St Or ee ute o ae Hi RO AAS He tpn Mette ‘ Se 4 iy ue o fy OC ie) OO Reeth 0 oe ae Ce 0 Pp be ms ie patra A * POOR CA AR Rr ee rire ee) PAocireeietas Se tt On ps arlvnrel dels Cee aah tt Ott aN ry Ca ats s Sree AMER, vest ole yy Gi rots - Cornell Aniversity Library BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henry W. Sage 1891 a eee THE CAMBRIDGE NATURAL HISTORY EDITED BY S. F. HARMER, M.A., Fellow of King’s College, Cambridge ; Super- intendent of the University Museum of Zoology AND A. E. SHIPLEY, M.A., Fellow of Christ’s College, Cambridge ; University Lecturer on the Morphology of Invertebrates VOLUME V ‘09 xy wey e yy +wopuoT ¥ 206 SL Gb 20€ Pell 20 SI of ‘dem ay} uo payesiput 30U SI 31 ‘[nJJQnop A1aA si saidads uesyEUINS sy) Jo aduaIsIxa oY) SY ‘dew ay} uo payesipur SUSIUT ‘nag Ul pure ‘sayeA, YING MAN UT ‘eOIDIA Ul puNoy usaq sey Sujodi4ag 1X2} 8Y) Ul pauotUaM sade{d ay} 0} UOTIppe UL ' Value 2081 259! 2OSt oSEl O21 2G0l »06 oh 009 ot 20f 2S! <0 g Reese 06 sal Reval “SNLivdldad JO NOILAGIYLSIO TWOlHdY YLSNT OL dVW es “at PERIPATUS By ADAm SEDGWICK, M.A., F.R.S., Fellow and Lecturer of Trinity College, Cambridge MYRIAPODS By F. G. Stncuatr, M.A., Trinity College, Cambridge INSECTS PART I. Introduction, Aptera, Orthoptera, Neuroptera, and a portion of Hymenoptera (Sessiliventres and Parasitica) By Davip SHarpP, M.A. (Cantab.), M.B. (Edinb.), F.R.S. London MACMILLAN AND CO. AND NEW YORK 1895 ow All rights reserved Ob ‘an 46 O17 1845 5 Cit \ Beas A.\S84S4 ‘Creavit in ccelo Angelos, in terra vermiculos: non superior in illis, non inferior in istis. Sicut enim nulla manus Angelum, ita nulla posset creare vermiculum.”—SainT AUGUSTINE, Liber soltloquiorum animae ad Dewm, Caput TX. CONTENTS PAGE SCHEME OF THE CLASSIFICATION: ADOPTED IN THIS Book 3 ‘ ix PERIPATUS CHAPTER I InTRODUCTION— EXTERNAL Fratures— Hasits —BreEepInc— ANATOMY— ALIMENTARY CANAL—NERVous SystEM—THE Bopy WALL—THE TRa- CHEAL SysTEM—TuHE MuscuLar SysrEM—THE VASCULAR SYSTEM—THE Bopy Caviry— NrpuHripiA — GENERATIVE ORGANS — DEVELOPMENT— SYNOPSIS OF THE SpEcIES—SUMMARY OF DISTRIBUTION . : ; , 3 MYRIAPODA CHAPTER II INTRODUCTION — HaBiTs — CLASSIFICATION — STRUCTURE — CHILOGNATHA— CHILOPODA — SCHIZOTARSIA — SYMPHYLA—PAUROPODA—EMBRYOLOGY— PALAEONTOLOGY F ; : : é 7 . 29 INSECTA CHAPTER III CHARACTERISTIC FraTures oF Insect LiFe—SocraAL INsEcTs—DEFINITION OF THE CLAss INsecrA—CoMPOSITION oF INSECT SKELETON—NUMBER OF SrcMEeNnTsS—NATURE OF SCLERITES—HEAD—APPENDAGES OF THE MouTu —Evyes—Tuorax—EnToTHorAx—Lecs— Wincs — ABDOMEN OR HIND Bopy—SrrracLEs—SyYsTEMATIC ORIENTATION ‘ . 88 v1 CONTENTS CHAPTER IV ARRANGEMENT OF INTERNAL ORGANS—MuscLes—NERvVoUS SYSTEM—GANG- LIONIC CHAIN—BRAIN—SENSE - ORGANS—ALIMENTARY CANAL —MAL- PIGHIAN Tubes — ResrrraTION — TRACHEAL SysTEM— FUNCTION OF ReEsPIRATION—Bioop or BLoop-cuyLtE—DorsaL VEsseL on HEart— Fat-BopyY—OvaRIES—TESTES— PARTHENOGENESIS—GLANDS , CHAPTER V DEVELOPMENT EMBRYOLOGY — Ecos — MicropyLes — ForMATION OF EMBRYO — VENTRAL PLuatTE—EcropERM AND ENDODERM—SEGMENTATION—LATER STAGES— Direct OBSERVATION oF EmMBRYO—METAMORPHOSIS—COMPLETE AND IxcoMPLETE — InsTAn — HYPERMETAMORPHOSIS — METAMORPHOSIS OF INTERNAL OnGANS—INTEGUMENT—METAMORPHOSIS OF BLOWFLY—HIs- ToLtysis—ImacinaL Discs—PuyYsIoLocy or METAMORPHOSIS—EcDYsIs . CHAPTER VI CLASSIFICATION — THE NINE OrpeERS oF INsecTSs— THEIR CHARACTERS— PackARD’s ARRANGEMENT—BRAUER’S CLASSIFICATION—CLASSIFICATIONS BASED ON METAMORPHOSIS — SUPER-ORDERS— THE SUBDIVISIONS OF ORDERS CHAPTER VII THe Ornprr APTERA—DEFINITION—CHIEF CHARACTERISTICS—THYSANURA— CamMpopEA—JApPYX — Macnitis — LerismA — Diversity oF INTERNAL STRUCTURE IN THYSANURA — EcTorROPHI AND ENTOTROPHI — COLLEM- BOLA—LIPURIDAE—PopunIDAE — SMYNTHURIDAE—THE Sprinc — THE VENTRAL TUBE—ABDOMINAL APPENDAGES—PROSTEMMATIC ORGAN— TRACHEAL SystrM— ANURIDA MARITIMA—COLLEMBOLA ON SNow— Lirr-Historirs OF CoLLEMBOLA—FossIL APTERA—APTERYGOGENEA— ANTIQUITY AND DISTRIBUTION OF CAMPODEA CHAPTER VIII ORTHOPTERA—FORFICULIDAE, EARWIGS—HEMIMERIDAE PAGE 143 171 180 198 CONTENTS vil CHAPTER IX PAGE ORTHOPTERA CONTINUED—BLATTIDAE, COCKROACHES 220 CHAPTER X ORTHOPTERA CONTINUED—-MANTIDAE, SOOTHSAYERS 242 CHAPTER XI ORTHOPTERA CONTINUED—PHASMIDAE, WALKING-LEAVES, STICK-INSECTS 260 CHAPTER XII ORVHOPTERA CONTINVED—ACRIDIIDAE, Locusts, GRASSHOPPERS . 279 CHAPTER XIII ORTHOPTERA CONTINUED—LOCUSTIDAE, GREEN GRASSHOPPERS, KATYDIDS 311 CHAPTER XIV ORTHOPTERA CONTINUED—GRYLLIDAE, CRICKETS 200 CHAPTER XV NEvUROPTERA—M ALLOPHAGA—EMBIIDAE 341 CHAPTER XVI NEUVROPTERA CONTINUED—TERMITIDAE, TERMITES OR WHITE ANTS 356 vill CONTENTS CHAPTER XVII PAGE NEUROPTERA CONTINUED—PsocIDAE (Boox-Licr AND DEaTH-WATCHES)—THE Firsr Famity oF AMPHIBIOUS NEUROPTERA (PERLIDAE, STONE-FLIES) 390 CHAPTER XVIII AMPHIBIOUS NEUROPTERA CONTINUED—ODONATA, DRAGON-FLIES é 409 CHAPTER XIX AMPHIBIOUS NEUROPTERA CONTINUED—EPHEMERIDAE, MAy-FLIES i 429 CHAPTER XX NEvnroprera PLANIPENNIA—SIALIDAE, ALDER-F Lies, SNAKE-FLIES—PANOR- PIDAE, SCORPION-FLIES—HEMEROBIIDAE, ANr-Lions, LAcEWINGS, ETc. 444 CHAPTER XXI NEUROPTERA CONTINUED — TRICHOPTERA, THE PHRYGANEIDAE OR CADDIS- FLuies . ‘ : ‘ 7 , » 473 CHAPTER XXII HYMENOPTERA—IIYMENOPTERA SESSILIVENTRES—CEPHIDAE—ORYSSIDAE— SIRICIDAE—TENTHREDINIDAE OR SAWFLIES . ‘ : 487 CHAPTER XNIII HYMENOPTERA PETIOLATA—PARASITIC HYMENOPTERA—CYNIPIDAE OR GALL- Fiirs— Procrorrypman — CHALCIDIDAE — ICHNEUMONIDAE— BRracon- IDAE — STEPHANIDAE — MrcALyrmar — EVANIIDAE — PELECINIDAE TRIGONALIDAE ‘ , i y : : ‘ . 519 INDEX . ‘ 3 x 567 SCHEME OF THE CLASSIFICATION (RECENT FORMS) ADOPTED IN THIS BOOK PROTOTRACHEATA Peripatus (p. 1) MYRIAPODA Order. Family. POLYXENIDAE (p. 43), GLOMERIDAE (p. 48). SPHAEROTHERIIDAE (p. 48). JULIDAE (p. 48). BLANJULIDAE (p. 44). CHORDEUMIDAE (p. 44). POLYDESMIDAE (p. 44). POLYZONIIDAE (p. 44). CHILOGNATHA (=DIPLOPODA) ; LirHopiipaE (p. 45). SCOLOPENDRIDAE (p. 45). — = CHILOPODA | NoropHILipaz (p. 45). GEOPHILIDAE (p. 46). SCHIZOTARSIA CERMATIIDAE (=SCUTIGERIDAE) (p. 46). SYMPHYLA. SCOLOPENDRELLIDAE (p. 46), PAUROPODA : PAUROPIDAE (p. 47). INSECTA Order. oa Family. CAMPODEIDAE (p. 183), Thysanura JAPYGIDAE (p. 184). (p. 182) MAcHILIDAE (p. 184). LEPISMIDAE (p. 185). APTERA (p. 180) . | LIPURIDAE (p. 190). a ie { PopDURIDAE (p. 190). Pp. SMYNTHURIDAE (p. 191). SCHEME OF INSECTA Order. ORTHOPTERA J (p. 198) r Division, Series, or Sub-Order. Orthoptera cursoria Orthoptera saltatoria (Continucd on the next page.) Family. Tribe or Sub-Family. ForFIcuLiDAE (p. 202), HEMIMERIDAE (p. 217). BLATTIDAE (p. 220) MANTIDAE (p. 242) PHASMIDAE (p. 260) ACRIDIIDAE (p. 279) LocustTipaE (p. 311) - Ectobiides. Phyllodromiides. Nyctiborides. Epilamprides. Periplanetides. Panchlorides. Blaberides. Corydiides. Oxyhaloides. Perisphaeriides, Panesthiides. ? Geoscapheusides. Amorphoscelides. Orthoderides. } Mantides. Harpagides. | Vatides. Empusides. , Lonchodides. Bacunculides. Bacteriides. Necroscides. Clitumnides. Acrophyllides. Cladomorphides. Anisomorphides. Phasmides. Aschipasmides. Bacillides. Phylliides. Tettigides. Pneumorides. Mastacides. Proscopiides. ’ Tryxalides. Oedipodicdes. Pyrgomorphides. Pamphagides. Acridiides. Phaneropterides. Meconemides. Mecopodides. Prochilides. Pseudophyllides. Conocephalides. Tympanophorides. » Sagides. Locustides. Decticides. Callimenides. Ephippigerides. Hetrodides. Gryllacrides. | Stenopelmatides. SCHEME OF INSECTA xl Order. oe Family. Tribe or Sub-Family. Group. Tridactylides, Gryllotalpides. ORTHOPTERA Orthoptera | Gayrrpan Myrmecophilides. (continued) saltatoria (p. 330) Gryllides. (continued) P. Occanthides. ‘Trigonidiides. \ Eneopterides. Mallophaga \ Leiotheides. (p. 345) Philopterides. EMBIIDAE (p. 351). Reaudoe ‘i ye) (p. 356). neuroptera | Psocipan (p. 390). PERLIDAE (p. 398). Gomphinae. Cordulegasterinae. Anisopterides Aeschninae. ee ODONATA | i Corduliinae. an 10-- (p. 409) bela . alepteryginae. Zygopterides | Agrioninae. \ EPHEMERIDAE (p. 429). SIALIDAE Sialides. (p. 444) Raphidiides. NEUROPTERA PANORPIDAE (p. 449). (p. 341) Myrmeleonides (p. 454). Ascalaphides f Holophthalmi. (p. 459) \ Schizophthalmi. Neuroptera Nemopterides (p. 462), planipennia tHemERoniiDAR Mantispides (p. ee cp Sa) Hemerobiides Nymphidina. (p. 465) Osmylina. Hemerobiina. Chrysopides (p. 469). \ Coniopterygides (p. 471). Phryganeides (p. 480). Limnophilides (p. 481). é Sericostomatides (p. 482). Trichoptera eco’ IDAe Leptocerides (p. 482), Bs Hydropsychides (p. 482). Rhyacophilides (p. 483). X Hydroptilides (p, 484). CEPHIDAR (p. 504). Oe OryssIDAE (p. 506). iventres ~) SIRICIDAE (p. 507). TENTHREDINIDAE (p. 510). ; CYNIPIDAE (p. 523). PROCTOTRYPIDAE (p. 533). HYMENOPTERA | Soe eaten (p. 539). . 487 CHNEUMONIDAE (p. 551). : eae: BRACONIDAE (p. 558). ine 2 t) STEPHANIDAE (p. 561). aha. {par Meca.yripA& (p. 562). EVANIIDAE (p. 562). PELECINIDAE (p. 563). (To be continued in Vol. VI.) TRIGONALIDAE (p. 564). PERIPATUS BY ADAM SEDGWICK, M.A, F.RS, Fellow of Trinity College, Cambridge. VOL. V £ CHAPTER I PERIPATUS INTRODUCTION EXTERNAL FEATURES — HABITS BREEDING — ANATOMY — ALIMENTARY CANAL——NERVOUS SYSTEM— THE BODY WALL — THE TRACHEAL SYSTEM — THE MUSCULAR SYSTEM —-THE VASCULAR SYSTEM — THE BODY CAVITY — NEPHRIDIA——GENERATIVE ORGANS——-DEVELOPMENT——SYNOPSIS OF THE SPECIES—-SUMMARY OF DISTRIBUTION. THE genus Peripatus was established in 1826 by Guilding? who first obtained specimens of it from St. Vincent in the Antilles. He regarded it as a Moilusc, being no doubt deceived by the slug -like appearance given by the antennae. Specimens were subsequently obtained from other parts of the Neotropical region and from South Africa and Australia, and the animal was vari- ously assigned by the zoologists of the day to the Annelida and Myriapoda. Its true place in the system, as a primitive member of the group Arthropoda, was first established in 1874 by Moseley,2 who discovered the tracheae. The genus has been monographed by Sedgwick, who has also written an account of the development of the Cape species* A bibliography will be found in Sedgwick’s Monograph. 11. Guilding, ‘‘ Mollusca caribbaeana: an Account of a New Genus of Mollusca,” Zool. Journ. vol. ii. 1826, p. 443, pl. 14; reprinted in Jszs, vol. xxi. 1828, p. 158, pl. ii. 2 H. N. Moseley, ‘On the Structure and Development of Peripatus capensis,” Phil. Trans. elxiv. pls. lxxii.-lxxv. pp. 757-782 ; and Proc. &, S. xxii. pp. 344-350, 1874. 3 A. Sedgwick, ‘‘A Monograph of the Genus Peripatus,” Quart. Journ. of Mic. Science, vol. xxviii., and in Studies from the Morphological Laboratory of the Uni- versity of Cambridge, vol. iv. 4A. Sedgwick, ‘‘A Monograph of the Development of Peripatus capensis,” Studies from the Morphological Laboratory of the University of Cambridge, vol. iv. 4 PERIPATUS CHAP. There can be no doubt that Pertpatus is an Arthropod, for it possesses the following features, all characteristic of that group, and all of first-class morphological importance: (1) The presence of appendages modified as jaws; (2) the presence of paired lateral ostia perforating the wall of the heart and putting its cavity in communication with the pericardium; (3) the presence of a vas- cular body cavity and pericardium (haemocoelic body cavity) ; (+) absence of a perivisceral section of the coelom. Finally, the tracheae, though not characteristic of all the classes of the Arthropoda, are found nowhere outside that group, and constitute a very important additional reason for uniting Peripatus with it. Peripatus, though indubitably an Arthropod, differs in such important respects from all the old-established Arthropod classes, that a special class, equivalent in rank to the others, and called Prototracheata, has had to be created for its sole occupancy. This unlikeness to other Arthropoda is mainly due to the Anne- lidan affinities which it presents, but in part to the presence of the following peculiar features: (1) The number and diffusion of the tracheal apertures; (2) the restriction of the jaws to a single pair; (3) the disposition of the generative organs; (4) the tex- ture of the skin; and (3) the simplicity and similarity of all the segments of the body behind the head. The Aunelidan affinities are superficially indicated in so marked a manner by the thinness of the cuticle, the dermo- muscular body wall, the hollow appendages, that, as already stated, many of the earlier zoologists who examined Peripatus placed it amongst the segmented worms; and the discovery that there is some solid morphological basis for this determination constitutes one of the most interesting points of the recent work on the genus. The Annelidan features are: (1) The paired nephridia in every segment of the body behind the first two (Saenger, Balfour!); (2) the presence of cilia in the generative tracts (Gaffron). It is true that neither of these features are absolutely distinctive of the Annelida, but when taken in con- junction with the Annelidan disposition of the chief systems of organs, viz. the central nervous system, and the main vascular trunk or heart, may be considered as indicating affinities in that 1 F, M. Balfour, ‘‘The Anatomy and Development of Peripatus capensis,” edited by Professor H. N. Moseley and A. Sedgwick, Quart. Journ. Mic. Sci. xxiii. pp. 213-259, pls. xili.-xx. 1883. I EXTERNAL FEATURES 5 direction. Peripatus, therefore, is zoologically of extreme interest from the fact that, though in the main Arthropodan, it possesses features which are possessed by no other Arthropod, and which connect it to the group to which the Arthropoda are in the general plan of their organisation most closely related. It must, therefore, according to our present lights, be regarded as a very primitive form; and this view of it is borne out by its extreme isolation at the present day. Peripatus stands absolutely alone as a kind of half-way animal between the Arthropoda and Anne- lida. There is no gradation of structure within the genus; the species are very limited in number, and in all of them the peculiar features above mentioned are equally sharply marked. Peripatus, though a lowly organised animal, and of remark- able sluggishness, with but slight development of the higher organs of sense, with eyes the only function of which is to enable it to avoid the light—though related to those animals most re- pulsive to the aesthetic sense of man, animals which crawl upon their bellies and spit at, or poison, their prey—is yet, strange to say, an animal of striking beauty. The exquisite sensitiveness and constantly changing form of the antennae, the well-rounded plump body, the eyes set like small diamonds on the side of the head, the delicate feet, and, above all, the rich colouring and velvety texture of the skin, all combine to give these animals an aspect of quite exceptional beauty. Of all the species which I have seen alive, the most beautiful are the dark green individuals of Capensis, and the species which I have called Balfouri. These animals, so far as skin is concerned, are not surpassed in the animal kingdom. TI shall never forget my astonishment and delight when on bearing away the bark of a rotten tree-stump in the forest on Table Mountain, I first came upon one of these animals in its natural haunts, or when Mr. Trimen showed me in confinement at the South African Museum a fine fat, full-grown female, accompanied by her large family of thirty or more just- born but pretty young, some of which were luxuriously creeping about on the beautiful skin of their mother’s back. External Features. The anterior part of the body may be called the head, though it is not sharply marked off from the rest of the body (Fig. 1). The head carries three pairs of appendages, a pair of simple eyes, 6 PERIPATUS CHAP. and a ventrally placed mouth. The body is elongated and yermifori; it bears a number of paired appendages, each termi- nating in a pair of claws, and all exactly alike. The number varies in the different species. The anus is always at the Fic. 1.—Peripatus capensis, drawn from life. Life size. (After Sedgwick. ) posterior end of the body, and the generative opening is on the ventral surface just in front of the anus; it may be between the legs of the last pair (Fig. 2), or it may be behind them. There is in most species a thin median white line extending the whole length of the dorsal surface of the body, on each side of which Fic. 2.—Ventral view of hind -end of Fic. 3.—Ventral view of the head of P, LP. Novae-Zealandiue. (Alter Sedg- capensis. (After Sedgwick.) ant, An- wick.) gy, Generative opening; a, tennae ; or.p, oral papillae ; 7.7, first anus. leg ; 7, tongue. the skin pigment is darker than elsewhere. The colour varies considerably in the different species, and even in different indi- viduals of the same species. The ventral surface is nearly always flesh-coloured, while the dorsal surface has a darker colour. In the I EXTERNAL FEATURES 7 South African species the colour of the dorsal surface varies from a dark green graduating to a bluish gray, to a brown vary- ing to a red orange. The colour of the Australasian species varies 1n like manner, while that of the Neotropical species (8. American and W. Indian) is less variable. The skin is thrown into a number of transverse ridges, along which wart-like papillae are placed. The papillae, which are found everywhere, are specially developed on the dorsal surface, less so on the ventral. Each papilla carries at its extremity a well-marked spine. The appendages of the head are the antennae, the jaws and the oral papillae. The antennae, which are prolongations of the dorso-lateral parts of the head, are ringed, and taper slightly till near their termination, where they are slightly enlarged. The rings bear a number of spines, and the free end of the antennae is covered by a cap of spiniferous tissue like that of the rings. The mouth is at the hinder end of a depression called the buccal cavity, and is surrounded by an annular tumid Lp, raised into papilliform ridges and bearing a few spines (Fig. 3). Within the buccal cavity are the two jaws. They are short, stump-like, muscular structures, armed at their free extremities by a pair of cutting blades or claws, and are placed one on each side of the mouth. In the median line of the buccal cavity in front is placed a thick muscular protuberance, which may be called the tongue, though attached to the dorsal instead of to the ventral wall of the mouth (Fig. 3). The tongue bears a row of small chitinous teeth. The jaw- claws (Figs. 4 and 5), which re- semble in all essential points the claws borne by the feet, and like these are thickenings of the We ae i cuticle, are sickle-shaped. They — pensis. (After pensis. (After have their convex edge directed — ?/0™™) oe forwards and their concave or cutting edge turned backwards. The inner cutting plate (Fig. 4) usually bears a number of cutting teeth. The jaws appear to be used for tearing the food, to which the mouth adheres by means of the tumid suctorial lips. The oral papillae are placed at the sides of the head (Fig. 3). The 8 PERIPATUS CHAP. ducts of the slime-glands open at their free end. They possess two main rings of projecting tissue, and their extremities bear papillae irregularly arranged. The ambulatory appendages vary in number. There are seventeen pairs in P. capensis and eighteen in P. Balfouri, while in P. £dieardsii the number varies from twenty-nine to thirty-four pairs. They consist of two main divisions, which we may call the leg and the foot (Figs. 6 and 7). The leg (Z) has the form of a truncated cone, the broad end of which is attached to the ventro-lateral wall of the body, of which it is a prolonga- tion. It is marked by a number of rings of papillae placed Fic, 6.—Ventral view of last leg of a Fic, 7.—Leg of P. capensis seen from the male P. capensis. (After Sedg- front. (After Sedgwick.) 7, Foot; 2, leg; wick.) f, Foot; 2, leg; p, spini- P, spiniferous pads. ferous pads. The white papilla on the proximal part of this leg is characteristic of the male of this species. transversely to its long axis, the dorsal of which are pigmented like the dorsal surface of the body, and the ventral like the ventral surface. At the narrow distal end of the leg there are on the ventral surface three spiniferous pads, each of which is continued dorsally into a row of papillae. The foot is attached to the distal end of the lee. It is shghtly narrower at its attached extremity than at its free end. It bears two sickle-shaped claws and a few papillae. The part of the foot which carries the claws is especially retractile, and is generally found more or less telescoped into the proximal part. The legs of the fourth and fifth pairs differ from the others in E HABITS 9 the fact that the proximal pad is broken up into three, a small central and two larger lateral. The enlarged nephridia of these legs open on the small central division. The males are generally rather smaller than the females. In those species in which the number of legs varies, the male has a smaller number of legs than the female. Habits. They live beneath the bark of rotten stumps of trees, in the crevices of rock, and beneath stones. They require a moist atmosphere, and are exceedingly susceptible to drought. They avoid light, and are therefore rarely seen. They move with great deliberation, picking their course by means of their antennae and eyes. It is by the former that they acquire a knowledge of the ground over which they are travelling, and by the latter that they avoid the light. The antennae are extra- ordinarily sensitive, and so delicate, indeed, that they seem to be able to perceive the nature of objects without actual contact. When irritated they eject with considerable force the contents of their slime reservoirs from the oral papillae. The force 1s sup- plied by the sudden contraction of the muscular body wall. They can squirt the slime to the distance of almost a foot. The slime, which appears to be perfectly harmless, is extremely sticky, but it easily comes away from the skin of the animal itself. I have never seen them use this apparatus for the capture of prey, but Hutton describes the New Zealand species as using it for this purpose. So far as I can judge, it is used as a defensive weapon; but this of course will not exclude its offensive use. They will turn their heads to any part of the body which is being irritated and violently discharge their slime at the offending object. Locomotion is effected entirely by means of the legs, with the body fully extended. Of their food in the natural state we know little; but it is probably mainly, if not entirely, animal. Hutton describes his specimens as sucking the juices of flies which they had stuck down with their slime, and those which I kept in captivity eagerly devoured the entrails of their fellows, and the developing young from the uterus. They also like raw sheep’s liver. They move their mouths in a suctorial manner, tearing the food with their jaws. They have the power of extruding their jaws from 10 PERIPATUS CHAP, the mouth, and of working them alternately backwards or for- wards. This is readily observed in individuals immersed in water. Breeding. All species are viviparous. It has been lately stated that one cf the Australian species is normally oviparous, but this has not been proved. The Australasian species come nearest to laying eggs, inasmuch as the eges are large, full of yolk, and enclosed ima shell; but development normally takes place in the uterus, though, abnormally, incompletely developed eggs are extruded. The young of P. capensis are born in April and May. They are almost colourless at birth, excepting the antennae, which are yreen, and their length is 10 to 15 mm. A laree female will produce thirty to forty young in one year. The period of vesta- tion is thirteen months, that is to say, the ova pass into the oviduets about one month before the young of the preceding year are born. They are born one by one, and it takes some time for a female to get rid of her whole stock of embryos; in fact, the embryos in any given female differ slightly in age, those next the oviduct being a little older (a few hours) than those next the vagina. The mother does not appear to pay any special attention to her young, which wander away and get their own food. There does not appear to be any true copulation. The male deposits small, white, oval spermatophores, which consist of small bundles of spermatozoa cemented together by some glutinous substance, indiscriminately on any part of the body of the female. Such spermatophores are found on the bodies of both males and females from July to January, but they appear to be most nume- rous in our autumn. It seems probable that the spermatozoa make their way from the adherent spermatophore through the body wall into the body, and so ly traversiny the tissues reach the ovary. The testes are active from June to the following March. From March to June the vesiculae of the male are empty. There are no other sexual differences except in some of the South African species, in which the last or penultimate lee of the male bears a small white papilla on its ventral surface (Fig. 6). Whereas in the Cape species embryos in the same uterus are all practically of the same age (except in the month of April, when two broods overlap in P. capensis), and birth takes place at a fixed season; in the Neotropical species the uterus, which is I ALIMENTARY CANAL I] always pregnant, contains embryos of different a probably take place all the year round. ves, and births In all species of Peripatus the youne are fully formed at birth, and differ from the adults only in size and colour. ANATOALY The Alimentary Canal (ig. 8). The buceal cavity, as explained above, is a secondary furma- tion around the true mouth, which is at its dorsal posterior end. It contains the tongue and the jaws, which have already been 19 Fic. 8.—Peripatus capensis dissected so as to show the alimentary canal, slime glands, and salivary glands. (After Balfour.) The dissection is viewed from the ventral side, and the lips (Z) have been cut through in the middle line behind and pulled outwards so as to expose the jaws (j), which have been turned outwards, and the tongue (7) bearing a median row of chitinous teeth, which branches behind into two. The muscular pharynx, extend- ing back into the space between the first and second pairs of legs, is followed by a short tubular oeso- phagus. The latter opens into the large stomach with plicated walls, extending almost to the hind end of the animal. The stomach at its point of junc- tion with the rectum presents an §-shaped ventro- dorsal curve. .1, Anus; af, antenna; J. 1, 2.2, first and second feet; j, jaws; JZ, lips; oe, oesophagus ; 07.p, oral papilla ; pk, pharynx; R, rectum ; s.d/, salivary duct; s.g, salivary gland ; si.d, slime reservoir; si.g, portion of tubules of slime gland; s¢, stomach; 7, tongue in roof of mouth, described, and into the hind end of it there opens ventrally by a median opening the salivary glands (s.). The mouth leads into a muscular pharynx (pl), which is connected ly a short oeso- phagus (ve) with a stomach (sé). The stomach forms by far the 12 PERIPATUS CHAP. largest part of the alimentary canal. It is a dilated soft-walled tube, and leads behind into the short narrow rectum (#), which opens at the anus. There are no glands opening into the alimentary canal. Nervous System. The central nervous system consists of a pair of supra- oesophageal ganglia united in the middle line, and of a pair of widely divaricated ventral cords, continuous in front with the supra-oesophageal ganglia (Fig. 9). The ventral cords at first sight appear to be without gangh- onic thickenings, but on more careful examination they are found to be enlarged at each pair of legs (Fig. 9). These enlarge- ments may be regarded as imperfect ganglia. There are, there- Fic. 9.—Brain and anterior part of the ventral nerve- cords of Peripatus capensis enlarged and viewed from the ventral surface. (After Balfour.) The paired appendages (d@) of the ventral surface of the brain are seen, and the pair of sympathetic nerves (sy) arising from the ventral surface of the hinder part. From the commencement of the oesopha- geal commissures pass off on each side a pair of nerves to the jaws (Jn). The three anterior commissures between the ventral nerve-cords are placed close together; immediately behind them the nerve-cords are swollen, to form the ganglionic enlargements from which pass off to the oral papillae a pair of large nerves on each side (077). Behind this the cords present a series of enlarge- ments, one pair for each pair of feet, from which a pair of large nerves pass off on each side to the feet (pn). atn, Antennary nerves; co, commissures between ventral cords; d, ventral appendages of brain ; HZ, eye; en, nerves passing outwards from ventral cord ; /.g.1, ganglionic enlargements from which nerves to feet pass off ; jn, nerves to jaws ; org, ganglionic enlargement from which nerves to oral papillae pass off ; orn, nerves to oral papillae ; pe, posterior lobe of brain; pn, nerves to feet ; sy, sympathetic nerves, ‘yp i! fore, as many pairs of ganglia as there are pairs of legs. There is in addition a ganglionic enlargement at the commencement of the oesophageal commissures, where the nerves to the oral papillae are given off (Fig. 9, 07.9). The ventral cords are placed each in the lateral compart- ments of the hody cavity, immediately within the longitudinal layer of muscles. They are connected with each other, rather like the pedal nerves of Ch/éfon and the lower Prosobranchiata, by a number of commissures. These commissures exhibit a I NERVOUS SYSTEM AND BODY WALL 13 fairly regular arrangement from the region included between the first and the last pair of true feet. There are nine or ten of them between each pair of feet. They pass along the ventral wall of the body, perforating the ventral mass of longitudinal muscles. On their way they give off nerves which innervate the skin. Posteriorly the two nerve-cords nearly meet immediately in front of the generative aperture, and then, bending upwards, fall into each other dorsally to the rectum. They give off a series of nerves from their outer borders, which present throughout the trunk a fairly regular arrangement. From each ganglion two large nerves (pn) are given off, which, diverging somewhat from each other, pass into the feet. From the oesophageal commissures, close to their junction with the supra-oesophageal ganglia, a nerve arises on each side which passes to the jaws, and a little in front of this, apparently from the supra-oesophageal ganglion itself, a second nerve to the jaws also takes its origin. The supra-oesophageal ganglia (Fig. 9) are large, somewhat oval masses, broader in front than behind, completely fused in the middle, but free at their extremities. Each of them is pro- longed anteriorly into an antennary nerve, and is continuous behind with one of the oesophageal commissures. On the ventral surface of each, rather behind the level of the eye, is placed a hollow protuberance (Fig. 9, d), of which I shall say more in dealing with the development. About one-third of the way back the two large optic nerves take their origin, arising laterally, but rather from the dorsal surface (Fig. 9). Each of them joins a large ganglionic mass placed immediately behind the retina. The histology of the ventral cords and oesophageal commis- sures is very simple and uniform. They consist of a cord almost wholly formed of nerve-fibres placed dorsally, and of a ventral layer of ganglion cells. The Body Wall. The skin is formed of three layers. (1) The cuticle. (2) The epidermis or hypodermis. (3) The dermis. The cuticle is a thin layer. The spines, jaws, and claws are special developments of it. Its surface ig not, however, smooth, Iq PERIPATUS CHAP. but is everywhere, with the exception of the perioral region, raised into minute secondary papillae, which in most instances bear at their free extremity a somewhat prominent spine. The whole surface of each of the secondary papillae just described is in its turn covered by numerous minute spinous tubercles. The epidermis, placed immediately within the cuticle, is composed of a single layer of cells, which vary, however, a good deal in size in different regions of the body. The cells excrete the cuticle, and they stand in a very remarkable relation to the secondary papillae of the cuticle just described. Each epidermis cell is in fact placed within one of these secondary papillae, so that the cuticle of each secondary papilla is the product of a single epidermis cell. The pigment which gives the characteristic colour to the skin is deposited in the protoplasm of the outer ends of the cells in the form of small granules. At the apex of most, if not all, the primary wart-like papillae there are present oval aggregations, or masses of epidermis cells, each such mass being enclosed in a thickish capsule and bearing a long projecting spine. These structures are probably tactile organs. In certain regions of the body they are extremely numerous ; more especially is this the case in the antennae, lips, and oral papillae. On the ventral surface of the peripheral rings of the thicker sections of the feet they are also very thickly set and fused together so as to form a kind of pad (Figs. 6 and 7). In the antenuae they are thickly set side hy side on the rings of skin which give such an Arthropodan appearance to these organs in Peripatus. The Tracheal System. The apertures of the tracheal system are placed in the depres- sions between the papillae or ridges of the skin. Each of them leads into a tube, which may be called the tracheal pit (Fig. 10), the walls of which are formed of epithelial cells bounded towards the lumen of the pit by a very delicate cuticular membrane con- tinuous with the cuticle covering the surface of the body, The pits vary somewhat in depth ; the pit figured was about 0°09 mm. It perforates the dermis and terminates in the subjacent muscular layer. Internally it expands in the transverse plane and from the expanded portion the tracheal tubes arise in diverging bundles. Nuclei similar in character to those in the walls of the tracheal I TRACHEAL, MUSCULAR AND VASCULAR SYSTEM 15 pit are placed between the tracheae, and similar but slightly more elongated nuclei are found along the bundles. The tracheae are minute tubes exhibiting a faint transverse striation which is prob- ably the indication of a spiral fibre. They appear to branch, but Fic. 10,—Section through a tracheal pit and diverging bundles of tracheal tubes taken transversely to the long axis of the body. (After Balfour.) tv, Tracheae, showing rudimentary spiral fibre ; tr.c, cells resembling those lining the tracheal pits, which occur at intervals along the course of the tracheae ; ¢r.o, tracheal stigma ; ir.p, tracheal pit. only exceptionally. The tracheal apertures are diffused over the surface of the body, but are especially developed in certain regions. The Muscular System. The general muscular system consists of—(1) the general wall of the body; (2) the muscles connected with the mouth, pharynx, and jaws; (3) the muscles of the feet ; (+) the muscles of the alimentary tract. The muscular wall of the body is formed of—(1) an external layer of circular fibres; (2) an internal layer of longitudinal muscles. The main muscles of the body are unstriated and divided into fibres, each invested by a delicate membrane. The muscles of the jaws alone are transversely striated. The Vascular System. The vascular system consists of a dorsal tubular heart with paired ostia leading into it from the pericardium, of the pericar- dium, and the various other divisions of the perivisceral cavity (Fig. 14, D). As in all Arthropoda, the perivisceral cavity is a haemocoele ; i.e. it contains blood and forms part of the vascular system. The heart extends from close to the hind end of the body to the head. 16 PERIPATUS CHAP. The Body Cavity. The body cavity is formed of four compartments—one central, two lateral, and a pericardial (Fig. 14, D). The former is by far the largest, and contains the alimentary tract, the generative organs, and the slime glands. It is lined by a delicate endo- thelial layer, and is not divided into compartments nor traversed by muscular fibres. The lateral divisions are much smaller than the central, and are shut off from it by the inner transverse band of muscles. They are almost entirely filled with the nerve-cord and salivary gland in front and with the nerve-cord alone behind, and their lumen is broken up by muscular bands. They further contain the nephridia. They are prolonged into the feet, as is the embryonic body cavity of most Arthropoda. The pericardium con- tains a pecuhar cellular tissue, probably, as suggested by Moseley, equivalent to the fat-bodies of insects. Nephridia. In Peripatus capensis nephridia are present in all the legs. In all of them (except the first three) the following parts may be recognised (Fig. 11) :— (1) A vesicular portion opening to the exterior on the ventral surface of the legs by a narrow passage. (2) A coiled portion, which is again subdivided into several sections. (3) A section with closely packed nuclei ending by a some- what enlarged openine. (4) The terminal portion, which consists of a thin-walled vesicle. The last twelve pairs of these organs are all constructed in a very similar manner, while the two pairs situated in the fourth and fifth pairs of legs are considerably larger than those behind and are in some respects very differently constituted. It will be convenient to commence with one of the hinder nephridia. Such a nephridium from the ninth pair of legs is represented in Fig. 11. The external opening is placed at the outer end of a transverse groove at the base of one of the legs, while the main portion of the organ lies in the body cavity in the base of the leg, and extends into the trunk to about the level 2 I NEPHRIDIA 17 of the outer edge of the nerve-cord of its side. The external opening (0s) leads into a narrow tube (s.d), which gradually dilates into a large sac (s). The narrow part is lined by small epithelial cells, which are directly continuous with and perfectly similar to those of the epidermis. The sac itself, which forms a kind of bladder or collecting vesicle for the organ, is provided with an extremely thin wall, lined with very large flattened cells. The second section of the nephridium is formed by the coiled tube, the epithelial lining of which varies slightly in the different parts. The third section (s.0.¢), constitutes the most distinct portion of the whole organ. Its walls are formed of columnar cells almost filled by oval nuclei, which absorb colouring matters with very great avidity, and thus render this part extremely Fic. 11.—Nephridium from the 9th pair of legs of P. capensis. o.s, External opening of seg- mental organ; p,f, internal opening of nephridium into the body cavity (lateral com- partment) ; s, vesicle of seg- mental organ; s.¢.1, s8.¢.2, 5.6.8, 8.c.4, successive regions of coiled portion of nepliri- dium; s.0.¢, third portion of nephridium broken off at p.f from the internal vesicle, which is not shown. conspicuous. The nuclei are arranged in several rows. It ends by opening into a vesicle (Fig. 14, D), the wall of which is so delicate that it is destroyed when the nephridium is removed from the body, and consequently is not shown in Fig. 11. The fourth and fifth pairs are very considerably larger than those behind, and are in other respects peculiar. The great mass of each organ is placed behind the leg on which the external opening is placed, immediately outside one of the lateral nerve- cords. The external opening, instead of being placed near the base of the leg, is placed on the ventral side of the third ring (counting from the outer end) of the thicker portion of the leg. It leads into a portion which clearly corresponds with the collect- ing vesicle of the hinder nephridia. This part is not, however, dilated into a vesicle. The three pairs of nephridia in the three foremost pairs of legs are rudimentary, consisting solely of a vesicle and duct. The salivary glands are the modified nephridia of the segment of the oral papillae. VOL. V C 18 PERIPATUS CHAY. Generative Organs. Matr.—The male organs (Fig. 12) consist of a pair of testes (te), a pair of vesicles (v), vasa deferentia (v.d), and accessory glandular tubules (7). All the above parts lie in the central compartment of the body cavity. In P. capensis the accessory glandular bodies or erural glands of the last (17th) pair of legs are enlarged and prolonged into an elongated tube placed in the lateral compartment of the body cavity (7.9). The right vas deferens passes under both nerve-cords to join Fia. 12.—Male generative organs of Peripatus capensis, viewed from the dorsal surface. (After Balfour.) a@.y, Enlarged crural glands of last pair of legs ; #16, 17, last pairs of legs ; f, small accessory glandular tubes ; p, common duct into which the vasa deferentia open ; ¢e, testis; v, seminal vesicle ; v.c, nerve-cord ; v.d, vas deferens. the left, and form the enlarged tube (y), which, passing beneath the nerve-cord of its side, runs to the external orifice. The enlarged terminal portion possesses thick muscular walls, and possibly constitutes a spermatophore maker, as has been shown to be the case in P. .V. Zealandiae, by Moseley. In some specimens a different arrangement obtains, in that the left vas deferens passes under both nerve-cords to join the right. FEMALE.—The ovaries consist of a pair of tubes closely ap- pled together, and continued posteriorly into the oviducts. The oviducts, after a short course, become dilated into the uteruses, which join behind and open to the exterior by a median I GENERATIVE ORGANS AND DEVELOPMENT Ig opening. The ovaries always contain spermatozoa, some of which project through the ovarian wall into the body cavity. Sperma- tozoa are not found in the uterus and oviducts, and it appears probable that they reach the ovary directly by boring through the skin and traversing the body cavity. In the neotropical species there is a globular receptaculum seminis opening by two short ducts close together into the oviduct, and there is a small receptaculum ovorum with extremely thin walls opening into the oviduct by a short duct just in front of the receptaculum seminis. The epithelium of the latter structure is clothed with actively moving cilia. In the New Zealand species there is a receptaculum seminis with two ducts, but the receptacula ovorum has not been seen. There appear to be present in most, if not all, the legs some accessory glandular structures opening just externally to the nephridia. They are called the crural vlands. DEVELOPMENT. As stated at the outset, Peripatus is found in three of the great regions, viz. in Africa, in Australasia, and in South America and the West Indies. It is a curious and remarkable fact that ‘although the species found in these various localities are really closely similar, the principal differences relating to the structure of the female generative organs and to the number of the legs, they do differ in the most striking manner in the structure of the ovum and in the early development. In all the Austral- asian species the egg is large and heavily charged with food- yolk, and is surrounded by a tough membrane. In the Cape species the eges are smaller, though still of considerable size; the yolk is much less developed, and the egg membrane is thinner though dense. In the neotropical species the egg is minute and almost entirely devoid of yolk. The unsegmented uterine ovum of P. Vovae-Zealandiae measures 1°5 min. in length by °8 mm. in breadth ; that of P. capensis is 56 mm. in length; and that of P. Lrinidadensis (04 mm. in diameter. In correspondence with these differences in the ovum there are differences in the early development, though the later stages are closely similar. But unfortunately the development has only been fully worked 1See Whitman, Journad of Morphology, vol. i. 20 PERIPATUS CHAP. out in one species, and to that species—P. capensis—the follow- ing description refers. The ova are apparently fertilised in the ovary, and they pass into the oviducts in April and May. In May the brood of the preceding year are born, and the new ova, which have meanwhile undergone cleavage, pass into the uterus. There are ten to twenty ova in each uterus. The seginentation is peculiar, and leads to the formation of a solid gastrula, consisting of a cortex of ectoderm nuclei surrounding a central endodermal mass, Which consists of a much-vacuolated tissue with sume Fia. 18.