the entire leaf, the leaflets fall simultaneously 
 through an angle of equal amplitude. But summation action 
 can now be brought to bear, for on second stimulus the leaflets 
 will fall through an angle of 24°-28° and in a correspondingly 
 short time. On third stimulus the leaflets will fall through 
 I2°-I4° in a still shorter interval, while a fourth stimulus will 
 cause a fall through 4°- 5° in a shorter interval than the last. 
 By this time the leaflets will be folded downward back to back 
 as in night-sleep, or a fifth stimulus effecting a slight additional 
 movement may be needed to complete the process. 
 
 A small bit of ice weighing ^ of a grain, if delicately placed 
 on the tip of a terminal leaflet so as not to touch or directly 
 stimulate the pulvinus cells, starts motion in the one opposite 
 within 7 seconds. A steady impulse is then propagated down 
 the leaf- stalk from pair to pair, the time interval, as in 
 mechanically stimulated leaves, depending on the age of the 
 leaf. If, as has repeatedly been noticed, a pair of leaflets is 
 encountered which is somewhat benumbed from the effect of 
 previously applied chemical or other agents, these will remain 
 motionless, or nearly so, but the same interval of time will elapse 
 before the next pair beneath will contract as would have been 
 
196 BIOLOGICAL LECTURES. 
 
 needed to start movement in the benumbed ones as well as in 
 these. On several occasions, a behavior has been noted, both in 
 Oxalis deiidroides and the common sensitive plant, that is worth 
 recording, whether the suggested explanation of the behavior 
 is the correct one or not. A bit of ice laid directly on the 
 pulvini of two opposite leaflets failed to excite them to motion 
 and even a pair beneath would only partially contract, while 
 those still further down would move in normal fashion. I 
 satisfied myself that the position and weight of the ice particle 
 offered no obstacle, and learned also that if within 20-30 
 seconds the ice be removed, the leaflets after an added interval 
 of 7-15 seconds fall backwards as if recently stimulated. We 
 believe a probable explanation here to be that during the latent 
 period of excitation, the ice had so lowered the temperature of 
 the subjacent cells as to benumb the protoplasm, which only 
 regained its contractile properties with returning irritability 
 after removal of the ice. 
 
 We may next inquire whether a peripheral or centripetal 
 stimulus is propagated to the leaf base or to the stem more 
 rapidly than a centrifugal stimulus initiated at the basal leaflets. 
 The only plant that has hitherto been experimented on is 
 the common sensitive plant, but Dutrochet and Bert expressed 
 different views. Oxalis is much more convenient for the deter- 
 mination of this question. Each leaf carries 15-24 pairs of 
 leaflets. A particle of ice placed on the pulvini of the 
 middle pair, i.e., the tenth if there are 19 pairs, will excite all 
 the pairs above it within 15-17 seconds, but 21-23 seconds will 
 elapse before the lowest pair in such a leaf as the tenth from 
 the apex-bud closes. With the ice in varying positions and 
 on leaves of different age I have invariably found that a cen- 
 trifugal is more rapid than a centripetal impulse, and I have 
 studied many examples. But the records are less satisfactory 
 as regards simultaneous basal and apical initiation of excitation, 
 though the balance of experimental proof is in favor of centri- 
 fugal stimulus. 
 
 As with sensitive plants in general, carbonate of ammonia is 
 a powerful stimulant, and its rapidity is proportioned to the 
 strength of the solution. When a small drop of a 20 ^ 
 
IRRITO-CONTRACTILITY IN PLANTS. I 97 
 
 solution is laid on the tip of a terminal leaflet, striking changes 
 occur. Both of the terminal leaflets close within 7 seconds, and 
 the succeeding pairs below begin to close at the rate already 
 given. But before 5 or 6 pairs out of, it may be, 19-22 have 
 closed, a leaflet near the base may be noticed to twitch, or, as 
 often happens, leaflets on distinct leaves, that are placed 
 however, on the same side of the plant as the excited one, may 
 twitch or even fold together in succession, or move irregularly. 
 When this was first observed, it seemed likely that the volatile 
 fumes were the cause, but though they do act as slow excitants, 
 I was soon convinced that twitches and other movements give 
 us a hint as to the true rate of propagation of stimuli through 
 the special conducting tissue, and that the rate of conduc- 
 tivity is greatly more rapid than that more specialized or 
 detailed exhibition of it which ends in the falling back of the 
 leaflets. 
 
 Before passing from this species I may observe that the 
 leaves as a whole seem to be very feebly responsive to shocks, 
 but they, as well as the flower stalks, perform periodic move- 
 ments of great regularity. There seems to be an equally 
 marked periodic movement in the carpels at time of dehiscence, 
 for they always open in the morning while still green, and 
 after scattering of the seeds in the forenoon they close again 
 permanently. 
 
 The above species, I believe, will prove to be the most 
 valuable plant that can be chosen for laboratory purposes, not 
 alone to the botanist, but as well to the animal physiologist. 
 
 Mimosa piidica deserves well its common appellation, '' tJie 
 se7isitive plant,'' for whether we take account of its short latent 
 period, rapid contraction, relatively rapid expansion, delicacy of 
 sensitiveness and rapidity of propagation of an impulse, it 
 deservedly earns its popular name. It has engaged the 
 attention of such earnest workers as Lindsay, Dutrochet, 
 Briicke, Sachs, Batalin, Bert, Millardet, Pfeffer, and during 
 the past year or two of Cunningham and Gaston Bonnier. 
 But much yet remains to be done. 
 
 While tracing out and comparing the contraction and expan- 
 sion periods in plants six weeks old, ten weeks old, and fifteen 
 
198 BIOLOGICAL LECTURES. 
 
 weeks old respectively, it was found that expansion in a leaf of 
 one of the first took place within 4^-5^ minutes, in one of the 
 second (selecting the fifth or sixth leaf from the cotyledons) 
 the expansion period was 8^-10^ minutes, in one of the third 
 (selecting the eleventh or twelfth leaf) the expansion period was 
 13-16 minutes. To fully verify the observations, I compared 
 plants of known age in several establishments, and found the 
 results in all cases to agree, the longest period occupied in 
 expansion — 23 minutes — having been witnessed in a plant 
 kindly placed at my disposal by Dr. Schively and which was 
 four or five years old, but had formed fresh shoots for the 
 season. 
 
 The relative rapidity of contraction and expansion shown by 
 leaves at different levels on the stem is to a large extent retained 
 during the life of each, though with age the movements 
 become more sluggish. 
 
 As regards rate of propagation of stimuli Dutrochet calculated 
 it to be 2-3 m. m. per second in the stem, and 8-15 m. m. in 
 the petiole. Bert in comparing his own results with those of 
 Dutrochet considered that this estimate was much too high and 
 gave 2-5 m. m. per second as the rate. But undoubtedly the 
 estimates of both observers are greatly below the true rate for 
 certain parts of the leaf, as the following will prove. With 
 forceps I delicately pinched the tip of a terminal leaflet borne 
 on a primary leaflet that had 17 pairs of secondary ones. The 
 end leaflets closed within a second, the next lower pair after 5 
 seconds, and all had closed within 9^ seconds. Now, even if we 
 grant that the wave of excitation started immediately on applica- 
 tion of the excitatory stimulus, the entire distance having been 
 65 m. m. an average rate of 7 m. m. per second would be the 
 outcome. But many experiments which cannot here be detailed 
 convinced me not only that excitations can be started over any 
 part of the leaflets, but that there is a rapid propagation along 
 the leaf stalk. The starting of cold stimuli by ice clearly 
 verified this. Whether delicately held in the leaf axil against 
 the pulvinus, or placed alongside the pulvinus or against its 
 lower surface that is specially irritable, a bit of ice made the 
 leaf fall within i^ — if seconds. Now the length of each 
 
IRRITO-CONTRACTILITY IN PLANTS. 1 99 
 
 primary petiole is 48-55 m. m. If a bit of ice or a drop or two 
 of ice-water be applied to its distal end, the petiole will fall in 
 as short a time as already stated. This shows that in the 
 primary petiole at least, the rate of propagation is not less than 
 25 m. m. per second, a rate quite equal to that met with in the 
 contractile tissues of various animals. 
 
 Confirmatory evidence is got by the use of various chemicals. 
 When a minute drop of carbonate of ammonia is delicately 
 placed on the tip of a young leaflet, one notices X\\2X for the first 
 4-4^ seconds a chajige m color or density gradually creeps doivn 
 the leaf substance, but by the time that this has spread over half 
 the leaflet contraction ensues, and thereafter the other leaflets 
 close at the time rate already given for them. But even by the 
 time that the second or third pair has contracted, twitching and 
 partial closure of pairs near the leaf base prove that the stimu- 
 lus has already travelled down the secondary mid-rib greatly 
 faster than is indicated by the movement of the leaflets. 
 
 Ether is a very serviceable stimulant, though I will not now 
 enter into disputed questions as to the action of its vapor. A 
 small drop of 20/0 ether was placed on one of two end 
 leaflets. The others closed in succession within 8 seconds, the 
 leaf fell at 14 seconds, within 18 seconds the leaf next above 
 fell, and within 31 seconds the leaf still higher. From the 
 leaflet tip to the pulvinus of the last mentioned leaf, the distance 
 was 160 m. m., so that the average rate of propagation necessary 
 for movement of parts was, at least, 5 m. m. a second. Guided 
 by Elfving's experiments on various of the lower plants, where 
 he found that 2 to 5 /o chloroform and 15 ^ ether might not 
 prove permanently injurious to some organisms, experiments 
 were made with 6 fo ether. When a drop was applied to the 
 tip of a leaflet very slight movement followed in most instances; 
 in three cases there was a half-closing of the terminal leaflets, 
 and in one only did they close, to re-open again in 4J- minutes. 
 In two of them the second and third pairs of leaflets were 
 visibly affected and slightly moved upward and forward. No 
 injurious effect followed the application. 
 
 Hot water and heated wire applied to any part of the petiole 
 or of the leaflets stimulate rapidly. 
 
200 BIOLOGICAL LECTURES. 
 
 Sachs, Pfeffer and others have noticed that Mimosa plants 
 when left unwatered for a few days lose their power of con- 
 tractility. This is true of all irritable plants that I have 
 examined, and is capable of ready explanation. 
 