—A series of embryos of P. capensis. The hind end of embryos B, C, D is uppermost in the figures, the primitive streak is the white patch behind the blasto- pore. (After Sedgwick.) A, Gastrula stage, ventral view, showing blastopore. B, Older gastrula stage, ventral view, showing elongated blastopore and primitive streak. ©, Ventral view of embryo with three pairs of mesoblastic somites, dumb- bell-shaped blastopore and primitive streak. D, Ventral view of embryo, in which the blastopore has completely closed in its middle portion, and given rise to two openings, the embryonic mouth and anus. The anterior pair of somites have moved to the front end of the body, and the primitive groove has appeared on the primitive streak. E, Side view of embryo, in which the hind end of the body has begun to elongate in a spiral manner, and in which the appendages have begun. ld, antenna ; d, dorsal projection ; y.s, preoral somite. F, Ventral view of head of embryo intermediate between E and G@. The cerebral grooves are wide and shallow. The lips have appeared, and have extended behind the openings of the salivary glands, but have not yet joined in the middle line. Af, antennae; ¢.g, cerebral groove ; j, jaws ; j.s, swelling at base of jaws ; Z, lips ; JZ, mouth ; o7.p, oral papillae ; 0.8, opening of salivary gland. G, Side view of older embryo with the full number of appendages, to show the position in which the embryos lie in the uterus. irregularly-shaped nuclei. The endoderm mass is exposed at one point—the blastopore (gastrula mouth). The central vacuoles of the endoderm now unite and form the enteron of the embryo, and at the same time the embryo elongates into a markedly oval form, and an opacity—the primitive streak—appears at the hind end of the blastopore (Fig. 13, B). This elongation of the embryo is accompanied by an elongation of the blastopore, which soon becomes dumb-bell shaped (Fig. 13, C). At the same time the mesoblastic somites (embryonic segments of mesoderm) have made I DEVELOPMENT 21 their appearance in pairs at the hind end, and gradually travel for- ward on each side of the blastopore to the front end, where the somites of the anterior pair soon meet in front of the blastopore (Fig. 13,D). Meanwhile the narrow middle part of the blastopore has closed by a fusion of its lips, so that the blastopore is represented by two openings, the future mouth and anus. A primitive groove makes its appearance behind the blastopore (Fig. 13, D). At this stage the hind end of the body becomes curved ventrally into a spiral (Fig. 13, E), and at the same time the appendages appear ‘as hollow processes of the body wall, a mesoblastic somite being prolonged into each of them. The first to appear are the antennae, into which the praeoral somites are prolonged. The remainder appear from before backwards in regular order, viz. jaw, oral papillae, legs 1-17. The full number of somites and their appendages is not, however, completed until a later stage. The nervous system is formed as an annular thickening of ectoderm passing in front of the mouth and behind the anus, and lying on each side of the blastopore along the lines of the somites. The praeoral part of this thickening, which gives rise to the cerebral ganglia, becomes pitted inwards on each side (Fig. 13, F, eg). These pits are eventually closed, and form the hollow ventral appendages of the supra-pharyngeal ganglia of the adult (Fig. 9, 7). The lips are formed as folds of the side wall of the body, extending from the praeoral lobes to just behind the jaw (Fig. 13, F, Z). They enclose the jaws (/), mouth (1/7), and opening of the salivary glands (o.s), and so give rise to the buceal cavity. The embryo has now lost its spiral curvature, and becomes completely doubled upon itself, the hind end being in contact with the mouth (Fig. 13, G). It remains in this position until birth. The just-born young are from 10-15 mm. in lenyth and have green antennae, but the rest of the body is either quite white or of a reddish colour. This red colour differs from the colour of the adult in being soluble in spirit. The mesoblastic somites are paired sacs formed from the anterior lateral portions of the primitive streak (Fig. 13, ©). As they are formed they become placed in pairs on each side of the blastopore. The somites of the first pair eventually obtain a position entirely in front of the blastopore (Fig. 13, D). They form the somites of the praeoral lobes. The full complement of somites is acquired at about the stage of Fig. 15, E. The relations Ny lo PERIPATUS CHAP. of the somites is shown in Fig. 14, .A, which represents « transverse section taken between the mouth and anus of an embryo of the stage of Fig. 13, D. The history of these somites is an exceed- ingly interesting one, and may be described shortly as follows :— They divide into two parts—a ventral part, which extends into Fic. 14.—A series of diagrams of transverse sections through Peripatus embryos to show the relations of the coelom at successive stages. (After Sedgwick.) A, Early stage: 1, gut; 2, mesoblastic somite ; no trace of the vascular space ; endoderm and ectoderm in contact. B, Endoderm has separated from the dorsal aud ventral ectoderm. The somite is represented as having divided on the left side into a dorsal and ventral portion: 1, gut; 2, somite ; 3, haemocoele. €, The haemocoele (3) has become divided up into a number of spaces, the arrangement of which is unimportant. The dorsal part of each somite has travelled dorsalwards, and uow constitutes a small space (triangular in section) just dorsal to the gut. The ventral portion (2’) has assumed a tubular character, and has acquired an external opening. The internal vesicle is already indicated, and is shown in the diagram by the thinner black line: 1, gut; 2’, nephridial part of coelom; 3, haemocoele ; 3’, part of lhaemocoele which will form the heart—the part of the haemocoele on each side of this will form the pericardium; 4, nerve-cord. D represents the conditions at the time of birth; numbers as in C, except 5, slime glands. The coelom is re- presented as surrounded by a thick black line, except in the part which forms the internal vesicle of the nephridium. the appendage, and a dorsal part (Fig. 14, B). The ventral part acquires an opening to the exterior just outside the nerve-cord, and becomes entirely transformed into a nephridium (Fie. 14, D, 2’). The dorsal part shifts dorsalwards and diminishes rela- tively in size (Fig. 14, C). Its fate differs in the different parts I SPECIES 23 of the body. In the anterior somites it dwindles and disappears, but in the posterior part it unites with the dorsal divisions of contiguous somites of the same side, and forms a tube—the generative tube (Fig. 14, D, 2). The last section of this tube retains its connexion with the ventral portion of the somite, and so acquires an external opening, which is at first lateral, but soon shifts to the middle line, and fuses with its fellow, to form the single generative opening. The praeoral somite develops the rudiment of a nephridium, but eventually entirely disappears. The jaw somite also disappears; the oral papilla somite forms ventrally the salivary glands, which are thus serially homologous with nephridia. The perivisceral cavity of Peripatus is, as in all Arthropoda, a haemocoele. Its various divisions develop as a series of spaces between the ectoderm and endoderm, and later in the mesoderm. The mesoderm seems to be formed entirely from the proliferation of the cells of the mesoblastic somites. It thus appears that in Peripatus the coelom does not develop a perivisceral portion, but gives rise only to the renal and reproductive organs. SYNOPSIS OF THE SPECIES OF PERIPATUS. Peripatus, Guilding. Soft-bodied vermiform animals, with one pair of ringed antennae, one pair of jaws, one pair of oral papillae, and a varying number of claw-bearing ambulatory legs. Dorsal surface arched and more darkly pigmented than the flat ventral surface. Skin transversely ridged and beset by wart-like spiniferous papillae. Mouth anterior, ventral; anus posterior, terminal. Generative opening single, median, ventral, and posterior. One pair of simple eyes. Brain large, with two ventral hollow appendages ; ventral cords widely divaricated, without distinct ganglia. Alimentary canal simple, uncoiled. Segmentally arranged, paired nephridia are present. Body cavity is continuous with the vascular system, and does not communicate with the paired nephridia. Heart tubular, with paired ostia, Respiration by means of tracheae. Dioecious; males smaller and generally less numerous than females, Generative glands tubular, continuous with the ducts. Viviparous. Young born fully developed. They shun the light, and live in damp places beneath stones, leaves, and bark of rotten stumps. They eject when irritated a viscid fluid through openings at the apex of the oral papillae. Distribution : South Africa, New Zealand, and Australia, South America and the West Indies [and in Sumatra ?}. ; 24 PERIPATUS CHAP. SoutH AFRICAN SPECIES. With three spinous pads on the legs and two primary papillae on the anterior side of the foot, and one accessory tooth on the outer blade of the jaw ; with a white papilla on the ventral surface of the last fully developed leg of the male. Genital opening subterminal, behind the last pair of fully- developed legs. The terminal unpaired portion of vas deferens short. Ova of considerable size, but with only a small quantity of food-yolk. (Colour highly variable, number of legs constant in same species (?).) P. capensis (Grube).—South African Peripetus, with seventeen pairs of claw-bearing ambulatory legs. Locality, Table Mountain. P. Banrourt (Sedgwick),—South African Peripatus, with eighteen pairs of claw-bearing ambulatory legs, of which the last pair is rudimentary. With white papillae on the dorsal surface. Locality, Table Mountain. P. Brevis (De Blainville).—South African Peripatus, with fourteen pairs of ambulatory legs. Locality, Table Mountain. (I have not seen this species. Presumably it has the South African characters.) P. MoseLEyi (Wood Mason),—South African Peripatus, with twenty-one and twenty-two pairs of claw-bearing ambulatory legs. Locality, near Williamstown, Cape Colony ; and Natal# Doubtful Spectes, (1) South African Peripatus, with twenty pairs of claw-bearing ambu- latory legs (Sedgwick). Locality, Table Mountain. (Also Peters, locality not stated.) (2) South African Pertpatus, with nineteen pairs of ambulatory legs (Trimen). Loeality, Plettenberg Bay, Cape Colony. (Also Peters, locality not stated.) AUSTRALASIAN SPECIES. With fifteen pairs of claw-bearing ambulatory legs, with three spinous pads on the legs, and a primary papilla projecting from the median dorsal portion of the feet. Genital opening between the legs of the last pair. Receptacula seminis present. Unpaired portion of vas deferens long and complicated. Ova large and heavily charged with yolk. (Colour variable, number of legs constant in same species (?).) P. Novag Zeavanpiar (Hutton).—Australasian Peripatus, without an accessory tooth on the outer blade of the jaw, and without a white papilla on the base of the last leg of the male. New Zealand. P. Leuckartr (Saenger).—Australasian Peripatus, with an accessory tooth on the outer blade of the jaw, and a white papilla on the base of the last leg of the male. Queensland. NEOTROPICAL SPECIES, With four spinous pads on the legs, and the generative aperture between ' There are now, I am told by Professor Jeffrey Bell, specimens from Natal (I believe undescribed) at the British Museum with twenty-three and twenty - four pairs of legs. I SPECIES 25 the legs of the penultimate pair. Dorsal white line absent. Primary papillae divided into two portions. Inner blade of jaw with gap between the first minor tooth and the rest. Oviducts provided with receptacula ovorum and seminis. Unpaired part of vas deferens very long and compli- cated. Ova minute, without food-yolk. (Colour fairly constant, number of legs variable in samie species (?).) P. Epwarpsit.!—Neotropical Peripatus from Caracas, with a variable number of ambulatory legs (twenty-nine to thirty-four). Males with twenty-nine or thirty legs, and tubercles on a varying number of the posterior legs. The basal part or the primary papilla is cylindrical. P. TRINIDADENSIS (n. sp.).—Neotropical Peripatus from Trinidad, with twenty-eight to thirty-one pairs of ambulatory legs, and a large number of teeth on the inner blade of the jaw. The basal portion of the primary papillae is conical. P. rorauarus (Kennel).— Neotropical Pertpatus from Trinidad, with forty-one to forty-two pairs of ambulatory legs. With a transversely placed bright yellow band on the dorsal surface behind the head. Doubtful Species, The above are probably distinct species. Of the remainder we do not know enough to say whether they are distinct species or not. The following is a list of these doubtful species, with localities and principal characters :— P. suLiFoRMIS (Guilding).—Neotropical Peripatus from St. Vincent, with thirty-three pairs of ambulatory legs. P. Cuiniensis (Gay).—Neotropical Peripatus from Chili, with nineteen pairs of ambulatory legs. P. DEMERARANUS (Sclater).—Neotropical Peripatus from Maccasseema, Demerara, with twenty-seven to thirty-one pairs of ambulatory legs and conical primary papillae. PERIPATUS FROM CAYENNE (Audouin and Milne-Edwards).—With thirty pairs of legs, Named P. Epwarpsir by Blanchard. PERIPATUS FROM VALENTIA Lake, Cotumpra (Wiegmann).—With thirty pairs of legs. PERIPATUS FROM St. THouas (Moritz).—No description. Peripatus FRoM Coronra Towar, VENEZUELA (Grube).—With twenty- nine to thirty-one pairs of ambulatory legs. Named P. Epwarpsti by Grube. Peripatus FROM Santo Domingo, Nicaracua (Belt).—With thirty-one pairs of ambulatory legs. Perrpatus FROM Doutnica (Angas).—Neotropical Peripatus, with twenty- six to thirty (Pollard) pairs of ambulatory legs. PeRIPaATUS FROM JAMAICA (Gosse).—With thirty-one and thirty-seven pairs of ambulatory legs. PERIPATUS FROM SANTARAM. — Neotropical Periputus, with thirty-one pairs of ambulatory legs. PeripaTtus From Ccpa.—wNo details. 1 This name was first applied by Blanchard to a species from Cayenne. The description, however, is very imperfect, and it is by no means clear that the Cayenne species is identical with the species here named Edwardsit. 26 PERIPATUS CHAP. I Peripatus FRoM Hoorvusea Creek, Demerara (Quelch)—With thirty pairs of legs. Peripatus FRom Marago (Branner).—No details. Pertpatus From Urvapo, Porto Rico (Peters).—With twenty-seven, thirty, thirty-one, and thirty-two pairs of legs. PERIPATUS FROM SuRINAM (Peters).—No details. Peripatus From Puzrro CaBELLo, VENEZUELA (Peters).—With thirty and thirty-two pairs of legs. Peripatus FRoM LaGuayra, VENEZUELA (Peters).—No details, Peripatus Quirensis (Schmarda).—From Quito, with thirty-six pairs of legs. PERIPATUS FROM SUMATRA (?).) P. Sumarranvus (Horst).—Peripatus from Sumatra, with twenty-four pairs of ambulatory legs, and four spinous pads on the legs. The primary papillae of the neotropical character with conical bases. Generative opening between the legs of the penultimate pair. Feet with only two papille.t SUMMARY OF DISTRIBUTION DISTRIBUTION OF THE SoutH AFRICAN SPECIES— Slopes of Table Mountain, neighbourhood of Williamstown, Plettenberg Bay—Cape Colony—Natal. DISTRIBUTION OF THE AUSTRALASIAN SPECIES— Queensland— Australia. North and South Islands—New Zealand. OrtENTAL REGION (7)— Sumatra. DISTRIBUTION OF THE NEOTROPICAL SPECIES— Nicaragua. Valencia Lake, Caracas, Puerto Cabello, Laguayra, Colonia Towar Venezuela, Quito—Ecuador. Maccasseema, Hoorubea Creek—Demerara. Surinam (Peters). Cayenne, Santarem, Marajo, at the mouth of the Amazon—Brazil. Chili. And in the following West Indian Islands—Cuba, Dominica, Porto Rico (Peters), Jamaica, St. Thomas, St. Vincent, Trinidad. 1 The existence of this species is very doubtful. The description of it was taken from a single specimen. The evidence that this specimen was actually found in Sumatra is not conclusive. MY RIAPODA BY F. G. SINCLAIR, M.A. (FoRMERLY F. G. HEATHCOTE) Trinity College, Cambridge. CHAPTER II MYRIAPODA INTRODUCTION —— HABITS — CLASSIFICATION —STRUCTURE— CHILO- GNATHA —CHILOPODA — SCHIZOTARSIA — SYMPHYLA PAUR- OPODA—-EMBRYOLOGY——PALAEONTOLOGY. TRACHEATA With separated head and numerous, fairly similar segments. They have one pair of antennae, two or three pairs of mouth appendages, aud numerous pairs of legs. The Myriapoda are a class of animals which are widely distributed, and are represented in almost every part of the globe. Heat and cold alike seem to offer favourable conditions for their existence, and they flourish both in the most fertile and the most barren countries. They have not attracted much notice until comparatively recent times. Compared with Insects they have been but little known. The reason of this is not hard to tind. The Myriapods do not exercise so much direct influence on human affairs as do some other classes of animals; for instance, Insects. They include no species which is of direct use to man, like the silk- worm or the cochineal insect, and they are of no use to him as food. It is true that they are injurious to his crops. For instance, the species of Millepede known as the “ wire worm ”? is extremely harmful; but this has only attracted much notice in modern times, when land is of more value than formerly, and agricul- ture is pursued in a more scientific manner, and the constant endeavour to get the utmost amount of crop from the soil has caused a minute investigation into the various species of animals which are noxious to the growing crop. The species of 1 Not to be confused with the larva of Elater lineatus, also known as “ wire-worm.” 30 MYRIAPODA CHAP. Myriapoda best known to the ancients were those which were harmful to man on account of their poisonous bite. Some writers have supposed that the word which is trans- lated “mole” in the Bible (Lev. xi. 30) is really Scolopendra (a genus of Centipede), and, if this is so, it is the earliest men- tion of the Myriapods. They were rarely noticed in the classical times; almost the only mention of them is by lian, who says that the whole population of a town called Rhetium were driven out by a swarm of Scolopendras. Pliny tells us of a marine Scolo- pendra, but this was most probably a species of marine worm. Linnaeus included Myriapods among the Insects; and the writers after him till the beginning of this century classed them with all sorts of Insects, with Spiders, Scorpions, and even among Serpents. It was Leach who first raised them to the importance of a separate class, and Latreille first gave them the name of Myriapoda, which they have retained ever since. Myriapods are terrestrial animals, crawling or creeping on the ground or on logs of wood, or even under the bark of trees. There is, however, a partial exception to this; various naturalists have from time to time given descriptions of marine Centipedes. These are not found in the sea, but crawl about on the shore, where they are submerged hy each tide. Professor F. Plateau has given an account of the two species of Myriapods that are found thus living a semi-aquatic life. They are named Geophilus maritemus and Geophilus submarinus, and Plateau found that they could exist in sea water from twelve to seventy hours, and in fresh water from six to ten days. They thus offer a striking example of the power that their class possess -of existing under unfavourable circumstances. With regard to their habits the different species differ very considerably. On the one hand we have the Chilopoda, or Centipedes, as they are called in this country, active, swift, and ferocious; Lving for the most part in dark and obscure places, beneath stones, logs of wood, and dried leaves, ete., and feeding on living animals. On the other hand, we have the Chilognatha, or Miullepedes, distinguished by their slow movements and vegetable diet; inoffensive to man, except by the destruction they occasion to his crops, and having as a means of defence no formidable weapon like the large poison claws of the Centipedes, but only a peculiarly offensive liquid secreted by special glands Il HABITS AND DISTRIBUTION 31 known by the unpleasant though expressive name of “stink glands,” or by the more euphonious Latin name of glandulae odoriferae. «As a general rule the larger species of Myriapods are found in the hotter climates, some of the tropical species being very large, and some, among the family of the Scolopendridae, extremely poisonous; and it is even said that their bite is fatal to man. If, however, the Centipede is sometimes fatal to man, it does Fic. 15.—Scolopendra obscura. (From C. L. Koch, Die Myriapoden.) not always have it its own way, for we read of man making food of Centipedes. It is hard to believe that any human being could under any circumstances eat Centipedes, which have been described by one naturalist as “a disgusting tribe loving the darkness.” Nevertheless, Humboldt informs us that he has seen the Indian children drag out of the earth Centipedes eighteen inches long and more than half an inch wide and devour them. Fic. 16.—Chordeuma sylvestre. (From C. L. Koch, Die Myriapoden.) This, I believe, is the only account of human beings using the Myriapoda as food, if we except the accounts of the religious fanatics among the African Arabs, who are said to devour Centi- pedes alive; though this is not a case of eating for pleasure, for the Scolopendras are devoured in company with leaves of the prickly pear, broken glass, etc, as a test of the unpleasant things which may be eaten under the influence of religious excitement. 32 MYRIAPODA CHAP. A cold climate, however, is not fatal to some fairly large species of Centipedes. A striking instance of this came under my own observation some years ago. In 1886 I was travelling in the island of Cyprus—the “ Enchanted Island,” as Mr. Mallock calls it in his book written about the same time—with the intention of observing its natural history. This island consists of a broad flat country crossed by two mountain ranges of con- siderable height, thus offering the contrast of a hot climate in the plains and a cold climate in the mountains. On the plain country I found among the Myriapoda that the most common species were a large Scolopendra and a large Lithobius. The Scolopendra was fairly common, living for the most part under large stones, and it was a pleasant task to search for them in a ruined garden near Larnaca. This garden was made for the public, and is situated about a quarter of a mile from the old town of Larnaca. It has been suffered to fall into decay, and is now quite neglected. Mr. Mallock has described many beautiful scenes in his book, but I think he could have found few more beautiful than this old garden with its deserted gardener’s house, now a heap of ruins, but overgrown with masses of Iuxuriant vegetation, with beauti- ful flowers peeping out here and there as if charitably endeavour- ing to hide the negligence of man, and to turn the desolation into a scene of beauty. I got several prizes in this garden, but found the Myriapods were principally represented by the species I have mentioned. After leaving Larnaca I rode across the plain country through blazing heat, which was rapidly parching up the ground to a uniform brown colour, At every stopping-place I found the same species of Scolopendra and of Lithobius. After a few days I began to get up among the mountains of the northern range, and the burning heat of the treeless plain was gradually exchanged for the cool shade of the pine-trees and the fresh air of the mountains. As I ascended higher and higher the tem- perature grew cooler till I reached the top of Mount Troodos, the ancient Olympus. Here in the month of May the snow still lingered in white patches, and the air was clear and cold, I remained on the top of Troodos for a week, while I made a close examination of the fauna to be found there. I was much surprised to find the identical species of Scolopendra and II HABITS AND DISTRIBUTION 33 Lithobius with which I had become acquainted in the heat of the low country, quite at home among the snow, and as common as in, what I should have imagined to be, the more congenial chmate. Nor were they any the less lively. Far from exhibit- ing any sort of torpor from the cold, the first one which I triumphantly seized in my forceps wrigeled himself loose and fastened on my finger with a vigour which made me as anxious to get rid of him as I had formerly been to secure him. How- ever, he eventually went into my collecting box. a On the whole, we may say that the Chilopoda are most largely represented in the hotter climates, where they find a more abundant diet in the rich insect life of the tropical and semi-tropical countries. The more brightly-coloured Myriapods, too, are for the most part inhabitants of the warmer countries. The ease with which they are introduced into a country in the earth round plants, and in boxes of fruit, may account to a great extent for the wide distribution of the various species in different countries. Mr. Pocock, who examined the Myriapods brought back from the “ Challenger ” Expedition, informs us that of ten species brought from Bermuda, four had been introduced from the West Indies. There is no doubt that animals which can bear changes of temperature and deprivation of food, and even a short immersion in the water, are well calculated to be introduced into strange countries in many unexpected ways. As might be expected from a class of animals so widely distributed, Myriapods show an almost infinite variety of size and colour. We find them so small that we can hardly see them with the naked eye, as in the case of the tiny Polyaenus, the Pauropidae, and the Scolopendrellidae. We also find them more than six inches in length, as the larger species of Scolo- pendridae. I am afraid we must dismiss as an exaggeration an account of Centipedes in Carthagena a yard in length, and more than six inches in breadth. The giver of this account— Ulloa —informs us that the bite of this gigantic serpent-like creature is mortal if a timely remedy be not applied. It is certainly extremely probable that the bite of a Centipede of this size would be fatal to any one. Some Centipedes are short and broad, and composed of few segments, as Glomeris ; some are long and thin, with more than a hundred segments, as Geophilus. They may be beautifully coloured with brilliant streaks of colour, as in some VOL. V D 34 MYRIAPODA CHAP. of the Julidae or Polydesmidae, or may be of a dull and rusty ‘iron colour, or quite black. One of the strangest peculiarities found among Myriapods is that some of them (eg. Geophilus electricus) are phosphorescent. As I was walking one summer evening near my home in Cambridgeshire I saw what I thought was a match burning. Looking more closely, I saw it move, and thinking it was a glow-worm I picked it up, and was surprised to find that it was a Geophilus shining with a brilliant phosphorescent hght. I let it crawl over my hand, and it left a bright trail of light behind it, which lasted some time. I have been told that this species is common in Epping Forest ; also in Cambridgeshire.’ Besides G. eleetricus, G. phosphoreus has been described as a luminous species by Linnaeus, on the authority of a Swedish sea captain, who asserted that it dropped from the air, shining like a glow-worm, upon his ship when he was sailing in the Indian Ocean a hundred miles from land. What the use of this phosphorescence may be is not Known with any degree of certainty. It may be either a defence against enennes, or else a means of attracting the two sexes to one another. The places which the Myriapods select for their habitation vary as much as their colour and size, though, with a few excep- tions, they chose dark and obscure places. A curious species of Myriapod is Pseudotremia cavernarum (Cope), which is found in certain caves in America. The peculiar hfe it leads in these caves seems to have a great influence on its colour, and also affects the development of its eyes. Mv. Packard’s account of them is worth quoting: “ Four specimens which I collected in Little Wyandotte cave were exactly the same size as those from Great Wyandotte cave. They were white tinged, dusky on the head and fore part of the body. The eyes are black and the eye-patch of the same size and shape, while the antennae are the same. “Six specimens from Bradford cave, Ind. (which is a small grotto formed by a vertical fissure in the rock, and only 300 to 400 yards deep), showed more variation than those from the two Wyandotte caves. They are of the same size and form, but shghtly longer and a little slenderer. .. The antennae are much whiter than in those from the Wyandotte caves, and the See L. Jenyns’ Observations in Nat. Hist. Loudon, 1846, p. 296. II HABITS AND DISTRIBUTION 35 head and body ave paler, more bleached out than most of the Wyandotte specimens... . It thus appears that the body is most bleached and the eyes the most rudimentary in the Bradford cave, the smallest and most accessible, and in which consequently there is the most variation in surroundings, temperature, access of light and changed condition of air. Under such cirewmstances as these we should naturally expect the most variation.” ! «A strong contrast to these animals is afforded us by the Scutigeridae (Schizotarsia). They are wnknown in this country, but abound in some of the Mediterranean countries and in parts of Africa. They remind one strongly of spiders, with their long Fic. 17.—Cermatia (Scutigera) variegata. (From C. L. Koch, Die Myriapoden.) legs and their peculiar way of running on stones and about the walls of houses. Some years ago I was in Malta, and I used to go and watch them on the slopes outside Valetta, where they were to be found in great numbers. They used to come out from beneath great stones and run about rapidly on the ground or on the stones and rubbish with which the ground was covered, now and again making a dart at some small insect which tempted them, and seemingly not minding the blazing sun at all. As might be expected from their habits, their eyes, far from being rudi- mentary, like those of the cave-living Pseudotremia, or absent 1 « A Revision of the Lysiopetalidae, a family of the Chilognath Myriapoda, with a notice of the genus Cambala,” by A. S. Packard, junior, Proc. Amer. Phil. Soc. xxi. 1884, p. 187. 36 MYRIAPODA CHAP. like those of the Polydesmidae, or of our own Cryptops, are highly developed, and form the only example among the Myriapods of what are known as facetted eyes. The Scutigeridae are also remarkable among Myriapods for the possession of a peculiar sense-organ which is found in no other Myriapod. The Myriapods most numerous in our own country are Lithobius and Julus. Lithobius, which will be described later on, may be found in almost any garden under dried leaves, stones, ete. Julus, the common wire-worm, is found crawling on plants and leaves and under the bark of trees, and does a good deal of damage in a garden. Polydesmus is also frequently found in great numbers, and usually a great many of them together. Glomeris is also found, though it is not so common as the first two mentioned animals. Geoph2z/us is also common, and especially in the south of Eneland. Scolopendridae are only represented by a single genus, Cryptops, which is not very common, though by no means rare. The best place to find them is in manure heaps. The animals of this species are sinall compared to most Scolopendras, and have the peculiarity of being without any eyes. Scutigera is unrepresented in this country. One was found in Scotland some years ago by Mr. Gibson Carmichael, but was shown to have been imported, and not bred in the place. The means of defence possessed by these animals also differ very much in the different species of Myriapods. In the Centipedes the animals are provided with a powerful weapon in the great poison claws which he just beneath the mouth, and which are provided with large poison glands, which supply a fluid which runs through a canal in the hard substance of the claw and passes into the wound made hy the latter. The effect of this fluid is instantaneous on the small animals which form the food of the Centipedes. I have myself watched Zi/hobivs in this country creep up to a blue-bottle fly and seize it between the poison claws. One powerful nip and the blue-bottle was dead, as if struck by lightning. I have also seen them kill worms and also other Lithobivs in the same way. When another Lithobius is wounded by the poison claws it seems to be paralysed behind the wound. The Millepedes, on the other hand, have no such offensive and defensive weapon. They rely for protection on the fluid secreted by the stigmata repugnatoria (or glandulae odori- ferae) mentioned before. This fluid has been shown to contain II HABITS, BREEDING iE prussic acid, and has a very unpleasant odour. Most of the Millepedes are provided with these glands; but in the cave Myriapods mentioned before, the animals have not to contend against so many adversaries, and these glands almost disappear. Other Myriapods defend themselves by means of the long and stiff bristles with which they are pro- vided, eg. the little Polyaenus. This means of defence seems to have been more common among the fossil Myria- pods than among those still living. Variations in the shape and size of the limbs are numerous,as might beexpected F1e-18.—Potysenus laguras (From 3 fe C. L. Koch, Die Myriapoden). in so large a class of animals. One of ; the most curious of such variations is found in a Centipede of the Seolopendra tribe, called Zucorybas, in which the last limbs are flattened out and provided with paddle-shaped lobes. The use of these is unknown, but it is probable that they are concerned in some way with the breeding habits of the animal. The habits of the Myriapods connected with their breeding are most interesting, but have been very insufficiently investigated. There is no doubt that a full inquiry into all such habits would he of great interest, and would help to answer some of the problems which are still unsolved in these forms. My own observations refer to two forms—Julus terrestris among the Millepedes, and Lithobius forfieatus among the Centipedes. Ju/us terrestris is one of the most common of the English Millepedes, and can be easily obtained. I kept them in large shallow glass vessels with a layer of earth at the bottom, and thus was able easily to watch the whole process. They breed in the months of May, June, and July. The female Ju/us when about to lay her eggs sets to work to form a kind of nest or receptacle for her eggs. She burrows down into the earth, and at some distance below the surface begins the work. She moistens small bits of earth with the sticky fluid secreted by her salivary glands, which become extraordinarily active in the spring. She works up these bits of earth with her jaws and front legs till they are of a convenient size and shape, and places them together. When complete, the nest is shaped like a hollow sphere, the inside being smooth and even, while the outside is rough and shows the shape of the small knobs of earth of which it is composed. 38 MYRIAPODA CHAP. She leaves a small opening in the top. The size of the whole nest is about that of a small nut. When she is ready to lay her eges she passes them through the hole in the top, and usually lays about 60 to 100 eggs at a time. The eggs, which are very small, are coated with a glutinous fluid which causes them to adhere together. When they are all laid she closes up the aperture with a piece of earth moistened with her saliva; and having thus hermetically sealed the nest, she leaves the whole to its fate. The eges hatch in about twelve days. A naturalist named Verloet has lately found that the males of some Julidae undergo certain changes in the form of the lees and other organs in autumn and spring. These changes are probably connected with the lreedine of the animal, and remind us of the changes undergone during the breeding season by salmon among the fishes. Julus breed very readily if carefully attended to and well supplied with food. It they cannot obtain the food they like they will not breed go well. I found that sliced apples with leaves and grass formed the best food for them. The process in the case of Lithobius is much harder to watch. Lithobius is not so plentiful as Julus terrestris, and the animals are more lnpatient of captivity, more shy in their habits, and do not breed so readily. In January 1889 I was given the use of a room in the New Museums at Cambridge, and was allowed to fit it up as I liked, so that I was able to try the effect of different degrees of light and darkness, and of different degrees of warmth. I succeeded in observing the whole process. The female Lithobius is furnished with two small movable hooks at the end of the under surface of the lody close to the opening of the oviduct. These small hooks have been observed by many naturalists, but their use has, so far as I know, never been described before. They play an important part in the proceedings following the laying of the egs. The time of breeding in Lithobius is rather later than in J/ulus, and begins about June and continues till August. There are first of all some convulsive movements of the last segments of the body, and then in about ten minutes the egg appears at the entrance of the oviduct. The egg is a small sphere (about the size of a number five shot), rather larger than that of Julus, and is covered with a sticky slime IL HABITS, BREEDING 39 secreted by the large glands inside the body, usually called the accessory glands. When the egg falls out it is received by the little hooks, and is firmly clasped by them. This is the critical moment in the existence of the Lithobius into which the egg is destined to develop. If a male Lithobius sees the egg he makes a rush at the female, seizes the ege, and at once devours it. All the subsequent proceedings of the female seem to be directed to the frustration of this act of cannibalism. As soon as the ege is firmly clasped in the little hooks she rushes off to a convenient place away from the male, and uses her hooks to roll the egg round and round until it is completely covered by earth, which sticks to it owing to the viscous material with which it is coated; she also employs her hind legs, which have glands on the thighs, to effect her purpose. When the operation is complete the egg resembles a small round ball of mud, and is indistinguishable from the surrounding soil. It is thus safe from the voracious appetite of the male, and she leaves it to its fate. The number of eggs laid is small when compared with the number laid by Julus. The food in the case of Lithobius consisted of worms and blue-bottles, which were put alive into the glass vessel containing the Lithobius. I tried raw meat chopped up, but they did not thrive on it in the same way that they did on the living animals. I also put into their vessel bits of rotten wood containing larvae of insects, ete. I have sueceeded in bringing back some specimens of Polydesmus alive from Madeira, and in getting them to breed in this country —of course in artificial warmth—and their way of laying eges and making a nest resembles that of Julus. Geophilus has one curious habit in connexion with the fertilisation of the female. The male spins a web and deposits in the middle of it a single spermatophore, and the female comes to the web to be fertilised. The Scolopendridae are said to bring forth their young alive, but I think the evidence for this is unsatisfactory. What have been taken for the young Scolopendrae are perhaps the large spermatophores of the male, which are not unlike a larval Myria- pod in size and shape. I have never been able to observe the process of breeding in this family. I have had the spermatophores sent me from Gibraltar as “eggs,” but a little examination soon showed me their real character. 40 MYRIAPODA CHAP. The mode of progression in the Myriapods differs considerably, as might be expected in a class in which the number of legs varies to such an extent. The swiftest among them are the Seutigeridae with their long spider-like legs. The Scolopendridae are also able to move with considerable rapidity, and are also able to move tail forward almost as well as in the ordinary manner. Where there are such a number of legs it becomes a curious question as to the order in which the animal moves them; and though several people have endeavoured to find this out, the number of legs to be moved and the rapid movements have rendered accurate observation impossible. Some years ago Professor E. Ray Lankester tried to study the order in which the legs of Centipedes moved, and came to the conclusion (recorded in an amusing letter in Witure, 23rd May 1889) that if the animal had to study the question itself, 16 would not get on at all. He finishes his letter with the follow- ing verses :— A Centipede was happy quite Until a toad in fun Said, “Pray which leg moves after which ?” This raised her doubts to such a pitch, She fell exhausted in the ditch, Not knowing how to run, The progression of Millepedes is much slower than that of the Centipedes, and it is remarkable that when the animal is in motion a sort of wave runs down the long fringe-like row of feet. I have endeavoured to make out this motion, but have never been able to understand it satisfactorily. MLy belief was that the feet were moved in sets of five. This wave-lke pecularity of motion is described in a curious old book, An Essay towards a Natural History of Serpents. Charles Owen, D.D. London, 1742: “The Ambua, so the natives of Brazil call the Millepedes and the Centipedes, are serpents. Those reptiles of thousand legs bend as they crawl along, and are reckoned very poisonous. In these Multipedes the mechanisia of the body is very curious; in their going it is observable that on each side of their bodies every leg has its motion, one regularly after another, so that their legs, being numerous, form a kind of undulation, and thereby communicate to the body a swifter progression than one could imagine where Il NAMES FOR MYRIAPODS 41 { so many short feet are to a so many short steps, that follow one another rolling on like the waves of the sea.” Before proceeding to the classification of Myriapods, which will form the next part of this account, a few words on the common names for them may not be without interest. In English we have the names Centipede and Millepede, and the Continental nations have similar names implying the possession of a hundred or a thousand legs, as the German “ Tausendfiisse ” and the French “ Millepieds.” Of course these are general words, simply implying the possession of a great number of legs. But we have also among the peasantry a name for Centipedes which conveys a much more accurate idea of the number. The people of the eastern counties (I daresay the term is more widely spread) call them “* forty legs.” This is not quite accurate, but as Lithobius has 17 legs on each side, and Scolopendra (Cryptops is the English species) has 21 on each side, it is a better approximation than Centipede. But another country has a still more accurate term. I found some Scolo- pendra in Beyrout, and asked my native servant what he called them. He gave them what I afterwards found was the common Arab name for them, “‘arba wal ‘arbarin,” forty-four legs. Now the Scolopendras, which in hotter climates are the chief representa- tives of the Centipedes, have actually forty-two legs, or, if the poison claws are counted, forty-four. In looking up the Arab term for Centipede I came across a curious description given of them by Avicenna, the great Arabian physician: “This is an animal known for its habit of going into ears. For the most part it is a palm’s length” [about four inches, which is the average length of many species]. “On each side of the body it has twenty- two feet, and moves equally well either backwards or forwards.” With regard to its alleged habit of going into ears, the learned Arabian has evidently made a false imputation on the character of owr animal, and has probably relied too much on the stories told him. He has also exaggerated in stating that it goes equally well either backwards or forwards. Some Centi- pedes can go backwards very easily and well, though not so well as forwards. Perhaps he preferred examining dead specimens, which afford an easy opportunity of counting their legs, to experi- menting with living animals, which might have resented liberties taken with them. 42 MYRIAPODA CHAr. The Persians have several words for them, less accurate than the Arabs and more like our own terms. For instance, they call them “Hazarpa,” or thousand feet, like our Millepedes ; also “Sadpa,” or hundred feet, equivalent to our Centipedes. Another teri resembles our common term before mentioned, “ Chehlpa,” forty feet. A more figurative term is “tashih dud,” a worm resembling a rosary with a hundred beads; this word is trans- lated in Richardson’s Persian Dictionary as “a venomous insect having eight feet and a piked tail.” Classification of the Myriapoda. Two of the principal writers on the classification of the Myriapods are Koch and Latzel, both of whom have classified the whole group. I do not wish for a moment to undervalue the many authors who have done excellent work on the classifi- cation of different groups and families, but I wish here to give an outline of a classification of the whole class, and I naturally have recourse to the authors who have treated the subject as a whole. Koch’s two works, the System der Myriapodent and Dir Myriapoden? cover the whole range of the class, and his divisions are clearly marked out and are easily understood, but both works are comparatively old. He does not include the Scolopendrellidae or the Pauropidae, which are now included ly all naturalists in the Myriapoda. Latzel is a more recent writer, and though his work is entitled Zhe Myriapods of the Austro-Hungarian Empire? he gives iwmuch information about Myriapods not found in Europe, and his work is fairly entitled to be considered as embracing the whole class. He divides the Myriapods into four Orders, including the Scolopendrellidae and Pauropidae. On the whole, I think it will be better here to take the classification of Koch, and to add to it the two Orders before mentioned, viz. Symphyla containing one family the Scolopendrellidae, and Pauro- poda with one family the Pauropidae. The Orders are as follows :— LC. L. Koch, System der Myriupoden. Regensberg, 1847. " C. L. Koch, Die Myriapoden. Walle, 1863. 5 Latzel, Die Myriapoden der Esterreichisch -Ungarischen Monarchic. Wien, 1880. I CLASSIFICATION 43 Order I. CHILOGNATHA ( = DIPLOPODA) Antennae 7 joints, three anterior body rings with one pair of legs to each ring. Posterior rings with two pairs of legs to eachi. Genital organs opening ventrally on the anterior rings of the posterior part of the body, ae. on one of the anterior of the segments bearing two pairs of legs; usually the 7th. This Order is divided into eight families :— Family 1. Polycenidae. Ten body rings, not counting the neck-plate. Thirteen pairs of limbs. Eyes hard to find, on the lateral corner of the head (Fig. 18, p. 37). Family 2. Glomeridae. 11 body rings. 17 pairs of legs. Eyes arranged in a row curved outwards. 3 ERG ae y Fic. 19.—Glomeris marginata. (From C. L. Koch, Die Myriapoden.) Family 3. Sphaerotheriidae. 12 body rings. 19 pairs of legs. Eyes crowded together in a cluster. Fic. 20.—Sphuerotherium grossum. (From C. L. Koch, Die Myriapoden.) Family 4. Julidae. Body cylindrical. More than 30 body rings. Many eyes crowded together in a cluster. Fic, 21.—Julus nemorensis. (From C. L. Koch, Die Myriapoden.) 44 MYRIAPODA CHAP. Family 5. Blanjulidae. Thin cylindrical body with more than 30 body rings.) Eyes either absent or in a simple row beneath the edge of the forehead. Fic, 22.—Blanjulus guttulatus. (From C. L. Koch, Die MLyriapoden.) Family 6. Chordewmidae, Resemble the Polydesmidae (Fam. 7), but the head is longer and less rounded in the forehead. The antennae are placed more at the side of the head. Eyes sinall and numerous, in a cluster. Body rings always 30 (Fig. 16). Family 7. Polydesmidae. Body cylindrical, with a lobe or keel on the posterior part of the upper surface of the body ring. Always 19 body rings. No eyes. Fic, 23.,—Polydesmus collaris, (From C. L. Koch, Die Myriapoden.) Family 8. Polyzoniidae, Body with varying number of rings arched transversely downwards and sharp at the sides. The anterior part of the ring somewhat hidden. The Fic. 24,—Polyzonium germanicum. (From C, L. Koch, Die Myriapoden.) eyes in a simple row. The stigmata very small and placed near the lateral corner of the body ring. Head small in proportion to the body. Order II. CuILopopa (or SYNGNATHA). Antennae with many joints, at least 14. Only one pair of legs to each body ring. The genital opening on the last ring of the body. Bases of the legs widely separate. There are four families in this Order :— II CLASSIFICATION 45 Family 1. Lithobiidae. Body with 9 principal and 6, subsidiary rings) On both principal and subsidiary rings one pair of legs, except on the last ring of the body. Many Fic. 25.