 My plan till now has been to lead you up from one or 
 two well-known plants that exhibit a rather sluggish irrito- 
 contractility to the true sensitive plant that is unique in its 
 physiology. I propose now to pass down the scale again and 
 briefly pass in review some common field weeds, that may, like 
 Oxalis stricter, be found around us here. Had time permitted 
 I should 'have pointed out how the sensitive plant is related 
 to its near ally. Mimosa bipulina, and this again to Mimosa 
 sensitiva, both of which I have had the opportunity of studying 
 from the Washington Botanic Garden, through the kindness of 
 Mr. Oliver. But from the last an easy transition is established 
 with our Eastern American weed. Cassia nictitans, while C. 
 chamaecrista unites it again with C. marylaiidica, that shows 
 a very feeble though measurable response to mechanical, 
 chemical, and other stimuli. 
 
 Cassia nictitans, the wild sensitive plant, is generally stated 
 in botanical manuals to be '' somewhat sensitive." When a 
 delicate mechanical shock is given to the leaf, close observation 
 will show that the leaflets almost instantaneously change 
 position slightly, but succeeding to this is what I can only at 
 present, for want of better knowledge, designate as a latent 
 period of 5^ seconds. Thereafter the leaf stalk falls through 
 an angle of 15-23° and the leaflets simultaneously move 
 forward and rotate inward so that their outer edges become 
 uppermost as in the sensitive plant. This is accomplished in 
 85-86 seconds on the average, and by the end of that time the 
 leaflets are half-closed. But if a second shock be given after 
 the effects of the first have ceased, the leaf will now fall through 
 an angle of 8-9 ° and the leaflets will come together till they 
 nearly lie face to face as in Mimosa pudica. A third stimulus 
 may even give slightly added results. 
 
 An interesting feature in this species is the propagation of 
 stimuli along the leaf though to a feebler degree than in 
 Mimosa. As many of you must have observed, a brownish- 
 
JRIUTO-CONTRACTILITY IN PLANTS. 20I 
 
 red knob-like gland is situated on the upper surface of the 
 petiole, about 3 m. m. below the insertion of the lowest 
 leaflets. If a minute drop of carbonate of ammonia be 
 cautiously placed on it, contraction of all the leaflets ensues, 
 proof this that a continuity of irritable tissue exists between 
 it and the leaflets that are inserted above. The structural 
 relations of this gland with the pulvini of the leaflets is inter- 
 esting, but cannot be dealt with now. Ice and cold water, 
 hot water and dry heat stimuli are all irritants to it, as are 
 chloroform and ether of 1 5 ^ strength and upwards. These 
 can all act so continuously that they cause the leaf to fall 
 and the leaflets to rise to the extent that is seen in the 
 nyctitropic state. 
 
 The hog pea-nut {AmphicarpcBa monoica), as delicate and 
 graceful as it is abundant, is convenient for study alike in the 
 field and laboratory, but we can expeditiously treat it along 
 with its companions of our woods and thickets, the tick trefoils 
 or Desmodiums. My attention has been mainly confined to 
 three species of the genus, viz., Dcsmodium cajiescens, Desmo- 
 dm7n paiiiciilatnni, and Dcsviodinm rotinidifolijnn. They show 
 a degree of sensitivity in the order that I have given them. 
 The latent period in A^nphicarpcea and Dcsuiodium canesccns 
 under ordinary conditions is 3^^-34 seconds, but when plants 
 are grown in a green-house it is shortened to 2|-2| seconds. 
 In Desmodiiim paniculatinn the motion is so slow that I have 
 failed as yet to determine it exactly. 
 
 The period of contraction is considerably longer than in any 
 yet described and is for AmpJiicarpcsa i 50- 160 seconds on clear 
 dry days, and 180-200 on close moist days; for Dcsinodiuni 
 canesce7is and Desmoditnh pajticulaiitm from 120-140 seconds. 
 The amplitude of movement in Arnphicarpcea is greater, however, 
 for equal stimuli than in the two last, thus while Amphicaipcea 
 after one stimulus falls in the forenoon of a dry day through as 
 much as 65-70°, the others seldom fall through more than 
 48-50°. But a result got with some plants of Ajuphicarpcea 
 on a close, warm, but dull day, is worth recording. Like most 
 leguminous species it raises its leaflets during the parathermo- 
 tropic period so as to point the tips at the sun. At 12.30 a 
 
202 BIOLOGICAL LECTURES. 
 
 leaf was mechanically stimulated and fell through 58° in 155 
 seconds, again stimulated it fell through 37° in 114 seconds, 
 again stimulated it fell through 16° in 85 seconds, and on 
 fourth stimulus it fell through 9 ° in 69 seconds. It thus swept 
 through an arc of 120° in little more than 7 minutes, but as I 
 have since proved, by shortening the time intervals between 
 stimuli, the same movement can be got in less than half 
 the 'period. The average rate of expansion is from 12-15 
 minutes in the first three species now under consideration, but 
 under certain conditions may be only 7-9. Ice and ice-water, 
 hot water and dry-heat stimuli, alcohol, ether, etc., are all 
 irritants. 6 ^ ether when placed not merely at the base of a 
 leaflet but even in the middle of it, excites to movement. 
 
 I have already referred to the fact that Cassia nictitanSy 
 though closely resembling Mimosa pudica in its leaf move- 
 "ments, shows a greatly reduced capacity for propagation of 
 stimuli from one leaflet or pair of leaflets to another. The 
 four species now under consideration are still less sensitive in 
 this respect, for it is possible to make a terminal or lateral 
 leaflet fall through 38°-67° without participation of the other 
 two leaflets in the change. 
 
 Desmodiiim rotjindifoliuin is the least sensitive of the genus, 
 for in its sluggish action and limited amplitude of movement 
 (amounting to io°-2 5°) it more nearly resembles some of the 
 Lespedezas. Now Ainphicarpcea, Dcsmodimn cajiesceiis, and 
 Dcsmodinm panicidatiim are all upright growers, and are 
 therefore exposed in their leaflets to the full effects of night 
 cold and heat radiation from the tissues, and I believe that 
 this may largely explain why in evolutionary development they 
 have become much superior to Dcsmodinm rotmidifoliimiy whose 
 long sucker-like shoots run along the ground, and give off 
 leaflets that nestle amongst surrounding herbage. 
 
 AmpJiicarpcea^ Dcsmodinm and Lcspcdcza all seem to resemble 
 the species of Oxalis, and to differ from such as Mimosa 
 p7idica or Cassia nictitans in that the primary stalk of the leaf 
 does not appear to move, or only moves so slightly that it 
 has hitherto escaped my observation. But this difference is 
 secondary and not fundamental, I believe, for in two such 
 
IRRITO-CONTRACTILITY IN PLANTS. 203 
 
 closely related species as Mimosa piidica and Mimosa hipulina, 
 the former has the most rapid motion in its leaf stalk at present 
 known, the latter seems to be quite stationary. 
 
 It may now be asked, How do the seed leaves of sensitive 
 plants behave ? De Candolle first noticed that the cotyledons 
 of Mimosa are irritable to touch, while Bert, Pfeffer and 
 Darwin have confirmed his observations. To the last writer, 
 also, we owe a list of additional plants with sensitive cotyledons, 
 for he pointed out that several species of Oxalis, Mimosa^ 
 Trifoliicm, Cassia and Lotus all show sleep movenients, and 
 further that eight species of Cassia, a species of Smit/iia, 
 Mimosa piidica and Mimosa sensitiva, also Oxalis sensitiva, 
 are irritable to contact. I have not only been able to add 
 several to Darwin's list, but have learned much as to their 
 extreme sensitiveness. Various of them are not merely irritable 
 to a single impact, but undergo a definite amount of contraction 
 that varies, as in the vegetative leaves, with age and environ- 
 ment. They contract to their fullest extent with a summation 
 of stimuli, they are highly irritable to heat and cold stimuli, 
 also to chemical agents that excite contractile tissue. 
 
 Those of the sensitive plant are most active during the 
 period that their activity is of greatest benefit, viz., in the 
 very young state (seedlings 2-10 days old), since their great 
 function is to protect the first leaves and growing bud. When 
 the latter have pushed out above the cotyledonary tips, the pro- 
 tective function has ceased, and their irritable movements are 
 greatly lost. This, of course, is owing to the protoplasm 
 becoming senile, for as their irritability becomes less their 
 green color is transformed into yellow, and they then shrivel 
 and soon after drop off. This may have misled Darwin into 
 supposing that the seed leaves of Mimosa piidica were feebly 
 sensitive, for he speaks of their rising after irritation by 
 rubbing, or by tapping for from 30 seconds to 3 minutes, 
 but I cannot understand why he considered so much effort 
 necessary, unless it be that he happened to choose rather 
 old seedlings or experimented at low temperatures. 
 
 The irritable movements of the cotyledons as compared with 
 the foliage leaves of Oxalis dendroides are of great importance. 
 
204 BIOLOGICAL LECTURES. 
 
 Some botanists have attempted to distinguish between plants 
 that show a heat-sleep with the leaflets directed upwards, and 
 a night-sleep in which they fall down, as compared with others 
 that have the same position alike in heat and sleep. But here 
 is a plant which folds upwards its seed leaves, and downwards 
 its foliage leaves under all kinds of stimuli. 
 
 In such a condensed statement as I now give, it would be 
 impossible to dwell on the anatomical details of the species 
 already named. Suffice it that they all exhibit beautiful 
 intercellular protoplasmic unions from cell to cell, as was first 
 demonstrated for the sensitive plant by Gardiner. 
 
 We may now attempt shortly to answer the question, How 
 are the irrito-contractile movements originated and propagated, 
 and what are the cell changes which accompany them .'* Until 
 within the last decade, botanists were compelled to view living 
 vegetable cells as organic units that were sharply demarcated 
 from each other by cellulose walls, and whose life phenomena 
 were due to protoplasmic activity of each cell. But no matter 
 how complex and intricate the chemical changes that were 
 effected, they still viewed the protoplasm as a rather watery 
 substance of no great consistency, tenacity, or structural 
 complexity. The study of nuclear changes during new cell 
 formation, of the existence of sensitive movements in different 
 plants, but especially the demonstration of intercellular proto- 
 plasmic threads that link together the cell protoplasms into 
 one harmonized body, compel us to accept the conclusion that 
 the protoplasm of a vacuolated cell is a very complex and 
 resistant substance that is extremely responsive to environ- 
 mental stimuli. Still, with few exceptions — and chief among 
 these we reckon Gardiner of Cambridge — botanists clung, 
 and even now cling, to the idea that irrito-contractile move- 
 ments are simply, or at least chiefly, due to migration of cell 
 sap from a living cell or cells into intercellular spaces, owing 
 to contraction of the cellulose walls. Sachs, Bert, Nageli and 
 Schwendener, Pfeffer and DeVries have propounded the view 
 that contraction of the walls is the important factor. 
 