—Lithobius erythrocephalus. (From C, L. Koch, Die Myriapoden.) eyes ; the posterior ones large and kidney-shaped. The antennae with many rings, Family 2. Scolopendridae. Body with 21 or 23 rings, no intermediate rings. Every ring with one pair of legs. The last pair very long. Last pair at the point of the last ving. Four or no eyes. Antennae with 17 or 20 joints. (Fig. 15, p. 31). Family 3. Notophalidae. Body very long, 200 to 350 rings; alternate principal and subsidiary Fic. 26.—WNotophilus taeniatus. (From C. L. Koch, Die Afyriapoden.) rings. A pair of legs to each principal ring. No eyes. Maxillary palps 46 MYRIAPODA CHAP. very thick. Compact or very short limbs. The terminal point of the last limb without claws. Family 4. Geophilidae. Body long, 80 to 180 rings, principal and subsidiary. No eyes. The Fic. 27.—Geophilus longicornis. (From C. L. Koch, Die Myriapoden.) maxillary palps not compact, and with first joint large. Last joint of the last pair of legs with a sharp claw. Order III. ScHIZOTARSIA. The tarsi of all the legs multiarticulate. The eyes facetted. Peculiar sense organ beneath the head. Family 1. Cermatiidae (Scutigeridae) Antennae with unequal number of joints. Body rings, each with one pair of less. Dorsal scutes not so large as ventral. Limbs long and multiarticulate. (Fig. 17, p. 35). Order IV. SymMpHy.a. Myvriapods resembling Thysanura. A pair of limbs to each segment. The antennae are simple and multiarticulate with un- equal joints. Eyes few. Mandibles short. One pair of maxillae. No maxillipedes. Genital orifice in the last segment of the body. A single pair of tracheae. Two abdominal glands on the posterior part of the body. Two caudal appendages. Free dorsal scutes. Ventral scutes often with parapodia. Family 1. Scolopendrellidae. With the characters of the Order. UI STRUCTURE 47 Order V. PAUROPODA. A par of Lmbs to each segment. Antennae branched. Eyes few or none. Labrum and labium indistinct. Cenital orifice at the base of the second pair of limbs. Free dorsal scutes. Nine pairs of feet (always?) Some segments with sensitive hairs. Last segment the smallest. Family 1. Pauropidae. Body slender. Dorsal scutes smooth. Limbs long and projecting from the lateral margins of the body. Colour pale. The Structure of the Myriapoda. Having now given a short view of the classification of the Class, I will proceed to give a general account of their structure, the variations in which have led to the divisions into the various Orders and Families. Their structure shows resemblances to several widely different classes of animals. One cannot help being impressed with their likeness to the Worms, at the same time they have affinities with the Crustaceans, and still more with the Insects. In the latter class the likeness of the Thy- sanuridae to Scolopendrella and Pauropus have induced a cele- brated Italian anatomist, Professor Grassi, to claim the former as the ancestors of the Myriapoda. Myriapods have a body which is segmented, as it is termed ; that is, composed of a number of more or less similar parts or segments joined together. One of the most important characteristics which distinguish Myriapods from other Arthropoda is the fact that they possess on the posterior segments of the body true legs which are jointed and take part in locomotion. The head is in all cases quite distinct from the body, and may be regarded as a number of segments fused together into one mass. Their heads are always provided with a single pair of antennae and mouth appendages, consisting of an upper lip, a pair of mandibles or -jaws, and one to two pairs of maaillae. The mandibles resemble those of Insects, and are strongly toothed. In the Chilognatha a pair of maxillae are fused so as to form a single oval appendage. In the Chilopoda they each consist of a single blade bearing a 48 MYRIAPODA CHAP. short palp or feeler. The mouth parts may have the forms known as chewing, biting, or suctorial (Po/yzoniwm) mouth appendages. With the exception of the terminal segment, and in many cases the first or the seventh, each segment bears one or two pairs of limbs. These may be very long, as in Seutigera, or very short, as in Polywenus. They may be attached close to one another near the ventral middle line of the body, or may have their bases far apart from each other, as im the Chilopoda. The exoskeleton or external armour is composed of chitin (Chilopoda) or of chitin with calcareous salts deposited in it (Chilognatha). Their internal structure has a great likeness to that of Insects. The general position of the internal organs may be seen from Fig. 28, which shows a Lithobius dissected so as to exhibit the digestive and nervous systems. Lhe digestive canal, which is a straight tube, extends through- out the whole length of the body, and terminates in the last segment of the body. It may be divided into the following parts :— 1. A narrow oesophagus, beginning with the mouth or buccal cavity, and receiving the contents of two or more salivary glands (¢). 2. A wide mesenteron or mid-eut (7) extending throughout almost the whole length of the body. . A rectum which at its junction with the mid-gut receives the contents of two or four Malpighian tubes (g, h) which function as kidneys. Their function was for a long time unknown, but the discovery of crystals of uric acid in them placed the matter beyond doubt. The heart has the form of a long pulsating dorsal vessel which extends through the whole length of the animal. It is divided into a number of chambers, which are attached to the dorsal wall of the body, and are furnished with muscles of a wing-like shape, which are known as the alary muscles, and which govern its pulsations. The chambers are furnished with valves and arteries for the exit of the blood, and slits known as ostia for the return of the blood to the heart. The blood enters the chambers of the heart from the body cavity through the » w IL STRUCTURE 49 ostia, and passes out through the arteries to circulate through the organs of the body and to return by the ostia. The two figures below (Figs. 29 and 30) show the position of the arteries and the ostia in a single segment of the body. The heart is too small and delicate to be seen with the naked eye; it Fic. 28.—Lithobius dis- sected. (After Vogt and Yung.) a, antennae. b, poison claws. c, brain. d, salivary glands. e, legs. J; nerve cord. g, Malpighian tube. h, Malpighian tube. 4, vesicula seminalis. j, accessory gland. k, accessory gland. Z, testis. m, thigh gland. n, digestive tube. therefore requires the aid of the microscope. A freshly-killed animal was therefore taken and prepared in the manner known to all microscopists, and extremely thin slices or sections cut horizontally from its back. One of these sections cut the whole length of the heart in one segment, which was accordingly drawn under the microscope (Fig. 29), and shows a longitudinal hori- VOL. V E 50 MYRIAPODA CHAP. zontal section through the whole length of the heart in a single segment, with the two ostia at each end of the segment and the two arteries in the middle. The arteries, when they leave the body, pass into masses of fatty tissue on either side of the heart, and the other figure (Fig. 30) is intended to showthe ar tery leaving the heart and penetrating into the fatty tissue. The figure is taken from the same section as the former one, but is much more highly magnified, so as to show more detail. The delicate coats of the heart are shown, the artery being covered with a clothing of large cells. Sosy a °e Art— Ht. Fie. 29.—Heart of Fic. 30, — Heart of Julus terrestris showing structure of Julus terrestris artery (A7¢.) and external coat of heart (ext.c), also fat body showing ostia (ost) (Fb), highly magnified. Ht, The cavity of the heart. The and arteries (.17¢) circular muscle fibres which surrounds the heart are shown magnified. just below the external coat (ext.c) ogl, Oil globules of the fat body. Myriapods breathe by means of tracheae, with the exception of the Scutigeridae, which have an elementary form of lung which resembles that of spiders, and will be mentioned further on. These tracheae, as in Insects, are tubes lined with chitin, which is arranged in spiral bands. The tracheae open to the exterior by openings called stigmata, through which they receive the external air, which passes into the main tracheal tubes and into their ramifications, and thus effects the aeration of the blood. The nervous system of the Myriapods consists, as in Insects, of a brain, which may be more or less developed, a circum- oesophageal ring embracing the oesophagus, and a ventral chain of gangha, and in some cases (Newport) of a system of visceral II STRUCTURE 51 nerves. With the nervous system we may mention the sense organs, the eyes, which are present in most cases, though wanting, as has been already stated, in many groups. They are usually present as clusters of ocelli or eye spots closely packed together, or (in Scutigera) as peculiarly formed facetted eyes. The sensory hairs on the antennae must be reckoned as sense organs, as also the tufts of sense hairs on the head of Polywenus. Scuti- gerd has also a peculiar sense organ beneath the head, consist- ing of a sac opening on the under side of the head full of slender hairs, each of which is connected at its base with a nerve fibre. Except the eyes, the Myriapod sense organs have usually the form of hairs or groups of hairs connected with nerve fibres, which communicate with the central nervous system. Mi sk ee ete of Scutigera coleoptrata, with sense organ. eo, Opening of sense organ to the exterior ; 0, sense organ shown through Fic, 32.—Highly magnified section through head the chitin; m, mouth; oc, of Polyxenus lagurus, showing sense organ. eye; mal, maxilla ; f, furrow in ext.cut, external cuticle; ¢, tube surrounding the chitin. (Heathcote, Sense base of sense hair; gang.c, ganglion cell. organ in Scutigera coleoptrata. ) (Heathcote, Anatomy of Polyxenus lagurus. ) These two sense organs are shown in Figs. 31 and 32. Fig. 31 shows the under side of the head of Sewtigera (Fig. 17), with the position of the sense organ and its opening. Fig. 32 is part of a section through the head of Polywenus with two of the sense hairs. Each spine or sense hair fits into a cup in the chitin of the head; and the lower or internal part, which is divided from the upper or external part by a rim, is joined to a ganglionic nerve cell (gang-c.). The Myriapods are of separate sexes, and the generative organs in both cases usually have the form of a long unpaired 52 MYRIAPODA CHAP. tube, which in the male is connected with accessory glands, and im the female is usually provided with double receptacula seminis. The generative openings usually he near the base of the second pair of legs (Chilognatha), or at the posterior end of the body (Chilopoda). In the Chilognatha there is usually in the male an external copulatory organ at the base of the seventh pair of legs, remote from the genital opening. The preceding account of the anatomy of the Myriapods has shown us the general characteristics of the whole group. I shall now take each of the five Orders into which the class is divided in the classification adopted in this account, and endeavour to explain the differences in anatomy which have led to the estab- lishment of the Order. The first Order with which we have to do is that of the Chilognatha, which includes a large number of Myriapods ; no less than eight families, some of them including a great number of forms. Order I. Chilognatha. The Chilognatha differ from other Orders in the shape of the body. This is in almost all cases, cylindrical or sub-cylindrical, instead of being more or less flattened as in the other Orders. The body, as in all other Myriapods, is composed of segments, but in the Chilognatha these segments are composed, in almost all cases, of a complete ring of the substance of which the exoskeleton (as the shell of the animal is called) is composed. This substance is in the case of the Chilognatha chitin (a kind of horny substance, resembling, for instance, the outer case of a heetle’s wing), containing a quantity of chalk salts and colouring matter ; the substance thus formed is hard and tough. In other Orders the chitin of the exoskeleton is without chalky matter and is much more flexible. The length of the body, as may be seen from the classification, may be either very long, as in Julus, or very short, as in Glomeris. The next anatomical character distinctive of the Order is the form of the appendages. First, the antennae. These are, as a general rule, much shorter than in the Chilopods, never reaching the length of half the body. They are, as a rule, club- shaped, the terminal half being thicker than the half adjoining the body. II STRUCTURE OF CHILOGNATHA 53 The next appendages to be mentioned are the mouth parts. These differ in form from those of the other Orders, and their differences are connected very largely with the fact that the Chilognatha live on vegetable substances. Their mouth parts are adapted for chewing, except in the case of the Polyzoniidae, the eighth family of the Order, in which, according to Brandt, the mouth parts are adapted for sucking, and are prolonged into a kind of proboscis. The mouth parts of the Chilognatha a consist of— (1) An upper lip. A transversely-placed plate, which is fused with the rest of the head. (2) A pair of powerful mandibles or jaws adapted for mastica- tion, and moved by powerful muscles. jf and g in Fig. 35 shows these mandibles, while the rest of the figure consti- tutes the broad plate (No. 3). (3) A broad plate covering the under part of the head and partially enclosing the mouth. This Fic. 33.— Mouth parts of 2 Chilognatha, (From C. L. structure, which, as we shall Koch, Die System der afterwards see, is formed by cane ae the fusion of two appendages — marked «, b, ¢ d, e are which are distinct in the — fmly mnited A se animal when just hatched, has They have received the been called the deutomalae, oe ee the jaws receiving the name of stipes; d, malellae; e, hypostoma. protomalae. After the mouth parts we come to the legs. We first notice the fact that the bases of the legs in each pair are closely approached to one another. They are so set into the body that the basal joints, or, as they are called, the coxal joints, nearly touch. This is the case in almost all Chilognatha, except in the Polyxenidae, and it is a fact connected with some important features in the internal anatomy. Then we have the peculiarity in the Chilognatha which has formed the basis of most classifi- cations which have placed these animals in a group by themselves. This is the possession in most segments of two pairs of legs. This characteristic has caused the group to be called by some naturalists Diplopoda. As a general rule, the first four segments 54 MYRIAPODA CHAP. have only three pairs of legs between them, one of them being without a pair of legs. This legless or apodal segment is usually the third. From the fifth segment to the end of the body all the segments have two pairs of legs each. The legs are shorter than those of the Chilopods, and are all nearly equal in size. This is not the case in the other Orders. The legs are commonly wanting in the seventh segment of the male, and are replaced by a copulatory organ. This peculiarity is related to the different position of the generative openings in the Chilo- gnatha. Another anatomical feature peculiar to the Chilognatha is the possession of the stink glands—the glandulae odoriferae before mentioned. This, however, is a character which does not hold for all the Chilognatha, since the Polyxenidae have none of these glands. All the other families, however, possess them, and they are present in none of the other Orders. As regards the internal anatomy of the Chilognatha, the digestive canal differs mainly in the glands which supply it with secretions. It receives the saliva from two long tubular salivary glands, which open at the base of the four-lobed plate which has been mentioned as the third of the mouth appendages. The secretion of these glands is used, as has already been said, in the process of preparing the nest for the eggs. We cannot fail to be reminded of a similar function of salivary glands in those swallows, which prepare the nests of which bird’s-nest soup is made with the secretion of the salivary glands. Another feature in the form of the digestive tube is that in many cases, if not in all, it is marked with constrictions which correspond with the segments of the body. The heart in the Chilognatha is not such a highly developed organ as in the other Orders. The muscles which have already been mentioned as the alary muscles (or wing-shaped muscles) are not so highly developed, and consist for the most part of a few muscular fibres. The muscular walls of the heart, which consist of three layers, have the muscles less strongly developed, and are in general adapted for a less energetic circulation. The tracheae, which open into the stigmata, as has already been said, branch into tufts of fine tubes, but the ramifications of these tufts never join (or anastomose, as it is called), and con- sequently we never get, as in the other Orders, long tracheal trunks running along the body. It STRUCTURE OF CHILOGNATHA 55 The nervous system, in addition to the existence of the visceral nerve system described by Newport, shows a marked peculiarity in the form of the ventral ganglionic chain. As has already been said, the nerve system consists of a brain or mass of ganglia fused together and connected with the ventral nervous cord by a collar of nervous substance surrounding the oesophagus, and generally known as the circumoesophageal collar. The ventral nerve cord is a stout cord of nervous substance passing along the whole length of the animal, and situated below (or ventral to) the digestive tube and the generative system. This cord is enlarged at certain points, and these enlargements or swellings are called ganglia, while from the ganglia pass off nerves which supply the different organs of the body. In the Chilognatha the cord has a compressed appearance as if the ganglia were pressed into one another in such a way that it is very hard to distinguish any ganglia at all. If we use the microscope and examine sections cut transversely through the cord, we see that it is not a simple cord. Even if we examine the nerve cord with a simple lens, we see that a furrow runs longitudinally down it, and the use of the compound microscope shows us that this furrow represents a division into two cords in such a way that the single stout cord as it appeared to the naked eye is in reality two cords running side by side, and so com- pressed together that the substance is partly fused together. The ganglia too are double, being swellings of the two cords and not a single enlargement on a single cord. As we shall see in the other Orders, this arrangement constitutes a characteristic distinction. The generative organs consist of a long tubular ovary or testis lying along almost the whole length of the body and placed between the digestive organ and the nervous system. Near its exit from the body the long tube divides into two short tubes, the oviducts in the female or the vasa deferentia in the male. These ducts open in the third segment of the body, unlike those of Myriapods belonging to other Orders. The accessory glands present in most other Myriapods are not present in the Chilognatha. The general arrangement of the organs of the Chilognatha may be seen from Fig. 34, which represents a transverse section through the body of Polywenus (Fig. 18). A comparison of 56 MYRIAPODA CHAP. these two figures (Figs. 34 and 18) will show the position of the organs mentioned in this account. The heart is shown with the suspensory and alary muscles attached. Ree.sen. san Cte Wo —— eg fre, _ Fic. 34.—Transverse section through Polyxenus lagurus : Mettily Feels ganglionic and fibrous parts of nerve cord; Rec.sen, receptaculum seminis ; 3 ori.det, oviduct ; Spmzoa, spermatoza. (From Heathcote, Anatomy of Polyxenus lagurus. ’) o Order II. Chilopoda. The shape of the body differs from that of the Order which has been just described (Chilognatha), inasmuch as it is not cylindrical but flattened, the back, however, being more arched than the ventral surface. In this respect, however, it cannot be said to differ from the other Orders which we have yet to describe. The segments are not formed by a single ring of the exoskeleton, which in this Order is formed of chitin, and is tough and flexible rather than hard and strong; but of two or i plates which form a covering to the segment. The back is covered by a large plate known as the tergum, the sides by two plates known as pleura, and the ventral part by a plate called the sternum. The pleura and sternum are, however, in most cases fused together or indistinguishable. In this, as in most of the anatomical peculiarities, there is a much greater difference between the two Orders Chilopoda and Chilognatha than between II STRUCTURE OF CHILOPODA 57 the Chilopoda and the other three Orders which have still to be described. The Chilopoda have only one pair of appendages to each segment of the body instead of two pairs like the Chilognatha. The antennae of the Chilopoda are as a rule very long, and are always longer than in the Chilognatha which we have just described. They differ from those of the Schizotarsia (the third Order, which will be the next to be described) in having the basal joints nearer together; in other words, they are differently placed on the head. They differ from those of the Pauropoda (the fifth Order) in being straight and not branched. As a rule the antennae of the Chilopoda taper towards the extremity. A B c Fic. 35.—Mouth parts of Lithobius (Latzel). A, Head of Lithobius seen from the under surface after removal of poison claws: u, second maxilla; }, e, the two shafts of the first maxilla. B, One of the mandibles. ©, The two poison claws. The mouth parts are more numerous than in the Order we have just described (the Chilognatha). They consist of— 1. An upper lip. This is a transverse plate as just described in the case of the Chilognatha, but it is not always fused with the rest of the head. It is also usually composed of three pieces, two lateral and a middle piece. 2. A pair of jaws or mandibles, which are not of so simple a form as those of the Chilognatha, but rather resemble those of some of the Crustacea. 3 and 4. Two pairs of appendages called maxillae resem- bling feet, but used to aid the act of eating instead of locomotion. They are very different in different Chilopods, but are mostly slender and weak and usually provided with feelers (or palps) growing out of the main stem. 58 MYRIAPODA CHAP. 5. The next pair of appendages are the first pair of the legs of the body, which are also metamorphosed to serve a function different from the ambulatory function of the other limbs. These are the poison claws, and the possession of these forms another distinction between the Order we are now discussing and that of the Chilo- gnatha. At the same time the third Order, that of the Schizotarsia, has poison claws, so that this feature does not separate the Chilopoda from all the other Orders. These poison claws are large curved claws connected with poison glands, the secretion of which flows through a canal which opens near the point. The /egs are longer than those of the Chilognatha, but not so long as those in the next Order to be described (the Schizotarsia). Their number is very various, from 15 pairs in Lithobius to 173 in the Geophilidae. Latzel notes a curious point in the number of the legs in this Order, namely, the number of pairs of legs is always an uneven one. There are always one pair to each seg- ment. The last pair of legs is always longer than the other pairs, and this is a peculiarity of the Order. The digestive tube resembles that of the other Orders, but the salivary glands are not long and tubular but short (Fig. 28, d). tis, moreover, not marked with constrictions corresponding with the segments of the body. The tracheal system or the system of respiration may be said to be more highly developed in this Order than in any other. The tracheal branches anastomose with one another (that is, the branches join), and in some cases form lone tracheal stems running along the body almost for its whole length. The number of the tracheal openings or stigmata varies and does not correspond with the number of segments. The nervous system differs considerably from that in the Order Chilognatha; it resembles that in the Schizotarsia, and differs again from that in the other two Orders, Symphyla and Pauropoda. The brain shows some differences from other Orders chiefly in the development of the different lobes which are con- nected with the sense organs, the eyes and antennae, for instance ; but the most marked difference is in the ventral ganglionic cord. First, the ganglionic swellings are much more clearly marked than in the Chilognatha. Secondly, the first three ganglia differ IL STRUCTURE OF SCHIZOTARSIA 59 from the others in being nearer to one another and forming a single mass when seen by the naked eye, though when examined by the aid of a microscope we can see all the different parts are there. Thirdly, the division into two cords mentioned in the Chilognatha is carried to a much greater extent. The ganglia in each segment can be seen plainly to be double, and the cords connecting the ganglia are two in number. We can plainly see that the ventral nervous system of the Chilopoda consists of two cords lying parallel to one another, and each haying a ganglionic enlargement in every segment. Whether a visceral nervous system is present in the group is doubtful. The eighth family of the Chilognatha, the Polyxenidae, show an approach to the Chilopod nervous system. The generative system differs chiefly in the opening of the genital apparatus at the end of the body instead of in the third segment ; though this difference only separates the Order from the Chilognatha and not from the other Orders. They also have two pairs of large accessory glands (as they are called) connected with the genital openings. Order III. Schizotarsia. The third Order of Myriapods, the Schizotarsia, show a much greater resemblance to the Chilopoda than to the first Order, the Chilognatha. There are, however, important differences to dis- tinguish them from all the other Orders. The shape of the body is short, thick, and very compact. The composition of the individual segments resembles that found in Chilopoda rather than that of Chilognatha. The antennae are very long, longer than in any of the Chilopods, and are composed of a great number of very small joints. The mouth parts show a greater length and slenderness than do those of the other Orders mentioned as yet. They con- sist of — 1. An upper lip partly free, but fused at the sides with the rest of the head. The upper lip is in three parts, as in the Chilopoda, but with the middle part very small and the lateral pieces large. 2. A pair of jaws or mandibles. These are provided not only with teeth, as in the other Myriapods, but also with a sort of comb of stiff bristles. 60 MYRIAPODA CHAP. 3 and 4. Two pairs of mavillae or foot jaws distinguished by their length and slenderness. 5. The poison claws long, slender, and not sharply curved. The bases of the poison claws hardly fused together and short. The respiratory system in the Schizotarsia differs from that in all other Myriapods in the fact before mentioned, that they breathe by means of lungs and not by tracheae. There are, as before mentioned, eight dorsal scales in these animals; each dorsal scale except the last bears one of the peculiar organs which I have called lungs. At the hinder end of the scale there is a slit which leads into an air sac, from which a number of short tubes project into the blood in the space round the heart and serve to aerate it before it enters the heart. The heart, therefore, sends aerated blood to the organs, while in the tracheal-breathing Myriapods the blood is aerated in the organs themselves by means of tracheae. The poison claws are followed by segments bearing fifteen pairs of true ambulatory legs. These are covered by eight large dorsal plates, increasing in size from before to the middle of the body, the middle plate being the largest, and then diminishing in size. The nervous system resembles that of the Chilopoda, but there is a special pair of nerves which supply the sense organ, which has been mentioned as peculiar to the Order. The ventral nerve cord shows a very clear division into two, the ganglia of the two cords being almost entirely separate. The first few ganglia are fused, as has been mentioned in the Chilopoda. The digestive tube resembles that of the Chilopoda. The legs are very long and slender, and the joints are beset with bristles. Both sexes have small hook-like appendages at the sides of the genital openings. The eyes have already been mentioned as being more highly developed than in other classes, in correspondence with the more active habits of the animal. The generative organs open at the hind end of the body, as in Chilopoda. The heart is highly developed, quite as much so as the Chilopod heart, the alary muscles being strong and broad, and the arteries being quite as perfect as those in any Myriapod. The muscular coats which govern the pulsations by their con- tractions are powerful and well developed. II STRUCTURE OF SYMPHYLA 61 Order IV. Symphyla. We next come to one of the last two Orders which have been recently added to the Myriapoda. These little animals have a great resemblance to the Thysanura among the Insects, and especially to Campodea among the Thysanura. It will be well, therefore, to begin our account with a few of the reasons which have induced naturalists to include them among the Myriapods rather than among the Thysanura. 1. Campodea has three pairs of mouth appendages, while Scolopendrella has only two. . Scolopendrella has broad plates covering the back, not only on the anterior (thoracic) segments, but on the whole body. 3. The terminal appendages of Scolopendrella differ from those in Campodea. 4. Scolopendrella has a sense organ which is absent in Campodea. . Campodea breathes by means of three stigmata in the anterior part of the body. The stigmata of Scolopen- drella are hard to see, and are not in the same position. 6. Scolopendrella has twelve pairs of legs, and Campodea, like all Insects, has only three. I will now go on to an account of their anatomy. The body is small and slender, and is covered with a delicate shell or exo- skeleton of chitin, which is so thin as to be almost transparent. The antennae are long, and are coraposed of many joints of equal size. The mouth parts consist of— 1. An upper lip. 2. A pair of mandibles. 3. A pair of maxillae. The segments are not all of equal size. Some are larger than others. The larger and smaller segments are arranged alter- nately, and the smaller do not bear legs. As before stated, there are twelve leg-bearing segments. At the end of the body there are two hook-like appendages which are pierced by a canal, through which is poured the secretion of a pair of glands. Near the sides of these appendages are a pair of sense organs, consisting of long hairs connected with nerves. bo Ot 62 MYRIAPODA CHAP. The digestive canal is a long straight tube passing through the length of the body. In the middle it is much enlarged, so as to form a stomach with a glandular coat. Posterior to the stomach the digestive tube receives the contents of two Mal- pighian tubes which act as kidneys. The tracheal system consists of a single pair of stigmata on the under surface of the head, and the tracheae connected with them. Order V. Pauropoda. The Pauropoda, which form the fifth Order of Myriapods, are as yet very imperfectly known. Pawropus was discovered by Sir John Lubbock, and its discovery was announced by him in 1866. He found this little Centipede in his kitchen garden among some Thysanura, and at first considered it as a larval form, but continued observation showed that it was a mature creature. He described it as a small, white, bustlng, intelligent little creature about y!; inch in length. The antennae are very curious and highly characteristic of the Order. They resemble those of Crustacea rather than those of Myriapoda. Each antenna is composed in the following manner. First there is a shaft of four joints. From the fourth joint of this shaft spring two branches; one of these two branches is narrower than the other, and ends in a long thin bristle composed of a great number of joints. The other and broader branch bears two such bristles, and between them a small pear-shaped or globular body, the function of which is unknown. The mouth parts consist of two minute pairs of appendages, the anterior pair toothed and the posterior pointed. The body is rather narrower in front; the segment behind the head has one pair of legs, the second, third, fourth, and fifth behind the head two each. The posterior legs are the longest; the genital organs open at the base of the second pair of legs, between these and the third pair. The manner of breathing is as yet unknown, tracheae not having been discovered. Pauropus at first looks most like a Chilopod, but differs from that Order— 1. In the form of the antennae. 2. In the absence of poison claws and in the form of the mouth parts. Ir EMBRYOLOGY 63 3. The opening of the generative organs being in the front part of the body. It differs from Chilognatha in the following respects :— 1. The legs are not of equal length, the posterior legs being the longest, as in Chilopods. 2. The mouth parts differ from those of Chilognaths almost as much as from those of Chilopods. 3. The form of the antennae. Only a few Pauropoda have been discovered as yet. Embryology. The preceding account of the anatomy of Myriapods would be incomplete without some reference to the wonderful manner in which the different organs of the body are built up; the whole of the complex organism proceeding by a gradual and regulated process of development from a simple cel] called the ovum derived from the female body, and united with a cell from the male body (called the spermatozoon). I hope to be able to give my readers some idea of the interest which the pursuit of the difficult study of embryology adds to anatomy, by offering us a key to the inter- pretation of the relations between our knowledge of the forms at present living on the earth and those which, we learn from Palaeontology, have inhabited our planet in past ages. Like all living creatures with which we are acquainted, the starting-point of Myriapod life is the ovwm, as it is called. This ovwm is a cell resem- bling the cells of which the body of all living animals are built up, and which may be compared to the bricks of which a building is composed. This cell or ovum is a small sphere of living trans- ., Fic. 36.—Young ovum of parent substance called protoplasm, and it Fulus terrestris meucl. is nucleated—that is, it contains a small nucleolus ; mw, nucleus ; RR, first appearance of spot of denser protoplasm called the yok; # follicle cells. nucleus, and within that a still smaller spot of still more dense protoplasm called the nucleolus. In the process of impregnation the ovum unites with the male cell, and the cell so formed is called the impregnated ovum. This ovum has the property of dividing into two cells, each resembling the 64 MYRIAPODA CHAP. parent cell from which it is derived ; each of these cells has, like the parent cell, the same property of dividing into two more, and go on, Thus from this continual process of division or reproduc- tion of every living cell, the materials are provided for the building up of the body. The regularity of the process of the division of the ovum, or, as it is called, segmentation of the ovum, is interfered with by the presence of food yolk. The cells formed by the process of cell division just described need nourishment, and this nourish- ment is supplied to them by the food yolk formed in the body of the ovum before the process of segmentation begins. It 1s easy to understand that this yolk, which is not alive like the Wire, 37.—Later stage: nv, nucleolus ; c.p, nucleus ; y.sp, yolk spherules ; ch, shell. cells, cannot divide like them, and therefore the segmentation of the ovum in Myriapods is irregular, as it is called. I will now go back a little and describe what happens to the ovum before the process of segmentation is complete. It increases in size and forms the supply of food yolk which is to provide the nutriment of the ovum. Then after impregnation the egg-shell is formed round it, and it becomes what we know as the egy. This egg is not a perfect sphere, but is oval (in most Myriapods) in shape. The egg is laid, and the process of segmentation begins shortly after it is laid, as has already been described. When it has been laid for about 36 hours, if we take an egg and, after proper preparation, cut it into thin slices known to Il FORMATION OF THE EGG 65 microscopists by the name of sections, and examine it by means of the microscope, we shall see that segmentation has resulted in this. Just beneath the egg-shell there is a thin layer of cells, one cell thick, which completely surrounds the ege. Inside this coat of cells is the food yolk, with a few cells scattered about in it at rare intervals, something like the raisins in a plum-pudding. With the next process the formation of the young Myriapod may be said to begin. A strip along the length of the oval- shaped egg is thickened, and this thick mass of cells represents the future ventral surface of the animal. The rest of the thin layer of cells already mentioned just below the shell will form the shell or exoskeleton of the future animal. The thick strip of cells at the ventral surface has by this time split into layers, so that, resorting to our microscope again, a section through the short axis of the oval-shaped egg—a transverse section— will show us— 1. The egg-shell. 2, A layer of cells completely surrounding the egg, thin everywhere but on the ventral surface. This layer is known to embryologists as the epiblast. The thick part of the epiblast on the ventral surface gives rise to the nervous system. 3 and 4. Two layers of cells connected in the middle, along the line of the thick strip, but separate elsewhere, and not extending round the whole of the inside. These layers constitute what is known as the mesoblast, and give rise to the muscles and most of the internal organs. 5. The scattered cells in the yolk. They are known as the hypoblast and give rise to the digestive canal. After this point is reached the formation of the organs begins. The segments are formed in order from before back- wards. First the head, then the next segment, and so on. When the number of segments with which the animal will be hatched are formed, another process begins, and the tail end of the animal, which can already be distinguished, is bent towards the head. This is a process that takes place in many animals besides Myriapods, and is called the formation of the ventral flexure. Shortly after this the animal bursts the shell and comes VOL. V F 66 MYRIAPODA CHAP. into the outer world. The various processes may be understood by reference to the Figs. 36, 37, 38, 39, which are succes- sive stages in the development of a Chilognath. Figs. 37, 38, are thin slices through the shorter diameter of the egg, which, as mk. Fic. 38.— Transverse section through next stage: mh, keel-like mass of cells from which the mesoblast is pro- duced ; ec, epiblast. (From Reh , Heathcote, Post. Emb. Dev. pede F\:) yy of Julus terrestris; Phil. le, =a i Ly Trans, vol. 179, 1888, B.) ies! ' ) fh before mentioned, is an oval in shape. Fig. 39 is a section through the longer diameter of an egg in a more advanced stage of development, in fact just about to burst the shell. The body of the future animal is marked by constrictions, the future segments. Some of the organs are already formed, as the brain Fic. 39. — Longitu- dinal section through later stage: Segs. 2, 8, etc., seg- ments ; Ceph. Seg, head ; mes, meso- blast ;en,hypoblast ; st,future mouth; pr, future anus ; mesen, gut; mem.ex, as in Fig. 41. (From Heathcote, Post. Emb. Dey. of Julus terrestris. ) and the digestive tube, the openings of which will form the mouth (st) and the anus (7). Myriapods are hatched at different stages of development. The Chilognatha have only three appendages, which are so little developed that they are only small shapeless stumps, while II FORMATION OF THE YOUNG ANIMAL 67 the Chilopoda have the full number of legs in some cases; in others only a small number of legs, but yet more than the three pairs of legs of the Chilognatha, and fully developed instead of stunp-like. The eyes are usually developed late in the life of the young animal. The bursting of the egg-shell is assisted in some Myriapods by a special kind of spike on the back part of the head. ; The Fig. 40 shows a young Chilognath which has just burst the shell and come into the outer world. It is still surrounded with a membrane which has been formed by its skin or epiblast within the egg. One eye-spot has been formed. Fig. +1 shows a longitudinal section through the young Chilognath shown in : Fig. 40, and the next (Fig. 42) a transverse Fic. 40.—Young Julus ter- , section through the same. In comparing a aaa the two Figs. 41 and 42 it must be remembered that they are gan i. amesen. mes. Fic. 41.—Longitudinal section through late stage : Sup.oe.gl, First appearance of brain ; st, mouth ; pr, anus ; mesen, gut; n, nerve cord; n.gang, nerve ganglion ; mem.ex, membrane surrounding the animal; v.f, ventral flexure 3 mes, mesoblast cells, (Heathcote, Post, Emb. Dev. of Julus terrestris. ) sections in different planes through the animal shown in Fig. 40, and therefore they only show a small portion, a thin slice, of the organs. 68 MYRIAPODA CHAP. The first appearance of the mouth appendages has been already mentioned, and these are shown in Fig. $5, where the e O O00 Or oe O OQ EO aap | Fic. 42.—G, gut; Malp.7, Malpighian tube; N.C, nerve cord; 7r.J, deep invagina- tion by which the tracheae are formed ; y.s, yolk spherules still present ; L, first appearance of legs; SiS, part of mesoblast. (Heathcote, Post. Emb, Dey. of Julus terrestris.) small stumps that later on change to jaws are shown. The figure shows the head of a young Chilog- nath seen from the lower side, and the second pair of stumps fuse together later on and produce the broad plate already mentioned as the characteristic mouth appendave of the Order. After the animal is hatched it has \ still, in the case of most Myriapods Fro, 43-—Under surface of the (those which are not hatched with all iead of a young Julus ter- restris: prom, rodimentary the segments complete), to undergo a Se . AU pea further development, and in particular the eyes are still unformed. The pro- cess of development of the eye has only been followed out as yet in the Chilognatha, and in only one form, Judus, and is so curious that a short account may he of interest here. The develop- ment of the eye begins (in Julus) on the fourth day after hatch- ing, and continues until the animal is full grown. A single ra FORMATION OF THE YOUNG ANIMAL 69 ocellus or eye-spot appears first, and the vest are added one by one until the full number are reached. The first appearances connected with the formation of the eye take place in the cellular layer just beneath the chitinous exoskeleton, This layer, called the hypodermis, plays an im- portant part in the organisation of the animal. It forms the inner layer of what we may call the skin of the animal, and the cells of which it is composed secrete the chitin of which the shell or exoskeleton of the animal is composed, and which is moulted every year. The first process in the formation of the eye-spot is the thickening of the hypodermis beneath the chitin, just in the place where the eye will come. At the same time the cells of this thickened mass of hypoder- mis secrete a quantity of pigment of a dark ved brown colour. Next the cells of the thick mass of hypodermis begin to separate from one another in such a way that a vesicle is formed. This vesicle is hollow inside, and the thick walls are formed from the cells of the thickened hypodermic mass. This can be seen from Fig. 44, which represents a section through an ocellus when it is partly formed. From this vesicle the eye is formed. The wall of the vesicle near- est the exoskeleton gives rise to Fic. 44.—Section through eye when first the lens of the eye, while the — forming: Hyp, hypodermis; Zn, lens; : F.W.V, tront wall of optic vesicle ; other walls of the vesicle form b.w.v, back wall of vesicle; cap, the retinal parts of the eye. capsule. The cells from the brain grow out and form the optic nerve connecting the retina with the brain. The whole eye spot is covered internally by a thin membrane, formed not from the hypodermis but by cells from the inside of the body (mesoblast cells). In the Chilognatha, the first Order of Myriapods, the young 7O MYRIAPODA CHAP. animal leaves the egg with three pairs of appendages; the first have already the form of antennae, the second will form the jaws,. but have not yet taken their proper form, while the third pair will fuse together and alter their shape so as to form the curious plate that has already been mentioned as forming the second pair of mouth appendages. Behind the mouth append- ages will come the first three pairs of legs. The whole young animal on leaving the egg is enveloped in two membranes. These membranes are secreted by the outside layer of cells in the same way that the shell or exoskeleton of the animal will be eventually formed, and represent the first two moults of the animal, which continues to moult its shell every year through- out hfe. Of the Chilopoda, the second Order of Myriapods, all the families leave the egg-shell with the full number of legs, with the exception of the Lithobiidae, which have seven pairs of legs including the poison-claws. The Schizotarsia, the third Order, also have seven pairs of legs when hatched. The legs make their appearance not one by one but in batches Gn Julus terrestris in batches of five). The addition of legs and segments to the body takes place, not at the end of the body, but between the end segment and the penultimate. This is a short sketch of the gradual development of the Myriapoda from the ovum to the fully-grown animal. It is, I am aware, a short and insufficient account of all the beautiful processes by which the different organs take their rise, but space is insufficient here, and too much detail would be out of place in a work of this nature, which only aims at giving an outline sketch of the group, which shall be intelligible to the general reader who has not made a special study of such matters. Before leaving the subject, however, I must mention a few of the points of interest which are to be learned from the examination of the course of development which has been sketched here. One of the greatest puzzles in the natural history of the Order Chilognatha has always been the double segments, as they are called; that is, in fact, the possession of two pairs of legs to each segment, which is, as we have already said, a distinguishing characteristic of the Order. As we have seen, the Chilognatha at an early stage of existence do not possess this characteristic, which is only peculiar to the adult is GENERAL EMBRYOLOGY 71 and half-grown forms. Now what does this mean? Does each double segment in the full-grown Millepede represent two segments which have become fused together, or is each double segment, so called, a real segment resembling the segments present in the other Orders (for instance, Chilopoda), which has grown an extra pair of legs? Both these views have been advocated by distinguished naturalists. Neither of them is, in my opinion, quite right when viewed in the light cast on the subject by recent investigations into the life history of the Chilognatha. A close examination into the minutiae of the growth of the different organs has shown us that the double characters of the double segments are more deeply seated than was imagined. The circulatory system, the nerve cord, and the first traces of segmentation in the mesoblast all show this double character, and the only single part about the segment is the broad plate covering the segment. Now in some of the most ancient of the fossil Myriapods this broad plate shows traces of a division, as if it were in reality two plates fused together. We have also to consider that the life history of the Chilognatha allows us to beleve that the peculiar cylindrical shape of the body shown in the greatest degree in the Julidae is attained by the unequal development of the dorsal and ventral surfaces of the body; the ventral surface being compressed together till it is extremely narrow, and the dorsal surface, as it were, growing round it till the originally dorsal surface forms almost a complete ring round the body. Taking all this into consideration, we are justified, in my opinion, in concluding that each double segment in the Chilognatha is not two segments fused together, nor a single segment bearing two pairs of legs, but is two complete segments perfect in all particulars, but united by a large dorsal plate which was originally two plates which have been fused together, and which in most Chilognatha surrounds almost the whole of two segments in the form of a ring. Again in the Chilopoda we see that a great distinctive feature that separates them from the Chilognatha is the character of the ventral nerve cord, the cord being double and not single, a character connected with the fact that the bases of the legs are widely separated from one another, and not closely approached to each other, as in the Chilognatha. As we before said, a more 72 MYRIAPODA CHAP. minute anatomical examination showed us that this difference was not so great as appeared at first sight, the cord showing traces of a duplication. Well, are these traces superficial, or do they represent a state of affairs more or less similar to that in the Chilopoda? Embryology helps us to answer this question also. In the early stages of the Chilognatha we find that the nerve cord has exactly the form of that in Chilopoda, showing us that the appearances in the anatomy had led us to a right con- clusion, and giving us a valuable confirmation of our views. These two examples will serve to show the kind of interest which attaches to embryology. Palaeontology. We have seen that embryology enables us to look at the structure of the Myriapods from a new standpoint, and to correct and supplement the knowledge gained from an examination of the adult animal. In the same way a study of the forms of Myriapods which have become extinct on the globe, and have been preserved to us in a fossil form, gives a further opportunity of considering the relations of one form to another, and again of the relations of our group to other groups of animals now exist- ing on the earth. Myriapod fossils have been found in strata of great antiquity. The oldest of such fossils must have been among the first land animals. The figure below shows a. fossil Myriapod found in America, belonging to the Order of the Protosyngnatha which are only found in the Palaeozoic strata. It is a good example of the manner in which Myriapods were protected by bundles of bristles in the same way as the Polyxenus of the present time. The oldest fossil Myriapods which have been discovered at the present time are two species which have been found in the Old Red Sandstone in Scotland. To realise the antiquity of these Myriapods, it will be worth while recalling the typical fossils found in the Old Red Sandstone, so as to see what the contem- poraries of these ancient Myriapods were like. Amoug the plants there were Algae, Ferns, and Conifers, belonging to the lower divisions of the plant tribe. Among the animals there were Sponges, Corals, Startish, Worms, Shell-fish, and Fishes, but none of the more highly organised of the animal or vegetable tribe II PALAEONTOLOGY 73 had appeared on the earth. The Myriapods of the Old Red Sandstone, as has been before said, differ considerably from those of the present day, and as we proceed towards the species found in the more recent strata we find them more and more like the ones at present living, till we get to the Polywenus and other species found in amber, which are hardly to be distinguished from living forms. The next oldest fossil Myriapods are found in the coal measures, When both the animal and vegetable kingdoms were represented by more numerous and more specialised forms. The fossil fauna of this period is characterised by the number of gigantic Amphibia, many remains of which have been found. The great forests and the abundant vegetation of this time must have been favourable to the existence of our class, and accord- ingly we find no less than 32 species of fossil Myriapods. Of Fic. 45.—Palaeocampa an- thrax, (After Meek and Worth.) From Mazon Creek, Illinois. these most have been found in America, some in Great Britain, and some in Germany. One well-preserved fossil of Aylobius sigillariae was found by Dr. Dawson in America in the stump of a tree in the remains of a fossil forest. The eyes, head, and legs were plainly seen under the microscope. All these fossils belong to the earliest or Palaeozoic period. The figure below (Fig. 46) shows a fossil also from the coal formations of Illinois, America, belonging to the family of the Euphoberiidae mentioned further on. It shows a nearer approach to the Julidae of the present time. The limbs, however, were of very curious shape, and may possibly have been adapted to loco- motion in water as well as on land, and the small supposed branchiae on the ventral surface shown in Fig. £6, B, may possibly have been an arrangement to render respiration in the water possible. 74 MYRIAPODA CHAP. In the secondary period the Myriapods were scantily repre- sented, or, at any rate, geologists have failed to find their fossils. The class is represented by a single specimen found in the chalk im Greenland. This fossil, which has been included in the Julidae under the name of Julopsis eretacea, may perhaps belong to the Archipolypoda. Passing on to the Tertiary or Recent period, we find the Myriapods again numerous, and more nearly resembling those living at the present time. They belong mostly to the Chilo- gnatha and Chilopoda, They have been found in the fresh-water gypsum of Provence in France, the brown coal of Germany, and the green river formations of America. Several have been found in amber. Fossil Myriapods have been divided into four Orders, two Fic. 46.—Acan- therpestes major. (After Meek and Worth.) Mazon Creek, America. A, The whole animal ; B, branchiae on the ventral sur- face. of which coincide with the Orders of living Myriapods: the differences between the fossils and the living Myriapods having been held insufficient to warrant the establishment of a new Order. These two Orders are the Chilopoda and the Diplopoda or Chilognatha (Diplopoda is another name used by some writers for the group which we have hitherto called Chilognatha). The other two Orders have sufficient differences from living forms to render it necessary to include them in separate Orders. The fossil Myriapods, then, ave arranged as follows :— Order I. Protosyngnatha. Order IT. Chilopoda. Order III. Archipolypoda. Order IV. Chilognatha (or Diplopoda). The following table will show the species that have been dis- covered in the different strata :— ul PALAEONTOLOGY 75 Devonie : 2 on Hea Genii \ 2 species of Archipolypoda. { 1 species Protosyngnatha "| 31 species Archipolypoda Permian (Rothliegendes of Germany), 4 specimens belonging to the Julidae or Archipolypoda, Carboniferous { Archipolypoda or \ Chalognatha 17 species Chilopoda : Diplopoda 2 Se a { (Chilognatha) f Diplopoda \ (Chilognatha) Cretaceous, 1 species Oligocene | Miocene, . 1 species I will now give a short account of the different Orders, and the fossil forms which are included in them. Order I. Protosyngnatha, This Order is represented by a single fossil (Fig. 45), dis- covered in the coal at Mazon Creek, Illinois, America, by Meek and Worth. It differs greatly from any of those in existence at the present day. The body is cylindrical, and composed of ten segments. The cephalic appendages (that is, the antennae and mouth parts) are inserted into a single unsegmeuted cephalic mass (the head). Each segment behind the head bears a single dorsal and ventral plate of equal breadth and length. The limbs are placed in these plates with a wide space between the base of each leg and that of the opposite one of the pair. Along the back, bundles of bristles are arranged in longitudinal rows. Order II. Chilopoda. The fossil forms of this Order resemble those of the Chilopoda of the present day. The oldest of them are found in amber. The following families have been found :— Lithobiidae. Several species have been found in amber. Scolopendridae. One species in amber, several species in later Tertiary formations. Geophilidae. Three species in amber. Two species resembling the Schizotarsia of the present day have been found in amber. 76 MYRIAPODA CHAP. Order III. Archipolypoda. The most numerous of the fossil families. With a few exceptions, all the Palaeozoic (that is, the oldest) Myriapods belong to this Order. The Carboniferous Archipolypoda seem to be much more numerous in the coal of America than in that of England. They resemble for the most part the Myriapods of the present day, except that all the segments without exception bear legs. The families are three in nwnber. Family 1. Archidesmidae. Resemble the Polydesmidae of the present day. Two species have been found by Page in the Old Red Sandstone of Forfarshire. He named them Kampecaris. One found by Peach in the same formation is called Archi- desmus. Family 2. Euphoberiidae. They show some resemblance to the Julidae of the present day, but the dorsal scutes, or plates of the back, are more or less perfectly divided into two divisions corresponding with the pairs of legs, The following are the principal fossils of this family :— Acantherpestes. Found by Meek and Worth in the coal at Mazon Creek in America (Fig. 46). Euphoberia, About 12 species found at the same place as the last named. Amiylispes. Found by Scudder, Mazon Creek, America. Hileticus. Scudder, Mazon Creek, America. Family 3. Archijulidae. The dorsal plates nearly consolidated, but the division still apparent. Fossil forms are— Trichijulus. Scudder, Mazon Creek, America. Xylobius. Dawson. Found in the coal in Nova Scotia. Two species found at Mazon Creek, America. Order IV. Chilognatha. Families corresponding to those of the present day. The oldest specimens come from the chalk in Greenland; most of the others from amber. Family 1. Glomeridae. One form, G. denticulata, has been found in amber, Family 2. Polydesmidae. Two species in amber. Family 3. Lysiopetalidac. A number of species, amongst which are 6 Craspedosoma, mostly from amber. II GENERAL CONCLUSIONS 77 Family 4. Julidae. A number of species of this family have been found, some in amber, some in other Tertiary strata. Amongst the latter a probable example of Julus terrestris, living at the present time. Family 5. Polyxenidae. Five species have been found in amber. Now that we have considered the structure of the Myriapods and the groups into which they are subdivided or classified, we may proceed to consider what position they hold in the house- hold of nature. That they present certain features of similarity to other classes has been already mentioned, and that this is the fact cannot be doubted when we look back at the way in which they have been classified in the works of early writers. For example, Lamarck, the great French naturalist, classifies them with spiders in his well-known work, La Philosophie Zoologique, under the name of Aruchnides antennistes. Cuvier, the com- parative anatomist, unites them with the Insects, making them the first Order, while the Thysanura is the second. We have already seen that one Order of Myriapods, the Symphyla, bears a great resemblance to the Thysanura. The English naturalist Leach was the first to establish Myriapods as a class, and his arrangement has been followed by all naturalists after his time. But while their peculiarities of structure and form are sufficiently marked to separate them as a class, it cannot be denied that the older naturalists were right to recognise that they have many essential characteristics in common with other classes of animals. Aud recent investigations have emphasised this fact. For in- stance, let us consider the recent discoveries of the Orders of Symphyla and Pauropoda, Orders which, while bearing so many of the characters of Myriapods that naturalists have agreed to place them in that class, yet resemble in many important points the Insect Order of Thysanura. This seems to justify Cuvier in claiming the close relationship for them that he did. Recent investigations have also brought out more prominently the resemblances to the Worms. Of late, considerable atten- tion hag been directed to Peripatus (see pp. 1-26), and the resem- blances to the Myriapods in its anatomy and development are such that Latzel has actually included it in the Myriapods as an Order, Malacopoda. Now Peripatus also shows resemblances to the annelid Worms, and thus affords us a connexion to the Worm type hardly less striking than that to the Insect. This 78 MYRIAPODA CHAP. resemblance to the Worms, which Myriapods certainly bear, was noticed by the ancient writers, and as they had for the most part only external appearances to consider, they pushed this idea to extremes in actually including some of the marine Worms (Annelida) among the Centipedes. Pliny talks of a marine Scolopendra as a very poisonous animal, and there is ttle doubt that he meant one of the marine worms. An old German naturalist, Gesner, in a very curious book published in 1669 gives an account of an annelid sea-worm which he calls Scolopendra marina, and which is in all probability the sea Scolopendra which Pliny mentions. From Gesner’s account it seems to have been used as a medicine (externally only). “The use of this animal in medicine. The animal soaked in oil makes the hair fall off. So do its ashes mixed in oil.” It was also pounded up with honey. This idea of Centipedes living in water survived among later naturalists. Charles Owen, the author before quoted, mentions them as amphibious in 1742. “The Scolopendra is a little venomous worm and amphibious. When it wounds any, there follows a blueness about the affected part and an itch all over the body like that caused hy nettles. Its weapons of mischief are much the same with those of the spider, only larger; its bite is very tormenting, and produces not only pruriginous pain in the flesh, but very often distraction of mind. These little creatures make but a mean figure in the ranks of animals, yet have been terrible in their exploits, particularly in driving people out of their country. Thus the people of Rhytiun, a city of Crete, were constrained to leave their quarters for them (Aclian, lib. xv. cap. 26).” Myriapods have been considered to bear resemblances to the Crustacea, and this to a certain extent is true, though only to a certain extent, the resemblances being confined to the more general characteristics that they share with other groups of anunals, Of late years attempts have been made to speculate about the origin of the Myriapods—that is, to endeavour to obtain by means of investigation of their anatomy, embryology, and palaeontological history, some idea of the history of the group. Such attempts at research into the phylogeny, as it is called, of a group must be more or less speculative until our knowledge is much greater than i GENERAL CONCLUSIONS 79 it is at present. But such inquiries have their value, and the schemes of descent and phylogenetic trees, at any rate, indicate a real relation to different groups, even if they do not provide us with a real and actual history of the animals. There have been two main theories about the descent of the Myriapoda. One of these derives them directly from the Insecta through the forms known as the Thysanura, which resemble in such a degree the Myriapod Orders of Symphyla and Pauro- poda. The other theory holds that the Myriapods, as well as the Insecta, have been derived from some ancestor bearing a resem- blance to Peripatus. In other words, one theory claims that the relationship of Myriapoda to Insecta is that of father and son ; the other that the relationship between the two is that of brother to brother. The arguments by which these theories are respectively supported consist for the most part of an analysis of the different characters of the anatomy and embryology and the determination of the most primitive among them. For example, the supporters of the theory that the Thysanura are the most nearly allied to the Myriapod ancestor lay great weight on the fact that some Myriapods are born with three pairs of legs only, and they compare this stage in the life history of the Myriapoda to the metamorphosis and larval stage of Insects. For the supporters of this view the Orders of Symphyla and Pauropoda are the most primitive of the Myriapods. On the other hand, the followers of the other theory do not allow that the characters in which the Myriapods are like Insects are primitive ones, but they lay more stress on the characters found in the early development, such as the character of the process of the forma- tion of the body segments, the mesoblastic segmentation, and the origin of the various organs of the body. It may be easily understood that such differences in the estimation of the primitive characters of the embryology of a group may arise. Embryology has been compared by one of the greatest of modern embryologists to “an ancient manuscript with many of the sheets lost, others displaced, and with spurious passages interpolated by a later hand.” What wonder is it that different people examining such a record should come to different conclusions as to the more doubtful and difficult portions of it. It is this very difficulty which makes the principal interest in the study, and although our knowledge of the language in So MYRIAPODA CHAP. II which this manuscript is written is as yet imperfect, still we hope that constant study may teach us more and more, and enable us to read the great book of nature with more and more ease and certainty. If any of my readers should wish for a more full account of the natural history of this group I must refer them to the following works, which I have used in compiling the above account. In the first of these there is an excellent bibliography of the subject :— Latzel, Die Myriapoden der Oesterreichisch-Ungarischen Monarchie, Wien, 1880. Zittel, Handbuch der Palaeontologie, 1 Abth, II. Bd., Leipzig, 1881-1885. Korschelt and Heider, Lehrbuch der vergleichenden Entwicklungsgeschichte der wirbellosen Thiere, Jena 1891. VOL. V INSECTA BY DAVID SHARP, ALA. MB, FERS. Q CHAPTER III CHARACTERISTIC FEATURES OF INSECT LIFE—-SOCIAL INSECTS— DEFINITION OF THE CLASS JVSECTA——COMPOSITION OF INSECT SKELETON——NUMBER OF SEGMENTS——-NATURE OF SCLERITES—- HEAD——APPENDAGES OF THE MOUTH——EYES——THORAX— ENTOTHORAX—LEGS—— WINGS——ABDOMEN OR HIND BODY— SPIRACLES—-SYSTEMATIC ORIENTATION. Insects form by far the larger part of the land animals of the world; they outnumber in species all the other terrestrial animals together, while compared with the Vertebrates their numbers are simply enormous. Yet they attract but little attention from the ordinary observer, this being probably primarily due to the small size of the individual Insect, which leads the unreflecting to treat the creature as of little importance. “It can be crushed in a moment” is perhaps the unformulated idea that underlies the almost complete neglect of knowledge concerning Insects that prevails even in the educated classes of society. The largest Insects scarcely exceed in bulk a mouse or a wren, while the smallest are almost or quite imperceptible to the naked eye, and yet the larger part of the animal matter existing on the lands of the globe is in all probability locked up in the forms of Insects. Taken as a whole they are the most successful of all the forms of terrestrial animals. In the waters of the globe the predominance of Insect life disappears. In the smaller collections of fresh water many Insects find a home during a portion of their lives, and some few contrive to pass their whole existence in such places; but of the larger bodies of fresh water they invade merely the fringes, and they make only the feeblest attempt at existence in the ocean ; the genus Halobates containing, so far as we know, the sole Insects 84 INSECTS CHAP. that are capable of using the ocean as a medium of existence at a distance from the shore. It will probably be asked, how has it come about that creatures so insignificant in size and strength have nevertheless been so successful in what we call the struggle for existence? And it is possible that the answer will be found in the peculiar relations that exist in Insects between the great functions of circulation and respiration ; these being of such a nature that the nutrition of the organs of the body can be carried on very rapidly and very efficiently so long as a certain bulk is not exceeded. Rapidity of growth is carried to an almost ineredible extent in some Insects, and the powers of multiplication—which may be considered as equivalent to the growth of the species—even surpass the rapidity of the increase of the individual; while, as if to augment the favourable results attainable by the more usual routine of the physiological processes, “ metamorphosis” has been adopted, as a consequence of which growth and development can be isolated from one another, thus allowing the former to go on unchecked or uncomplicated by the latter. A very simple calculation will show how favourable some of the chief features of Insect life are. Let it be supposed that growth of the individual takes time in proportion to the bulk attained, and let A be an animal that weighs one ounce, B a creature that weighs ten ounces, each having the power of producing 100 young when full grown; a simple calculation shows that after the lapse of a time necessary for the production of one generation of the larger creature the produce of the smaller animal will enormously out- weigh that of its bulkier rival. Probably it was some considera- tion of this sort that led Linnaeus to make his somewhat para- doxical statement to the effect that three flies consume the carease of a horse as quickly as a lion.! Astonishing as may be the rapidity of the physiological pro- cesses of Insects, the results attained by them are, it must be admitted, scarcely less admirable: the structures of the Insect’s body exhibit a perfection that, from a mechanical point of view, is unsurpassed, while the external beauty of some of the creatures makes them fit associates of the most delicate flowers or no mean rivals of the most gorgeous of the feathered world. The words ? Tres muscac consumunt cadaver equi, aeque cito ac leo. Syst. Nat., ed. xii. ref. I. pt. 2, p. 990. I SOCIAL INSECTS 85 of Linnaeus, “ Natura in minimis maxime miranda,” are not a mere rhetorical effort, but the expression of a simple truth. Saint Augustine, too, though speaking from a point of view somewhat remote from that of the great Swedish naturalist, expressed an idea that leads to a similar conclusion when he said, “ Creavit in coelum angelos, in terram vermiculos ; nec major in illis nee minor in istis.” The formation of organised societies by some kinds of Insects is a phenomenon of great interest, for there are very few animals except man and Insects that display this method of existence. Particulars as to some of these societies will be given when we treat of the Termitidae, and of the Hymenoptera Aculeata; but we will take this opportunity of directing attention to some points of general interest in connexion with this subject. In Insect societies we find that not only do great numbers of separate individuals live together and adopt different modes of industrial action in accordance with the position they occupy in the association, but also that such individuals are profoundly modified in the structures of their body and in their physiological processes in such ways as to specially fit them for the parts they have to play. We may also see these societies in what may be considered different stages of evolution; the phenomena we are alluding to being in some species much less marked than they are in others, and these more primitive kinds of societies being composed of a smaller number of individuals, which are also much less different from one another. We, moreover, meet with complex societies exhibiting some remarkably similar features among Insects that are very different systematically. The true ants and the white ants belong to groups that are in structure and in the mode of growth of the individual essentially dissimilar, though their social lives are in several important respects analogous. It should be remarked that the phenomena connected with the social life of Insects are still only very imperfectly known ; many highly important points being quite obscure, and our ideas being too much based on fragments gathered from the lives of different species. The honey bee is the only social Insect of whose economy we have anything approaching to a wide knowledge, and even in the case of this Insect our information is neither so complete nor so precise as is desirable. The various branches of knowledge. connected with Insects 86 INSECTS CHAP. are called collectively Entomology. Although entomology is only a department of the great science of zoology, yet it is in practice a very distinct one; owing to its vast extent few of those who work at other branches of zoology also occupy them- selves with entomology, while entomologists usually confine themselves to work in the vast field thus abandoned to them. Before passing to the consideration of the natural history and structure of the members of the various Orders of Insects we will give a verbal diagrammatic sketch,if we may use such an expression, with a view to explaining the various terms that are ordinarily used. We shall make it as brief as possible, taking in succession (1) the external structure, (2) internal structure, (3) development of the individual, (4) classification. In the course of this introductory sketch we shall find it necessary to mention the names of some of the Orders of Insects that will only be explained or defined in subsequent pages. We may therefore here state that the term “Orthoptera” includes grasshoppers, locusts, earwigs, cockroaches; “ Neuroptera” com- prises dragon-flies, May-flies, lacewings, stone-flies and caddis-flies ; to the “ Hymenoptera” belong bees, wasps, ants, sawflies, and a host of little creatures scarcely noticed by the ordinary observer : “ Coleoptera” are beetles; “Lepidoptera,” butterflies and moths ; “ Diptera,” house-flies, blue-bottles, daddy-longlegs, and such ; “ Hemiptera ” or “Rhynchota” are bugs, greently, ete. Class Insecta: or Insecta Hexapoda. Definition —Insects are small animals, having the body divided into three regions placed in longitudinal succession—head, thorax, and abdomen: they take in air by means of tracheae, a system of tubes distributed throughout the body, and opening externally by means of orifices placed at the sides of the body. They have six legs, and a pair of antennae; these latter are placed on the head, while the legs are attached tothe thorax, or second of the three great body divisions ; the abdomen has no true legs, but not infrequently has terminal appendages and, on the under surface, protuberances which serve as feet. Very frequently there are two pairs of wings, sometimes only one pair, in other cases none: the wings are always placed on the thorax. Insects are transversely seg- mented—that is to say, the body has the form of a succession of I STRUCTURE 87 rings; but this condition is in many cases obscure; the number of these rings rarely, if ever, exceeds thirteen in addition to the head and to a terminal piece that sometimes exists. Insects usually change much in appearance in the course of their growth, the annulose or ringed condition being most evident in the early part of the individual’s life. The legs are usually elongate and apparently jomted, but in the immature condition may be alto- gether absent, or very short; in the latter case the jointing is obscure. The number of jointed legs is always six, External Structure. The series of rings of which the external crust or skeleton of Insects is composed exhibits great modifications, not only in the various kinds of Insects but even in the different parts of the same individual, and at successive periods of its development ; so that in the majority of mature Insects the separate rings are readily distinguished only in the hind body or abdomen. The total number of the visible rings, segments, somites, or arthromeres, as they are variously called by different writers, is frequently thirteen in addition to the head. This latter part is considered to be itself composed of the elements of several rings, but mor- phologists are not yet agreed as to their number, some thinking this is three while others place it as high as seven; three or four being, perhaps, the figures at present most in favour, though Viallanes, who has recently discussed’ the subject, considers. six, the number suggested by Huxley, as the most probable. Cholodkovsky is of a similar opinion. However this may be, the three rings behind the head constitute the thorax, which is always largely developed, though, like the head, its segmenta- tion is usually very much obscured by unequal development of different parts, or by consolidation of some of them, or by both of these conditions. The third great division of the body, the abdomen, is also usually much modified by one or more of the terminal segments being changed in form, or even entirely with- drawn into the interior of the body. The existence of ten segments in the hind body can, however, be very frequently actually demonstrated, so that it is correct to speak of ten as the normal number. 1 Ann. Sci. Nat. (7) iv. 1887, p. 111. 83 INSECTS CHAP. It is no reproach to morphologists that they have not yet agreed as to the number of segments that may be taken as typical for an Insect, for all the branches of evidence bearing on the point are still imperfect. It may be well, therefore, to state the most extreme views that appear to be at all admissible. Hagen! has recently stated the opinion that each thoracic segment consists really of three segments—an anterior or wing-bearer, a middle or leg-bearer, and a posterior or stigma-bearer. There seems to be no reason for treating the stigma as being at all of Fic. 47—Diagram of exterior of insect: the two vertical dotted lines indicate the divisions between H, head; T, thorax; and A, abdomen: a, antenna; 0, labrum ; c, mandible ; d, maxillary palpus ; ¢, labial palpus ; /, facetted eye ; g, pronotum ; h, mesonotum ; 7, metanotum ; /, wings; 2, to dj, abdominal segments ; m, the internal membranous portions uniting the apparently separated segments ; 7, cerci ; o, stigma; p, abdominal pleuron bearing small stigmata; q%, qo, gz, pro-, meso-, meta-sterna ; 7,, mesothoracic episternum ; 5), epimeron, these two forming the mesopleuron ; 7., S,, metathoracic episternum and epimeron; ¢, coxa; v, trochanter ; w, femur; a, tibia; y, tarsus ; z, gula. the nature of an appendage, and the theory of a triple origin for these segments may be dismissed. There are, however, several facts that indicate a duplicity in these somites, among which we may specially mention the remarkable constancy of two pleural pieces on each side of each thoracic segment. The hypothesis of these rings being each the representative of two segments cannot there- fore be at present considered entirely untenable, and in that case the maximum and minimun numbers that can be suggested appear to be twenty-four and eleven, distributed as follows :— 1 Stettin, Ent. Zeit. 1. 1889, p. 165. Mt STRUCTURE 89 Maximum. Minimun. Head : 7 3 Thorax 6 3 Abdomen . El 5 Total . 94 11 Although it is not probable that ultimately so great a difference as these figures indicate will be found to prevail, it is certainly at present premature to say that all Insects are made up of the same number of primary segments. -\ brief account of the structure of the integument will be found in the chapter dealing with the post-embryonic develop- ment. The three great regions of the Insect body are functionally as well as anatomically distinct. The head bears the most important of the sense organs, viz. the antennae and ocular organs ; it includes the greater of the nerve-centres, and carries the mouth as well as the appendages, the trophi, connected therewith. The thorax is chiefly devoted to the organs of locomotion, bearing externally the wings and legs, and including considerable masses of muscles, as well as the nerve centres by which they are innervated ; through the thorax there pass, however, in the longitudinal direction, those structures by which the unity of the organisation is com- pleted, viz. the alimentary canal, the dorsal vessel or “heart ” for distributing the nutritive fluid, and also the nerve cords. The abdomen includes the greater part of the organs for carrying on the life of the individual and of the species; it also frequently bears externally, at or near its termination, appendages that are doubtless usually organs of sense of a tactile nature. In the lower forms of Insect life there is little or no actual in- ternal triple division of the body; but in the higher forms such separation becomes wonderfully complete, so that the head may communicate with the thorax only by a narrow isthmus, and the thorax with the abdomen only by a very slender link. This arrangement is carried to its greatest extreme in the Hymenoptera Aculeata. It may be looked on as possibly a means for separating the nutrition of the parts included in the three great body divisions. Along each side of the body extends a series of orifices for the admission of air, the stigmata or spiracles; there are none of these on the head, but on each side of most of the other segments go SEGMENTS CHAP. there is one of these spiracles. This, however, is a rule subject to many exceptions, and it is doubtful whether there is ever a spiracle on the last abdominal segment. Even in the young stage of the Insect the number of these stigmata is variable; while in the perfect Insect the positions of some of the stigmata may be much modified correlatively with the unequal development or consolidation of parts, especially of the thorax when it is highly modified for bearing the wings. The segments of the Insect are not separate parts connected with one another by joints and ligaments; the condition of the Insect crust is in fact that of a continuous long sac, in which there are slight constrictions giving rise to the segments, the interior of the sac being always traversed from end to end by a tube, or rather by the invaginated ends of the sac itself which connect with an included second sac, the stomach. The more prominent or exposed parts of the external sac are more or less hard, while the constricted parts remain delicate, and thus the continuous bag comes to consist of a series of more or less hard rings connected by more delicate membranes. This condition is Fic. 48—Tillus elongatus, fully distended larva. readily seen in distended larvae, and is shown by our figure 48 which is taken from the same specimen, whose portrait, drawn during life, will be given when we come to the Coleoptera, family Cleridae. The nature of the concealed connexions between the apparently separate segments of Insects is shown at im, Fig. 47, p. 88. As the number of segments in the adult Insect corresponds— except in the head—with the number of divisions that appear very early in the embryo, we conclude that the segmentation of the adult is, even in Insects which change their form very greatly during growth, due to the condition that existed in the embryo ; but it must not be forgotten that important secondary changes occur in the somites during the growth and development of the individual. Hence in some cases there appear to be more than the usual number of segments, eg. Cardiophorus larva, and in others the number of somites is diminished by amal- II STRUCTURE gI gamation, or by the extreme reduction in size of some of the parts. Besides the division of the body into consecutive segments, another feature is usually conspicuous; the upper part, in many seements, being differentiated from the lower and the two being connected together by intervening parts in somewhat the same sort ot way as the segments themselves are connected. Such a differen- tiation is never visible on the head, but may frequently be seen in the thorax, and almost always in the abdomen. A dorsal and a ventral aspect are thus separated, while the connecting bond on either side forms a pleuron. By this differentiation a second form of symmetry 1s introduced, for whereas there is but one upper and one lower aspect, and the two do not correspond, there are two lateral and similar areas. This bilateral symmetry is conspicuous in nearly all the external parts of the body, and extends to most of the internal organs. The pleura, or lateral regions of the sae, frequently remain membranous when the dorsal and ventral aspects are hard. The dorsal parts of the Insect’s rings are also called by writers terga, or nota, and the ventral parts sterna. The appendages of the body are :—(1) a pair of antennae ; (2) the trophi, constituted by three pairs of mouth-parts ; (3) three pairs of legs ; (4) the wings!; (5) abdominal appendages of various kinds, but usually jointed. Before considering these in detail we shall do well to make ourselves more fully acquainted with the elementary details of the structure of the trunk. In the adult Insect the integument or crust of the body is more or less hard or shell-like, sometimes, indeed, very hard, and on examination it will be seen that besides the divisions into segments and into dorsal, ventral, and pleural regions, there are lines indicating the existence of other divisions, and it will be found that by dissection along these lines distinct pieces can be readily separated. Each hard piece that can be so separated is called a sclerite, and the individual sclerites of a segment have received names from entomotomists. The sclerites are not really 1 The wings, by many morphologists, are not included in the category of “appendages”; they apparently, however, differ but little in their nature from legs, both being outgrowths of the integument ; the wings are, however, always post-embryonic in actual appearance, even when their rudiments can be detected in the larva. No insect is hatched from the egg in the wing-bearing form. 92 HEAD CHAP. quite separate pieces, though we are in the habit of speaking of them as if such were the case. If an Insect be distended by pressure from the interior, many of the sclerites can be forced apart, and it is then seen that they are connected by delicate membrane. The structure is thus made up of hard parts meeting one another along certain lines of wnion—sutures—so that the original membranous continuity may be quite concealed. In many Insects, or in parts of them, the sclerites do not come into apposition by sutures, and are thus, as it were, islands of hard matter surrounded by membrane. A brief consideration of some of the more important sclerites is all that is necessary for our present purpose: we will begin with the head. The head is most variable in size and form; as a part of its surface is occupied by the eyes and as these organs differ in shape, extent, and position to a surprising degree, it is not a matter for astonishment that it is almost impossible to agree as to terms for the areas of the head. Of the sclerites of the head itself there are only three that are sufficiently constant and definite to be worthy of description here. These are the clypeus, the epicranium, and the gula. The clypeus is situate on the upper surface of the head-capsule, in front; it bears the labrum which may he briefly described as a sort of flap forming an upper hp. The labrum is usually possessed of some amount of mobility. The clypeus itself is excessively variable in size and form, and sometimes cannot be delimited owing to the obliteration of the suture of connexion with the more posterior part of the head; it is rarely or never a paired piece. Occasionally there is a h more or less distinct piece @ Ow interposed between the ee ey clypeus and the labrum, ( and which is the source of considerable difficulty, as it may be taken for the clypeus. Some authors call Fic, 49.—Capsule of head of beetle, Harpalus the clypeus the epistome, but caliginosus ; A, upper ; B, under surface: a, 1b 18 better to use this latter clypeus; 4, epicranium ; c, protocranium ; a 3 Sate d, gula; e, facetted eye; f, occipital fora- term for the PUL pOse of indi- men; g, submentum ; h, cavity for insertion cating the part that 1s imme- of antenna. s : diately behind the labrum, vhether that part be the clypeus, or some other sclerite; the Il HEAD 93 term is very convenient in those cases where the structure cannot be, or has not been, satisfactorily determined morphologically. In Figure 50 the parts usually visible on the anterior aspect of the head and its appendages are shown so far as these latter can be seen when the mouth is closed; in the case of the Insect here represented the bases of the mandibles are clearly seen (y), while their apical portions are entirely covered by the labrum, just below the lower margin of which the tips of the maxillae are seen, looking as if they were the continuations of the mandibles. The labrum is a somewhat perplex- ing piece, morphologists being not yet agreed as to its nature; it is usually placed quite on the front of the head, and varies extremely in form; it is nearly always a single or unpaired piece; the French morphologist Chatin Fic. 50.