 The untenableness of this position is being gradually recog- 
 nized, and one can see that a change is coming. The 
 
IRRITO-CONTRACTILITY IN PLANTS. 205 
 
 aggregation j^rocess which Darwin first observed in the cells 
 of Droscra tentacle has been carefully studied, and is now 
 known to be due to expulsion of cell sap through the 
 protoplasmic sac of certain cells, and that this escapes into 
 intercellular spaces in at least some instances, {e.g. Mimosa 
 pudica), is practically demonstrated by Pfeffer's experiments. 
 The opinion is now being gradually accepted that irritation of 
 the lower region of the pulvinus causes a sudden exudation of 
 the cell sap through special pores in the protoplasmic sac, and 
 that this sap then escapes into the intercellular spaces, or to 
 the exterior if an incision be made. As the cells of the 
 upper pulvinus region are now more turgid, fall of the leaf 
 follows.^ 
 
 But from Wortmann's studies on PJiycomyccs and other 
 plants, it is demonstrated that irritation of any part of a cell 
 causes the protoplasmic sac to retreat from the wall at the 
 irritated region, owing to extrusion of a quantity of the sap 
 that is enclosed within the sac. The process of expansion 
 then would consist in the gradual resorption of sap into the 
 contracted cell. Many results point to this conclusion, and 
 the fact that sensitive plants if starved in their water supply 
 cease to be irritable, is in its favor. 
 
 I previously showed, however, for Dioiicea, — and have now 
 proved for several other plants, — that summation stimuli can 
 be given with definite results ; also, that under heat and cold 
 stimuli, chemical stimuli, and electrical stimuli, plant tissues 
 behave exactly as do the contractile tissues of animals, while 
 the rate of propagation of the stimulus is greater than that in 
 various animal tissues. It may be affirmed, then, of many 
 plants that their protoplasm is irritated by, and responds to, 
 
 1 Since writing the above the author has observed a striking change to occur in 
 the leaflet pulvini of Mimosa pudica, M. lupulina Schrattkia^aiigttstata, and most 
 beautifully in Mimosa sensitiva. After stimulation of a leaflet, and toward the 
 close of the latent period a sudden flush travels centrifugally across the surface 
 of the pulvinus. Immediately thereafter the leaflet contracts, and the pulvinus 
 previously of a whitish hue assumes a dull greenish aspect. The author has 
 grounds for believing that this is due to migration of liquid into the upper region 
 of the pulvinus, and corresponds to a similar change in a girdle of tissue above 
 the swollen leaf pulvinus, which is possibly the area referred to by Lindsay nearly 
 seventy years ago. 
 
2o6 BIOLOGICAL LECTURES. 
 
 mechanical, thermal, luminous, chemical and electrical stimuli, 
 and that the degree of contraction is proportioned to the rela- 
 tive molecular activity of the protoplasm and the strength or 
 continuity of the stimulus. 
 
 Accepting this position, I venture to think that we can 
 harmonize many movements that appeared superfluous or dis- 
 tinct from each other. It may be asked, — and indeed has 
 been asked by Darwin, — Why are plants that are nyctitropjc 
 and parathermotropic often very sensitive to impact, though 
 apparently deriving no benefit from impact sensitivity 1 We 
 reply that, being sensitive to, or irritated by, light, heat, or 
 cold, they must of necessity be also sensitive to impact, 
 even though deriving no benefit therefrom, since contraction- 
 sensitivity involves response to all forms of energy. But let 
 us be cautious in assuming that no benefit is got from a 
 certain movement unless such benefit is patent to us. Sachs 
 says about the sensitive plant, " So far as I am aware, no one 
 has attempted an explanation of the use of the irritability of 
 the leaves of Mimosa; but I believe that I am able to afford 
 one ; for I have often had opportunities of observing that after 
 a severe hail-storm, when plants of the most various kinds — 
 and even robust plants, close to my mimosas, before the 
 window or in the open — have been dashed and broken by 
 the hail-stones, the mimosas, in spite of their delicate 
 structure, have come out quite uninjured ; a few minutes after 
 the rough weather they expanded their leaves again, entirely 
 unhurt." He might have added that not merely from hail, 
 but from beating winds and rain, the leaves are the better 
 protected ; as I have proved for Mimosa^ Oxalis^ Dcsnio- 
 dium, AmpJiicarpcea^ etc. As with animal contractile tissues, 
 then, every irritable plant is to a greater or less degree 
 irritable to all forms of stimuli. We derive now from this a 
 likely explanation of nyctitropic and parathermotropic move- 
 ments in plants. It is universally recognized that every 
 species has an optimiim as well as a minimum and maximum 
 temperature relation. To return to Oralis stricta again, the 
 optimum during the day is 24°-26° C, but when it is exposed 
 to a steady heat-stimulus from the sun's rays of 30°-32° C, 
 
IRRITO-CONTRACTILITY IN PLANTS. 207 
 
 the protoplasm will almost certainly contract, and the leaflets 
 will fall. But as evening advances, lowering of the air temper- 
 ature, radiation from the leaflets, — and still more importantly, 
 I believe, — the cutting off of the light stimuli along with 
 reduced temperature of the soil, will all act steadily, and the 
 leaflets, newly recovered from the parathermotropic state, will 
 pass soon after into the nyctitropic state. 
 
 To distinguish the relation to altered environmental surround- 
 ings, we speak of night-sleep ©r nyctitropism, and heat-sleep or 
 parathermotropism, but fundamentally both are due, we believe, 
 to one and the same fundamental peculiarity of the protoplasm, 
 though we cannot stop here to discuss Briicke's assertion of a 
 difference owing to difference of tension. 
 
 A distinct exception to this principle, however, seemed to be 
 involved in Pfeffer's statement first made in \{\?> Pflaiiz en physi- 
 ologic, and afterwards extended into a paper published in his 
 Laboratory Journal . He there asserted that sensitive plants like 
 Mimosa, Oxalis, Dioncea, etc. differed fundamentally from such 
 stem or leaf parts as tendrils and from the hairs of Drosera, 
 in that the former were sensitive to impact, the latter only to 
 contact. So many cases of summation of stimuli being needed 
 to effect movement had been met with by me, that I deter- 
 mined to ascertain experimentally, whether coiling of a tendril 
 was not due to a summation of distinct impacts combined, of 
 course, with circumnutation of the organ. Fortunately, I had 
 fine plants of those he experimented on growing in my garden 
 or within easy reach. Pfeffer states that the long, graceful 
 tendril of Sicyos — the bur cucumber — only coils into a helix 
 if subjected to contact rubbing. I first selected a primary 
 tendril of EcJiinocystis lobata, that was 5| inches long and 
 faintly incurved at its tip, as is usual. Thirty delicate 
 mechanical shocks were given in series of five at intervals of 
 10 seconds, and spread over i^ inches of the tip. Soon 
 after delivery of the second five — i.e., within 25 seconds — 
 there was a distinct curving of the irritated region. In 6 
 minutes the tendril had curved sharply through | of a circle, 
 and in 23 minutes through ij of a circle. It was first 
 irritated at 7.21 p.m., and when examined i^ hours later 
 
208 BIOLOGICAL LECTURES. 
 
 by lamplight, it was still incurved. Next morning it had 
 again straightened out. I have often, and admiringly, 
 repeated the experiment on primary and secondary tendrils, 
 have varied the time-interval between the shocks, and have 
 varied the number of shocks given, but they have never failed 
 to respond. Though in a few instances Sicyos tendrils did 
 not sensibly respond when given 20 to 30 stimuli, the majority 
 behaved like those of Ecliinocystis. 
 
 Thereafter, a large and vigorous plant of Ciicinnis maxima, 
 was experimented with. Series of 5 stimuli at intervals of one 
 second were given every i- minute, and in 6 minutes, i.e. after 
 60 stimuli, two had incurved very distinctly. After 14 minutes 
 one had curved through | of a circle, the other through ]. 
 Three of different length and age were then chosen with 
 essentially similar outcome. The whole subject of tendril 
 movement, as viewed in the above light, opens up a wide field 
 for comparative and critical investigation. Why not merely 
 elongation of cells but growth in thickness of tissue should 
 then follow on the side away from that irritated, is not difficult 
 to understand, in view of De Vries' and Wortmann's studies of 
 protoplasmic movement.^ 
 
 Equally must I take exception to Pfeffer's assertion that 
 Drosera tentacle does not inflect after contact stimulus. 
 Darwin stated that inflexion usually took place after three or 
 more touches, though this is denied by Pfeffer. I find that if 
 the leaves of D. rotniidifolia, D. iiitcrvicdia or D. dichotonia 
 are healthy and secreting their viscous juice freely, two stimuli 
 with a time-interval between of at least 25 seconds, causes 
 powerful incurving, but only after a latent period of 55-70 
 seconds. Few things in the range of plant life have seemed 
 so impressive as watching Drosera tentacle after second stim- 
 ulus. To know that, as the seconds pass with apparently 
 no change in the tentacle, active though invisible molecular 
 movement is progressing which culminates after about 60 
 seconds in a steady, sweeping incurvation of the tentacle for 
 
 1 McDougall's experiments {Bot. Gazette, Vol. XVIII, 1S93) on the stimulation 
 and movements of tendrils, suggest broad lines of investigation that may yield 
 good results. 
 
IRRirO-CONTRACTILITY IN PLANTS. 209 
 
 65-70 seconds, is a revelation to us of the complexity of proto- 
 plasmic machinery. Drosera, then, like Dioncea, moves only 
 after a summation of at least two stimuli. 
 
 I cannot sit down without acknowledging here my great 
 indebtedness to Mr. Oliver, of the Washington Botanic Garden, 
 for fine specimens of the rarer species experimented with, and 
 to my friend and former student, Mr. Aldrich Pennock, who 
 not only threw open his hot-houses for my use, but aided me 
 practically in many ways. 
 
TENTH LECTURE. 
 
 THE MARINE BIOLOGICAL STATIONS OF EUROPE. 
 
 HASH FORD DEAN, 
 
 Columbia College, New York. 
 
 Among European nations the Marine Laboratory has long 
 been recognized as an important aid to the advancement of 
 biological studies. Groups of universities, centralizing their 
 marine work in convenient localities, have caused the entire 
 coast line of Europe to become dotted with stations, well 
 equipped and well maintained. Societies, individuals and not 
 infrequently governments contribute to their support. 
 
 Marine stations have become distributing centers, important 
 equally in every grade of biological work or training. A 
 student, for example, should he visit a small university in the 
 interior of France, would receive his first lessons aided 
 by material sent regularly from Roscoff or Banyuls : — he 
 would examine living sponges, pennatulids, heroes, hydroids, 
 Loxosoma, Comatula, Amphioxus. Or, at Munich, remote 
 from the coast, as in the laboratory of Prof. Richard Hertwig, 
 he is enabled by means of material from Naples to demonstrate 
 the larval characters of ascidians, or the fertilization processes 
 of the sea-urchin. During his winter studies the marine 
 station would thus provide him with the best material — 
 sometimes preserved and well fixed, sometimes living, to be 
 prepared according to his wants. In summer it affords him 
 the best opportunities to see and collect his study types, without 
 physical discomforts and with the greatest economy of time. 
 To the investigator the station has become, in the broadest 
 sense, a university. He may there meet the representative 
 students of far and wide, fellow-workers perhaps in the very 
 
212 BIOLOGICAL LECTURES. 
 
 line of his own research, and must himself unknowingly teach 
 and learn. He finds out gradually of recent work, of technical 
 methods which often happen most pertinent to his needs. 
 He carries on his work quietly and thoroughly ; his works of 
 reference are at hand ; he has the most necessary comforts in 
 working, and is untroubled by the rigid hours of demonstrations 
 or lectures. The station, becomes, in short, a literal emporium, 
 cosmopolitan, bringing together side by side the best workers 
 of many universities, tending, moreover, to make their observa- 
 tions upon the best material sharper by criticism, most fruitful 
 in results. It has often been remarked how large a proportion 
 of recently published researches was dependent, directly or 
 indirectly, upon marine laboratories. 
 
 A brief account of the more important of these stations 
 should not prove lacking in suggestions ; especially as in 
 America the work of the marine laboratory is often imperfectly 
 understood. Its aims have been associated popularly with 
 those of practical fish culture ; and even among the trustees 
 of universities a disposition has often been to regard an annual 
 subscription for a work place in a summer school as among the 
 little needed expenditures of a biological department. So little 
 important has a marine station seemed that the greatest 
 difficulties have ever been encountered to ensure the support 
 of an American table at Naples, — although it was well known 
 how large a number of our investigators were each year 
 indebted to foreign courtesy for the privileges of this station. 
 
 General interest in the advancement of pure science has in 
 Europe become a prominent feature of the past decade, and 
 there can be no doubt of the importance that has come to be 
 attached to studies bearing upon the problems of life, evolution, 
 heredity. Nor, at the same time, does it appear that matters 
 relating to practical fisheries have in any way lost their interest 
 or support. To these, on the contrary, the rise of pure biology 
 has often given important aids. What has appeared abstract 
 theory to-day has often been converted into practice to-morrow. 
 And even so ardent a partisan of pure biology as Prof, 
 de Lacaze-Duthiers does not hesitate to urge this, as sufificiently 
 important in general argument, to vindicate the governmental 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 
 
 213 
 
 support of the laboratories of Roscoff and Banyuls. " Facts 
 have been found at every step of science which were valueless 
 at their discovery, but which, little by little, fell into line and 
 led to applications of the highest importance — how the obser- 
 vation of the tarnishing of silver or the twitching leg of the 
 frog was the origin of photography or telegraphy — how 
 the purely abstract problem of spontaneous generation gave 
 rise to the antiseptics of surgery." 
 
 ^■~^- 
 
 .^ SOLOVETSKAIA 
 
 UNIV.iCHRrlSTlANlA^ ^^^r-T 
 
 r'sEBASTOPOL ^^ 
 
 As a preface to the present discussion the general number 
 and location of the European marine stations might conven- 
 iently be indicated in the accompanying outline map. 
 
 I. — France. 
 
 The extended sea-coast has ever been of the greatest aid to 
 the French student — along the entire northern coast the 
 channel is not unlike our Bay of Fundy in the way it sweeps 
 the waters out at the lunar tides. The rocks on the coast of 
 Britany, massive bowlders, swept and rounded by the rushing 
 
2 14 BIOLOGICAL LECTURES. 
 
 waters, will at these times become exposed to a depth as great 
 as forty feet. This is the harvest-time of the collector; he is 
 enabled to secure the animals of the deep with his own hand, 
 to take them carefully from the rocky crevices where they would 
 ever have avoided the collecting dredge. From earliest times 
 this region has not unreasonably been the field of the naturalist. 
 It was here that Cuvier, during the Reign of Terror, made 
 his studies on marine invertebrates which were to precede 
 his Rhgjic Animal. The extreme westernmost promontories of 
 Brittany have, for the last half-century, been the summer 
 homes of de Quatrefages, Coste, Audouin, Milne-Edwards and 
 de Lacaze-Duthiers. Coste created a laboratory at Concarneau, 
 but this has come to be devoted to practical fish culture, and 
 is, at the present day, of little scientific interest. It is owing 
 to the exertions of Professor de Lacaze-Duthiers of the 
 Sorbonne, that the two governmental stations of biology have 
 since been founded. The first was established at Roscoff, in 
 one of the most attractive and favorable collecting regions in 
 Brittany, and has continued to grow in importance for the last 
 twenty years. As this station, however, could be serviceable 
 during summer only, it gave rise to a smaller dependency of 
 the Sorbonne in the southernmost part of France, on the 
 Mediterranean, at Banyuls, which had the additional advantage 
 of a Mediterranean fauna. 
 
 To these French stations should be added that of Professor 
 Giard, at Wimereux near Boulogne, in the rich collecting 
 funnel of the Straits of Dover; that of Professor Sabatier at 
 Cette, not far from Banyuls, a dependency of the University of 
 Montpelier; that of Marseilles, and the Russian station at Ville- 
 Franche, near the Italian frontier. An interesting station in 
 addition, is that at Arcachon near Bordeaux, founded by a local 
 scientific society. Smaller stations are not wanting, as at the 
 Sables d'Olonne. 
 
 At Roscoff the laboratory building looks directly out upon 
 the channel. In its main room on the ground floor, work 
 places are partitioned off for a dozen investigators; this on the 
 one hand leads to a large glass-walled aquarium room, seen in 
 the accompanying figure, while on the other opens directly to 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 
 
 215 
 
 adjoining buildings which include lodging quarters, a well- 
 furnished library and a laboratory for elementary students. 
 Surrounding the building is an attractive garden which gives 
 one anything but a just idea of the barrenness of the soil of 
 Brittany. From the sea wall of the laboratory one looks out 
 over the rocks that are becoming exposed by the receding tide. 
 A strong enclosure of masonry serves as a vivierXo be used for 
 
 Marine Station at Roscoff, Brittany. 
 (From photograph, July, 1891.) 
 
 experiments as well as to retain water for supplying the 
 laboratory. The students are, in the main, those of the Sor- 
 bonne, and under the direction of Dr. Prouho, their uiaitre de 
 conferences. They are given every opportunity to take part in 
 the collecting excursions, frequently made in the laboratory's 
 small sailing vessels, among the rocky islands of the neighbor- 
 ing coast. Strangers, too, are not infrequent, and are 
 generously granted every privilege of the French student. 
 
2l6 
 
 BIOLOGICAL LECTURES. 
 
 Liberality is one of the characteristic features of Roscoff. The 
 stranger who writes to Professor de Lacaze-Duthiers is accorded 
 a work place which entitles him gratuitously to every privilege 
 of the laboratory — his microscope, his reagents, even his 
 lodging-room should a place be vacant. It seems, in fact, to 
 be a point of pride with Professor Lacaze that the stranger 
 shall be welcomed to Roscoff, and upon entering the laboratory 
 
 Roscoff. Inierior of Aquarium Room. 
 (July, 1891.) 
 
 for the first time, feel entirely at home. He finds his table in 
 order, his microscope awaiting him, and the material for which 
 he had written displayed in stately array in the glass jars and 
 dishes of his work place. So, too, he may have been assigned 
 one of the large aquaria in the glass aquarium room — massive 
 stone-base stands, aerated by a constant jet of sea water. 
 
 He finds a surprising wealth of material at Roscoff, and his 
 wants are promptly supplied. 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 
 
 17 
 
 At Banyuls, the second station pf the Sorbonne, the build- 
 ings are less imposing than those of Roscoff. It is a plain, 
 three-story building facing the north, at the edge of the prom- 
 ontory which shelters the harbor at Banyuls. The vivicr is in 
 front of the station, behind is a reservoir cut in the solid rock 
 — receiving the waters of the Mediterranean and distributing 
 it throughout the building. On the first floor is a large 
 aquarium room lighted by electricity, well-supplied with tanks 
 
 siiHi I 
 
 fStIi I 
 
 French Marine Station at Banyuls-Sur-Mer. 
 (October, 1891.) 
 
 and decorated not a little with statuary donated by the 
 Administration of the Beaux-Arts. The bust of Arago 
 occupies an important place, as the laboratory has been named 
 in his honor. A suit of a diver sugests the different tactics in 
 collecting made necessary by the slightly falling tides of the 
 Mediterranean. The wealth of living forms in the aquaria 
 
2l8 
 
 BIOLOGICAL LECTURES. 
 
 shows at once by variety of bright colors the richness of 
 southern fauna. Sea lilies are in profusion; and are gathered 
 at the very steps of the laboratory. The work-rooms of the 
 students are on the second floor, equipped in a manner similar 
 to those of Roscoff. The director of this station is Dr. Frederic 
 Guitel. It is usual during the holidays at fall or winter, for the 
 entire classes of the Sorbonne to spend several days in 
 collecting-trips in the neighborhood. The region, with its 
 
 Banyuls-Sur-Mer. Interior of Aquarium Room. 
 (October, 1891.) 
 
 little port, is famous for its fisheries, and one in especial is that 
 of the Angler, LopJiiiis, a fish that would not be regarded as 
 especially dainty on our side of the Atlantic. 
 
 The station on the Straits of Dover, at Wimereux, has 
 earned a European reputation in the work of Professor Giard. 
 It is but a small frame building, scarcely large enough to 
 include the advanced students selected from the Sorbonne. 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 219 
 
 The laboratory is, in a way, a rival of Roscoff, and it is 
 noteworthy that its workers seem to make a point of studying 
 the laboratory methods of the German universities. 
 