—Front view of head of field-cricket (Gryllus): a, epicranium ; 6, compound eye; c, antenna; d, post-: considers that it is really a paired structure. The gula (Fig. 49, B @ and Fig. 47, e, ante-clypeus ; f, labrum ; g, base of mandible ; h, max- illary palpus ; 7, labial pal- pus ; 4, apex of maxilla. z) is a piece existing in the middle longitudinally of the under-surface of the head; in front it bears the mentum or the submentum, and extends backwards to the great occipital foramen, but in some Insects the gula is in front very distant from the edge of the buccal cavity. The epicranium forms the larger part of the head, and is con- sequently most inconstant in size and shape ; it usually occupies the larger part of the upper - surface, and is reflected to the under-surface to meet the gula. Sometimes a transverse line exists (Fig. 49, A) dividing the epicranium into two parts, the posterior of which has been called the protocranium; which, however, is not a good term. The epicranium bears the antennae ; these organs do not come out between the epicranium and the clypeus, the foramen for their insertion being seated entirely in the epicraniwn (see Fig. 50). In some Insects there are traces of the epicranium being divided longitudinally along the middle line. When this part is much modified the antennae may appear to be inserted on the lateral portions of the head, or even 94 INSECTS CHAP. on its under-side; this arises from extension of some part of the epicranium, as shown in Fig. 49, B, where h, the cavity of insertion of the antenna, appears to be situate on the under- surface of the epicranium, the appearance being due to an infolding of an angle of the part. There is always a gap in the back of the head for the passage of the alimentary canal and other organs into the thorax; this opening is called the occipital foramen. Various terms, such as frons, vertex, occiput, temples, and cheeks, have been used for designating areas of the head. The only one of these which is of importance is the gena, and even this can only be defined as the anterior part of the lateral portion of the head-capsule. An extended study of the comparative anatomy of the head-capsule is still a desideratum in entomology. The appendages of the head that are engaged in the operations of feeding are frequently spoken of collectively as the trophi, a term which includes the labrum as well as the true buccal appendages. The appendages forming the parts of the mouth are paired, and consist of the mandibles, the maxillae, and the labium, the pair in this latter part being combined to form a single body. The buccal appendages are frequently spoken of as gnathites. The gnathites are some, if not all, of them composed of apparently numerous parts, some of these being distinct sclerites, others membranous structures which may be either bare or pubescent— that is, covered with delicate short hair. In Insects the mouth functions in two quite different ways, by biting or by sucking. The Insects that bite are called Mandibulata, and those that suck Haustellata. In the mandibulate Insects the composition of the gnathites is readily comprehensible, so that in nearly the whole of the vast number of species of that type the corresponding parts can be recognised with something like certainty. This, however, is not the case with the sucking Insects; in them the parts of the mouth are very different indeed, so that in some cases morphologists are not agreed as to what parts really correspond with some of the structures of the Mandibulata. At present it will be sufficient for us to consider only the mandibulate mouth, leaving the various forms of sucking mouth to be discussed when we treat of the Orders of Haustellata in detail. The upper or anterior pair of gnathites is the mandibles, (Fig. 50, 7). There is no part of the body that varies more than m1 MOUTH-PARTS 95 does the mandible, even in the mandibulate Insects. It can scarcely be detected in some, while in others, as in the male stag- beetle, it may attain the length of the whole of the rest of the body; its form, too, varies as much as its size; most usually, however, the pair of mandibles are somewhat of the form of callipers, and are used for biting, cutting, holding, or crushing purposes. The mandibles are frequently armed with processes spoken of as teeth, but which must not be in any way confounded with the teeth of Vertebrates. The only Insects that possess an articulated tooth are the Passalidae, beetles armed with a rather large mandible bearing a single mobile tooth among others that are not so. Wood Mason and Chatin consider the mandibles to Fic. 51. — Mandibles, maxillae, and labium of Locusta viridis. sima: A, mandibles ; B, maxillae (lateral parts) and labium (middle parts) united : a, cardo; 4, stipes; c, palpiger ; d, max. palp. ; e, lacinia; 7, galea; g,submentum ; h, mentum; 7, pal- piger ; %, labial pal- pus; 2, ligula; m, paraglossa (galea); 2, lacinia ; 0, lingua. be, morphologically, jointed appendages, and the latter authority states that in the mandible of Hmbia he has been able to distin- guish the same elements as exist in the maxillae. In aculeate Hymenoptera the mandibles are used to a considerable extent for industrial purposes. The maxilla is a complex organ consisting of numerous pieces, viz. cardo, stipes, palpiger, galea, lacinia, palpus. The galea and lacinia are frequently called the lobes of the maxilla. The maxilla no doubt acts as a sense organ as well as a mechanical apparatus for holding; this latter function being subordinate to the other. In Fig. 68, p. 122, we have represented a complex maxillary sense-organ. The labium or lower lip has as its basal portion the un- 96 INSECTS CHAP. divided mentum, and closes the mouth beneath or behind, according as the position of the head varies. In most Insects the labium appears very different from the maxilla, but in many cases several of the parts corresponding to those of the maxilla ean be clearly traced in the labiwn. The mentum is an undivided, frequently very hard, piece, continuous with either the submentum or the gula, and anterior to this are placed the other parts, viz. the labial palpi and their supports, the palpigers ; beyond and between these exists a central piece (Fig. 52, B, e), about whose name some difference of opinion prevails, but which may be called the ligula (languette of French authors), and on each side of this is a paraglossa. In the Orthoptera the single median piece —the ligula of Coleopterists — is represented by two divided parts. In some Insects (many Coleoptera) there is interposed between the mentum and the palpigers a piece called the hypoglottis (Fig. 52, B, ob). It is not so well ascer- tained as it should he, that the pieces of the lower lip bearing the same names in different Orders are in all cases really homologous, and comparison suggests that Fig, 52.—Maxilla and lower the hypoglottis of Coleoptera may pos- lip of Coleoptera. A, Max- . ‘ is illa of Passalus: a, cardo; Sibly represent the piece corresponding ata Re pane to the mentum of Orthopterists, the so- rior lobe or lacinia; f, Called mentum of beetles being in that ae a joe ct case the submentum of Orthopterists. pulus caliginosus: a, men- There is another part of the mouth Peas ie ‘2 to which we may call special atten- labial palp); ¢, palp; e, tion, as it has recently attracted more Bey Ry attention than it formerly did; it is a membranous lobe in the interior of the mouth, very conspicuous in Orthoptera, and called the tongue, lingua, or hypopharynx ; it reposes, in the interior of the mouth (Fig. 51, 0), on the middle parts of the front of the labium; it is probably not entirely lost in Coleoptera, but enters into the composition of the Il STRUCTURE 97 complex middle part of the lp by amalgamation with the para- glossae. It has recently been proposed to treat this lingua as the morphological equivalent of the labium or of the maxillae, giving it the name of the endolabium, but the propriety of this course remains to be proved;' the view is apparently suggested chiefly by the structure of the mouth of Hemimerus, a very rare and most peculiar Insect that has not as yet been sufficiently studied. As the maxillae and labium are largely used by taxonomists in the systematic arrangement of the mandibulate Insects, we give a figure of them as seen in Coleoptera, where the parts, though closely amalgamated, can nevertheless be distinguished. This Fig. 52 should be compared with Fig. 51. In speaking of the segments of the body we pointed out that they were not separate parts but constituted an uninter- rupted whole, and it is well to remark here that this is also true of the gnathites. Although the mouth parts are spoken of as separate pieces, they really form only projections from the great body wall. Fig. 51, B, shows the intimate connexion that exists between the maxillae and labium; the continuity of the mandibles with the membrane of the buccal cavity is capable of very easy demonstration. The head bears, besides the pieces we have considered, a pair of antennae. These organs, though varying excessively in form, are always present in the adult Insect, and exist even in the majority of young Insects. They are very mobile, highly sensitive organs, situate on or near the front part of the head. The antennae arise in the embryo from the procephalic lobes, the morphological import of which parts is one of the most difficult points connected with Insect embryology. The eyes of Insects are of two sorts, simple and compound. The simple eyes, or ocelli, vary in number from one to as many as eighteen or twenty; when thus numerous they are situated in groups on each side of the head. In their most perfect form, as found in adult aculeate Hymenoptera, in Orthoptera and Diptera, ocelli are usually two or three in number, and present the appearance of small, perfectly transparent lenses inserted in the integument. In their simplest form they are said to consist of some masses of pigment in connexion with a nerve. The compound, or facetted, eyes are the most remarkable of all 1 See on this subject, p. 217. VOL. V H 98 EYES CHAP. the structures of the Insect, and in the higher and more active forms, such as the Dragon-flies and hover- ing Diptera, attain a complexity and deli- cacy of organisation that elicit the highest admiration from every one who studies them. They are totally different in structure and very distinct in function from the eyes of Vertebrata, and are seated on very large special lobes of the brain (see Fig. 65), which indeed are so large and so complex in structure that Insects may be described as possess- ing special ocular brains brought into relation with the lights, shades, and movements of the external world by a remarkably complex optical apparatus. This instrumental part of the eye is Fic. §3.—Two ommatidia from called the dioptric part in contradistinc- the eye of Colymbetes fus- , - ci j cus, x 160. (After Exner.) t10n from the percipient portion, and con- a, Cornea; 0, crystalline gists of an outer corneal lens (a, Fig. 53), cone; ¢, rhabdom; d, fenestrate membrane with Whose exposed surface forms one of the nerve structures below it; facets of the eye; under the lens is placed e, iris-pigment ; 7, retina- é ‘ a pigment. the crystalline cone (}), this latter being borne on a rod-like object (¢), called the rhabdom. There are two layers of pigment, the outer (e), called the iris-pigment, the inner (/), the retinal-pigment ; underneath, or rather we should say more central than, the rhabdoms is the fenestrate membrane (d), beyond which there is an extremely complex mass of nerve - fibres; nerves also penetrate the fenestrate membrane, and their distal extremi- ties are connected with the delicate sheaths by one of which each rhabdom is surrounded, the combination of sheath and nerves forming a retinula. Each set of the parts above the fene- strate membrane constitutes an ommatidium, and there may he many of these ommatidia in an eye; indeed, it is said that the eye of a small beetle, Mordella, contains as many as 25,000 ommatidia. As a rule the larvae of Insects with a complete metamorphosis bear only simple eyes. In the young of Dragon- flies, as well as of some other Insects having a less perfect meta- morphosis, the compound eyes exist in the early stages, but they II HEAD AND THORAX 99 have then an obscure appearance, and are probably functionally imperfect. In the interior of the head there exists a horny framework called the tentorium, whose chief office apparently is to protect the brain. It is different in kind according to the species. The head shows a remarkable and unique relation to the following segments. It is the rule in Insect structure that the back of a segment overlaps the front part of the one following it; in other words, each segment receives within it the front of the one behind it. Though this is one of the most constant features of Insect anatomy, it is departed from in the case of the head, which may be either received into, or overlapped by, the segment following it, but never itself overlaps the latter. There is perhaps but a single Insect (Hypocephalus, an anomalous beetle) in which the relation between the head and thorax can be considered to be at all similar to that which exists between each of the other segments of the body and that follow- ing it; and even in Aypocephalus it is only the posterior angles of the head that over- lap the thorax. Although the head usually pig. 54. — Extended head appears to be very closely connected with — and front of thorax of * A 3 a beetle, Luchroma: a, the thorax, and is very frequently in re- back of head; 6, front pose received to a considerable extent within — of pronotum ; ¢, chitin- . : ous retractile band; d, the latter, it nevertheless enjoys great catvioal sclerites: freedom of motion; this is obtained by means of a large membrane, capable of much corrugation, and in which there are seated some sclerites, so arranged as to fold together and occupy little space when the head is retracted, but which help to prop and support it when extended for feeding or other purposes. These pieces are called the cervical sclerites or plates. They are very largely developed in Hymenoptera, in many Coleoptera, and in Blattide, and have not yet received from anatomists a sufficient amount of attention. Huxley suggested that they may be portions of head segments. Thorax. The thorax, being composed of the three consecutive rings behind the head, falls naturally into three divisions—pro-, meso-, 100 THORAX CHAP. and imetathorax. These three segments differ greatly in their relative proportions in different Insects, and in different stages of the same Insect’s life. In their more highly developed con- ditions each of the three divisions is of complex structure, and the sclerites of which it is externally made up are sufficiently constant in their numbers and relative positions to permit of their identification in a vast number of cases; hence the sclerites have received names, and their nomenclature is of practical importance, because some, if not all, of these parts are made use of in the classification of Insects. Each division of the thorax has an upper region, called synonymically dorsum, notum, or tergum; an inferior or ventral region, called sternum; and on each side a lateral region, the pleuron. These regions of each of the three thoracic divisions are further distinguished by joining to their name an indication of the segment spoken of, in the form of the pretixes pro-, meso-, and meta-; thus the pronotum, prosternmu, and propleura make wp the prothorax. The thoracic regions are each made up of sclerites whose nomenclature is due to Audouin.* He considered that every thoracie ring is com- posed of the pieces shown in Fig. 55, viz. (1) the sternum (B’, a), an unpaired ventral piece; (2) the notum (A), composed of four pieces placed in consecutive longitudinal order (A’), and named praescutum (a), seutum (0), seutellum (c), and post-scutel- lum (d); (3) lateral pieces, of which he distinguished on each side an episternwn (BY, ¢),epimeron (e), and parapteron (d), these together forming the pleuron. We give Audouin’s Figure, but we cannot enter on a full discussion of his views as to the thorax ; they have become widely known, though the constancy of the parts is not so great as he supposed it would prove to be. Some- times it is impossible to find all the elements he thought should be present in a thoracic ring, while in other cases too many sclerites exist. As a rule the notum of the meso- and metathoraces is in greater part composed of two pieces, the scutum and the scutellum ; while in the pronotum only one dorsal piece can be satisfactorily distinguished, though a study of the development may show that really two are frequently, if not usually, present. On the other hand, one, or more, of the notal sclerites in some vases shows evidence of longitudinal division along the middle. The sternum or ventral piece, though varying greatly in form, is 1 Ann. Sci. Nat. 1. 1824, p. 97, ete. ul THORAX 1OIL the most constant element of a thoracic segment, but it has sometimes the appearance of consisting of two parts, an anterior and a posterior. The pleuron nearly always consists quite evidently of two parts, the episternum, the more anterior and inferior, and the epimeron.t The relations between these two parts vary much; in some cases the episternum is conspicuously the more anterior, while in others the epimeron is placed much above it, and may extend nearly as far forwards as it. It may be said, as a rule, that when the sternum extends farther back- wards than the notum, the epimeron is above the episternum, Fia. 55.—Mesothorax of Dytiscus, after Audouin. A, notum; A’, pieces of the notum separated: a, praescutum ; 4, scutum; c, scutellum; d, post-scutellum: B, the sternum and pleura united ; B’, their parts separated: a, sternum; v, episternum ; d, parapteron; e, epimeron. as in many Coleoptera; but if the sternum be anterior to the notum, then the episternum is superior to the epimeron, as in dragon-flies. We would here again reiterate the fact that these “pieces” are really not separate parts, but are more or less in- durated portions of a continuous integument, which is frequently entirely occupied by them; hence a portion of a sclerite that im one species is hard, may in an allied form be wholly or partly membranous, and in such case its delimitation may be very evident on some of its sides, and quite obscure on another. 1 See also Fig. 47 (p. 88). 102 THORAX CHAP. The parapteron of Audouin does not appear to be really a distinct. portion of the pleuron; in the case of Dytiscus it is apparently merely a thickening of an edge. Audouin supposed this part to be specially connected with the wing-articulation, and the term has been subsequently used by other writers in connexion with several little pieces that exist in the pleural region of winged Insects. The prothorax is even more subject to variation in its development than the other divisions of the thorax are. In the Hymenoptera the prosternum is disconnected from the pronotum and is capable, together with the first pair of legs, of movement independent of its corresponding dorsal part, the pronotum, which in this Order is always more or less completely united with the meso-thorax; in the Diptera the rule is that the three thoracic segments are closely consolidated into one mass. In the majority of Insects the prothorax is comparatively free, that is to say, it is not so closely united with the other two thoracic segments as they are with one another. The three thoracic rings are seen in a comparatively uniform state of development in a great number of larvae; also in the adult stages of some Aptera, and among winged insects in some Neuroptera such as the Embiidae, Termitidae, and Perlidae. In Lepidoptera the pro- notuin bears a pair of erectile processes called patagia; though frequently of moderately large size, they escape observation, being covered with scales and usually closely adpressed to the sides of the pronotun. The two great divisions of the body—the mesothorax and the metathorax-—are usually very intimately combined in winged Insects, and even when the prothorax is free, as in Coleoptera, these posterior two thoracic rings are very greatly amalgamated. In the higher forms of the Order just mentioned the meso- sternum and mesopleuron become changed in direction, and form as it were a diaphragm closing the front of the metasternum. The meso- and meta-thorax frequently each bear a pair of wings. We have described briefly and figured (Fig. 55) the sclerites of the mesothorax, and those of the metathorax correspond fairly well with them. In addition to the sclerites usually described as constituting these two thoracic divisions, there are some small pieces at the bases of the wines. Jurine discriminated and named no less than seven of these at the base of the anterior Ill THORAX 103 wing of a Hymenopteron. One of them becomes of considerable size and importance in the Order just mentioned, and seems to be articulated so as to exert pressure on the base of the costa of the wing. This structure attains its maxiinum of development in a genus (2 nondescript) of Scoliidae, as shown in Fig. 56. The best name for this sclerite seems to be that proposed by Kirby and Spence, tegula. Some writers call it paraptere, hypo- ptere, or squamule, and others have termed it patagium; this latter name is, however, inadmissible, as it is applied to a process of the prothorax we have already alluded to. Fic. 56. — Head and To complete our account of the structure ran ge of the thorax it is necessary to mention cer- base of wing, tain hard parts projecting into its interior, but of which there is usually little or no trace externally. A large process in many Insects projects upwards from the sternum in a forked manner. It was called by Audouin the entothorax ; some modern authors prefer the term apophysis. Longitudinal partitions of very large size, descending from the dorsum into the interior, also exist; these are called phragmas, and are of great importance in some Insects with perfect flight, such as Hymenoptera, Lepidoptera, and Diptera. There is no phragma in connection with the prono- tum, but behind this part there may be three. A phragma has the appear- ance of being a fold of the dorsum; it Fie. 57, —Transverse section of Serves a8 an attachment for muscles, skeleton of metathorax of and may probably be of service in Goliathus druryi, seen fromm Other ways. More insignificant projec- behind: @, metanotum ; 8, : : : : : ioe aad : ala oe tions into the interior are the little d, entothorax (apophysis or _. % 7 furca); e, apodeme; 7, ten- Pieces called apodemes (Fig. 57, ¢); don of articulation. (After these are placed at the sides of the Kolbe.) “ thorax near the wings. The apophyses are no doubt useful in preserving the delicate vital organs from shocks, or from derangement by the muscular movements and the changes of position of the body. The appendages of the thorax are (a) inferior, the legs; (6) 104 LEGS CHAP. superior, the wings. The legs are always six in number, and are usually present even in larvae, though there exist many apodal larvae, especially in Diptera. The three pairs of legs form one of the most constant of the characters of Insects. They are jointed appendages and consist of foot, otherwise tarsus ; tibia, femur, trochanter, and coxa; another piece, called trochantin more or less distinctly separated from the coxa, exists in many Insects. The legs are prolongations of the body sac, and are in closer relation with the epimera and with the episterna than with other parts of the crust, though they have a_ close relation with the sternum. If we look at the body and leg of a neuropterous Insect (Fig. 58) we see that the basal part of the leo—the coxa—is apparently a continua- tion of one of the two pleural pieces or of both; in the latter case one of the prolonged pieces forms the coxa proper, and the tip of the other forms a supporting piece, which may possibly be the homologue of Fic. 58.—Hind leg of Pan- the trochantin of some Insects. In some i ee is Orthoptera, especially in Blattidae, and in coxal fold of epimeron ; Termitidae, there is a transverse chitinised Z pee ues fold interposed between the sternum and the coxa, and this has the appearance of being the same piece as the trochantin of the anterior legs of Coleoptera. Beyond the coxa comes the trochanter; this in many Hymenoptera is a double piece, though in other Insects it is single; usually it is the most insignificant part of the leg. The femur is, on the whole, the least variable part of the leg; the tibia, which follows it, being frequently highly modified for industrial or other purposes. The joint between the femur and the tibia is usually bent, and is therefore the most conspicuous one in the leg; it is called the knee. The other joints have not corresponding names, though that between the tibia and the tarsus is of great importance. The spines at the tip of the tibia, projecting beyond it, are called spurs, or calcares. The tarsus or HI FEET 105 foot is extremely variable; it is very rarely absent, but may consist of only one piece—joint, as it is frequently called '— or of any larger number up to five, which may be considered the characteristic number in the higher Insect forms. The terminal joint of the tarsus bears normally a pair of claws; between the claws there is frequently a lobe or process, according to circumstances very varied in different Insects, called empodium, arolium, palmula, plantula, pseudonychium, or pulvillus. This latter name should only be used in those cases in which the sole of the foot is covered with a dense pubescence. The form of the individual tarsal joints and the armature or vestiture of the lower surface are highly variable. The most remarkable tarsus is that found on the front foot of the male Dytiscus. It has been suggested that the claws and the terminal append- age of the tarsus ought to be counted as forming a distinct joint ; hence some authors state that the higher Insects have six joints to the feet. These parts, however, are never counted as separate joints by systematic entomologists, and it has recently been stated that they are not such originally. The parts of the foot at the extremity of the last tarsal joint proper are of great importance to the creature, and vary greatly in different Insects. The most constant part of this apparatus is a pair of claws, or a single claw. Between the two claws there may exist the additional apparatus referred to above. This in some Insects—notably in the Diptera—reaches a very complex development. We figure these structures in Pelopaeus spinolae, a fossorial Hymenopteron, remarking that our figures exhibit the apparatus in a state of retraction (Fig. 59). According to the nomenclature of Dahl and Ockler? the plate (>) on the dorsal aspect is the pressure plate (Druck-Platte), and acts as an agent of pressure on the sole of the pad (C,¢); ¢ and d on the underside are considered to be extension-agents; c, extension- plate; d, extension-sole (Streck-Platte, Streck-Sohle). These agents are assisted in acting on the pad by means of an elastic bow placed in the interior of the latter. The pad (e) is a very remarkable structure, capable of much extension and retraction ; 1 In entomological language the piece between each two joints of an appendage is itself called a joint, though segment is doubtless a better term. 2 Arch. f. Naturgeschichte, lvi. 1890, p. 221. 106 FEET CHAP. when extended it is seen that the pressure plate is bent twice at aright angle so as to form a step, the distal part of which runs along the upper face of the basal part of the pad; the apical portion of this latter consists of two large lobes, which in repose, as shown in our Figure (/), fall back on the pad, something in the fashion of the retracted claws of the cat, and conceal the pres- sure-plate. The mode in which Insects are able to walk on smooth perpendicular surfaces has been much discussed, and it appears highly probable that the method by which this is accomplished is the exudation of moisture from the foot; there is still, how- ever, much to he ascertained before the process can be satisfactorily Fic. 59.—Foot of Pelopaeus, a fossorial wasp: A,tarsus entire ; B, terminal joint, upper side ; C, under side. a, claw; 3, base of pressure-plate; c, ex- tension - plate; dd, extension- sole; e, pad; 7, lobe of pad retracted. comprehended. The theory to the effect that the method is the pressure of the atmosphere acting on the foot when the sole is In perfect apposition with the object walked on, or when a shght vacuum is created between the two, has apparently less to support it. The legs of the young Insect are usually more simple than those of the adult, and in caterpillars they are short appendages, and only imperfectly jointed. If a young larva, with feet, of a beetle, such as Crioceris asparagt be examined, it may be seen that the leg is formed by protuberance of the integument, which becomes divided into parts by sunple creases ; an observa- tion suggesting that the more highly developed jointed leg is formed in a similar manner. This appears to be really the case, II WINGS 107 for the actual continuity of the limb at the chief joint—the knee—can be demonstrated in many Insects by splitting the outer integument longitudinally and then pulling the pieces a little apart; while in other cases even this is not necessary, the knee along its inner face being membranous to a consider- able extent, and the membrane continuous from femur to tibia. Turning to the wings, we remark that there may be one or two pairs of these appendages. When there is but one pair it is nearly always mesothoracic, when there are two pairs one is invari- ably mesothoracic, the other metathoracic. The situation of the wing is always at the edge of the notum, but the attachment varies in other respects. It may be limited to a small spot, and this is usually the case with the anterior wing; or the attachment may extend for a considerable distance along the edge of the notum, a condition which frequently occurs, especially in the case of the posterior wings. The actual connexion of the wings with the thorax takes place by means of strong horny lines in them which come into very close relation with the little pieces in the thorax which we have already described, and which were styled by Audouin articulatory epidemes. There is extreme variety in the size, form, texture, and clothing of the wings, but there is so much resemblance in general characters amongst the members of each one of the Orders, that it is usually possible for an expert, seeing only a wing, to say with certainty what Order of Insects its possessor belonged to. We shall allude to these characters in treating of the Orders of Insects. Each wing consists of two layers, an upper and a lower, and between them there may be tracheae and other structures, especially obvious when the wings are newly developed. It has been shown by Hagen that the two layers can be separated when the wings are recently formed, and it is then seen that each layer is traversed by lines of harder matter, the nervures. These ribs are frequently called wing-veins, or nerves, but as they have no relation 1o the anatomical structures bearing those names, it is better to make use of the term nervures. The strength, number, form and inter - relations of these nervures vary exceedingly; they are thus most important aids in the classification of Insects. Hence various efforts have been made to establish a system of nomenclature that shall be uniform throughout the different Orders, but at present success has not 108 WINGS CHAP. attended these efforts, and it is probable that no real homology exists between the nervures of the different Orders of Insects. We shall not therefore discuss the question here. We may, however, mention that German savants have recently distin- guished two forms of nervures which they consider essentially distinct, viz. convex and concave. These, to some extent, alter- nate with one another, but a fork given off by a convex one is not considered to be a concave one. The terms convex and con- cave are not happily chosen; they do not refer to the shape of the nervures, but appear to have been suggested by the fact that the surface of the wing being somewhat “undulating the convex veins more usually run along the ridges, the concave veins along the depressions. The convex are the more important of the two, being the stronger, and more closely connected with the articula- tion of the wing. The wings, broadly speaking, may be said to be three- margined: the margin that is anterior when the wings are extended is called the costa, and the edge that is then most distant from the body is the outer margin, while the limit that hes along the body when the wings are closed is the inner margin. The only great Order of Insects provided with a single pair of wings is the Diptera, and in these the metathorax possesses, instead of wings, a pair of little capitate bodies called halteres or poisers. In the abnormal Strepsiptera, where a large pair of wings is placed on the metathorax, there are on the mesothorax some small appendages that are considered to represent the anterior wings. In the great Order Coleoptera, or beetles, the anterior wings are replaced by a pair of horny sheaths that close together over the back of the Insect, concealing the hind-wings, so that the beetle looks like a wingless Insect: in other four- winged Insects it is usually the front wings that are most useful in flight, but the elytra, as these parts are called in Coleoptera, take no active part in flight, and it has been recently suggested by Hoffbauer? that they are not the homo- logues of the front wings, but of the tegulae (see Fig. 56), of other Insects. In the Orthoptera the front wings also differ in con- sistence from the other pair over which they lie in repose, and are called tegmina. There are many Insects in which the wings 1 Zettschr. wiss. Zool. liv. 1892, p. 579. Ill ABDOMEN 109g exist in a more or less rudimentary or vestigial condition, though they are never used for purposes of flight. The abdomen, or hind body, is the least modified part of the body, though some of the numerous rings of which it is composed may be extremely altered from the usual simple form. Such change takes place at its two extremities, but usually to a much greater extent at the distal extremity than at the base. This latter part is attached to the thorax, and it is a curious fact that in many Insects the base of the abdomen is so closely connected with the thorax that it has all the appearance of being a portion of this latter division of the body; indeed it is sometimes difficult to trace the real division between the two parts. In such cases a further differentiation may occur, and the part of the abdomen that on its anterior aspect is intimately attached to the ‘thorax may on its posterior aspect be very shghtly connected with the rest of the abdomen. Under such circumstanees it is difficult at first sight to recognise the real state of the case. When a segment is thus transferred from the abdomen to the metathorax, the part is called a median segment. The most remarkable median segment exists im those Hymenoptera which have a stalked abdomen, but a similar though less perfect condition exists in B , aia}, Fia. 60.—Simple abdomen of Japysx (A) contrasted any Insects. When such with the highly modified one of an ant, Crypto- a union occurs, it is usually cerus (B). The segments are numbered from most complete on the dorsal —P*!"* Rates surface, and the first ventral plate may almost totally disappear : such an alteration may involve a certain amount of change in the sclerites of the next segment, so that the morphological deter- mination of the parts at the back of the thorax and front of the abdomen is by no means a simple matter. A highly modified hind-body exists in the higher ants, Myrmicidae. In Fig. 60 we contrast the simple abdomen of Japya with the highly modi- fied state of the same part in an ant. Unlike the head and thorax, the abdomen is so loosely knitted together that it can undergo much expansion and contraction. I1O ABDOMEN CHAP. This is facilitated by an imbricated arrangement of the plates, and by their being connected by means of membranes admitting of much movement (Fig. 47, m, p. 88). In order to understand the structure of the abdomen it should be studied in its most dis- tended state; it is then seen that there is a dorsal and a ventral hard plate to each ring, and there is also usually a stigma; there may be foldings or plications near the line of junction of the dorsal and ventral plates, but these margins are not really distinct pieces. The pleura, in fact, remain membranous in the abdominal region, contrasting strongly with the condition of these parts in the thorax. The proportions of the plates vary greatly ; some- times the ventral are very large in proportion to the dorsal, as is usually the case in Coleoptera, while in the Orthoptera the reverse condition prevails. Cerci or other appendages frequently exist at the extremity of the abdomen (Fig. 47, , p. 88); the former are sometimes like antennae, while in other cases they may be short com- pressed processes consisting of very few joints. The females of many Insects possess saws or piercing instruments concealed within the apical part of the abdomen; in other cases an elongate exserted organ, called ovipositor, used for placing the eggs in suitable positions, is present. Such organs consist, it is thought, either of modified appendages, called gonapophyses, or of dorsal, ventral, or pleural plates. The males frequently bear within the extremity of the body a more or less complicated apparatus called the genital-armour. The term gonapophysis is at present a vague one, including stings, some ovipositors, por- tions of male copulatory apparatus, or other structures, of which the origin is more or less obscure. The caterpillar, or larva, of the Lepidoptera and some other Insects, bears a greater number of legs than the three pairs we have mentioned as being the normal number in Insects, but the posterior feet are in this case very different from the anterior, and are called false legs or prolegs. These prolegs, which are placed on the hind body, bear a series of hooks in Lepidopterous larvae, but the analogous structures of Sawfly larvae are destitute of such hooks. Placed along the sides of the body, usually quite visible in the larva, but more or less concealed in the perfect Insect, are little apertures for the admittance of air to the respiratory III SPIRACLES III system. They are called spiracles or stigmata. There is extreme variety in their structure and size; the largest and most remarkable are found on the prothorax of Coleoptera, especially in the groups Copridae and Cerambycidae. The exact position of the stigmata varies greatly, as does also their number. In the Order Aptera there may be none, while the maximum number of eleven pairs is said by Grassi’ to be attained in Japyx solifugus : in no other Insect have more than ten pairs been recorded, and this number is comparatively rare. Both position and number frequently differ in the early and later stages of the same Insect. The structure of the stigmata is quite as inconstant as the other points we have mentioned are. The admission of air to the tracheal system and its confine- ment there, as well as the exclusion of foreign bodies, have to be provided for. The control of the air within the system is, according to Landois? and Krancher? usually accomplished by means of an occluding apparatus placed on the tracheal trunk a little inside of the stigma, and in such case this latter orifice serves chiefly as a means for preventing the intrusion of foreign bodies. The occluding apparatus consists of muscular and mechanical parts, which differ much in their details in different Insects. Lowne supposes that the air is maintained in the tracheal system in a compressed condition, and if this be so, this apparatus must be of great importance in the Insect economy. Miall and Denny * state Fic. 61.—Membranous that in the anterior stigmata of the cock- “Pace between pro: roach the valves act as the occluding agents, muscles being attached directly to the inner face of the valves, and in some other Insects the spiracular valves appear to act partially by muscular agency, but there are many stigmata having valves destitute of muscles. and meso-thoraces of a beetle Huchroma, showing stigma (sé) ; a, hind margin of pronotum ; 6, front leg ; c, front margin of mesonotum ; d, base of elytra; e, mesosternum. According to Lowne® there exist valves in the blowfly at the entrance to the trachea proper, and he gives the following as the arrangement of parts for the admission of air :—there is a spiracle 1 Mem. Ace. Lincet Rom. (4) iv. 1888, p. 554. 2 Zeitschr. wiss. Zool. xvii. 1867, p. 187. 3 Zool. Anz. iii, 1880, p. 584. + The Cockroach, 1886, p. 151. > Anatomy of the Blowfly, 1893, p. 362. P12 INSECTS CHAP. leading into a chamber, the atrium, which is limited inwardly by the occluding apparatus; and beyond this there is a second chamber, the vestibule, separated from the tracheae proper by a valvular arrangement. He considers that the vestibule acts as a pump to force the air into the tracheae. Systematic Orientation. Terms relating to position are unfortunately used by writers on entomology in various, even in opposite senses. Great confusion exists as to the application of such words as base, apex, transverse, longitudinal. We can best explain the way in which the relative positions and directions of parts should he described by reference to Figure 62. The spot 3 represents an imaginary centre, situated between the thorax and abdomen, to which all the parts of the body are supposed to be related. The Insect should always be described as if it were in the position shown in the Figure, and the terms used should not vary as the position is changed. The creature is placed with ventral surface beneath, and with the appendages extended, like the Insect itself, in a horizontal plane. In the Figure the legs are, for clearness, made to radiate, but in the proper position the anterior pair should be approximate in front, and the middle and hind pairs directed backwards under the body. The legs are not to be treated as if they were hanging from the body, though that is the position they frequently actually assume. The right and left sides, and the upper and lower faces (these latter are frequently also spoken of as sides), are still to retain the same nomenclature even when Fic. 62. — Diagrammatic Insect to explain sal : . terms of position. A, apex; B, base: the position of the specimen is 1, tibia ; 2, last abdominal segment ; 3, eee. reversed. The base of an or gan is that margin that is nearest to the ideal centre, the apex that which is most distant. Il ORIENTATION 113 Thus in Fig. 62, where 1 indicates the front tibia, the apex (A) is broader than the base (B); in the antennae the apex is the front part, while in the cerci the apex is the posterior part ; in the last abdominal segment (2) the base (B) is in front of the apex (A). The terms longitudinal and transverse should always be used with reference to the two chief axes of the body-surface ; longitudinal referring to the axis extending from before back- wards, and transverse to that going across, i.e. from side to side. VOL. V I CHAPTER IV ARRANGEMENT OF INTERNAL ORGANS——-MUSCLES—-NERVOUS SYSTEM GANGLIONIC CHAIN——-BRAIN——SENSE-ORGANS——ALIMENTARY CANAL —— MALPIGHIAN TUBES —— RESPIRATION —— TRACHEAL SYSTEY BLOOD- CHYLE—DORSAL VESSEL OR HEART——FAT-BODY—OVARIES— TESTES—PARTHENOGENESIS——GLANDS. THE internal anatomy of Insects may be conveniently dealt with under the following heads :—(1) Muscular system; (2) nervous (a a aay aa ' i aa H iy ik, n Fic. 63.—Diagram of arrangement of some of the internal organs of an Insect : a, mouth ; 4, mandible; c, pharynx ; d, oesophagus ; e, salivary glands (usually extending further backwards) ; /, eye; g, supra-oesophageal ganglion ; h, sub-oesophageal ganglion ; 2, tentorium; j, aorta; ky, ky, ky, entothorax; J,-ls, ventral nervous chain; m, crop; , proventriculus ; 0, stomach ; p, Malpighian tubes; g, small intestine ; 7, large intestine ; s, heart; ¢, pericardial septum ; w, w, ovary composed of four egg-tubes ; v, oviduct ; w,spermatheca (or an accessory gland): <, retractile ovipositor ; y, cercus ; z, labrum. system ; (3) alimentary system (under which may be included secretion and excretion, about which in Insects very little is known); (4) respiratory organs ; (5) circulatory system ; (6) fat- body ; (7) reproductive system. CHAP. IV MUSCLES 115 Many of the anatomical structures have positions in the body that are fairly constant throughout the class. Parts of the respiratory and muscular systems and the fat-body occur in most of the districts of the body. The heart is placed just below the dorsal surface; the alimentary canal extends along the middle from the head to the end of the body. The chief parts of the nervous system are below the alimentary canal, except that the brain is placed above the beginning of the canal in the head. The reproductive system extends in the abdomen obliquely from above downwards, commencing anteriorly at the upper part and terminating posteriorly at the lower part of the body cavity. In Fig. 63 we show the arrangement of some of the chief organs of the body, with the exception of the imuscular and respiratory systems, and the fat-body. It is scarcely necessary to point out that the figure is merely diagrammatic, and does not show the shapes and sizes of the organs as they will be found in any one Insect. Muscles. The muscular system of Insects is very extensive, Lyonnet * having found, it is said, nearly 4000 muscles in the caterpillar of the goat-moth ; a large part of this number are segmental repetitions, nevertheless the muscular system is really complex, as may be seen by referring to the study of the flight of dragon- flies by von Lendenfeld.’ The minute structure of the muscles does not differ essentially from what obtains in Vertebrate animals. The muscles are aggregations of minute fibrils which are transversely striated, though in variable degree. Those in the thorax are yellow or pale brown, but in other parts the colour is more nearly white. The muscles of flight are described as being penetrated hy numerous tracheae, while those found elsewhere are merely surrounded by these aerating tubules. The force brought into play by the contractions of Insect muscles is very great, and has been repeatedly stated to be much superior to that of Vertebrate animals; very little reliance can, however, be 1 Lyonnet, Traité anatomique de la Chenille qui ronge le bois de Saute. La Haye, 1762. On p. 188 he says that he found 1647 muscles, without counting those of the head and internal organs of the body. He puts the number found in the human body at 529. 2 §B. Ak. Wien, Abth. 1, Ixxxiii. 1881, pp. 289-376. 116 INSECTS CHAP. placed on the assumptions and calculations that are supposed to prove this, and it is not supported by Camerano’s recent researches! Some of the tendons to which the muscles are attached are very elaborate structures, and are as hard as the chitinous skeleton, so as to be like small bones in their nature. A very elaborate tendon of this kind is connected with the prothoracic trochantin in Coleoptera, and may be readily examined in Hydro- philus. Tt has been suggested that the entothorax is tendinous in its origin, but other morphologists treat it, with more reason, as an elaborate fold inwards of the integument. Nervous System. Insects are provided with a very complex nervous system, which may be treated as consisting of three divisions :—(1) The cephalic system; (2) the ventral, or ganglionic chain; (3) an accessory sylupathetic system, or Se s Je systems. All these divisions VV 6 are intimately connected. We hf will consider first the most ex- tensive, viz. the ventral chain. ; Cp This consists of a series of small = YS masses of nervous matter called = (7) ganglia which extend in the longitudinal direction of the Y body along the median line of ( the lower aspect, and are con- a nected by longitudinal commis- WN sures, each ganglion being joined Ke to that following it by two Y i threads of nervous matter. Each \ of the gangla of the ventral iy chain really consists of two ( ganglia placed side by side and A, connected by commissures as ‘PN well as cellular matter. In Fic. 64.—Cephalic and ventral chain of larvae some of the ganglia may ganglia: A, larva of Chironomus ; B . Ss ; é . fmanen ot Arppobomen,- Latter Beads, } be contiguous, so that the com- muissures do not exist. From the ganglia motor nerves proceed to the various parts of the ' Mem. Ace. Torino (2), xliii. 