 The marine laboratory of Arcachon, one of the oldest of 
 France, was built in 1867 by the local scientific society, and 
 was carried on independently until the time of the losses of the 
 Franco-Prussian War. Its management was then fused with 
 that of the faculty of medicine of Bordeaux, with whose assist- 
 ance, aided by that of a small subsidy from the government, 
 the work of the institution is carried on. Arcachon, near 
 Bordeaux, is in itself a most interesting locality. It has become 
 a summering place, noted for its pine lands and the broad, sandy 
 plage, picturesque in summer with swarms of quaintly-dressed 
 children, the local head-dress of the peasant mingling with the 
 latest toilets from Paris. Here and there is to be seen that 
 accompaniment of every French watering place, the goat boy 
 in smock and berret, fluting to his dozen charges who walk 
 in a stately way before him. The Bay of Arcachon is a 
 small, tranquil, inland sea, long known for its rich fauna. In 
 large part it is laid out in oyster parks, which constitute to no 
 small degree the source of wealth of the entire region. . Shal- 
 low and warm waters seem to give the marine life the best 
 conditions for growth and development. The laboratory is 
 placed just at the margin of the water. It includes a dozen or 
 more work places for investigators, well supplied with aquaria, 
 a library on the second floor, a small museum containing col- 
 lections of local fauna, including numerous relics of Cetaceans 
 that have found their way into this inland sea. A small 
 aquarium room, opened to the public, is well provided with 
 local forms of fishes, and like that of Naples, is eagerjy visited. 
 Those who are entitled freely to the use of the work places are 
 instructors in French colleges, members of the Society, and all 
 the advanced students from the colleges of the State. For 
 other students, work place is given upon the payment of a fee 
 whose amount is regulated each year by the trustees. As at 
 Roscoff, material is plentifully supplied. 
 
 The Zoological Station at Cette is a direct annex of the 
 University of Montpelier, and it will be gladly learned that 
 
220 BIOLOGICAL LECTURES. 
 
 its temporary building is being replaced by one of stone, 
 which will enable Professor Sabatier to add in no little way to 
 the working facilities of his students. The region, in every 
 essential regard, is similar to that of Banyuls. 
 
 The station at Marseilles is devoted in great part to ques- 
 tions relating to the Mediterranean fisheries, and owes, in a 
 measure, its financial support to this practical work. 
 
 The station at Ville-Franche is essentially Russian. An 
 account of this with figures has recently been published 
 (Russian text) in Cracow. The station itself is well known 
 through the work of Dr. Bolles Lee, and it is here that 
 Professor Carl Vogt has been a constant visitor. 
 
 II. — England. 
 
 The laboratory at Plymouth is quite a recent one, its 
 foundation due in the first instance to the efforts of Professor 
 Ray Lankester. Its building, first opened in 1888, is, in many 
 regards, hardly second to Naples. This locality was found 
 well-suited for the needs of an extensive marine station. 
 Opposite Brittany it takes advantage of the same extremes of 
 tide, and the rocky Devonshire coast affords one of the richest 
 collecting grounds. The situation of the building is a remark- 
 able one; it stands at one end of the ancient Hoe of Plymouth 
 — a broad, level park whose high situation looks far off over 
 the channel. At the rear of the building are the old fortifica- 
 tions of the town. As shown in the adjoining figure, the 
 building is, at the ends, three-storied. On the ground floor is 
 the general aquarium room, well-supplied with local marine 
 fauna, and open to the public. The laboratory proper is upon 
 the second floor, divided into eleven compartments, the work 
 places of the students. A series of small tanks passes down 
 the middle of the room. In the western end are the library, 
 the museum, the chemical, photographic, and physiological 
 rooms : in the eastern are the living quarters of the director. 
 The water supply of the laboratory is contained in two small 
 reservoirs directly between the building and the fortifications, 
 and is carried throughout the building by gas engines. Tidal 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 
 
 221 
 
 aquaria are in constant use for developmental studies. The 
 collecting for the laboratory is aided by a 38-foot steam launch. 
 
 The present support of the station is not, unfortunately, as 
 generous a one as might be desired. The station is obliged to 
 consider in the work of its director matters relating to public 
 fisheries, and is only enabled by this means to secure govern- 
 mental assistance. The building itself was constructed by the 
 efforts of the Marine Biological Association of the United 
 
 British Marine Laboratory, Plymouth. 
 (August, 1892.) 
 
 Kingdom, under whose auspices the present work is being 
 carried on. The investigators' tables are occupied by any 
 founder of the Association, or his representative, by the natu- 
 ralist or institutions who have rented them. The subscription 
 price per year of an investigator's place is £,^0, but tables may 
 be leased for as short a time as a month. The laboratory pro 
 
22 2 BIOLOGICAL LECTURES. 
 
 vides material for investigation and the ordinary apparatus of 
 the marine laboratory, excluding microscopes and accessories. 
 The use of the larger tanks of the main aquarium is also per- 
 mitted to the working student. The work of the laboratory 
 includes investigation of fishery matters, the preservation of 
 animals to supply the classes of zoology in the universities 
 and the formation of type collections of the British marine 
 fauna. The naturalist of this station has been, for a number 
 of years, Mr. J. T. Cunningham, whose experiments upon the 
 hatching of the Sole have here been carried on. 
 
 Other British marine stations are those of Liverpool and St. 
 Andrews, northeast, and Dunbar, southeast, of Edinburgh. 
 The work of these stations is only in part purely biological ; 
 the practical matters of fisheries must be considered to insure 
 financial support. In addition to these is to be mentioned a 
 station, recently equipped, on the Isle of Man. Still another, 
 most favorable in its locality, has been established in the 
 Channel Isands. 
 
 At St. Andrews, Professor Macintosh has studied the ques- 
 tions relating to the hatching and development of the North 
 Sea fishes. Its situation upon the promontory leading into 
 the Firth of Forth seems to have been especially favorable 
 for the study of the North Sea fauna — the locality, moreover, 
 is far enough northward to include a numer of boreal forms. 
 The importance of St. Andrews is at length better recognized, 
 and a substantial grant from the government will enable a 
 large and permanent marine station to be here constructed. 
 The facilities for work have, up to the present time, been 
 somewhat primitive, — a simple wooden building, single-storied, 
 has been partitioned off into small rooms, a general laboratory, 
 with work places for half a dozen investigators, a director's 
 room, aquarium, and a small out-lying engine house with 
 storage tanks. To the laboratory belongs a small sail-boat to 
 assist in the work of collecting. 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 223 
 
 III. — Holland. 
 
 Holland, in the summer of 1890, opened its zoological 
 station in the Helder, a locality which, for this purpose, had 
 long been looked upon with the greatest favor. There is here 
 an old town at the mouth of the Zuyder Zee, the naval strong- 
 hold of Holland, a station favorable for biological work on 
 account of the rapid-running current renewing the waters of 
 
 Dutch Zoological St.uion ai ihk IIkldkr. 
 (Fig. from Tijdschr. d. Ned. Dierk. Vereen. 5 Juli, 1S90.) 
 
 the Zee. The station was founded by the support of the 
 Zoological Society of the Netherlands, whose valuable work 
 by the contributions of Hubrecht, Hoek, and Horst, has long 
 been known in connection with the development of the oyster 
 industry of Holland. The work of the Society had formerly 
 been carried on by means of a portable zoological station 
 
224 
 
 BIOLOGICAL LECTURES. 
 
 which the investigators caused to be transplanted to different 
 points along the East Schelde, favorable on account of their 
 nearness to the supplies of spawning oysters. The present 
 station at the Helder is situated directly adjoining the great 
 Dyke, a small stone buiding, two stories, surrounded by a 
 small park, as seen in the adjacent figure. In itself the labo- 
 ratory is a model one, — the rooms are carefully finished, and 
 every arrangement has been made to secure working conven- 
 iences. A large vestibule leads directly into two laboratory 
 rooms, and, by a hallway, communicates with the large, well- 
 lighted library and the rooms of the director. The aquarium 
 room has, for convenience, been placed in a small adjacent 
 building. The director of this station is Professor Hoek, and 
 the President of the Society is Professor Hubrecht. 
 
 IV. — Naples. 
 
 The Stazione Zoologica at Naples during the past twenty 
 years has earned its reputation as the center of marine bio- 
 logical work. Its success has been aided by the richness of 
 the fauna of the Gulf, but is due in no small degree to 
 careful and energetic administration. The director of the 
 station. Professor Dohrn, deserves no little gratitude from 
 every worker in science for his untiring efforts in securing its 
 foundation and systematic management. Partly by his private 
 generosity and partly by the financial support he obtained, the 
 original or eastern building was constructed. Its annual main- 
 tenance was next assured by the aid he obtained throughout 
 (mainly) Germany and Austria. By the leasing of work tables 
 to be used by the representatives of universities, a sufficient 
 income was maintained to carry on the work of the station 
 most efficiently. A gift by the German government of 
 a small steam launch added not a little to the collecting 
 facilities. 
 
 Attractiveness is one of the striking features of the Naples 
 station. It has nothing of the dusty, uncomfortable, gloomy 
 air of the average university laboratory. Its situation is one 
 of the brightest ; it has the gulf directly in front, about it the 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 
 
 225 
 
 city gardens, rich in palm trees and holm oaks. The building 
 itself rises out of beds of century plant and cactus like a white 
 palace ; the fashionable drive-way alone separates it from the 
 water's edge. In full view is the Island of Capri, to the east- 
 ward is Vesuvius, — a bright and restful picture to one who 
 leaves his work for a five minutes' stroll on the long, covered 
 balcony which looks out over the sea. 
 
 The Stazione Zoologica at Naples. 
 (May, 1892.) 
 
 The student, in fact, knows the Naples station before he 
 visits it, although he can hardly anticipate the busy and 
 profitable stay that there awaits him. He has received the 
 circular from the Secretary of the laboratory while perhaps in 
 Germany, when he secured the privilege of a table. He is 
 told of the best method of reaching Naples, the precautions he 
 must take to secure the safe arrival of his boxes and instru- 
 
2 26 BIOLOGICAL LECTURES. 
 
 ments. He is told to send directions as to the material he 
 desires for study ; he is notified of the supplies which will be 
 allowed him, and of the matters of hotels, lodging, and bank- 
 ing, necessary even to a biologist. At the first sight of the 
 building he is impressed most favorably, and it is not long 
 before he comes to look upon his work-place as his particular 
 home, open to him day, night, and holiday. He likes the gen- 
 eral air of quietness — in no little way significant of system in 
 every branch of the station's organization ; his neighbors are 
 friendly, and he feels that even the attendants are willing, 
 often anxious to give him help. 
 
 At present the station at Naples consists of two buildings ; 
 the first, shown in the foreground in the accompanying figure, 
 is the older, the main building ; behind it is the newly built 
 physiological laboratory. In the basement of the main 
 building is the aquarium, well managed, open to the public, and 
 eagerly visited. Passing into the aquarium room from the 
 main entrance, one descends into a long, dark, concreted room, 
 lighted only through wall-tanks brilliant on every side with the 
 varied forms of life. There are in all about two dozen large 
 aquaria embedded in the walls of the sides and of the main 
 partition of the room. The water is clear and blue. The 
 background in each aquaria, built of rock work, catches the 
 light from above and throws in clear relief the living inmates. 
 The first tank will perhaps be full of star fish and sea urchins, 
 bright in color, often clustered on the glass each with a dim 
 halo of pale, thread-like feet. In the background may be a 
 living clump of crinoids, flowering out like a garden of bright- 
 colored lilies. In a neighboring tank, rich with dark-colored 
 seaweeds, will be a group of flying gurnards, reddish and 
 brilliantly spotted, feeling cautiously along the bottom with the 
 finger-like rays of their wing-shaped fins. Here, too, may be 
 squids, delicate and fish-like, swimming timidly up and down ; 
 perhaps a series of huge triton snails below amid clustered 
 eggs of cuttle fish. In another tank would be a bank of sea 
 anemones with all the large and brilliant forms common to 
 southern waters. Here maybe corals in the background and a 
 forest of sea fans in orange, red and yellow, with a precious 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 227 
 
 fringe of pink coral, flowering out in yellow star-like polyps. 
 There may again be a host of ascidians, delicate, transparent, 
 solitary forms, the lanky Ciona, the brilliantly crimson Cynthia 
 and huge masses of varied, compound forms. Swimming in 
 the water may be chains of Salpa and occasionally a number 
 of Amphioxus, the latter, as they from time to time emerge 
 from the sandy bottom, flurry about as if with sudden fright, 
 quickly to disappear. Variety is one of the striking characters 
 of neighboring tanks. In one, brilliant forms will outvie the 
 colors of their neighbors ; in another, the least obtrusive 
 mimicry will be exemplified. The stranger has often to examine 
 carefully before, in the seemingly empty tank, he can determine 
 on every side the living forms whose color characters screen 
 them effectively. Thus he will see sand-colored rays and 
 flounders, the upturned eyes of the curious star-gazer almost 
 buried in the sand, a series of mottled crustaceans wedged in 
 a rocky background, an occasional crab wandering cautiously 
 about, carrying a protective garden of seaweeds on his broad 
 back ; odd sea horses posing motionless mimicing the rough 
 stems of the seaweeds. In the larger tank sea turtles float 
 sluggishly about ; and coiled amid broken earthern jars are 
 the sharp-jawed murrys, suggestive of Roman dinners and of 
 the cultural experiments of Pollio. Aeration in the aquaria 
 is secured effectively by streams of air which are forced in at 
 the water surface and subdivide into bright clouds of minute 
 silvery bubbles. The tanks are cared for from the rear passage- 
 ways ; attendants are never seen by visitors, and constant 
 attention has given the aquaria a well earned reputation. Well 
 illustrated catalogues in French, German, English and Italian 
 enable the stranger to better appreciate the aquarium. 
 
 To the remainder of the building strangers are not admitted. 
 A marble stairway leads from the door of the aquarium to a 
 loggia which opens into the territory of the students. A long 
 pathway of grating extends across the open center of the 
 building, — whose skylight top admits the light to the aquarium 
 below. On the one hand is the main laboratory room, on 
 the other the library and separate rooms intended for more 
 fortunate investigators. One enters the main laboratory, passes 
 
228 BIOLOGICAL LECTURES. 
 
 a wall of student aquaria and sees a series of alcoves formed 
 by low partitions, each work-place with its occupant, his 
 apparatus, his books, his jars — altogether often a picture not 
 of the utmost tidiness. A small iron staircase leads to a 
 gallery which gives a second tier of work places and doubles 
 
 The Library of the Naples Station. 
 (June, 1892.) 
 
 the working capacity of the room. Here, side by side, will be 
 representative workers from universities of every country of 
 Europe. 
 
 The library room adds not a little to the attractiveness of 
 the Naples station. It is a long room, and, as shown in the 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 229 
 
 figure, is adorned with frescoes in a truly Italian style. It 
 looks out into a long loggia with view of the sea and Capri, 
 where the student is wont to retire in after luncheon hour 
 with easy-chair and book. The working library is of the 
 best and is sure to contain the results of the most recent 
 researches. The desk shown in the figure is one on which 
 each day is to be found the latest publications. In the 
 upper pigeon-holes are the cards prepared for each investigator 
 on his advent to Naples ; with these he replaces the volumes 
 which he has taken to his work place. Every division of the 
 laboratory is carefully organized and is under the charge of a 
 special assistant. Prof. Hugo Eisig, the assistant director, has 
 taken the welfare of each student under his personal charge, 
 and it is not until the end of his stay that the visitor recognizes 
 how much has been done for him. 
 
 There is no more interesting department of the station 
 than that of receiving and distributing the material. Its 
 headquarters is in the basement of the physiological laboratory, 
 and here Cav. Lo Bianco is to be found busy with his aids 
 and attendants amid a confusion of pans, dishes and tables, 
 encountering the Neapolitan fishermen who have learned to 
 bring all of their rarities to the station. The specimens are 
 quickly assorted by the attendants ; such as may not be needed 
 for the immediate use of the investigators are retained and 
 prepared for shipment to the universities throughout Europe. 
 The methods of killing and preserving marine forms have been 
 made a most careful study by Lo Bianco, and his preparations 
 have gained him a world-wide reputation. Delicate jelly-fish 
 are to be preserved distended, and the frail forms of almost 
 every group have been successfully fixed. The methods of the 
 Naples station were kept secret only until it was possible to 
 verify and improve them, as it was not deemed desirable to 
 have them given out in a scattered way by a number of 
 investigators. 
 
 Lo Bianco has made the best use of the rich material passing 
 daily through his department, and has been enabled to prepare 
 the most valuable records as to spawning seasons and as to 
 larval conditions. He knows the exact station of the rarest 
 
230 . BIOLOGICAL LECTURES. 
 
 species, and it seems to the stranger a difficult matter to ask 
 for a form which cannot be directly or indirectly procured. It 
 adds no little to the time saving of the student to find each 
 morning at his work place the fresh material which he has 
 ordered the day before, and there is usually an embarrassment 
 rather than a dearth of riches. 
 
 A collecting trip often occurs as a pleasant change from the 
 indoor work of the investigator. An excursion to Capri may 
 be planned ; the launch will be brought to the quay near the 
 station and the party will embark. The collecting tubs are 
 soon scattered over the deck and filled with the dredge 
 contents. Some of the passengers are quickly at work sorting 
 out their material, one seizing brachiopods, another compound 
 ascidians, another sponges. Others will wait until the surface 
 nets have been brought in and the contents turned into jars. 
 All will depend upon Lo Bianco as an appellate judge in 
 matters of identification. 
 
 Many Americans have availed themselves of the privileges 
 of Naples and the former lack of support of an American 
 table needs little comment. Of those who have hitherto 
 visited Naples more than three-quarters have been indebted 
 to the courtesies of German universities. At present of the 
 two American tables one is supported by the Smithsonian 
 Institution, the other by gift of Mr. Agassiz. 
 
 The entire Italian coast is so rich in its fauna that it is due, 
 perhaps only to the greatness of Naples, that so few stations 
 have been founded. Messina has its interesting laboratory well 
 known in the work of its director. Professor Kleinenberg. The 
 Adriatic, especially favorable for collecting, has at Istria a 
 small station on the Dalmatian coast, and at Trieste is the 
 Austrian station. 
 
 V. — Trieste. 
 
 Trieste possesses one of the oldest and most honored of 
 Marine Observatories, although its station is but small in 
 comparison with that of Naples, Plymouth or Roscoff. Its 
 work has in no small way been limited by scanty income; it 
 has offered the investigator fewer advantages and has there- 
 
MARINE BIOLOGICAL STATIONS 
 
 OF EUROPE. 231 
 
 fore become outrivalled. During a greater part of the year it 
 is but little more than the supply station of the University of 
 Vienna, providing fresh material for the students of Professor 
 Claus. Its percentage of foreign investigators appears small; 
 its visitors are usually from Vienna and of its university. 
 
 Trieste is in itself a small but busy city, growing in active 
 commerce. Its quays are massive and bristle with odd-shaped 
 shipping of the Eastern Mediterranean. Its deep and basin- 
 
 The Station at Trieste. 
 
 like harbor affords a collecting ground as rich as the Gulf of 
 Naples. 
 
 The station has been located at a quiet corner of the harbor, 
 just beyond the edge of the lighthouse. Its building is some- 
 what chalet-like, situated on a small, well-wooded knoll, as seen 
 in the adjacent figure. About it are trellis-covered grounds 
 enclosed by high walls, and separated from the harbor only by 
 the main roadway of the quays. One enters the laboratorv 
 
232 
 
 BIOLOGIC A L LEC TURKS. 
 
 garden through a large gateway and passes into a court-yard 
 whose outhouses disclose the pails and nets of the marine 
 laboratory. Perhaps an attendant will here be sorting out the 
 plunder which a bronze-legged fisherman has just brought in. 
 
 A library and the rooms of the director, Dr. Graeffe, are 
 close by the entrance of the building. In the basement is the 
 aquarium room, — somewhat dark and cellar-like ; its tanks 
 small and shallow, their inmates representing especially stages 
 of Adriatic hydroids and anthozoans. On the second story are 
 the investigators' rooms, — large, well-lighted, looking out over 
 garden and sea. Near by is a museum of local fauna, rich in 
 crustaceans and in the larv^al stages of Adriatic fishes. 
 
 VI-IX. — Germany, Norway, Sweden, Russia. 
 