1893, p. 229. Iv NERVOUS SYSTEM 117 body for the purpose of stimulating and co-ordinating the contractions of the muscles. The number of the ganglia in the ventral chain differs greatly in different Insects, and even in the different stages of metamorphosis of the same species, but never exceeds thirteen. As this number is that of the segments of the body, it has been considered that each segment had primitively a single ganglion. Thirteen ganglia for the ventral chain can, however, be only demonstrated in the embryonic state ; in the later stages of lite eleven appears to be the largest number that can be distinguished, and so many as this are found but rarely, and then chiefly in the larval stage. The diminution in number takes place by the amalgamation or coalescence of some of the ganglia, and hence those Insects in which the ganglia are few are said to have a highly concentrated nervous system. The modes in which these gangha combine are very various; the most usual is perhaps that of the combination of the three terminal ganglia into one body. As arule it may be said that concentration is the concomitant of a more forward posi- tion of the ganglia. As a result of this it is found that in some cases, as in Lamellicorn beetles, there are no ganglia situate in the abdomen. In the perfect state of the higher Diptera, the thoracic and abdominal ganglia are so completely concentrated in the thorax as to forma sort of thoracic brain. In Fig. 64 we represent a very diffuse and a very concentrated ganglionic chain; A being that of the larva of Chironomus, B that of the imago of Hippobosca. In both these sketches the cephalic ganglia as well as those of the ventral chain are shown. Turning next to the cephalic masses, we find these in the perfect Insect to be nearly always two in number: a very large and complex one placed above the oesophagus, and therefore called the supra-oesophageal ganglion; and a smaller one, the sub- or infra-oesophageal, placed below the oesophagus. The latter ganglion is in many Insects so closely approximated to the supra-oesophageal ganglion that it appears to be a part thereof, and is sometimes spoken of as the lower brain. In other Insects these two ganglia are more remote, and the infra- oesophageal one then appears part of the ventral chain. In the embryo it is said that the mode of development of the supra-oesophageal ganglion lends support to the idea that it may be the equivalent of three ganglia; there being at one 118 NERVOUS SYSTEM CHAP. time three lobes, which afterwards coalesce, on each side of the mouth, This is in accordance with the view formulated by Viallanes! to the effect that this great nerve-centre, or brain, as it is frequently called, consists essentially of three parts, viz. a Proto-, a Deuto-, and a Trito-cerebron. It is, however, only proper to say that though the brain and the ventral chain of vanglia may appear to be one system, and in the early embryonic condition to be actually continuous, these points cannot be con- sidered to be fully established. Dr. L. Will has informed us? that in Aphididae the brain has a separate origin, and is only subsequently united with the ganglionic chain. Some authorities say that in the early condition the sub-oesophageal ganglion is formed from two, and the supra-oesophageal from the same number of ganglia; the division in that case being 2 and 2, not 5 and 1, as Viallanes’ views would suggest. The inquiries that are necessary to establish such points involve very complex and delicate in- vestigations, so that it is not a matter of surprise that it cannot yet be said whether each of these views may be in certain cases correct. The supra- and sub-oesophageal gangla are always intimately connected by a commissure on each side of the oesophagus ; when very closely approximated they look like one mass through which passes the oesophagus (Fig. 66, A). The large supra-cesophageal ganglion supples the great nerves of the cephalic sense-organs, while the smaller sub-oesophageal centre gives off the nerves to the parts of the mouth. From the lower and anterior part of the supra-oesophageal ganglion a nervous filament extends as a ring round the anterior part of the oesophagus, and supplies a nerve to the upper lip? This structure is not very well known, and has been chiefly studied by Lienard,* who considers that it will prove to be present in all Insects. Whether the two cephalic ganglia be considered as really part of a single great ganglionic chain, or the reverse, they are at any rate always intimately connected with the ventral ganglia. We have already stated that the two cephalic masses are themselves closely approximated in many Insects, and may add that in some Hemiptera the first thoracic ganglion of the ventral chain is amalgamated into one body with the sub-oesophageal ganglion, 1 Bull. Soc. Philom. Paris (7), xi. 1887, p. 119, ete., and C. R. civ. 1887, p. 444. 2 Zool. Jahrbuch. Anat. iii. 1888, p. 276. 8 Kolbe, Linfiihrung, 1893, p. 411. 4 Arch. de Biol. i, 1880, p. 881. IV BRAIN 119 and further that there are a few Insects in which this latter centre is wanting. If the cephalic ganglia and ventral chain he looked on as part of one system, this may be considered as composed originally of seventeen ganglia, which number has been demonstrated in some embryos. The anatomy of the supra-oesophageal ganglion is very complex ; it has been recently investigated by Viallanes* in the wasp (Vespa) and in a grasshopper (Caloptenus italicus). The development and complication of its inner structure and of some of its outer parts appear to be proportional with the state of advancement of the instinct or intelligence of the Insect, and Viallanes found the brain of the grasshopper to be of a more simple nature than that of the wasp. Fic. 65.—Brain of Worker Ant of Formica rufa, (After Leydig, highly magnified. ) Explanation in text. Brandt, to whom is due a large part of our knowledge of the anatomy of the nervous system in Insects, says that the supra-oesophageal ganglion varies greatly in size in various Insects, its mass being to a great extent proportional with the development of the compound eyes; hence the absolute size is not a criterion for the amount of intelligence, and we must rather look to the complication of the structure and to the development of certain parts for an index of this nature. The drone in the honey -bee has, correlatively with the superior development of its eyes, a larger brain than the worker, but the size of the hemispheres, and the development of the gyri cerebrales is superior in the latter. In other words, the mass of 1 Ann. Sct. Nat. Zool. (7) ii. 1887, and iv. 1887. 120 NERVOUS SYSTEM CHAP. those great lobes of the brain that are directly connected with the faceted eyes must not be taken into account in a considera- tion of the relation of the size and development of the brain to the intelligence of the individual. The weight of the brain in Insects is said by Lowne to vary from 3,5 to s-5o of the weight of the body. Figure 65 gives a view of one side of the supra-oesophageal ganglion of the worker of an ant,—Formica rufa—and is taken from Leydig, who gives the following elucidation of it: 4, primary lobe, «, homogeneous granular inner substance, 0, cellular envelope; 2, stalked bodies (gyri cerebrales), a, 6, as before; c, presumed olfactory lobes, ¢, inner substance, d, gang- fy 66. — Stomato - gastric nerves of Cockroach: A, with brain in situ, after Koestler ; B, with the brain removed, after Miall and Denny: s.g, supra- oesophageal ganglion ; 0, optic nerve ; a, antennary nerve; f.g, frontal gang- lion; ve, oesophagus ; ¢, connective; p.g, paired ganglia ; v.g, crop or ven- tricular ganglion; 7, re- current nerve. lionie masses; D, ocular lobes, e, f, g, h, various layers of the same; £, origin of lateral commissures; ¥, median commissure in interior of brain; «, lower brain (sub-oesophageal ganglion) ; H, ocelli; J, faceted eye. Besides the brain and the great chain of ganglia there exists an accessory system, or systems, sometimes called the sym- pathetic, vagus, or visceral system. Although complex, these parts are delicate and difficult of dissection, and are consequently not so well known as is the ganglionic chain. There is a con- uecting or median nerve cord, communicating with the longi- tudinal comimissures of each segment, and itself dilating into ganglia at intervals; this is sometimes called the unpaired system. There is another group of nerves having paired ganglia, Iv SENSES 121 starting from a small ganglion in the forehead, then connecting with the brain, and afterwards extending along the oesophagus to the crop and proventriculus (Fig. 66). This is usually called the stomatogastric system. The oesophageal ring we have already spoken of. By means of these accessory nervous systems all the organs of the body are brought into more or less direct relation with the brain and the ganglionic chain. Our knowledge of these subsidiary nervous systems is by no means extensive, and their nomenclature is very unsettled ; little is actually known as to their functions. Organs of Sense. Insects have most delicate powers of perception, indeed they are perhaps superior in this respect to the other classes of animals. Their senses, though probably on the whole analogous to those of the Vertebrata, are certainly far from corresponding therewith, and their sense organs seem to be even more different from those of what we call the higher animals than the functions themselves are. We have already briefly sketched the structure of the optical organs, which are invariably situate on the head. This is not the case with the ears, which certainly exist in one Order,—the Orthoptera,—and are placed either on the front legs below the knee, or at the base of the abdomen. Notwith- standing their strange situation, the structures alluded to are undoubtedly auditory, and somewhat approximate in nature to the ear of Vertebrates, being placed in proximity to the inner face of a tense membrane; we shall refer to them when considering the Orthoptera. Sir John Lubbock considers—no doubt with reason —that some ants have auditory organs in the tibia. Many Insects possess rod-like or bristle-like structures in various parts of the body, called chordotonal organs; they are considered by Graber’ and others to have auditory functions, though they are not to be compared with the definite ears of the Orthoptera. The other senses and sense organs of Insects are even less known, and have given rise to much perplexity; for though many structures have been detected that may with more or less prob- ability be looked on as sense organs, it is difficult to assign a 1 Zool. Anz. iv. 1881, p. 452. SENSES CHAP. particular function to any of them, except it be to the sensory nf ) BV LUT TS, hairs. These are seated on various parts of the body. The chitinous covering, being a dead, hard substance, has no nerves distributed in it, but it is pierced with orifices, and in some of these there is implanted a hair which at its base is in connexion with a nerve; such a structure may pos- sibly be sensitive not only to contact with solid bodies, but even to vari- Fic. 67. — Longitudinal section of ous kinds of vibration. We give a portion of caudal appendage of figure (Fig. 67) of some of these hairs Acheta domestica (after Vom Rath): ch, chitin ; hyp, hypo- on the caudal appendage of a cricket, dermis ; 7, nerve; h, integu- after Vom Rath. The small hairs on mental hairs, not sensitive ; 7, ordinary hair ; f°, sensory hair ; the outer surface of the chitin in this AA, bladder-like hair ; sz, sense- figure have no sensory function, but cell. each of the others probably has; and these latter, being each accompanied by a different structure, must, though so closely approximated, be supposed to have a different function ; but in what way those that have no direct connexion with a nerve may act it is difficult to guess. The antennae of Insects are the seats of a great variety of sense organs, many of which are modifications of the hair, pit and nerve structure we have described above, but others cannot be brought within this category. Amongst these we may mention the pits covered with membrane (figured by various writers), perforations of the chitin without any hair, and membranous bodies either con- cealed in cavities or partially protruding therefrom. Various parts of the mouth are also Fic. 68.—Longitudinal section of apex of palpus of Pieris brassicae: sch, scales ; ch, chitin ; hyp, hypodermis ; n, nerve; sz, sense cells ; sh, sense hairs. (After Yom Rath.) the seats of sense organs of different kinds, some of them of a compound character; in such cases there may be a considerable number of hairs seated on branches of a common nerve as figured Iv ALIMENTARY SYSTEM 123 by Vom Rath? on the apex of the maxillary palp of Locusta rirudissima, or a compound organ such as we represent in Fig. 68 may be located in the interior of the apical portion of the palp. The functions of the various structures that have been detected are, as already remarked, very difficult to discover. Von Rath thinks the cones he describes on the antennae and palpi are organs of smell, while he assigns to those on the maxillae, lower lip, epipharynx, and hypopharynx the réle of taste organs, but admits he cannot draw any absolute line of distinction between the two forms. The opinions of Kraepelin, Hauser, and Will, as well as those of various earlier writers, are considered in Sir John Lubbock’s book on this subject.’ Alimentary and Nutritive System. The alimentary canal occupies the median longitudinal axis of the body, being situated below the dorsal vessel, and above the ventral nervous chain ; it extends from the mouth to the opposite extremity of the body. It varies greatly in the different kinds of Insects, but in all its forms it is recognised as con- sisting essentially of three divisions: anterior, middle, and pos- terior. The first and last of these divisions are considered to be of quite different morphological nature from the middle part, or true stomach, and to be, as it were, invaginations of the extremities of a closed bag; it is ascertained that in the embryo these invaginations have really blind extremities (see Fig. 82, p. 151), and only subsequently become connected with the middle part of the canal. There are even some larvae of Insects in which the posterior portion of the canal is not opened till near the close of the larval life; this is the case with many Hymenoptera, and it is probable, though not as frequently stated certain, that the occlusion marks the point of junction of the proctodaewm with the stomach. The anterior and posterior parts of the canal are formed by the ectoderm of the embryo, and in embryological and morphological language are called respectively the stomodaeum and proctodaeum ; the true stomach is formed from the endoderm, 1 Zeitschr. wiss. Zool. xlvi. 1888, pl. xxxi. ° On the Senses, Instincts, and Intelligence of Animals, with special reference to Insects. Vol. LXV. International Scientific Series, 1888. 124 ALIMENTARY SYSTEM CHAP. and the muscular layer of the whole canal from the meso- derm. The alimentary canal is more complex anatomically than it is morphologically, and various parts are distinguished, viz. the canal and its appendicula; the former consisting of oesophagus, crop, gizzard, true stomach, and an intestine divided into two or more parts. It should be remarked that though it is probable that the mor- phological distinctions correspond to a great extent with the anatomical lines of demarcation, yet this has not been sufficiently ascertained : the origin of the proctodaeum in Jfusca is indeed a point of special difficulty, and one on which there is consider- able diversity of opinion. In some Hemiptera the division of the canal into three parts is very obscure, so that it would be more correct, as Dufour says, to define it as consist- ing in these Insects of two main divisions—one anterior to, the other posterior to, the insertion of the Mal- pighian tubes. It should be borne in mind that the alimentary canal is very different in different Insects, so that the brief general description we must confine ie, eae aes a ourselves to will not be found to Ayphidria camelus (atter Du- apply satisfactorily to any one In- as a Haale dec % sal- sect. The oesophagus is the part be- ary glands ; ¢, oesophagus; 7, | . j crop; e, proventriculus; f, chyle, hind the mouth, and is usually narrow, ea a oe as it has to pass through the most pighian tubes ; %, termination of Lnportant nervous centres ; extremely Body variable in length, it dilates behind to form the crop. It may, too, have a dilatation immediately behind the mouth, and in such case a pharynx is considered to exist. The crop is broader than the oesophagus, and must be looked on as a mere dilatation of the latter, as no lne of Iv ALIMENTARY SYSTEM 125 demarcation can be pointed out between the two, and the crop may be totally absent. In some of the sucking Insects there is a lateral diverticulum, having a stalk of greater or less length, called the sucking- stomach; it 1s by no means certain that the function this name implies is correctly assigned to the organ. The gizzard or proventriculus (French, gésier ; German, Awumagen) is a small body interposed in some Insects between the true stomach and the crop or oesophagus. It is frequently remarkable for the development of its chitinous lining into strong toothed or ridged processes that look as if they were well adapted for the comminution of food. The function of the proventriculus in some Insects is obscure; its structure is used by systematists in the classification of ants. The extremity of the proventriculus not infrequently projects into the cavity of the stomach. The true stomach, or chylific ventricle (Ifagen or Mitteldarm of the Germans), is present in all the post-embryonic stages of the Insect’s life, existing even in the imagines of those who live only for a few hours, and do not use the stomach for any alimentary purpose. It is so variable in shape and capacity that no general description of it can be given. Sometimes it is very elongate, so that it is coiled and like an intestine in shape; it very frequently bears diverticula or pouches, which are placed on the anterior part, and vary greatly in size, sometimes they are only two in number, while in other cases they are so numerous that a portion of the outside of the stomach looks as if it were covered with villi, A division of the stomach into two parts is in some cases very marked, and the posterior portion may, in certain cases, be mistaken for the intestine; but the position of the Malpighian tubes serves as a mark for the distinction of the two structures, the tubes being inserted just at the junction of the stomach with the intestine. The intestine is very variable in length: the anterior part is the smaller, aud is frequently spoken of as the colon; at the extremity of the body the gut becomes much larger, so as to form a rectum. There is occasionally a diverticulum or “ caecum ” connected with the rectum, and in some Insects stink- glands. In some Hemiptera there is no small intestine, the Malpighian tubes being inserted at the junction of the stomach with the 126 ALIMENTARY SYSTEM CHAP. rectun. The total length of the alimentary canal is extremely variable ; it is necessarily at least as long as the distance between the mouth and anal orifice, but sometimes it is five or six times as long as this, and some of its parts then form coils in the abdominal cavity. The alimentary canal has two coats of muscles: a longitudinal and a transverse or annular. Both coexist in most of its parts. Internal to these coats there exists in the anterior and posterior parts of the canal a chitinous layer, which in the stomach is replaced by a remarkable epithelium, the cells of which are renewed, new ones growing while the old are still in activity. We figure a portion of this structure after Miall and Denny, and may remark that Oudemans?! has verified the correctness of their representation. The layers below represent the longi- tudinal and transverse muscles. Fic. 70.—Epithelium of stomach of Cockroach (after Miall and Denny): the lower parts indi- cate the transverse and longi- tudinal muscular layers, > DL ! e/a In addition to the various diverticula we have mentioned, there are two important sets of organs connected with the alimentary canal, viz. the salivary glands and the Malpighian tubes, The salivary glands are present in many Insects, but are absent in others. They are situate in the anterior portion of the body, and are very variable in their development, being sometimes very extensive, in other cases inconspicuous. They consist either of simple tubes lined with cells, or of branched tubes, or of tubes dilated laterally into little acini or groups of bags, the arrangement then somewhat resembling that of a bunch of grapes. There are sometimes large sacs or reservoirs con- nected with the efferent tubes proceeding from the secreting portions of the glands. The salivary glands ultimately discharge into the mouth, so that the Huid secreted by them has to be 1 Bijd. Dierkunde, 16, 1888, p. 192. Iv ALIMENTARY SYSTEM 127 swallowed in the same manner as the food, not improbably along with it. The silk so copiously produced by some larvae comes from very long tubes similar in form and situation to the simple tubes of the salivary glands. The Malpighian tubules are present in most Insects, though they are considered on good authority to be absent in many Collembola and in some Thysanura. They are placed near the posterior part of the body, usually opening into the alimentary canal just at the junction of the stomach and the intestine, at a spot called the pylorus. They vary excessively in length and in number,’ being sometimes only two, while in other cases there may be a hundred or even more of them. In some cases they are budded off from the hind-gut of the embryo when this is still very small; in other cases they appear later; frequently their number is greater in the adult than it is in the young. In Gryllotalpa there is one tube or duct with a considerable number of finer tubes at the end of it. There is no muscular layer in the Malpighian tubes, they being lined with cells which leave a free canal in the centre. The tubes are now thought, on considerable evidence, to be organs for the excretion of uric acid or urates, but it is not known how they are emptied. Marchal has stated? that he has seen the Malpighian tubes, on extrac- tion from the body, undergo worm-like movements; he suggests that their contents may be expelled by similar movements when they are in the body. The functions of the different portions of the alimentary canal, and the extent to which the ingested food is acted on by their mechanical structures or their products is very obscure, and different opinions prevail on important points. It would appear that the saliva exercises a preparatory action on the food, and that the absorption of the nutritive matter into the body cavity takes place chiefly from the true stomach, while the Malpighian tubes perform an excretory function. Beyond these elementary, though but vaguely ascertained facts, httle is known, though Plateau’s? and Jousset’s researches on the digestion of Insects throw some light on the subject. 1 For a review of their number see Wheeler, Psyche, vi. 1893, pp. 457, etc. 2 Ann. Soc. Ent. France, 1xi. 1892, Bull. p. eclvi. 3 Vem. Ac. Belgique (2), xli. 1875, and Bull. Ac. Belgique (2), xliv. 1877, p. 710. 128 RESPIRATION CHAP. Respiratory Organs. The respiration of Insects is carried on by means of a system of vessels for the conveyance of air to all parts of the body ; this system is most remarkably developed and elaborate, and contrasts strongly with the mechanism for the circulation of the blood, which is as much reduced as the air system is highly developed, as well as with the arrangement that exists in the Vertebrates. There are in Insects no lungs, but air is carried to every part of the body directly by means of tracheae. These tracheae con- nect, with the spiracles—the orifices at the sides of the body we have already mentioned when describing the external struc- tures —and the air thus finds its way into the most remote recesses of the Insect’s body. The tracheae are all intimately connected. Large tubes connect the spiracles longitudinally, others pass from side to side of the body, and a set of tracheae for the lower part of the body is connected with another set on the upper surface by means of several descending tubes. From these main channels smaller branches extend in all curections, forking and giving off twigs, so that all the organs inside the body can be supplied with air in the most Jiberal manner. On opening a freshly deceased Insect the abundance of the tracheae is one of the peculiarities that most attracts the attention; and as these tubes have a peculiar white glistening appearance, they are recognised without difficulty. In Insects of active flight, possibly in some that are more passive, though never in larvae, there are air-sacs, of more than one kind, con- nected with the tracheae, and these are sufficiently capacious to have a considerable effect in diminishing the specific gravity of the Insect. The most usual situation for these sacs is the basal portion of the abdominal cavity, on the great lateral tracheal conduits. In speaking of the external structure we have remarked that the stigmata, or spiracles, by which the air is admitted are very various in their size and in the manner in which they open and close. Some spiracles have no power of opening; while others are provided with a muscular and valvular apparatus for the purpose of opening and closing effectually. The structure of the tracheae is remarkable: they are elastic and consist of an outer cellular, and an inner chitinous layer ; this latter is strengthened by a peculiar spiral fibre, which gives Iv RESPIRATION 129 to the tubes, when examined with the microscope, a transversely, closely striated appearance. Packard considers! that in some tracheae this fibre is not really spiral, but consists of a large num- ber of closely placed rings. Such a condition has not, however, been recorded by any other observer. The spiral fibre is absent in the fine capillary twigs of the tracheal system, as well as from the expanded sacs. The mode of termination of the capillary branches is not clear. Some have supposed that the finest twigs anastomose with others; on the other hand it has been said that they terminate by penetrating cells, or that they simply come to an end with either open or closed extremities. | Wisting- Fic. 71.—Portion of the abdominal part of tracheal system of a Locust (Oedipoda): w, spiracular orifices ; 0, tracheal tubes ; c, vesicular dilatations ; d, tracheal twigs or capillaries. (After Dufour.) hausen” states that in the silk-glands the tracheal twigs anas- tomose, and he is of opinion that the fine terminal portions contain fluid. However this may be, it is certain that all the organs are abundantly supplied with a capillary tracheal net- work, or arboreal ramification, and that in some cases the tubes enter the substance of tissues. Near their terminations they are said to be 4, to zy millimetre in diameter. We must repeat that such a system as we have just sketched forms a striking contrast to the imperfect blood-vascular system, and that Insects differ profoundly in these respects from Verte- brate animals. In the latter the blood-vessels penetrate to all 1 American Naturalist, xx. 1886, pp. 438 and 558. 2 Zeitschr. wiss. Zool., xlix. 1890, p, 565. VOL. V Kk 130 RESPIRATION CHAP. the tissues and form capillaries, while the aerating apparatus is confined to one part of the body; in Insects the blood-circulating system is very limited, and air is carried directly by complex vessels to all parts; thus the tracheal system is universally recog- nised as one of the most remarkable of the characters of Insects. Many Insects have a very active respiratory system, as is shown by the rapidity with which they are affected by agents like chloroform; but the exact manner in which the breathing is carried on is unknown. In living Insects rapid movements of contraction and expansion of parts of the body, chiefly the abdomen, may be observed, and these body contractions are some- times accompanied by opening and shutting the spiracular orifices: it has been inferred that these phenomena are respira- tory. Although such movements are not always present, it is possible that when they occur they may force the air onwards to the tissues, though this is by no means certain. It is clear that the tracheal system is the usual means of supplying the organisation with oxygen, but it appears to be improbable that it can also act as the agent for removing the carbonaceous pro- ducts of tissue-changes. It has been thought possible that car- bonic acid might reach the spiracles from the remote capillaries by a process of diffusion,’ but it should be recollected that as some Insects have no tracheal system, there must exist some other mode of eliminating carbonic acid, and it is possible that this mode may continue to operate as an important agent of purification, even when the tracheal system is, as a bearer of air to the tissues, highly developed. Eisig’ has suggested that the formation of chitin is an act of excretion; if so this is capable of relieving the system of carbonic acid to some extent Others have maintained that transpiration takes place through the deli- cate portions of the integument. Lubbock? has shown that Melolontha larvae breathe “partly by means of their skin.” The mode in which the carbon of tissue-change, and the nitrogen of inspiration are removed, is still obscure; but it appears probable that the views expressed by Réaumur, Lyonnet, and Lowne* as to inspiration and expiration may prove to be nearer the truth than those which are more widely current. In ? See Miall and Denny, Cockroach, p. 158, * Eisig, Mon. Capitelliden, 1887, p. 781. ° Tr. Linn, Soc. London Zool. xxiii. 1860, p. 29. + Blow/ly, etc. p. 876. Iv RESPIRATION 131 connexion with this it should be recollected that the outer integument consists of chitin, and is cast and renewed several times during the life of the individual. Now as chitin consists largely of carbon and nitrogen, it is evident that the moulting must itself serve as a carbonaceous and nitrogenous excretion. If, as is suggested by Bataillon’s researches,’ the condition accompanying metamorphosis be that of asphyxia, it is probable that the secretion of the new coat of chitin may figure as an act of excretion of considerable importance. If there be any truth in this suggestion it may prove the means of enabling us to comprehend some points in the development of Insects that have hitherto proved very perplexing. Peyrou has shown” that the atmosphere extracted from the bodies of Insects (J/elolontha) is much less rich in oxygen than the surrounding atmosphere is, and at ordinary temperatures always contains a much larger proportion of carbonic acid: he finds, too, that as in the leaves with which he makes a comparison, the proportion of oxygen augments as the protoplasmic activity diminishes. Were such an observation carried out so as to dis- tinguish between the air in the tracheal system and the gas in other parts of the body the result would be still more interesting. We know very little as to the animal heat produced by insects, but it is clear from various observations® that the amount evolved in repose is very small. In different conditions of activity the temperature of the insect may rise to be several degrees above that of the surrounding medium, but there seems to be at present no information as to the physiological mode of its production, and as to the channel by which the products— whether carbonic acid or other matters—may be disposed of. In the order Aptera (Thysanura and Collembola) the tracheal system is highly peculiar. In some Collembola it apparently does not exist, and in this case we may presume with greater certainty that transpiration of gases occurs through the integu- ment: in other members of this Order tracheae are present in a more or less imperfect state of development, but the tracheae of different segments do not communicate with one another, 1 R. Ac. Set., cxv. 1892, p. 61, and Bull. Set. France Belgique, xxv. 1893, = 2 rend, Ac. Paris, cii. 1886, p. 1339. 3 See Newport, Phil. Trans. 1837, and Lubbock Linn. Trans. xxiii. 1860, p. 29, ete. 132 RESPIRATION CHAP. thus forming a remarkable contrast to the amalgamated tracheal system of the other Orders of Insects, where, even when the tracheal system is much reduced in extent (as in Coccidae), it is nevertheless completely unified. Gryllotalpa is, however, said by Dohrn! to be exceptional in this respect; the tracheae con- nected with each spiracle remaining unconnected. Water Insects have usually peculiarities in their respiratory systems, though these are not so great as might @ priort have been anticipated. Some breathe by coming to the surface and taking in a supply of air in various manners, but some appar- ently obtain from the water itself the air necessary for their physiological processes. Aquatic Insects are frequently provided with gills, which may be either wing-like expansions of the integument containing some tracheae (Ephemeridae larvae), or bunches of tubes, or single tubes (Trichoptera larvae). Such Insects may either possess stigmata in addition to the gills, or be destitute of them. In other cases air is obtained by taking water into the posterior part of the alimentary canal (many dragon-flies), which part is then provided with special tracheae. Some water-larvae appear to possess neither stigmata nor gills (certain Perlidae and Diptera), and it is supposed that these obtain air through the integument; in such Insects tracheal twigs may frequently be seen on the interior of the skin. In the imago state it is the rule that Water Insects breathe by means of stigmata, and that they carry about with them a supply of air sufficient for a longer or shorter period. A great many Insects that live in water in their earlier stages and breathe there by peculiar means, in their perfect imago state live in the air and breathe in the usual manner. There are, in both ter- restrial and aquatic Insects, a few cases of exsertile sacs without tracheae, but filled with blood (Pelobius larva, Machilts, ete.) ; and such organs are supposed to be of a respiratory nature, though there does not appear to be any positive evidence to that effect. Blood and Blood-Circulation. Owing to the great complexity of the tracheal system, and to its general diffusion in the body, the blood and its circulation are very different in Insects from what they are in Vertebrates, so 1 Zeitschr. wiss. Zool. xxvi. 1876, p. 137. Iv CIRCULATION 133 that it is scarcely conducive to the progress of physiological knowledge to call two fluids with such different functions by one name. The blood of Insects varies according to the species, and in all probability even in conformity with the stage of the life of the individual. Its primary office is that of feeding the tissues it bathes, and it cannot be considered as having any aerat- ing function. It is frequently crowded with fatty substances. Graber says: “The richness of Insect blood in unsaponified or unelaborated fat shows in the plainest manner that it is more properly a mixture of blood and chyle; or indeed we might say with greater accuracy, leaving out of consideration certain matters to be eliminated from it, that it is a refined or distilled chyle.” Connected in the most intimate manner with the blood there is a large quantity of material called vaguely the fat- body; the blood and its adjuncts of this kind being called by Wielowiejski' the blood-tissue. We shall return to the consideration of this tissue after sketching the apparatus for distributing the refined chyle, or blood as we must, using the ordinary term, call it. There is in Insects no complete system of blood-vessels, though there is a pulsating vessel to ensure distribution of the nutritive fluid. This dorsal vessel, or heart as it is frequently called, may be distinguished and its pulsations watched, in transparent Insects when alive. It is situate at the upper part of the body, extending from the posterior extremity, or near it, to the head or thorax, and is an elongate tube, consisting as it were of a number of united chambers; it is closed behind, except in some larvae, but is open in front, and has several orifices at the sides; these orifices, or ostia, are frequently absent from the front part of the tube, which portion is also narrower, being called the aorta—by no means a suitable term. Near the lateral orifices there are delicate folds, which act to some extent as valves, facilitating, in conjunction with the mode of contraction of the vessel, a forward movement of the blood. The composition of the tube, or series of chambers, is that of a muscular layer, with internal and external membranous coverings, the intima and adventitia. Olga Poletajewa states* that in Bombus the dorsal vessel consists of five chambers placed in longitudinal succession, and not very intimately connected, and that there is but little 1 Zeitschr. wiss, Zool. xiii. 1886, p. 512. 2 Zool. Anz. ix. 1886, p. 13. 134 CIRCULATION CHAP valvular structure. In Cimbea she finds a similar arrangement, but there are ten chambers, and no aorta. The dorsal vessel is connected with the roof of the body by some short muscles, and is usually much surrounded by fat-body into which tracheae penetrate; by these various means it is kept in position, though only loosely attached; beneath it there is a delicate, incomplete or fenestrate, membrane, delimiting a sort of space called the pericardial chamber or sinus; connected with this membrane are some very delicate muscles, the alary muscles, extending inwards from the body wall (0, Fig. 72): the curtain formed by these muscles and the fenestrate membrane is called Fia. 72. — Dorsal vessel Fic. 78.—Diagram of transverse section (c), and alary muscles of pericardial sinus of Oedipoda coeru- (b),of Gryllotalpa (after lescens, (After Graber, Arch. Mikr. Graber); «, aorta. Anat. ix.) H, heart; s, septum; m, V.B, — The ventral muscles—the upper suspensory, the aspect is here dorsal, lower alary. and nearly the whole of the body is removed to show these parts, the pericardial diaphragm or septum. The alary muscles are not directly connected with the heart. It has been thought by some that delicate vessels exist beyond the aorta through which the fluid is distributed in definite channels, but this does not appear to be really the case, although the fluid may frequently be seen to move in definite lines at some distance from the heart. There is still much uncertainty as to some of the details of the action of the heart, and more especially as to the influence of the alary muscles. The effect of the contraction of these must be to increase the area of the pericardial chamber by rendering Iv CIRCULATION 135 its floor or septum less arched, as shown in our diagram (Fig. 73), representing a transverse section through the pericardial chamber, H being the dorsal vessel with m its suspensory muscles, and s its septum, with m the alary muscles. The contraction of these latter would draw the septum into the position of the dotted line, thus ° increasing the area of the sinus above; but as this floor or septum is a fenestrated structure, its contraction allows fluid to pass through it to the chamber above; thus this arrangement may be looked on as a means of keeping up a supply of fluid to the dorsal vessel, the perforated septum, when it contracts, exerting pressure on the tissues below; these are saturated with fluid, which passes through the apertures to the enlarged pericardial chamber. Some misconception has prevailed, too, as to the function of the pericardial chamber. This space frequently contains a large quantity of fat-body—pericardial tissue—together with tracheae, and this has given rise to the idea that it might be lung-like in function; but, as Miall and Denny’ have pointed out, this is erroneous; the tissues in Insects have their own ample sup- plies of air. It has also been supposed that the alary muscles cause the contraction of the heart, but this is not directly the case, for they are not attached to it, and it pulsates after they have been severed. It has been suggested that the contractions of this vessel are regulated by small ganglia placed on, or in, its substance. However this may be, these contractions vary enor- mously according to the condition of the Insect; they may be as many, it is said, as 100 or more in a minute, or they may be very slow and feeble, if not altogether absent, without the death of the Insect ensuing. The expulsion of the blood from the front of the dorsal vessel seems to be due to the rhythm of the contrac- tion of the vessel as well as to its mechanical structure. Bataillon says? confirming an observation of Réaumur, that at the period when the silkworm is about to change to the chrysalis condition, the circulation undergoes periodical changes, the fluid moving during some intervals of about ten minutes’ duration in a reversed direction, while at other times the blood is expelled in front and backwards simultaneously, owing apparently to a rhythmical change in the mode of contraction of the dorsal vessel. 1 Cockroach, p. 140. 2 Bull. Sci. France Belgique, xxv. 1893, p. 22. 136 FAT-BODY CHAP. As the dorsal vessel consists of a number of distinct chambers, it has been suggested that there is normally one of these for each segment of the body; and it appears that the total number is sometimes thirteen, which is frequently that of the segments of the body without the head. The number of chambers differs, however, greatly, as we have previously stated, and cannot be considered to support the idea of an original segmental arrange- ment of the chambers. The dorsal vessel, though in the adult a single organ, arises in the embryo from two lateral, widely separated parts which only in a subsequent stage of the embry- onic development coalesce in the median line. Fat-Body. In discussing the tracheae we remarked on the importance of their function and on their abundant presence in the body. Equally conspicuous, and perhaps scarcely less important in func- tion, is the fat-body, which on opening some Insects, especially such as are in the larval stage, at once attracts attention. It consists of masses of various size and indefinite form distributed throughout the body, loosely connected together, and more or less surrounding and concealing the different organs. The colour varies according to the species of Insect. This fat-body is much connected with fine tracheal twigs, so that an organisation extend- ing throughout the body is thus formed. It may be looked on as a store of nutritious matter which may be added to or drawn on with great rapidity; and it is no doubt on this that many of the internal parasites, so common in the earlier stages of Insects’ lives, subsist before attacking the more permanent tissues of their hosts. There is some reason to suppose that the fat-body may have some potency in determining the hunger of the Insect, for some parasitised larvae eat incessantly. The matter extracted from the food taken into the stomach of the Insect, after undergoing some elaboration—on which point very little is known—finds its way into the body-cavity of the creature, and as it is not confined in any special vessels the fat- body has as unlimited a supply of the nutritive fluid as the other organs: if nutriment be present in much greater quantity than is required for the purposes of immediate activity, meta- morphosis or reproduction, it is no doubt taken up by the fat- Iv FAT-BODY 137 body which thus maintains, as it were, an independent feeble life, subject to the demands of the higher parts of the organisation. It undoubtedly is very important in metamorphosis, indeed it is possible that one of the advantages of the larval state may be found in the fact that it facilitates, by means of the fat-body, the storage in the organisation of large quantities of material in a comparatively short period of time. A considerable quantity of fat tissue is found in the. peri- cardial sinus, where it is frequently of somewhat peculiar form, and is spoken of as pericardial cells, or pericardial tissue. Some large cells, frequently of pale yellow colour, and containing no fat, are called oenocytes by Wielowiejski. They are connected with the general fat-body, but are not entirely mingled with it; several kinds have been already distinguished, and they are probably generally present. The phagocytes, or leucocytes, the cells that institute the process of histolysis in the metamorphosis of Muscidae, are a form of blood cell; though these cells are amoeboid some writers derive them from the fat-body. The cells in the blood have no doubt generally an intimate re- lation with the fat-body, but very little accurate information has been obtained as to these important physiological points, though Graber has inaugurated their study.’ Organs of Sex. The continuation of the species is effected in Insects by means of two sexes, each endowed with special reproductive organs. It has been stated that there are three sexes in some Insects—male, female, and neuter; but this is not correct, as the so-called neuters are truly sexed individuals,—generally females,—though, as a rule, they are not occupied with the direct physiological processes for continuing the species. The offspring is usually produced in the shape of eggs, which are formed in ovaries. These organs consist of egg-tubes, a cluster of which is placed on each side of the body, and is suspended, according to Leydig” and others, to the tissue connected with the heart by means of the thread-like terminations of the tubes. The number of egg-tubes varies greatly in different Insects ; there may be only one to each ovary (Campodea), but usually the 1 Biol. Centralbl. xi. 1891, p. 212. ° Acta. Ac. German. xxxiil. 1867, No. 2. 138 OVARIES CHAP. number is greater, and in the queen-bee it is increased to about 180. In the Queens of the Termitidae, or white ants, the ovaries take on an extraordinary development; they fill the whole of the greatly distended hind-body. Three thousand ege-tubes, each con- taining many hundred eggs, may be found in a Queen Termite, so that, as has been said by Hagen,’ an offspring of millions in number is probable. There is considerable variety in the arrangements for the growth of the eggs in the egg-tubes. Speaking concisely, the tubes may be considered to be centres of attraction for nutritive material, of which they frequently contain considerable stores. Next to the terminal thread, of which we have already spoken, there is a greater or smaller enlargement of the tube, called the terminal cham- ber; and there may also be nutri- ment chambers, in addition to the dilatations which form the egg-cham- bers proper. Korschelt * distinguishes three principal forms of egg-tubes, viz. (1) there are no special nutriment chambers, a condition shown in Figure 74; (2) nutriment chambers alter- nate with the ege-chambers, as shown ; in our Figure of an egg-tube of Fic. 74.—Sex organs of female of Dytiscus marginalis ; (3) the ter- Scolia tnterrupta (after Dufour); minal chamber takes on an unusual a, egg-tubes; 0, oviducts; c, . 