 The German universities have contributed to such a degree 
 to the building up of the station at Naples that they have 
 hitherto been little able to avail themselves of the more con- 
 venient but less favorable region of German coasts. The 
 collecting resources of the North Sea and of the Baltic have 
 perhaps been not sufficiently rich to warrant the establish- 
 ment of a central station. On the side of the Baltic, the 
 University of Kiel, directly on the coast, may itself be regarded 
 as a marine station. At present the interest in founding local 
 marine laboratories has, however, become stronger. The newly 
 acquired Heligoland has become the seat of a well-equipped 
 Governn%ental station. The island has been long known as 
 most favorable in collecting regions, and its position in the 
 midst of the North Sea fisheries gives it especial importance. 
 
 Its present building is three-storied, of stone, situated near 
 the water on the Jutland side of the island. Work places are 
 provided for four investigators. Its director is Dr. F. Heinke ; 
 his assistants, Drs. Hartlaub, Ehrenbaum, and Kuckuck. The 
 Istrian laboratory at Rovigno, a favorable collecting point on 
 the Adriatic, is to be included among the German stations It 
 was destined by Dr. Hermes, its founder, as the supply depot 
 of the Berlin aquarium. Of its work places, two have been 
 rented by the Prussian government, and a third is to be 
 obtained by application to Dr. Hermes. 
 
MARINE BIOLOGICAL STATIONS OF EUROPE. 233 
 
 Norway like Germany is strengthening its interest in local 
 marine laboratories. Two permanent stations have quite 
 recently been established, one at Bergen, — the other at 
 Drobak, a dozen miles south of Christiana. The former is 
 the larger, a dependency of the Museum of Bergen. It is 
 under the charge of Dr. Brunchorst, — to whom its founda- 
 tion is due, — and Drs. Appellof and Hansen. Its two- 
 storied villa-like building provides work places for eight 
 investigators : a well maintained aquarium on the first floor 
 is open to the public. The second and smaller station is 
 devoted almost exclusively to research in morphology. It 
 is a dependency of the University of Christiana and is under 
 the directorship of one of its professors, Dr. Johan Hjort. 
 With the richest collecting resources these new stations may 
 naturally be expected to yield most important results. 
 
 The Swedish station has long been associated with the work 
 of its late director, Professor Loven. It is situated on the west 
 coast near the city of Gothenburg. Its three original buildings, 
 a laboratory and two dwelling-houses, were constructed about 
 fifteen years ago by a gift of Dr. Regnell of Stockholm. The 
 laboratory is a wooden building well furnished with aquaria, 
 provided in its second story with separate work places for 
 investigators. It is at present maintained by governmental 
 subsidy ; its recently appointed director is Dr. Hjalmar Theel 
 of the State Museum at Stockholm. Its students are mainly 
 from the University of Upsala ; up to the present time 
 foreigners have not been admitted. 
 
 Russians have ever been most enthusiatic in marine research, 
 and their investigators are to be found in nearly every marine 
 station of Europe. The French laboratory on the Mediterranean 
 at Ville-Franche is essentially supported by Russians. At 
 Naples they are often next in numbers to the Germans and 
 Austrians. The learned societies of Moscow and St. Petersburg 
 have contributed in no little way to marine research. The 
 station at Sebastopol, on the Black Sea, has become permanent, 
 possessing an assured income. That near the Convent Solovet- 
 sky, on the White Sea, though small, is of marked importance. 
 It is already in its thirteenth year. Professor Wagner, of 
 
234 BIOLOGICAL LECTURES. 
 
 St. Petersburg, has been its most earnest promoter as well as 
 constant visitor. He in fact caused the Superior of the Convent 
 to become interested in its work and secured a permanent 
 building by the Convent's grant ; he was then enabled by an 
 appropriation from the government to provide an equipment. 
 Its annual maintenance is due to the Society of Naturalists of 
 St. Petersburg. The matter of the appointment of a perma- 
 nent director for the summer months is now being agitated by 
 him. The station Solovetskaia is said to possess the richest 
 collecting region of the Russian coasts. It is certainly the 
 only laboratory which has at its command a truly Arctic 
 fauna. 
 
APPENDIX 
 
 THE WORK AND THE AIMS OF THE MARINE 
 BIOLOGICAL LABORATORY. 
 
 C. O. WHITMAN. 
 
 The Marine Biological laboratory of Wood's HoU combines the 
 functions of a research laboratory with those of a school. While it 
 differs thus from the marine laboratories of Europe, it may also 
 be said to take a somewhat exceptional position among American 
 sea-side laboratories, both in its organization and its scope of work. 
 It supplements the work of the biological departments of the schools 
 and colleges, and at the same time serves as a scientific centre for 
 investigation. It provides not only for general courses of study 
 in zoology and botany, but also — what is of quite exceptional 
 importance -^-T^^r technical training preparatory to im'estigation and 
 special instruction and guidance for beginners in investigation. It is 
 this advanced instruction that makes the school tributary to the side 
 of original investigation, in which the work and the aims of the 
 laboratory centre. Research is the dominating function of the 
 laboratory ; instruction is merely a means to this end. 
 
 Although the laboratory is wholly free from government control, it 
 is truly national in organization and aims. It is governed by a board 
 of trustees, on which the leading colleges and universities of the 
 country are represented. Its officers of instruction and investigation 
 have been drawn from no less than fifteen educational institutions, 
 and its membership has extended to one hundred and thirty-one 
 colleges, universities, seminaries, academies, schools and laboratories. 
 
 From the beginning of this undertaking it has been clearly seen 
 that the realization of its aims depended largely on securing the general 
 support of the colleges, and the active cooperation of all who were 
 interested in the foundation of a national marine station. To secure 
 these ends the clearly defined aims of the laboratory were made 
 
236 APPENDIX, 
 
 known as widely as possible, and the invitation for united action was 
 extended to institutions and investigators throughout the country. 
 The result is that during the last session the following eighteen 
 institutions subscribed for rooms and tables : 
 
 Bowdoin College, Missouri Botanical Garden, 
 
 Brown University, Mt. Holyoke College, 
 
 Bryn Mawr College, Nortliwestern University, 
 
 Chicago University, Princeton College, 
 
 Cincinnati University, Rochester University, 
 
 Columbia College, Smith College, 
 
 Hamilton College, Vassar College, 
 Massachusetts Institute of Technology, Wellesley College, 
 
 Miami University, Williams College. 
 
 To this list may be added the American Association for the 
 Advancement of Science, as its subscription for next year has been 
 announced. 
 
 During the same session forty-one investigators were at work at 
 the laboratory, thirty-three of whom occupied private rooms, while 
 the rest had tables in the general laboratories for beginners in 
 investigation. The whole number of students and investigators 
 was one hundred and eleven, representing seventy-two colleges, 
 universities and schools, and no less than seventeen states. 
 
 To those who by word and example have encouraged cooperation, 
 this record will certainly be gratifying ; and perhaps it will be 
 accepted by all as an assurance that good-will and united effort have 
 not been fruitless. For six years the Marine Biological Laboratory 
 has stood for the first and the only cooperative organization in the 
 interest of Marine Biology in America. Gradually it has come to 
 ba understood that the creation of such an organization was a step 
 in the right direction. An important need was felt and there was 
 but one way to meet it. That way was cooparative action. It was 
 clearly seen that the Government could not be expected to undertake 
 the work. An independent foundation was needed and one removed 
 from all danger of sectional domination. The effort to reach such 
 a foundation through a cooperative organization was no menace to 
 any existing laboratory. Time has shown that the laboratory was 
 not an unneeded creation. It is no longer necessary to search " the 
 by-ways and hedges " for investigators, but our buildings have to 
 be extended every year or two in order to provide room for them. 
 Each summer now sees a conjiress of biolo2:ists assembled at the 
 
APPENDIX. 
 
 237 
 
 laboratory, and every new comer learns the value of scientific 
 fellowship. 
 
 Had the Marine Biological Laboratory done nothing beyond the 
 creation of a sound cooperative organization, it would at least have 
 fulfilled one all-essential part of its mission. That it has done, and 
 so effectively that it is not likely to be undone. 
 
 The record of the laboratory as a scientific station is shown in the 
 following list of works : 
 
 PAPERS PUBLISHED. 
 H. Ayers. 
 
 A Contribution to the Morphology of the Vertebrate Head. ZooL 
 
 Anz., 1890. 
 On the Origin of the Internal Ear and the Functions of the Semi- 
 circular Canals and Cochlea. Milwaukee, 1890. 
 Concerning Vertebrate Cephalogenesis. Joiirn.of Morph.^YV, 1890. 
 The Ear of Man ; its Past, its Present, and its Future. Btoi. 
 
 Lectures, I, Boston, 1890. 
 Die Membrana tectoria, was sie ist, und die Membrana basilaris, was 
 
 sie verrichtet. Anai. Anz.^ VI, 1891. 
 A Contribution to the Morphology of the Vertebrate Ear, with a 
 
 Reconsideration of its Functions. Journ. of Morph., VI, Nos. 
 
 I and 2, 1892. 
 The Macula Neglecta again. Anat. Anz.^ VIII, 1893. 
 Ueber das peripherische Verhalten der Gehornerven und den 
 
 Werth der Haarzellen des Gehororgans. Anat. Anz., VIII, 
 
 1893. 
 The Auditory or Hair-cells of the Ear and their Relations to the 
 
 Auditory Nerve. , Journ. of Morph., VIII, 1893. 
 Bdellostoma dombey. Biol. Lectures^ II, 1893. 
 
 H. C. BuMPUS. 
 
 The Embryology of the American Lobster. Journ. of Morph., 
 
 V, 1 891. 
 A New Method in the Use of Celloidin. Atner. Nat., 1892. 
 A Laboratory Course in Invertebrate Zoology. Providence, 1892. 
 
 Cornelia M. Clapp. 
 
 Some Points in the Development of the Toad-fish (Batrachus Tau). 
 Journ. of Morph., V, 1891. 
 
 E. G. CONKLIX. 
 
 ' The Cleavage of the Ovum in Crepidula fomicata. ZooL Anz.y 
 No. 391. 
 The Fertilization of the Ovum. Biol. Lectures, II, 1893. 
 
238 APPENDIX. 
 
 Bradley M. Davis. 
 
 Development of the Frond of Champia parvula, Harv., from the 
 Carpospore. Annals of Botany^ Vol. VIj No. 24, Dec, 
 1892. 
 
 E. G. Gardiner. 
 
 Weismann and Maupas, on the Origin of Death. Biol. Lectures 
 1,1890. 
 
 J. E. Humphrey. 
 
 Notes on Technique. Botanical Gazette., XV, 7, 1 890. 
 