2 poison glands ; d, duct of aeces- (evelopment, acting as a large nutri- sory gland (or spermatheca); ¢, ment chamber, there being no other external terminal parts of body. . oe 2 : special nutriment chambers. This condition is found in Rhizotrogus solstitialis. The arrangements as to successive or simultaneous production of the eggs in the tubes seem to differ in different Insects. In some forms, such as the white ants, the process of ege-formation (oogenesis) attains a rapidity that is almost incredible, and is continued, it is said, for periods of many months. There is no point in which Insects differ more than in that of the number of eggs produced by one 1 Linnaea entomologica, xii. 1858, p. 313. * Zeitschr, wiss. Zool. 1886, xliii. p. 539. iv OVARIES 139 female. The egg-tubes are connected with a duct for the con- veyance of the eges to the exterior, and the arrangements of the tubes with regard to the oviduct also vary much. An interesting condition is found in Machilis (see Fig. 94, p. 188), where the seven egg-tubes are not arranged in a bunch, but open at a distance from one another into the elongated duct. The two oviducts usually unite into one chamber, called the azygos portion or the uterus, near their termination. There are a few Insects (Ephemeridae) in which the two ovi- ducts do not unite, but have a pair of orifices at the extremity of the body. Hatchett-Jackson has recently shown? that in Vanessa io of the Order Lepidoptera, the paired larval oviducts are solid, and are fixed ventrally so as to represent an Ephemeridean stage; that the azygos system of ducts and appended structures develop separ- ately from the original oviducts, and that they pass through stages represeuted in other Orders of Insects to the stage peculiar to the Lepi- doptera. Afachilis, according to Oudemans, is a complete connecting lnk between the Insects with single and those with paired orifices. There are in different Insects more than one kind of diverticula and accessory glands in con- nexion with the oviducts or uterus; a recepta- culum seminis, also called spermatheca, is common. In the Lepidoptera there is added a remarkable structure, the bursa copulatrix, which is a pouch connected by a tubular isthmus with the common Fic. 75.—Egg-tube of Dytiscus mar- ginalis ; ec, egg- chamber; xc, nutriment cham- ber ; ¢.c, terminal chamber; 4&4, terminal thread. (After Kor- schelt. ) portion of the oviduct, but having at the same time a separate external orifice, so that there are two sexual orifices, the opening of the bursa copulatrix being the lower or more anterior. The organ called by Dufour in his various contributions glande sébifique, is now considered to be, in some cases at any rate, a spermatheca. The special functions of the accessory glands are still very obscure. The ovaries of the female are replaced in the male by a pair 1 Tr. Linn. Soc. London, 2nd ser. ; Zool. v. 1890, p. 173. 140 MALE-STRUCTURES CHAP. of testes, organs exhibiting much variety of form. The structure may consist of an-extremely long and fine convoluted tube, packed into a small space and covered with a capsule; or there may be several shorter tubes. As another extreme may be mentioned the existence of a number of small follicles opening into a common tube, several of these small bodies forming together a testis. As a rule each testis has its own capsule, but cases occur—very frequently in the Lepidoptera—in which the two testes are enclosed in a common capsule; so that there then appears to be only one testis. The secretion of each testis is conveyed out- wards by means of a slender tube, the vas deferens, and there are always two such tubes, even when the two testes are placed in one capsule. The vasa deferentia differ greatly in their length in different Insects, and are in some cases many times the length of the body; they open into a common duct, the ductus ejaculatorius. Usually at some part of the vas deferens there exists a reservoir in the form of a sac or dilata- tion, called the vesicula seminalis. There are in the male, as well as in the female, frequently diverticula, or glands, in connexion with the sexual passages; these sometimes exhibit very remarkable forms, as in the common cockroach, but their functions are quite obscure. There is, as we have already remarked, extreme variety in the details of the structure of the internal reproductive apparatus in the male, and there are a few cases in which the vasa deferentia do not unite behind, but terminate in a pair of separate orifices. The genus Machilis is as remarkable in the form of the sexual glands and ducts of the male as we have already mentioned it to be in F16.76.—Tenthredo Lhe corresponding parts of the female. cincta. a, Gt, Although the internal sexual organs are only eet i v,, fully developed in the imago or terminal stage : as eae , = : = yetitalls Semin: of the individual life, yet in reality their rudi- ity of body with ents appear very early, and may be detected copulatory ar- from the embryo state onwards through the mature, (After 2 Dufour. ) other preparatory stages. The spermatozoa of a considerable number of Insects, especially of Coleoptera, have been examined by Ballo- Iv PARTHENOGENESIS 14! witz;? they exhibit great variety; usually they are of extremely elongate form, thread-like, with curious sagittate or simply pointed heads, and are of a fibrillar structure, breaking up at various parts into finer threads. External Sexual Organs.—The terminal segments of the body are usually very highly modified in connexion with the external sexual organs, and this modification occurs in such a great variety of forms as to render it impossible to give any general account thereof, or of the organs themselves. Some of these segments—or parts of the segments, for it may be dorsal plates or ventral plates, or both—may be withdrawn into the interior, and changed in shape, or may be doubled over, so that the true termination of the body may be concealed. The com- parative anatomy of all these parts is especially complex in the males, and has been as yet but little elucidated, and as the various terms made use of by descriptive entomologists are of an unsatisfactory nature we may be excused from enumerat- ing them. We may, however, mention that when a terminal chamber is found, with which both the alimentary canal and the sexual organs are connected, it is called a cloaca, as in other animals, Parthenogenesis. There are undoubted cases in Insects of the occurrence of parthenogenesis, that is, the production of young by a female without concurrence of a male. This phenomenon is usually limited to a small number of generations, as in the case of the Aphididae, or even to a single generation, as occurs in the alterna- tion of generations of many Cynipidae, a parthenogenetic alter- nating with a sexual generation. There are, however, a few species of Insects of which no male is known (in Tenthredinidae, Cynipidae, Coccidae), and these must be looked on as perpetually parthenogenetic. It is a curious fact that the result of partheno- genesis in some species is the production of only one sex, which in some Insects is female, in others male; the phenomenon in the former case is called by Taschenberg”* Thelyotoky, in the latter case Arrhenotoky ; Deuterotoky being applied to the cases in which two sexes are produced. In some forms of partheno- 1 Zeitschr. wiss. Zool. 1. 1890, p. 317. 2 4bh. Ges. Haile, xvii. 1892. p. 365. 142 INSECTS CHAP. IV genesis the young are produced alive instead of in the form of eggs. A very rare kind of parthenogenesis, called paedogenesis, has been found to exist in two or three species of Diptera, young being produced by the immature Insect, either larva or pupa. Glands. Insects are provided with a variety of glands, some of which we have alluded to in describing the alimentary canal and the organs of sex; but in addition to these there are others in connexion with the outer integument; they may be either single cells, as described by Miall in Dicranota larva,! or groups of cells, isolated in tubes, or pouches. The minute structure of Insect glands has been to some extent described by Leydig ;” they appear to be essentially of a simple nature, but their special functions are ‘very problematic, it being difficult to obtain sufficient of their products for satisfactory examination. 1 Tr. Ent. Soc, London, 1893, p. 241. 2 Arch. Anat. Phys. 1855 and 1859. CHAPTER V DEVELOPMENT EMBRYOLOGY—-EGGS——-MICROPYLES—-FORMATION OF EMBRYO—VEN- TRAL PLATE—-ECTODERM AND ENDODERM——SEGMENTATION— LATER STAGES——DIRECT OBSERVATION OF EMBRYO——METAMOR- PHOSIS—-COMPLETE AND INCOMPLETE—INSTAR——HYPERMETA- MORPHOSIS—-METAMORPHOSIS OF INTERNAL ORGANS—INTEGU- MENT——METAMORPHOSIS OF BLOWFLY—HISTOLYSIS—-IMAGINAL DISCS—-PHYSIOLOGY OF METAMORPHOSIS—-ECDYSIS. THE processes for the maintenance of the life of the individual are in Insects of less proportional importance in comparison with those for the maintenance of the species than they are in Verte- brates. The generations of Insects are numerous, and the in- dividuals produced in each generation are still more profuse. The individuals have as a rule only a short life ; several successive generations may indeed make their appearances and disappear in the course of a single year. Although eggs are laid by the great majority of Insects, a few species nevertheless increase their numbers by the production of living young, in a shape more or less closely similar to that of the parent. This is well known to take place in the Aphi- didae or green-fly Insects, whose rapid increase in numbers is © such a plague to the farmer and gardener. These and some other cases are, however, exceptional, and only emphasise the fact that Insects are pre-eminently oviparous. Leydig, indeed, has found in the same Aphis, and even in the same ovary, an egg-tube producing eggs while a neighbouring tube is producing vivi- parous individuals! In the Diptera pupipara the young are 1 Acta. Ac. German. xxxili. 1867, No. 2, p. 81. 144 EGGS CHAP. produced one at a time, and are born in the pupal stage of their development, the earlier larval state being undergone in the body of the parent: thus a single large egg is laid, which is really a pupa. The eggs are usually of rather large size in comparison with the parent, and are produced in numbers varying according to the species from a few—15 or even less in some fossorial Hymenoptera—to many thousands in the social Insects: some- where between 50 and 100 may perhaps be taken as an average number for one female to produce. The whole number is frequently deposited with rapidity, and the parent then dies at once. Some of the migratory locusts are known to deposit batches of eggs after considerable intervals of time and change of locality. The social Insects present extraordinary anomalies as to the production of the eggs and the prolongation of the life of the female parent, who is in such cases called a queen. The living matter contained in the egg of an Insect is protected by three external coats: (1) a delicate interior oolemm ; (2) a stronger, usually shell-like, covering called the chorion ; (3) a layer of material added to the exterior of the ege from glands, at or near the time when it is , deposited, and of very various character, sometimes forming a coat on each egg and sometimes a common covering or capsule for a number of eggs. The egg- shell proper, or chorion, is frequently Fic. 77.—Upper or micro. COVered in whole or part with a complex pylar aspect of egg of minute sculpture, of a symmetrical char- Vanessa cardui, (After . : : Soudder,) acter, and in some cases this is very highly developed, forming an ornamenta- tion of much delicacy; hence some Insects’ eggs are objects of admirable appearance, though the microscope is of course necessary to reveal their charms. One of the families of butterflies, the Lycaenidae, is remarkable for the complex forms displayed by the ornamentation of the chorion (see Fig. 78, B). The egg-shell at one pole of the egg is perforated by one or more minute orifices for the admission to the interior of the spermatozoon, and it is the rule that the shell hereabouts is symmetrically sculptured (see Fiv. 77), even when it is unorna- v EMBRYOLOGY 145 mented elsewhere: the apertures in question are called micro- pyles. They are sometimes protected by a micropyle apparatus, consisting of raised processes, or porches: these are developed to an extraordinary extent in some eggs, especially in those of Fic. 78.—Eggs of In- sects: A, blowfly (after Henking); B, butterfly, Thecla (after Scudder) ; C, Hemipteron (Redu- viid). Hemiptera-Heteroptera (see Fig. 78, C). Some of these peculiar structures have been described and figured by Leuckart.! The purpose they serve is quite obscure. Formation of Embryo. The mature, but unfertilised, ege is filled with matter that should ultimately become the future individual, and in the process of attaining this end is the seat of a most remarkable series of changes, which in some Insects are passed through with extreme rapidity. The egg-contents consist of a comparatively structureless matrix of a protoplasmic nature and of yolk, both of which are distributed throughout the egg in an approximately even manner. The yolk, however, is by no means of a simple nature, but consists, even in a single egg, of two or three kinds of spherular or granular constituents; and these vary much in their appearance and arrangement in the early stages of the develop- ment of an egg, the yolk of the same egg being either of a homo- geneously granular nature, or consisting of granules and larger masses, as well as of particles of fatty matter; these latter when seen through the microscope looking sometimes like shining, nearly colourless, globules. The nature of the matrix—which term we may apply to both the protoplasm and yolk as distinguished 1 Miller's Arch. Anat. Phys, 1855, p. 90. VOL. V L 146 EMBRYOLOGY CHAP. from the minute formative portions of the egg—and the changes that take place in it have been to some extent studied, and Kowalewsky, Dohrn,’ Woodworth? and others have given some particulars about them. The early changes in the formative parts of the mature ege have been observed by Henking in several Insects, and particularly in Pyrrhocoris, his observations being of considerable interest. When the egg is in the ovary and before it is quite mature——at the time, in fact, when it is receiving nutriment from ovarian cells,—it contains a germinal vesicle including a germinal spot, but when the ege is mature the germinal vesicle has disappeared, and there exists in its place at one portion of the periphery of the egg- contents a cluster of minute bodies called chromosomes by Henking, whom we shall follow in brietly describing their changes. The group divides into two, each of which is arranged in a rod or spindle - like manner, and may then be called a directive rod or spindle. The outer of these two groups travels quite to the periphery of the egg, and there with some adjacent matter is extruded quite outside the ege- contents (not outside the egg- coverings), being in its aug- mented form called a polar or directive body. While this is : ue _-. Ede going on the ‘second directive re idioa Pe Pe cow peal het nee spindle itself divides into two included, and the formation of the groups, the outer of which is hoe he es then extruded in the manner we have already described in the case of the first polar body, thus completing the extrusion of two directive bodies. The essential parts of the bodies that are successively formed during these processes are the aggregates, called chromosomes; the number of these chromosomes appears to be constant in each species; their movements and dispositions are of a very interesting character, the systems they form in 1 Zeitschr. wiss. Zool. xxvi. 1876, p. 115. * Scudder, Butterflies of New England, i. 1889, p. 99. v EMBRYOLOGY 147 the course of their development having polar and equatorial arrangements. These we cannot further allude to, but may mention that the extrusion of the directive bodies is only temporary, they being again included within the periphery of the egg by the growth and extension of adjacent parts which meet over and thus enclose the bodies. The arrangements and movements we have briefly alluded to have been limited to the unfertilised condition of the egg (we should rather say, the fertilising element has taken no part in them), and have as their result the union of the chromosomes existing after the extrusion of the two polar bodies, into a small body called the female pronucleus or ege-nucleus (Kikern), while the position of the movements has been an extremely minute portion of the egg near to its outer surface or periphery. The introduction of a sperm, or male, element to the egg through the micropyle gives rise to the formation of another minute body placed more in the interior of the egg, and calléd the sperm- nucleus. The ege-nucleus, travelling more into the interior of the egg, meets the sperm-nucleus; the two amalgamate, forming a nucleus or body that goes through a series of changes resulting in its division into two daughter-bodies. These two again divide, and by repetitions of such division a large number of nuclei are formed which become arranged in a continuous manner so as to form an envelope enclosing a considerable part (if not quite the whole) of the egg-mass. This envelope is called the blastoderm, and together with its contents will form the embryo. We must merely allude to the fact that it has been considered that some of the nuclei forming the blastoderm arise directly from the egg-mass by a process of amalgamation, and if this prove to be correct it may be admitted that some portions of the embryo are not entirely the result of division or segmentation of combined germ and sperm-nuclei. Wheeler states? that some of the nuclei formed by the first differentiation go to form the vitellophags scattered throughout the yolk. We should also remark that, according to Henking, the blastoderm when com- pleted shows at one part a thickening, immediately under which (i.e. included in the area the blastoderm encloses) are the two polar bodies, which, as we have seen, were formed by the germinating body at an earlier stage of its activity. Fig. 79 1 J. Morphol. viii. 1893, p. 81; see also Graber’s table on p. 149. 148 EMBRYOLOGY CHAP, represents a stage in the development of Pyrrhocoris, showing the interior of the egg after a body has been formed by the union of the sperm and egeg-nuclei: this body is about to undergo division or segmentation, and the equatorial arrangement where this will take place is seen. The two polar bodies Ee Ess after having been excluded, are nearly reincluded in the egg. The Ventral Plate. The next important change after the formation of the blastoderm is the partial detachment of a part of its periphery to become placed in the interior of the other and larger portion. The way in which this takes place will be gathered from the accompanying dia- grammatic figures taken from Graber: a thickened portion (a 6) of the blastoderm becomes indrawn so as to leave a fold (e d) at each point of its withdrawal, and these folds afterwards grow and meet so as to enclose the thickened portion. The outer envelope, formed in part by the original blastoderm and in part by the new growth, is called the serosa (ef), the inner layer (g) of Fic. 80.—Stages of the Boia feo ; ‘ enclosure of the ven- the conjoined new folds being termed the tral plate: A, « %, amnion: the part withdrawn to the interior ventral plate; B, ¢, ‘ : d, folds of the blas- and covered by the serosa and amnion is eperinbene te fe called the ventral plate, or germinal band amnion and serosa; (Aermstre(f), and becomes developed into the 8 i es future animal. The details of the withdrawal of the ventral plate to the interior are very different in the various Insects that have been investigated. One of the earliest stages in the development is a differentia- tion of a portion of the ventral plate into layers from which the future parts of the organisation will be derived. This separation of endoderm from ectoderm takes place by a sort of invagination, analogous with that by which the ventral plate itself is formed. A longitudinal depression running along the middle of the ventral plate appears, and forms a groove or channel, which becomes obliterated as to its outer face by the meeting together of the two margins of the groove (except on the v EMBRYOLOGY 149 anterior part, which remains open). The more internal layer of the periphery of this closed canal is the origin of the endo- derm and its derivatives. Subsequently the ventral plate and its derivatives grow so as to form the ventral part and the internal organs of the Insect, the dorsal part being com- pleted much later by growths that differ much in different Insects; Graber, who has specially investigated this matter, informing us? that an astonishing multifariousness is displayed. It would appear that the various modes of this development do not coincide with the divisions into Orders and Families adopted by any systematists. We should observe that the terms ectoderm, mesoderm, and endoderm will probably be no longer applied to the layers of the embryo when embryologists shall have decided as to the nature of the derived layers, and shall have agreed as to names for them. According to the nomenclature of Graber* the blasto- derm differentiates into Ectoblast and Endoblast; this latter undergoing a further differentiation into Coeloblast and Myoblast. This talented embryologist gives the following table of the relations of the embryonic layers and their nomenclature, the first term of each group being the one he proposed to use :— Periblast Ectoblast Part of yolk cells. (Epiblast, (Ectoderm, outer blastoderm). layer). Coeloblast Protoblast. (Endoderm in nar- Centroblast Endoblast rower sense). (Yolk-cells, hypo- or Hypoblast, Darmdriisenblatt. blast, endoderm inner layer. in part- of Bal- (Mesoblast of Bal- Myoblast —(Meso- four). four.) derm of most Mesoderm and endo- authors). Darm- derm. muskelblatt. Nusshaum considers * that “there are four layers in the cock- roach-embryo, viz. (1) epiblast, from which the integument and nervous system are developed; (2) somatic layer of mesoblast, mainly converted into the muscles of the body-wall; (3) splanchnic layer of mesoblast, yielding the muscular coat of the alimentary canal; and (4) hypoblast, yielding the epithelium of the mesen- teron.” Turning our attention to the origin of the segmentation, that is so marked a feature of Insect structure, we find that evidence 1 Denk. Ak. Wien, lv. 1888, p. 109, ete. 2 Morph. Jahrb. xiv. 1888, p. 347. 3 In Miall and Denny, Cockroach, p. 188. 150 EMBRYOLOGY CHAP. of division or arrangement of the body into segments appears very early, as shown in our Figure of some of the early stages of development of Zina (a beetle), Fig. 81. In A the segmen- tation of the ectoderi has not commenced, but the procephalic lobes (P C) are seen; in B the three head segments are distinct, while in C the thoracic segmentation has occurred, and that of the abdomen has commenced. Graber considers that in this species the abdomen consists of ten segmental lobes, and a terminal piece or telson. According to Graber’ this is not a primitive condition, but is preceded by a division into three or C Frc. 81.—Early stages of the segmentation of a beetle (Zina): A, segmentation not visible, 1 day ; B, segmentation of head visible ; C, segmentation still more advanced, 2} days ; PC, procephalic lobes; g', g, g*, segments bearing appendages of the head ; th, thorax ; th}, th?, th®, segments of the thorax ; a}, a”, anterior abdominal, four parts, corresponding with the divisions that will afterwards be head, thorax, and abdomen. This primary segmentation, he says, takes place in the Hypoblast (Endoderm) layer of the ventral plate; this layer being, in an early stage of the development of a common grasshopper (Stenobothrus variabilis), divided into four sections, two of which go to form the head, while the others become thorax and abdomen respectively. In Zina the primary segmentation is, Graber says, into three instead of four parts. Graber’s opinion on the primary segmentation does not appear to be generally accepted, and Wheeler, who has studied? the 1 Morph. Jahrb. xiv. 1888, p. 345. 2 J. Morphol. viii. 1893, p. 1. v EMBRYOLOGY isi embryology of another Orthopteron, considers it will prove to be incorrect. When the secondary segmentation occurs the anterior of the two cephalic divisions remains intact, while the second divides into the three parts that afterwards bear the mouth parts as appendages. The thoracic mass subsequently segments into three parts, and still later the hind part of the ventral plate undergoes a similar differentiation so as to form the abdominal segments; what the exact number of these may be is, however, by no means easy to decide, the division being but vague, especially posteriorly, and not occurring all at once, but progressing from before backwards. The investigations that have been made in reference to the seementation of the ventral plate do not at present justify us in asserting that all Insects are formed from the same number of embryonic segments. The matter is summarised by Lowne, to the effect that posterior to the procephalic lobes there are three head segments and three thoracic segments, and a number of abdominal segments, “ rarely less than nine or more than eleven.” Tt will be seen by referring to Figure 81 that the segmentation appears, not simultaneously, but progressively from the head back- ar wards; this of course greatly in- aaa creases the difficulty of determin- ing by means of a section the real number of segments. The later stages in the develop- ment of Insects are already proved to be so various that it would be impossible to attempt to follow them in detail; but in Fig. 82 eee we represent a median section th? th? of the embryo of Zygaena filipen- me at eat se pig dula at the fifth day. It shows amnion ; s, serosa; p, procephalic well some of the more important lobes ; sé, stomodaeum ; pr, procto- : daeum ; g', g?, g®, the mouth parts of the general features of the de- or nead appendages ; th!, t?, i’, . tac 4 nt to appendages of the thoracic segments ; velopment ab a BLES pulpeae aa, abdominal segments ; s.//, Sali- those represented in Fig. 81, A, B, vary gland. C. The very distinct stomodaeum (st) and proctodaeum (pr) are seen as inflexions of the external wall of the body; the segmentation and the development of the 152 EMBRYOLOGY CHAP. ventral parts of the embryo are well advanced, while the dorsal part of the embryo is still quite incomplete. The method of investigation by which embryologists chiefly carry on their researches is that of dividing the egg after proper preparation, into a large number of thin sections, which are afterwards examined in detail, so as to allow the arrange- ment to be completely inferred and described. Valuable as this method is, it is nevertheless clear that it should, if possible, be supplemented by direct observation of the processes as they take place in the living egg: this method was formerly used, and by its aid we may still hope to obtain exact knowledge as to the arrangements and rearrangements of particles by which the structures develop. Such questions as whether the whole formative power in the egg is absolutely confined to one or two small centres to which the whole of the other egg contents are merely, as it were, passive accessories, or whether an egg is a combination in which some portion of the powers of rearrangement is possessed by other particles, as well as the chromosomes, in virtue of their own nature or of their position at an early period in the whole, can scarcely be settled without the aid of direct observation of the processes during life. The importance of the yolk is recognised by most of the recent writers. Nussbaum states (/oc. cit.) that “ scattered yolk- cells associate themselves with the mesoblast cells, so that the constituents of the mesoblast have a twofold origin.” Wheeler finds’ that amoeboid cells—he styles them vitellophags — traverse the yolk and assist in its rearrangement; he insists on the importance both as regards quantity and quality of the yolk. The eggs of some insects are fairly transparent, and the process of development in them can, to a certain extent, be observed by simple inspection with the microscope; a method that was used by Weismann in his observations on the embry- ology of Chironomus, There is a moth (Limacodes testudo), that has no objection to depositing its eggs on glass microscope-slides. These eggs are about a millimetre long, somewhat more than half that width, are very flat, and the ege-shell or chorion is very thin and perfectly transparent. When first laid the contents of this egg appear nearly homogeneous and evenly distributed, a finely granular appearance being presented throughout; but in twenty- 1 J. Morphol. viii. 1893, pp. 64, 65, and 81. ¥ EMBRYOLOGY 163 four hours a great change is found to have taken place. The whole superficial contents of the egg are at that time arranged in groups, having the appearance of separate rounded or oval masses, pressed together so as to destroy much of their globular symmetry. The egg contents are also divided into very distinct forms, a granular matter, and a large number of transparent globules, these latter being the fatty portion of the yolk; these are present everywhere, though in the centre there is a space where they are very scanty, and they also do not extend quite to the circum- ference. But the most remarkable change that has taken place is the appearance in the middle of the field of an area different from the rest in several particulars; it occupies about one-third of the width and one-third of the length; it has a whiter and more opaque appearance, and the fat globules in it are fewer in number and more indistinct. This area is afterwards seen to be occupied by the developing embryo, the outlines of which become gradually more dis- tinct. Fig. 83 gives an idea of the appearance of the egg about the middle period of the development. In warm weather the larva emerges from this egg ten or eleven days after it has been deposited. meee The period occupied by the develop- *", ete earn ment of the embryo is very different in the development of the em- ‘ : A bryo ; B, micropyles and sur- the various kinds of Insects; the blowfly rounding sculpture of chorion. embryo is fully developed in less than twenty-four hours, while in some of the Orthoptera the embryonic stage may be prolonged through several months. According to Woodworth the blastoderm in Vanessa antiopa is complete in twenty-four hours after the deposition of the egg, and the involution of the ventral plate is accomplished within three days of deposition. Metamorphosis. The ontogeny, or life history of the individual, of Insects is peculiar, inasmuch as a very large part of the development takes 154 METAMORPHOSIS CHAP. place only late in life and after growth has been completed. Insects leave the egg in a certain form, and in that condition they con- tinue—with, however, a greater or less amount of change according to kind—till growth is completed, when, in many cases, a very great change of form takes place. Post-embryonic development, or change of form of this kind, is called metamorphosis. It is not a phenomenon peculiar to Insects, but exists to a greater or less extent in other groups of the Metazoa; while simpler post- embryonic development occurs in nearly all, as in scarcely any complex animals are all the organs completely formed at the time the individual becomes possessed of a separate existence. In many animals other than Insects the post-embryonic development assumes most remarkable and complex forms, though there are perhaps none in which the phenomenon is very similar to the metamorphosis of Insects. The essential features of metamor- phosis, as exhibited in the great class we are writing of, appear to be the separation in time of growth and development, and the limitation of the reproductive processes to a short period at the end of the individual life. The peculiar phenomena of the post- embryonic development of the white ants show that there exists some remarkable correlation between the condition of the repro- ductive organs and the development of the other parts of the organisation. If we take it that the post-embryonic physio- logical processes of any individual Insect are of three kinds, —growth, development, and reproduction,—then we may say that in the higher Insects these three processes are almost completely separated, and go on consecutively, the order being,— first, growth ; second, development; third, reproduction. While, if we complete the view by including the processes comprised in the formation of the egg and the development therein, the series will he—(1) oogenesis, or egg-growth ; (2) development (embry- onic); (2) growth (post-embryonic); (4) development (post- embryonic); (5) reproduction. The metamorphosis of Insects is one of the most interesting parts of entomology. It is, however, as yet very little known from a scientific point of view, although the simpler of its external characters have for many ages past attracted the attention and elicited the admiration of lovers of nature. It may seem incorrect to say that little is yet known scientifically of a phenomenon concerning which references almost innumer- v METAMORPHOSIS 155 able are to be found in literature: nevertheless the observations that have been made as to metamorphosis, and the analysis that has been commenced of the facts are at present ttle more than sufficient to show us how vast and complex is the subject, and how great are the difficulties it presents. There are three great fields of inquiry in regard to meta- morphosis, viz. (1) the external form at the different stages ; (2) the internal organs and their changes; (3) the physiological processes. Of these only the first has yet received any extensive attention, though it is the third that precedes or underlies the other two, and is the most important. We will say a few words about each of these departments of the inquiry. Taking first the external form—the instar. But before turning to this we must point out that in limiting the inquiry to the post-embryonic development, we are making one of those limitations that give rise to much misconception, though they are necessary for the acquisi- tion of knowledge as to any complex set of phenomena. If we assume five well-marked stages as constituting the life of an Insect with extreme metamorphosis, viz. (1) the formation and growth of the ege; (2) the changes in the egg culminating in its hatching after fertilisation; (3) the period of growth; (4) the pupal changes ; (5) the life of the perfect Insect ; and if we limit our inquiry about development to the latter three, we are then shutting out of view a great preliminary question, viz. whether some Insects leave the egg in a different stage of development to others, and we are consequently exposing ourselves to the risk of forgetting that some of the distinctions we observe in the subsequent metamorphosis may be consequential on differences in the embryonic development. Instar and Stadium. Figs. 84 and 85 represent corresponding stages in the life of two different Insects, Fig. 84 showing a locust (deridiwm), and Fig. 85 a white butterfly, In each A represents the newly-hatched individual; B, the insect just before its perfect state; C, the perfect or imago stage. On comparing the two sets of figures we see that the C stages correspond pretty well as regards the most important features (the position of the wings being unimportant), that the A stages are moderately different, 156 METAMORPHOSIS CHAP. while the B states are not to be recognised as equivalent condi- tions. Every Insect after leaving the egg undergoes during the process of growth castings of the skin, each of which is called Fic. 84. — Locust (Acridium per- egrinum): A, newly hatched ; B, just ante- cedent to last ecdysis ; C, per- fect Insect. a moult or ecdysis. Taking for our present purpose five as the number of ecdyses undergone by both the locust and butterfly, we may express the differences in the successions of change we portray in Figs. 84 and 85 by saying that previous to the Fic. 85.—Butterfly (Pieris) : A, the newly hatched young, or larva magnified ; B, pupa (natural size) just antecedent to last ecdysis ; C, perfect Insect. first ecdysis the two Insects are moderately dissimilar, that the locust undergoes a moderate change before reaching the fifth ecdysis, and undergoes another moderate change at this moult, thus reaching its perfect condition by a slight, rather gradual series of Vv METAMORPHOSIS 157 alterations of form. On the other hand, the butterfly under- goes but little modification, remaining much in the condition shown by +e aspect: a, inner margin; }, outer margin ; cover. De Saussure’s opinion, ce, nervure bearing stridulating file. to a somewhat different effect, we have already mentioned. The tegmina of the male are extremely different from those of the female, so that it is a matter of much difficulty to decide what nervures correspond. The wine-covers of the male differ from those of the Locustidae, inasmuch as the pair are of similar formation, each bearing a stridulating file on its lower aspect. This file projects somewhat, inwards, so that its position is marked on the outer aspect of the wing-cover by a depression. Usually the right tegmen overlaps the other, an arrangement contrary to that which prevails in other Orthoptera. The wings are ample and delicate; they possess numerous nervures that are not much forked and have a 1 See Pungur, Termes. Fiizetek, 1877, p. 223. lo ORTHOPTERA CHAP. Ow Os simple, somewhat fan-like arrangement; the little transverse nervules exhibit only slight variety. These wings are frequently rolled up at the apex, and project beyond the body like an additional pair of cerci (Fig. 204). The abdomen is chiefly remarkable for the large development of the pleura, the stigmata leing consequently very conspicuous. The cerci are not jointed, though they are flexible and, often, very long; they bear a variety of sense-organs (Fig. 67). The saltatorial powers of the crickets are frequeitly considerable. Graber has observed the post-embryonic development of the field-cricket, Gryllus campestris, though unfortunately not from the very commencement, so that we do not know whether there are five, six, or seven ecdyses; the number is probably either six or seven. The manner in which the alar organs are developed is similar to that we have described and figured in the Locustidae. In the earlier instars there is a slight prolongation of each side of the meso- and meta-notum, but about the middle of the development a considerable change occurs—the rudimentary organs then become free appendages and assume a different position. The Gryllidae possess a pair of tympana on each front leg, but these organs contrast with those of the Locustidae in that the pair on each leg usually differ from one another, the one on the outer or posterior aspect being larger than that on the inner or front face of the leg. The ears of the Gryllidae have not been so well investigated as those of the Locustidae, but are apparently of a much less perfect nature. No orifice for the admission of air other than that of the prothoracic stigma has been detected, except in’ (ryllotalpa. On the other hand, it is said? that in addition to the tibial organs another pair of tympana exists, and is seated on the second abdominal segment in a position analogous to that occupied by the ear on the first segment of Acridiidae. The musical powers of the crickets are remarkable, and are fainiliar to all in Europe, as the performance of the house-cricket gives a fair idea of them. Some of the Insects of the family are able to make a very piercing noise, the note of Brachytrypes megacephalus haying been heard, it is said, at a distance of a mile from where it was being produced. The mode of produc- ‘Brunner, Verh, zool.-bot. Ges. Wien, xxiv. 1874, p. 288. x1V MOLE-CRICKET 333 tion is the same as in the Locustidae, rapid vibration of the tegmina causing the edge of one of them to act on the file of the other. The mole-cricket, Gryllotalpa vulgaris—the Werre of the Germans, Courtiliére of the French —is placed with a few alles in a special group, Gryllotalpides, characterised by the dilated front legs, which are admirably adapted for working underground. Like the mole, this Insect has a subterranean existence. It travels in burrows of its own formation, and it also forms beneath the surface a habitation for its eggs and family. Its habits have been alluded to by Gilbert White,’ who tells us that “a gardener at a house where I was on a visit, happening to be mowing, on the 6th of May, by the side of a canal, his scythe struck too deep, pared off a large piece of turf, and laid open to view a curious scene of domestic economy: there were many caverns and winding passages leading to a kind of chamber, neatly smoothed and rounded, and about the size of a moderate snuff-box. Within this secret nursery were deposited near a hundred eges of a dirty yellow colour, and enveloped in a tough skin, but too lately excluded to contain any rudiments of young, being full of a viscous substance. The eggs lay but shallow, and within the intluence of the sun, just under a little heap of fresh moved mould like that which is raised by ants.” The front legs are remark- able structures (Fig. 206), being beautifully adapted for burrow- ing; the tibiae and tarsi are arranged so as to act as shears when it may be necessary to sever a root. The shear - like action of the tarsus and tibia is very remarkable; the first and second joints of the former are furnished with hard processes, which, when the tarsus is moved, pass over the edges of the tibial teeth in such a way as to be more effective than a pair of shears. In consequence of its habit of cutting roots, Fic. 206.—Front leg of the mole-cricket. A, outer ; B, inner aspect : ¢, ear-slit. 1 Natural History of Selborne, Letter xe. 334 GRYLLIDAE CHAP. the mole-cricket causes some damage where it is abundant. It is now a rare Insect in England, and is almost confined to the southern counties, but in the gardens of Central and Southern Europe it is very abundant. Its French name cowrtiliére is supposed to be a corruption of the Latin curtilla. Its fondness for the neighbourhood of water is well known. De Saussure says that in order to secure specimens it is only necessary to throw water on the paths between the flower-beds of gardens and to cover the wetted places with pieces of board; in the morning some of these Insects are almost sure to be found under the boards disporting themselves in the mud. The Gryllotalpae swim admirably by aid of their broad front legs. Ears exist in the mole-cricket, and are situate on the front leg below the knee, as in other Gryllidae, although it seems strange that a leg so profoundly modified for digging and excavating as is that of the mole-cricket should be provided with an ear. In Gryllotalpa the ear is concealed and protected by being placed in a deep slit or fold of the surface, and this depression is all that can be seen by examination of the exterior (Fig. 206, e). In the allied genus Scapteriscus the tympanal membrane is, how- ever, destitute of special protection, being completely exposed on the surface of the leg. Although the tegmina or upper wings in Gryllotalpa are of small size, yet the true wings are much more ample; they are of delicate texture and traversed by many nearly straight radii, so that they close up in the most complete manner, and form the two long delicate, flexible processes that in the state of repose may be seen projecting not only beyond the tegmina, but actually surpassing the extremity of the body hanging down behind it, and looking like a second pair of cerci. The mole-cricket is believed to be chiefly carnivorous in its chet, though, like many other Orthoptera, it can accommodate its appetite to parts of the vegetable as well as of the animal kingdom. The Insect is capable of emitting a sound consisting of a dull jarring note, somewhat like that of the goat-sucker. For this purpose the tegmina of the males are provided with an apparatus of the nature we have already described, but which is very much smaller and less elaborate than it is in the true crickets. The alimentary canal and digestive system of Gryllotalpa XIV MOLE-CRICKET nag present peculiarities worthy of notice. Salivary glands and reservoirs are present; the oesophagus is elongate, and has on one side a peculiar large pouch (Fig. 207, ce); beyond this is the gizzard, which is embraced by two lobes of the stomach. This latter organ is, beyond the lobes, continued backwards ag a neck, which subsequently becomes larger and rugose-plicate. On the neck of the stomach there is a pair of branching organs, which Dufour considered to be peculiar to the mole- cricket, and compared to a spleen or pancreas. The single tube into which the Mal- pighian tubules open is seated near the commencement of the small intestine. These tubules are very fine, and are about one hundred in num- ber. The arrangement by which the Malpighian tub- ules open into a common duct instead of into the intestine itself appears to be charac- teristic of the Gryllidae, but is said to occur also in Ephippigera, a genus of Locustidae. According to Leydig’ and Schindler the Malpighian tubules are of two kinds, differing in colour, and, according to Leydig, in contents and histological Fic. 207.— Alimentary canal and appendages of 4 the mole-cricket: u, head; 0, salivary structure. Near the posterior glands and receptacle ; ¢, lateral pouch ; d, extremity of the rectum Somstognrls nara; 6, etna lobe o there is a lobulated gland stomach ; h, plicate portion of same ; 1, Tec- having a reservoir connected "en; Tebulate land; / extremity of boty with it; this is the chief source of the foetid secretion the mole-cricket emits when seized. The nervous chain consists of three thoracic and four abdominal ganglia; these latter do not extend to the extremity of the body; 1 Miiller’s Arch, 1859, p. 159. 336 ORTHOPTERA cuap. the three anterior of the four ganglia are but small, the terminal one being much larger. The number of eggs deposited by a female mole-cricket is large, varying, it is said, from 200 to 400. The mother watches over them carefully, and when they are hatched, which occurs in a period of from three to four weeks after their deposition, she supplies the young with food till their first moult; after this oceurs they disperse, and begin to form burrows for themselves. It has been said that the young are devoured by their parents, and some writers have gone so far as to say that 90 per cent of the progeny are thus disposed of. M. Decaux, who has paid considerable attention to the economy of the mole-cricket,’ acquits the mother of such an offence, but admits that the male commits it. The number of eggs in one nest is said to be about 300. The embryonic development of the mole-cricket has been studied by Dohrn? and Korotneff and is considered by the former to be of great interest. The tracheae connected with each stigma remain isolated, while, according to Korotneff, the development of the alimentary canal is not completed when the young mole-cricket is hatched. Perhaps it may be this con- dition of the digestive organs that necessitates the unusual care the mother bestows on her young. The genus Cylindrodes (Fig. 208, C. kochi) comprises some curious and rare Insects of elongate, slender form. They are natives of Australia, where the first species known of the genus Fic. 208. — Cylindrodes kochi. was found in Melville Island by Major Australia. Fic, 209.