 E. O. Jordan. 
 
 The Habits and Development of the Newt. Journ. of Morph.^ 
 Vol. VII, No. 2, 1893. 
 
 J. S. KiNGSLEY. 
 
 The Ontogeny of Limulus. Preliminary. Zool. Anz., No. 345, 
 
 1890, and Amer. Nat.^ 1890. 
 The Embryology of Limulus. Jotirn. of Morph., Vol. VII, No. i, 
 
 and Vol. VIII, No. 2. 
 The Marine Biological Laboratory. Popular Science Monthly, 
 
 Sept., 1892. 
 
 Frederic S. Lee. 
 
 Ueber den Gleichgewichtssinn. Centralblatt fiir Physiologie., 1892. 
 
 Wm. Libbey, Jr. 
 
 The Study of Ocean Temperatures and Currents. Biol. Lectures., 
 I, 1890. 
 
 F. R. Lillie. 
 
 Preliminary Account of the Embryology of Unio complanata. 
 fourn. of Morph., 'Vl\l,l>^o. T,, i^c)2,. 
 
 Wm. a. Locy. 
 
 The. Formation of the Medullary Groove, and Some Other Features 
 
 of Embryonic Development in the Elasmobranchs. Journ. of 
 
 i^^r/y^.. Vol. VIII, No. 2. 
 The Optic Vesicles in Elasmobranchs and their Serial Relation to 
 
 Other Structures on the Cephalic Plate. Journ. of Morph.., 
 
 Vol. IX, No. I, 1893. 
 
 Jacques Loeb. 
 
 Ueber kiinstliche Umwandlung positiv heliotropischer Thiere in 
 
 negativ heliotropische und umgekehrt. Pfluger''s Archiv fur 
 
 Physiologic, Bd. LIV. 
 A Contribution to the Physiology of Coloration in Animals. Journ. 
 
 ^/J/^r/>^., Vol. VIII, 1893. 
 Investigations in Physiological Morphology, 3. Journ. of Morph., 
 
 Vol. VII. 
 
APPENDIX. 239 
 
 Ueber die Entwicklung von Fischembryonen ohne Kreislauf. 
 
 Pfluger's Archiv, Bd. LV. 
 On some Facts and Principles of Physiological Morphology. Biol. 
 
 Lectures, II, 1893. 
 
 J. MUIRHEAD MACFARLANE. 
 
 Irrito-Contractility in Plants. Biol. Lectures, II, 1893. 
 E. L. Mark. 
 
 Polychoerus caudatus, nov. gen. et nov. spec. Festschrift zum 
 siebenzigste7i Geburtstage Rudolf Letickarts, Leipzig, 1892.. 
 
 T. H. Morgan. 
 
 The. Relationships of the Sea Spiders. Biol. Lectures, I, 1892. 
 
 A Contribution to the Ontogeny and Phylogeny of the Pycnogonids. 
 
 Johns Hopkins Studies, Vol. V, No. i, 1891. 
 The Test-cells of the Ascidians. Journ. of M or ph., V, 1891. 
 The Growth and Metamorphosis of Tornaria. Journ. of Morph., 
 
 Vol. V, No. 2, 1892. 
 Spiral Modification of Metamerism. Journ. of Morph., Vol. VII, 
 
 No. 2, 1892. 
 Balanoglossus and Tornaria of New England. Zool. Anz., No. 
 
 407, 1892. 
 Experimental Studies on Teleost Eggs. Anat. Anz., Vol. VIII, 
 
 No. 2, 1893. 
 
 J. P. McMURRICH. 
 
 Contributions on the Morphology of the Actinozoa. (2) The 
 
 Embryology of the Hexactiniae. Journ. of Morph., Vol. IV, 
 
 1890. 
 Contributions on the Morphology of the Actinozoa. (3) The Phylo- 
 geny of the Actinozoa. Journ. of M or ph., Vol. V, 1891. 
 The Development of Cyanea arctica. Amer. Nat., XXV. 
 The Gastrasa Theory and its Successors. Biol. Lectures, I, 1890. 
 The Formation of the Germ-layers in the Isopod Crustacea. Zool. 
 
 Anz., No. 397, 1892. 
 Julia B. Platt. 
 
 Contribution to the Morphology of the Vertebrate Head. Journ. of 
 
 Morph., Vol. V, 1 89 1. 
 The Anterior Head-cavities of Acanthias. Zool. Anz., No. 344, 
 
 May, 1S90. 
 Further Contributions to the "Morphology of the A'ertebrate Head. 
 
 Atiat. Anz., Vol. VI, pp. 251. 
 
 H, F. OSBORX. 
 
 Evolution and Heredity. Biol. Lectures, \, i%C)0. 
 John A. Ryder. 
 
 Dynamics in Evolution. Biol. Lectures, II, 1893. 
 
240 
 
 APPENDIX. 
 
 W. A. Setchell. 
 
 Preliminary Notes on the Five Species of Doassansia Cornu. Proc. 
 
 Amer. Acad., XXVI, 1891. 
 An Examination of the Species of the Genus Doassansia Cornu. 
 Annals of Botany, VI, 1892. 
 
 Louise B. Wallace. 
 
 The Structure and Development of the Axillary Gland of Batrachus. 
 Journ. of Morph., Vol. VIII, No. 3, 1893. 
 
 S. Watase. 
 
 On Caryokinesis. Biol. Lectures, I, 1890. 
 
 The Origin of the Sertoli's Cell (abstract). Amer. Nat., May, 
 
 1892. 
 On the Significance of Spermatogenesis (abstract). Amer. Nat., 
 
 July, 1892. 
 On the Phenomena of Sex-Differentiation, fourn. of Morph., 
 
 Vol. VI, No. 3, 1892. 
 Homology of the Centrosome. fourn. of Morph., Vol. VIII, No. 
 
 2, 1893. 
 
 Herbert J. Webber. 
 
 On the Antheridia of Lomentaria. Annals of Botany, Vol. V, 
 April, 1 891. 
 
 Wm. M. Wheeler. 
 
 A Contribution to Insect Embryology, fourn. of Morph., Vol. 
 VIII, No. I, 1893. 
 
 W. P. Wilson. 
 
 The Influence of External Conditions on Plant Life. Biol. Lectures 
 11, 1893. 
 
 E. B. Wilson. 
 
 Some Problems of Annelid Morphology. Biol. Lectures, I, 1890. 
 Origin of the Mesoblast-Bands in Annelids, fourn. of Morph., 
 
 Vol. IV, No. 2, 1890. 
 The Cell-lineage of Nereis. A Contribution to the Cytogeny of 
 
 the Annelid Body, fourn. of Morph., Vol. VI, 1892. 
 The Mosaic Theory of Development. Biol. Lectures, II, 1893. 
 
 C. O. Whitman. 
 
 Specialization and Organization. Biol. Lectures, I, 1890. 
 
 The Naturalist's Occupation. Biol. Lectures, I, 1890. " 
 
 The Inadequacy of the Cell-theory of Development, fourn. of 
 
 Morph., Vol. VIII, No. 3, and Biol. Lectures, II, 1893. • 
 A Marine Observatory. Popular Science Monthly, Feb., 1893. 
 A Marine Observatory the Prime Need of American Biology. 
 
 Atlantic Monthly, June, 1893. 
 
APPENDIX. 241 
 
 The Work and Aims of the Marine Biological Laboratory. Biol. 
 
 Lectures., II, 1893. 
 The Echinoderm Egg and the Theory of Isotropism. Journ. of 
 
 Morph., Vol. IX, 1893. 
 The Metamerism of Clepsine. Festschrift zum siebenzigsten 
 
 Geburtstage Rudolf Leuckarts., Leipzig, 1892. 
 A Sketch of the Structure and Development of the Eye of 
 
 Clepsine. SpengeVs Zool. fahrb., VI, 1893. 
 
 PAPERS IN PRESS. 
 
 H. A VERS. 
 
 The Relations of the Peripheral Territory of the Auditory Nerve 
 
 as shown by Methylen-blue. 
 Certain Facts and Theories in Modern Neurology. 
 
 E. G. CONKLIN. 
 
 The Embryology of Crepidula. Part I. History of the Cleavage. 
 
 The Dynamics of Fertilization and Cleavage. 
 Elizabeth E. Bickford. 
 
 Experiments on Regeneration and Heteromorphosis in Tubularian 
 Hydroids. 
 Martha Bunting. 
 
 The Origin of the Sex-cells in Hydractinia and Podocoryne and the 
 Development of Hydractinia. fourn. of M or ph.., Vol. IX, 1894. 
 Elizabeth Cooke. 
 
 On the Osmotic Qualities of the Muscles of Marine Animals. 
 
 E. G. Gardiner. 
 
 Early Development of Polychoerus caudatus. 
 Ida H. Hyde. 
 
 The Nervous Mechanism of Respiratory Movements in Limulus. 
 
 F. S. Lee. 
 
 A Study of the Sense of Equilibrium in Fishes. I. fourn. of 
 Physiology. 
 
 D. J. LiNGLE. 
 
 On the Reversal of the Direction of the Contraction of the Heart 
 in Ascidians. 
 
 Jacques Loeb. 
 
 Ueber das Sauerstoffbediirfniss des Embryo in verschiedenen 
 
 Entwicklungsstadien. 
 Ueber die Herstellung zusammengewachsener Doppelt- und Mehr- 
 
 fachembr)-'onen by Seeigeln. 
 Ueber die Bedeutung von Gehirn und Auge fiir die Reactionen 
 
 niederer Thiere auf Licht. 
 
242 APPENDIX. 
 
 A. D. Morrill. 
 
 Pectoral Appendages and their Innervation in Prionotus. 
 Julia B. Platt. 
 
 The Ontogenetic Differentiation of the Ectoderm in Necturus. 
 (Preliminary Notice.) 
 Mary Schively. 
 
 Ueber den Einfluss der Concentration des Seewassers auf die 
 Herzthatigheit einiger Seethiere. Pfliiger's Archiv fiir 
 Physiologic. 
 
 S. Watase. 
 
 On the Nature of Cell-Organization. Biol. Lectures, Vol. II, 1894. 
 
 Wm. M. Wheeler. 
 
 Syncoelidium pellucidum, a New Marine Triclad. Journ. of Morph. 
 Planocera inguilina, a Polyclad Inhabiting the Branchial Chamber 
 of Sycotypus Canaliculatus Gill. Journ. of Morph.., Vol. IX, 
 1894. 
 
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