—Tridactylus variegatus, France. ORTHOPTERA CHAP. un Ww nw compose it are rare in collections, their saltatorial powers no doubt making it difficult to catch them; little is known as to their habits. In the undescribed Ama- zonian species we figure (Fig. 210), the wings, instead of being mere rudiments, as in Tridactylus, are elongate and project beyond the body; they are of a blue- black colour, and arranged so as to look as if they were the abdomen of the Insect ; they, moreover, have a transverse pallid mark, giving rise to an appearance of division. It is difficult to form any surmise as to the nature of so curious a modification of the wings. Fig. 210.—Rhipipterye sp., The Tridactylides have no tympana on See Tene the legs, and their affinity with the Gryl- lidae is very doubtful. Dufour thought 7. variegatus to be more allied to the Acridiidae. He based this opinion chiefly on some points of the internal anatomy, but pointed out that Zridactylus differs from the Acridiidae in having no air-sacs in the body. Not many of the Gryllidae are so peculiar as the forms we have mentioned. The family consists in larger part of Insects more or less similar to the common cricket, though exhibiting a great variety of external form. The common cricket of our houses, Gryllus (Acheta) domesticus (Fig. 204), has a very wide distribution in the Old World, and is also found in North America. It is believed to have had its natural distribution extended by conuerce, though really nothing is known as to its original habitat. The shrill chirping of this little Insect is frequently heard at night in houses, even in the most densely inhabited parts of great cities. Neither the female nor the young are musical, yet the chirping may be heard at all seasons of the year, as young and adults coexist independent of season. The pre- dilection of Gryllus domesticus for the habitations of man is very curious. The Insect is occasionally found out of doors in the neighbourhood of dwelling-houses in hot weather, but it does not appear that this species leads anywhere a truly wild life. It is fond of heat; though it rarely multiplies in dwelling-houses to any great extent, it is sometimes found in profusion in bake- RIV GRYLLIDAE 339 houses. Usually the wings in the cricket are elongate, and pro- ject backwards from under the tegmina like an additional pair of cerci; a variety, however, occurs in which these tails are absent, owing to abbreviation of the wings. There is no beauty in the appearance of any of the Gryllidae, though many of them are very bizarre in shape. Very few of them venture to leave the surface of the earth to climb on plants. The species of Oecanthus, however, do so, and may be found sitting in flowers. They have a more Locustoid appearance than other Gryllidae. One of the most curious forms of the family is Platyblemmus, a genus of several species found in the Mediter- ranean region, the male of which has the head prolonged into a curious pro- cess (Fig. 211); this varies greatly in development in the males of the same species. It would seem that this organ is of a similar nature to the extra- ordinary structures we have figured in Locustidae (Fig. 189) and Mantidae (Fig. 136), though it appears impossible to treat the cephalic appendages of Platy- ae ec eee blemmus as ornamental objects; their — head; B, profile of Insect import is at present quite obscure. Sea ee A curious form of variation occurs in this family, and is called micropterism by de Saussure; we have already mentioned its occurrence in the house-cricket. The hind wings, which are usually ample, and frequently have their extremities rolled up and protruding like cerci, are sometimes much smaller in size, and not visible till the tegmina are ex- panded. De Saussure at one time supposed these micropterous individuals to be distinct species; it is now, however, known that intermediate examples can be found by examining a great many specimens. Some species are always micropterous. In Britain we have only four representatives of the Gryllidae, viz. the mole-cricket, the house-cricket, and two field-crickets, one of which, Nemobius sylvestris, is considerably smaller than the house-cricket, while the other, Gryllus campestris, the true field-cricket, is a larger Insect. Its habits have been described in an interesting manner in Gilbert White’s 88th letter. 340 GRYLLIDAE CHAP. XIV This Insect, like so many others, is apparently becoming rare in this country. A single fossil from the Lias has been described as belonging to the Gryllidae, but in the Tertiary strata a variety of members of the family have been discovered both in Europe and North America. The classification of Gryllidae is due to de Saussure; and is said by Brunner to be very natural. In the following synopsis of the tribes of crickets we give de Saussure’s arrangement, except that we follow Brunner in treating Tridactylides as a distinct tribe :— 1. Antennae ten-jointed ; posterior tarsi aborted. Tribe 1. Tripactyiprs. (Fig. 209, Tridactylus variegatus ; Fig. 210, Rhipipteryx sp.) 1’. Antennae many jointed ; posterior tarsi normal. 2. Tarsi compressed, the second joint minute. 3, Anterior legs fossorial ; anterior tibiae at the apex with two to four divisions. Pronotum elongate, ovate, rounded behind. Female without ovipositor. Tribe 2. GRYLLOTALPIDES. (Fig. 206, front legs of Gryllotalpa ; Fig. 208, Cylindrodes kocht.) 3’. Anterior legs formed for walking. Ovipositor of the female visible (either elongate or rudimentary), 4, Posterior tibiae biseriately serrate. Tribe 3. Myrxzco- PHILIDES. 4’. Posterior tibiae biseriately spinose. Ovipositor straight. 5. Antennae short, thickish, almost thread-like. Facial scutellum exserted between antennae. Posterior tibiae dilated. Gen. Myrmecophila.? 5’, Antennae elongate, setaceous. Facial scytellum trans- verse, visible below the antennae. Tibiae slender. 6. Posterior tibiae armed with two strong spines, not serrate between the spines. Tribe 4. GryLiIDEs. (Fig. 204, Gryllus domesticus; Fig. 211, Platy- blemmus lusitanicus.) 6’. Posterior tibiae slender, armed with slender spines, and serrate between them. Tribe, 5. Oxcay- THIDES, 2’, Second joint of the tarsi depressed, heart-shaped. 3. Posterior tibiae not serrate, but biseriately spinose. 4. The spines on each side three and mobile 3 apical spurs on the inner side only two in number. Ovipositor short, curved, ‘Tribe 6, TRIGONIDIIDES. 4’. The spines numerous, fixed. Ovipositor elongate, straight. Gen. Stenogryllus, 3’. Posterior tibiae serrate and spinose on each side, the apical spurs, as usual, three on each side. Ovipositor straight or curved. Tribe 7. Enxoprrripes. > Mem. Soc. phys. Genéve, xxv. 1877, and Biol. Centr. Amer. Orthoptera, 1894, p. 198. * The genus Myrmecophila, bemg exceptional in several respects, is treated separately. CHAPTER XV NEUROPTERA——-MALLOPHAGA——EMBIIDAE Order ITI. Neuroptera. Imago with biting mouth ; with two pairs of wings, the anterior as well as the posterior membranous, usually with extensive neuration, consisting of elongate nervures and either of short cross-nervules forming numerous cells or of a com- plez minute mesh-work. (One division, Mallophaga, con- sists entirely of wingless forms; in Termitidae some of the individuals of each generation become winged, but others do not: except in these cases adult wingless forms are few.) The metamorphosis differs in the several divisions. Fic, 212.—Osmylus chrysops, New Forest. THE Neuroptera form a heterogeneous, though comparatively small, Order of Insects, including termites, stone-flies, dragon- flies, may-flies, caddis-flies, lace-wings, scorpion-flies, ant-lions, etc. Bird-lice are also included in Neuroptera, though they have no trace of wings. We treat the Order as composed of eleven distinct families, 342 NEUROPTERA CHAP. and, as a matter of convenience, arrange them in _ five divisions :— 1. Mallophaga,—Permanently wingless Insects, living on the bodies of birds or mammals, (Development very imperfectly known.) Fam. 1. Mallophaga, 2. Pseudoneuroptera.—tinsects with wings in adult life (in some cases wings are never acquired). The wings are developed in a visible manner outside the body. There is no definite pupa. Live entirely on land. Fam. 2. Embiidae ; 3. Termitidae; 4. Psocidae. 3. Newroptera amphibiotica—W ings developed as in division 2. Three ocelli usually exist. Life aquatic in the early stages, Fam. 5. Perlidae ; 6. Odonata ; 7. Ephemeridae. 4. Neuroptera planipennia.—Wings developed internally ; not visible in early stages, but becoming suddenly evident when the pupal form is assumed. Mandibles present in the adult Insect. Life in early stages aquatic or terrestrial. Fam. 8. Sialidae; 9. Panorpidae; 10. Hemerobiidae, . Trichoptera—Development as in division 4. Mandibles absent in the adult Insect. Life aquatic in the early stages. Fam. 11, Phryganeidae. ‘er The families we have enumerated in the preceding scheme are now generally adopted by entomologists. Great difference of opinion exists, however, as to the groups of greater value than the family, and for a long time past various schemes have been in vogue. Though it is necessary to allude to the more important of these systems, we can do so only in the briefest manner. Some of the families of Neuroptera are similar in many points of structure and development to Insects of other Orders; thus Termitidae ave somewhat allied to Blattidae, Perlidae to Phas- midae in Orthoptera, while the Phryganeidae or Trichoptera make a considerable approach to Lepidoptera. Some naturalists—among whom we may mention Burmeister and Grassi—unite our Aptera, Orthoptera, and most of our Neuroptera into a single Order called Orthoptera. Others treat our Neuroptera as consisting of eight or nine distinct Orders ; these, together with the names proposed for them, we have already alluded to in our chapter on classification, pp. 171-177. Erichson, impressed by the variety existing in Neuroptera, separated some of the groups into a sub-Order called Pseudo- neuroptera ; this sub-Order comprised our Termitidae, Psocidae, Ephemeridae, and Libellulidae. This division is still adopted in several treatises; the Pseudoneuroptera are indeed by some naturalists retained as an Order distinct from both Orthoptera xv FOSSIL NEUROPTERA 34% and Neuroptera. Gerstaecker subsequently made use of a system somewhat different from that of Erichson, uniting the Perlidae, Ephemeridae, and Odonata into a group called Orthoptera amphibiotica, from which the Termitidae and Psocidae were excluded. The divisions we have here adopted differ but little from those of Gerstaecker, though we have arranged them in a very different manner. It is probable that not one-tenth part of the Neuroptera existing in the world have yet been examined by entomologists, and of those that are extant in collections, the life-histories and development are very imperfectly known. We have, therefore, not considered it wise to adopt a system that would involve great changes of nomenclature, while there can be little hope of its permanency. Fossils When considering the subject of fossil Insects we briefly alluded to the discussions that have occurred as to whether the fossils of the palaeozoic period should be referred to existing Orders. Since the pages we allude to were printed, M. Brong- niart’s very important work! on the Insects of that epoch has appeared. He considers that these ancient fossils may be classi- fied with the existing Orders of Insects, though they cannot he placed in existing families; and he assigns the palaeozoic fossil Insects at present known, to the Orders Neuroptera aud Orthop- tera, and to the homopterous division of Hemiptera. The greater part of the species he looks on as Neuroptera, and places in six families—Megasecopterides, Protephemerides, Platypterides, Stenodictyopterides, Protodonates, and Protoperlides. Of these he considers the ancient Protephemerides, Protodonates, and Protoperlides as the precursors, which, we presume, we may inter- pret as the actual ancestors, of our existing Ephemeridae, Odonata, and Perlidae. Some of the fossils restored and described by the French ento- mologist are of great interest. We shall notice the Prote- phemerides, Protodonates, and Protoperlides in connexion with the families to which they are specially allied, and shall now only allude to the quite extinct families of Neuroptera, the Megasecopterides, Platypterides, and Stenodictyopterides. It is a peculiarity of these.ancient Insects that they were much larger creatures than the corresponding forms that now exist. This may be due, to some extent, to the fact that tiny, 1 Insectes fossiles des temps primatres, 1893, vol. i. and atlas. 344 NEUROPTERA CHAP. fragile forms have not been preserved in the rocks, or have not attracted the attention of collectors ; but as some of the palaeozoic Insects were absolutely the largest known—surpassing consider- ably in size any Insects at present existing—it is probable that, even if small forms existed at the remote epoch we are alluding to, the average size of the individual was greater than it is at present. The Megasecopterides of the carboniferous epoch were Insects of large size, with long, narrow wings, a small prothorax, and large meso- and meta-thorax, these two segments being equal in size; the abdomen was elongate and moderately voluminous, and was terminated by a pair of very elongate, slender filaments like those of the may-flies. The family includes several genera and species found at Commentry. One of these forms, Cory- daloides scudderi, is of great interest, as it is believed by Brong- niart that the imago possessed tracheal gills situated on the sides of the abdomen, analogous with those that exist at present in the immature condition of certain Ephemeridae. They are of interest in connexion with the gills found at the present time in the imagos of Pteronarcys (see p. 401). Although these fossils are of such enormous antiquity, the tracheae can, M. Brongniart says, be still perceived in these processes. The Platypterides include also a considerable number of Insects of large size, with four large equal wings, frequently spotted or variegate. Some of these Insects were provided with expansions or lobes on the sides of the prothorax (Fig. 213); these are looked on as analogous to the ex- pansions of meso- and meta- thorax, which are supposed by some wrilers to have been Fic. 213,.—Lithomantis carbonaria. Car- the rudiments from which boniferous strata of Commentry, France. wings were developed. These (After Brongniart.) : é ‘ : prothoracic wing -rudiments, if such they be, are said to have a system of nervures similar to what we find in true wings. The genus Lithomantis includes a Scotch fossil, and has already been mentioned by us on p. 259. The third family of extinct carboniferous Neuroptera is the Stenodictyopterides, in which Brongniart places the Dictyoneura of XV MALLOPHAGA S45 Goldenberg, the North American Haplophlebiwm, and several genera from Commentry. Some of them were very large Insects, with robust bodies, and possessed wing-like expansions on the prothorax, and lateral gill-like appendages on the sides of the abdomen. It is worthy of note that though so large a number of car- boniferous Neuroptera have now been discovered, no larvae or immature forms have been found. We now pass to the consideration of the divisions of Neurop- tera still living. Fam. I, Mallophaga—Bird-Lice or Biting Lice. Small Insects, wingless, with large head ; thorax usually of two, rarely of one or three segments ; prothorax always distinct ; hind body consisting of eight to ten segments, in addition to the pos- terior two thoracic segments which usually are but little or not at all separated from wt. The meta- morphosis is very slight. The creatures live on the skins of birds or mammals, finding nourishment in the epidermal products. The whole of the Insects of this family live a parasitic, or rather epizoic, life. They all creep about those parts that are near to the skin, the feathers of binds OF the os of mammals ; Tic. 214.—Trinoton luridum. they rarely come quite to the surface, Lives on the common duck so that they are not detected on a ee eh eee superficial examination. It is curious that under these cirewmstances they should exhibit so great a variety of form and of anatomical characters as they do. They are very depressed, that is, flat, Insects, with a large head, which exhibits a great variety of shape; frequently it is provided in front of the antennae with some peculiar tubercles called trabeculae, which in some cases are mobile. The antennae are never large, frequently very small; they consist of from three to five joints, and are sometimes concealed in a cavity on the 346 MALLOPHAGA CHAP. under side of the head. The eyes are very rudimentary, and consist of only a small number of isolated facets placed behind the antennae; sometimes they are completely absent. The mouth parts are situ- ated entirely on the under- surface of the head and in a cavity. The upper lip is frequently of remarkable form, as if it were a scrap- ing instrument (o0/, Fig. Fic. 215.—Under-surface of head of Lipeurus 215). The mandibles are heterographus. (After Grosse.) ol, Labium ; sharply toothed and appar- md, mandible ; mx, maxilla; uw, labium. ‘ ently act as cutting instru- ments. The maxillae have been described in the principal work on the family’ as possessing in some cases well-developed palpi. According to Grosse? this is erroneous ; the maxillae, he says, are always destitute of palpi, and are of peculiar form, being each merely a lobe of somewhat conical shape, furnished on one aspect with hooks or setae. The under lip is peculiar, and apparently of very different form in the two chief groups of Mallophaga. The large mentum bears, in Liotheides (Fig. 216, B), on each side a four-jointed palpus, the pair of palps being very widely separated; the leula is broad and undi- vided; on each side there is a paraglossa Fic. 216.—Under lip of Mirmus, A; and of Tetroph- i thalmus chilensis, B. (After Grosse.) m, Mentum ; bearing an oval pro- g, ligula; pl, palp; pg, paraglossa ; hy, lingua. cess, and above this is a projection of the hypopharynx. In Philopterides (Fig. 216, A) the palpi are absent, and the parts of the lower lip are— with the exception of the paraglossae—but little differentiated. The lingua (hypo-pharynx) in Mallophaga is largely developed, 1 Giebel and Nitzsch, Insecta epizotca, folio, 1874. ° Zeitschr. wiss. Zool. xii. 1885, p. 537. XV MALLOPHAGA 347 and bears near the front a chitinous sclerite corresponding with another placed in the epipharynx. The prothorax in Mallophaga is a distinct division of the body even when the meso- and meta-thorax appear to be part of the abdomen. The mesothorax is frequently very small; it and the metathorax are sometimes intimately connected. In other eases (Laemobothrium) the metathorax appears to differ from the following abdominal segment only by having the third pair of legs attached to it. In Zrinoton (Fig. 214) the three thoracic segments are well developed and distinct. The abdominal segments visible, vary in number from eight to ten; there is sometimes a difference according to sex, the male having one segment taken into the interior in connexion with the repro- ductive organs. The legs have short, broad coxae and small tarsi of one or two joints; very rarely three joints are present ; there are either one or two claws; the legs with one claw being adapted for clinging to or clutching hairs. The front pair of legs is used not for locomotion so much as for grasping the food and bringing it within the range of the mouth. No trace of wings has been detected in any species. The nervous system has been examined by Giebel in Lipewrus bacillus; there is a supra- and an infra-oesophageal ganglion, and three thoracic, but no abdominal ganglia. The supra-oesophageal is remarkably small, in fact not larger than the infra - oesophageal; it consists evi- dently of two conjoined halves. The alimentary canal has a slender, elon- pie, 217.—Ganglia of nervous sys- gate oesophagus, dilated behind into a ae er aaa crop; this is frequently received be- tween two cornua formed by the anterior part of the stomach, which, except for these, is simply tubular in form, though some- what narrower at the posterior extremity. In some forms— Philopterides—the crop is of a very peculiar nature (Fig. 218), forming an abrupt paunch separated from the stomach by the MALLOPHAGA CHAP. posterior portion of the oesophagus. There are only four Mal- pighian tubes; in some species the basal half of each tube is much dilated. The two divisions of the intestine are short and are separated by the intervention of a glandular girdle. Salivary glands exist ; (Hebel figures what we may consider to be an enormous salivary reservoir as exist- ing in Alenopon leucostomumn. The testes and ovaries are of a simple nature. The former consist of two or three capsules, each having a terminal thread; the vasa deferentia are tortuous and of variable length; they lead into the anterior part of the ejaculatory duct, where also opens the elongate duct pro- ceeding from the bicapsular vesicula seini- Fic. 218.—Alimentary canal of Docophorus fuscicollis. (After Giebel.) u, Oeso- phagus ; 6, paunch; @’, posterior division of oeso- phagus ; e, chylific ven- tricle or stomach ; d, Mal- pighian tubes ; e, small intestine ; 7, glandular nalis; these structures have been figured by Grosse’ as well as by Giebel. The ovaries consist of three to five short ege- tubes on each side; the two oviducts combine to form a short common duct with which there is connected a recepta- culum seminis. The eggs of some Mallophaga have been figured by Melnikow ;? they possess at one extremity a cover with a multiple micropyle- apparatus, and at the opposite pole are provided with seta-lke appendages. They are very like the eggs of the true lice, and are said in some cases to be suspended by threads to the hairs or feathers after the fashion of the eggs of Pediculi. Little is known as to the development; the young are ex- tremely like the adult, and are thought to moult frequently; the duration of life ig quite unknown. It has been stated by some writers that the mouth is truly of the sucking kind, and that the Mallophaga feed on the blood of their hosts. This is, however, erroneous; they eat the delicate portions of the feathers of birds, and of mammals perhaps the young hair, Their fertility is but small, and it is believed that girdle ; gy, rectum. 1 Zeitschr. wiss. Zool. xlii. 1885, pl. xviii. f. 15. ° Arch. f. Naturg. xxxv. i, 1869, p. 154, pls. x. xi. xv MALLOPHAGA 349 in a state of nature they are very rarely an annoyance to their hosts. The majority of the known species live on birds; the forms that frequent mammals are less varied and have been less studied ; most of them have only one claw to the feet (Fig. 220), while the greater portion of the avicolous species have two claws. Fic. 219.—Lipeurus ternatus, male ; Fra. 220.—Trichodectes latus, male ; inhabits Sarcorhamphus papa. inhabits the dog, Canis famili- (After Giebel.) aris. Most of the forms have the anterior legs small, and they are usually drawn towards the mouth, owing, it is believed, to their being used after the manner of hands to bring the food to the mouth; hence in some of our figures (219, 220) the body looks as if it had only four legs. Very diverse statements have been made as to whether allied forms of Mallophaga are found only on allied birds. It would appear that this is the case only to a limited extent, as certain species are found on quite a variety of birds; moreover, some birds harbour several species of bird-lice, even five genera having been found, it is said, on one species of bird. Docophorus icterodes has been recorded as occurring on many kinds of ducks and geese; the swan, however, harbours a distinct species, Doco- phorus cygni, and this is said to have also been found on the bean-goose. At least five species, belonging to three distinct genera, have been found on the common fowl. The parasite most frequently met with on this valuable creature is Menopon pallidum (Fig. 350 MALLOPHAGA CHAP. 221), which is said to have been figured by Redi two hun- dred years ago under the name of Pulex capt. This species multiplies to a con- siderable extent; it is of very active habits, and passes readily from one bird to another, so that it is found on other species besides the domestic fowl. It is even said that horses kept near hen- roosts have been seriously troubled by Menopon pallidum, but it is suggested by Osborn that these attacks may per- : haps have been really due to itch-mites. Fra. 221.—Menopon pallidum ; % x inhabits the common fowl, There is, however, no doubt that this Gallus domesticus. (After gnecies may infest poultry, especially if Piaget.) i sickly, to an enormous extent. The dust- baths in which poultry are so fond of indulging are considered to be of great use in keeping down the numbers of this Insect. A table of the birds and mammals on which Mallophaga have been found, together with the names of the latter, has been given by Giebel1 The classification of the group, so far as the principal divisions are concerned, by no means accords with the kind of animals that serve as hosts, for the only two genera peculiar to quadrupeds (7'richodectes, Fig. 220; and Cyropus) belong to the two chief divisions of Mallophaga. The genus Menopon includes numerous species found on birds, and three or four others peculiar to mammals. Two very natural divisions, Philopterides and Liotheides, were adopted by Giebel and Nitzsch, but unfortunately the chief character they made use of for diagnosing the two groups—the presence or absence of maxillary palpi—was illusory. Apparently the labial palps will serve the purpose of distinguishing the two divisions, they being present in the Liotheides and absent in the Philopterides. A table of the characters of the avicolous genera of these two groups is given by Grosse.” The Liotheides are more active Insects, and leave their host after its death to seek another. But the Philopterides do not do so, and die in about three days after the death of their host. Possibly Mallophaga may be transferred from one bird to another } Op. cit. pp. vii.-xiv. For classification, etc., see also Piaget, Les Pédiculines. Leyden, 1880. * Zeitschr. wiss. Zool, xlii. 1885, p. 532. XV EMBIIDAE 351 by means of the parasitic two-winged flies that infest birds. The writer has recorded} a case in which a specimen of one of these bird-flies captured on the wing was found to have some Mallophaga attached to it. We should perhaps point out that these Mallophaga, though called bird-lice, have nothing to do with the true lice which are so frequently found with them, and that live by sucking the blood of their hosts. It would in fact be better to drop the name of bird-lice altogether, and call the Mallophaga biting lice. Trichodectes latus, according to this method, would be known as the biting louse of the dog, the true or sucking louse of which animal is Haematopinus piliferus, and belongs to the anoplurous division of Hemiptera. Fam. II. Embiidae. Elongate feeble Insects ; with small prothorax, elongate meso- and meta - thorax, which may either bear wings or be without them. In the former case these organs are not %S caducous, are deli- cately membranous, and all of one consist- ence, with three or four indefinite longi- tudinal nervures and "088 - VEL Fra. 222.—Oligotoma michaeli. (After a few cross-veinltets. aay The development 1s incompletely known. The individuals do not form organised societies. The Embiidae are one of the smallest families of Insects ; not more than twenty species are known from all parts of the world, and it is probable that only a few hundred actually exist. They are small and feeble Insects of unattractive appearance, and shrivel so much after death as to render it difficult to ascertain their characters. They require a warm climate. Hence 1 P. ent. Soc. London, 1890, p. xxx. 352 NEUROPTERA CHAP. it is not a matter for surprise that little should be known about them. The simple antennae are formed of numerous joints, probably varying in number from about fifteen to twenty-four. The mouth is mandibulate. Chatin states! that the pieces homologous with those of a maxilla can be detected in the mandible of Bmbia. The labium is divided. The legs are inserted at the sides of the body, the coxae are widely separated (Fig. 223), the hind pair being, however, more approximate than the others. The abdo- men is simple and cylindrical, consisting of ten segments, the last of which bears a pair of biarticulate cerci. In the male sex there is a slight asymmetry of these cerci and of the terminal segment. The thorax is remarkable on account of the equal develop- ment of the meso- and meta-thorax and their elongation in comparison to the pro- thorax. When they bear wings there is no modification or combination of the segments Fic, 223.—Under-surface for the purposes of flight, the condition of of Zmbia sp. Andalusia. these parts being, even then, that of wing- less Insects; so that the Embiidae that have wings may be described as apterous- like Insects provided with two pairs of in- efficient wings. The wings are inserted on a small space at the front part of each of the segments to which they are attached. The legs have three- jointed tarsi, and are : ee Fic. 224.— Anterior wing of Oligotoma saundersii: A, the destitute of a terminal wing ; B, outline of the wing, showing nervures. appendage between (After Wood-Mason.) 1, Costal; 2, subcostal; 8, hie clase, radial ; 4, discoidal ; 5, anal nervure. The wings in Embiidae are very peculiar ; they are extremely Bull. Soc. Philom. (7) ix. p. 33. 2. as 4 6" Xv EMBIIDAE 383 flimsy, and the nervures are ill-developed; stripes of a darker brownish colour alternate with pallid spaces. We figure the an- terior wing of Oligotoma saundersit, after Wood-Mason ; but should remark that the neuration is really less definite than is shown in these figures; the lower one represents Wood-Mason’s inter- pretation of the nervures. He considers’ that the brown bands “mark the original courses of veins which have long since dis- appeared.” A similar view is taken by Redtenbacher, but at present it rests on no positive evidence. One of the most curious features of the external structure is the complex condition of the thoracic sternal sclerites. These are shown in Fig. 223, representing the under-surface of an Embia of uncertain species recently brought by Mr. Bateson from Andalusia. According to Grassi* there are ten pairs of stigmata, two thoracic and eight abdominal; these are connected by longi- tudinal and transverse tracheae into a single system. The ganglia of the ventral chain are, one suboesophageal, three thor- acic, and seven abdominal; these are segmentally placed, except that there is no ganglion in the fifth abdominal segment. There is a stomato-gastric system but no “sympathetic.” Salivary glands are present. The stomodaeal portions of the alimentary canal are remarkably capacious; the stomach is elongate and slender, without diverticula; the Malpighian tubes are elongate and slender; they vary in number with the age of the individual, attaining that of twenty in the adult. The ovaries are arranged somewhat after the fashion of those of Japya, there being in each five short egg-tubes, opening at equal intervals into a straight duct. The testes are remarkably large; each one con- sists of five masses of lobules, and has a large vesicula seminalis, into the posterior part of which there open the ducts of two accessory glands. The large joint of the front tarsus includes glands whose secretion escapes by orifices at the tips of certain setae interspersed between the short spines that are placed on the sole. Species of this genus occur in the Mediterranean region, but their characters have not yet been examined. Our information 1 P. Zool. Soc. London, 1883, p. 628. 2 Ann. Hofmus. Wien, i. 1886, p. 171. 3 Atti Ace. Gioenia, vii. 1893. bo > VOL. V 354 NEUROPTERA CHAP. as to these is chiefly to be found in Grassi’s work. The two species studied by him were wingless. They live under stones, where they spin webs by means of the front feet, whose first joint is, as we have said, enlarged and contains glands; the Insect uses the webs as a means of support in progression, acting on them by means of papillae and a comb-like structure placed on the four posterior feet. Grassi informs us that these Insects are not uncommon under stones in Catania; they require moisture as well as warmth, but not too much; sometimes there is only one individual found under a stone, at others eight or ten. In the winter and spring their galleries are found on the surface of the earth, but in the hot months of summer they secure the requisite amount of moisture by sinking their galleries to the depth of ten or fifteen centimetres. Their food consists chiefly of vegetable matter. They may be reared with ease in glass vessels. Other species of the family attain wings; the details of the process are not well known. Oligotoma michaeli (Fig. 222) was discovered in a hothouse in London among some orchid roots brought from India, and was found in more than one stage of development ; the young greatly resemble the adult, except in the absence of wings. A nymph-form is described by M‘Lachlan’ as possess- ing wings of intermediate length, and Hagen has suggested that this supposed nymph is really an adult female with short wings. If this latter view be correct, nothing is known as to the mode of development of wings in the family. It is still uncertain whether female Embiidae ever possess wings. Wood-Mason and Grassi have shown that there are wingless females in some species, and we know that there are winged males in others, but what the usual relation of the sexes may be in this respect is quite uncer- tain. These Insects have been detected in various parts of the world. In the Sandwich Islands Oligotoma insularis was dis- covered by the Rev. T. Blackburn in the wood and thatch form- ing the roofs of natives’ houses. A species has been found in Prussian amber, and Grassi thinks that Z£mbia solierimone of the Mediterranean species—is not to be distinguished with cer- tainty from the Insect found in amber. Embidae still remains one of the most enigmatic of the familes of Insects. Although Grassi’s recent observations are 1 J. Linn, Soc, Zool. xii. 1878, pl. xxi. f. 2. XV EMBIIDAE 355 of great value from an anatomical point of view, they rather add to, than diminish, the difficulties we encounter in endeavouring to understand the lives of these obscure creatures. That Embiidae form webs has long been known, and it was thought by some that the webs, like those of spiders, might be of assist- ance in procuring food. We may, however, infer from Grassi’s observations that this is not the case, but that the silken tunnels or galleries—as he calls them—serve chiefly as a means of locomotion and protection, the feet of the Insects being highly modified in conformity with this mode of life. Grassi seems to be of opinion that the galleries are also useful in preserving a proper degree of humidity round the Insects. We have already alluded to the mystery that surrounds the mode of growth of their wings. Nearly all that is known as to the Embiidae is contained in Grassi’s paper, or is referred to in Hagen’s monograph of the family. Considerable difference of opinion has prevailed as to the allies of thes: obscure Insects. It would seem that they are most nearly allied to Termitidae and Psocidae. Grassi, however, considers these affinities only remote, and suggests that Embiidae should form a separate Order, to be placed in a super- Order Orthoptera, which would include our Aptera, the two families mentioned above, Mallophaga, Embiidae, and the ordi- nary Orthoptera. Brauer places the family in his Orthoptera genuina. 1 Canadian Entomologist, xvii. 1885, throughout. CHAPTER XVI NEUROPTERA CONTINUED—TERMITIDAE, TERMITES OR WHITE ANTS Fam. III. Termitidae—White Ants, Termites. Each species is social, and consists of winged and wingless indi- viduals. The four wings are, in repose, laid flat on the back, so that the upper one only is seen except just at the bases ; they are membranous and very elongate, so that they A d Fic. 225.—TZermes (Hodotermes) mossambicus. Winged adult. (After Hagen.) extend far beyond the apex of the abdomen; the hind pair as remarkably similar in size, form, and consistence to the front pair: near the base of each wing there is a suture, or line of weakness, along which the wings can be broken off, the stumps in that case remaining as short horny flaps re- posing on the back. Ligula channelled but not divided into two parts. The wingless individuals are very numerous, and have the head and thirteen body segments distinct ; the body CHAP. XV1 TERMITIDAE 357 as terminated by a pair of short cerei. The metamorphosis as slight and gradual, and in some individuals is dispensed with. THE term White Ants has been so long in use for the Termitidae that it appears almost hopeless to replace it in popular use by another word. It has, however, always given rise to a great deal of confusion by leading people to suppose that white ants differ chiefly from ordinary ants by their colour. This is a most erroneous idea. There are scarcely any two divisions of Insects more different than the white ants and the ordinary ants. The two groups have little in common except that both have a social life, and that a very interesting analogy exists between the forms of the workers and soldiers of these two dissimilar Orders of Insects, giving rise to numerous analogies of habits. The word Termites—pronounced as two syllables—is a less objectionable name for these Insects than white ants. The integument in Termites is delicate, and the chitinous plates are never very hard; frequently they are so slightly developed that the creature appears to consist of a single mem- branous sac with creases in it, the head alone being very distinct. The head is exserted, frequently of large size, sometimes as large as all the rest of the body together. Termites may be quite blind, or possess facetted and simple eyes, the latter when present being two in number and always accom- panied by facetted eyes. The antennae pg 996, — Termes bellicosus. are simple, consisting of from nine to Labium, A, maxilla, B, of a x 4 “ i winged adult ; lower face of thirty-one joints, which differ but each. (After Hagen.) little from one another; the number in each individual increases as the development progresses. The parts of the mouth are large, the ligula consists of one piece (Fig. 226, A), but often has the appearance of being formed by two united pieces; on its extremity are seated two pairs of lobes. The head is articulated to the thorax by means of two very large cervical sclerites on each side, placed at right angles to one another, and visible on the under-surface. The prothorax is well developed and distinct from the parts behind it. The pro- 358 NEUROPTERA cHaP. notum, of variable form and size, is very distinct in the perfect Insects; with it are connected the largely developed pleura. The episternum is very peculiar, consisting of an elongate chitinous slip on each side hanging downwards, the two not quite meeting in the middle; they thus form the margin of the very large anterior orifice, and are in contiguity with the cervical sclerites ; behind them are the very large epimera. The prosternum appears to be usually entirely membranous; in some cases the sclerite in it is small and delicate, and apparently differs accord- ing to the species. The meso- and meta-thorax are sub-equal in size; the mesosternum forms a peculiar, large, adpressed fold. The metasternum is membranous, but is terminated behind by a sclerite apparently of variable form. The hind body is volumi- nous, simple in form, consisting of ten segments and bearing at the extremity two short distant cerci of a variable number of joints. The terminal ventral sclerites differ greatly in form according to the species and sometimes according to the sex; there are sometimes, if not always, present near the extremity two peculiar minute biarticulate styles, called appendices anales. The coxae are all large, free, and exserted; at the base of each is a transverse trochantin. The femora are articulated with the trochanters, not with the coxae; both femora and tibiae are slender, the tarsi small, four- jointed; the terminal joint elongate. It is now well established that Termites have a means of communication by sounds. The individuals have a peculiar way of jerking themselves, as has been frequently noticed by ob- Ne servers of the Insects; these con- S\&Y vulsive movements may possibly Fra. 227.—Front tibia and tarsus of De Connected with the production Calotermes rugosus larva, showing of sound, which may perhaps be ua organ, x 90. (After F. evoked by coutact between the back of the head and the pro- notum ; the exact mode by which the sounds are produced is not, however, known. The existence of an auditory organ in the front tibia has been demonstrated by Fritz Miiller! and we reproduce (Fig. 227) one of his figures. The structure seems to 1 Jena, Zeitschr. Naturw. ix. 1875, pl. xii. See also Stokes in Science, xxii. 1893, p. 273. XVI TERMITIDAE 359 be in plan and position similar to the ear of Locustidae, though much less perfect. The wings of Termitidae are not like those of any other Insects; their neuration is very simple, but nevertheless the wings of the different forms exhibit great differ- ences in the extent to which they are made up of the various fields. This is shown in Fig. 228, where the homologous nervures are numbered according to the systems of both Hagen and Red- tenbacher. The area, VII, that forms the larger part of th ing i \ re. Fic. 228.—Wings of Termites: A, Termes lucifugus ; the w ng im C, POLE B, Hodotermes brunneicornis; C, Culotermes sponds to the small portion nodulosus. (After Redtenbacher: B and C 7 diagrammatic.) III, V, VII, homologous areas at the base of the wane: and nervures according to Redtenbacher. 1, in B. The most re- Costal ; 2, subcostal ; 38, median; 4, submedian markable feature of the nervures according to Hagen. wing is, however, its division into two parts by a suture or line of weakness near the base, as shown in Fig. 225. The wings are used only for a single flight, and are then shed by detach- ment at this suture; the small basal portion of each of the four wings is horny and remains attached to the Insect, serving as a protection to the dorsal surface of the thorax. The nature of the suture that enables the Termites to cast their wings with such ease after swarming is not yet understood. There are no true transverse veinlets or nervules in Termites. Redtenbacher suggests ' that the transverse division of the wing at its base, as shown in Fig. 225, along which the separation of the wing occurs at its falling off, may have arisen from a coales- cence of the subcostal vein with the eighth concave vein of such a wing as that of Blattidae. The same authority also informs us that the only point of resemblance between the wings of Termi- tidae and those of Psocidae is that both have an unusually small number of concave veins. The information that exists as to the internal anatomy of 1 Ann. Hofmus. Wien, i. 1886, p. 183. 360 NEUROPTERA CHAP. Termites is imperfect, and refers, moreover, to different species ; it would appear that considerable diversity exists in many respects, but on this point it would be premature to generalise. What we know as to the respiratory system is chiefly due to F. Miller." The number of spiracles is ten; Hagen says three thoracic and seven abdominal, Miiller two thoracic and eight abdominal. In fertile queens there usually exist only six abdominal stigmata. There is good reason for supposing that the respiratory system undergoes much change correlative with the development of the individual; it has been suggested that the supply of tracheae to the sexual organs is deficient where there is arrest of development of the latter. The alimentary canal is only of moderate length. Salivary glands exist, as also do salivary reservoirs; these latter are large, in some species remarkably so. The oesophagus is slender, but abruptly enlarged behind to form a large crop; a proventriculus is apparently either present or absent; the chylific ventricle, or stomach, is slender and simple. The Malpighian tubules are very long; their number is probably from four to eight in the adult, and in the earlier stages less. Behind the tubes the alimentary canal forms a large paunch, and after this there is a small intestine and rectum. The paunch is a_ peculiar structure, and probably of great import- ance in the economy of Termites. These creatures emit minute quanti- Fia, 229,—Head and alimentary ties of a secretion that is corrosive, and canal of Termes lueifugus can act on metal and even glass;” its (nymph). a, head ; 6, salivary S i glands ; ¢, salivary receptacles; Nature and source are not understood. re eee ; eG Hagen describes peculiar structures in large intestine ; 7, Malpighian the rectum to which he is inclined? ee eo of body. to aseribe the origin of this substance, but this is very uncertain. The brain is small; the infra-oesophageal ganglion is placed Jena, Zeitschr, Naturw. ix. 1875, p. 257. * Bidie, in Nature, xxvi. 1882, p. 549. 3 Linnaca Entomologica, xii. 1858, p. 805. % XVI TERMITIDAE 361 immediately under the supra-oesophageal ; there are three thoracic and six abdominal ganglia. The nervous system apparently differs but little in the various forms, or in the different stages of life, except that in the fertile females the abdominal ganglia become so much enlarged that they even exceed the brain in size. The testes are unusually simple; each conisists of eight capsules opening into the vas deferens; the two vasa converge and are continued as a short ejaculatory duct ; at the point of convergence there is a pair of curled vesiculae seminales. The ovarian system is also simple; there is a variable number of elongate egg-tubes, each of which opens separately into the oviduct ; the two ducts unite to form a short uterus, on which there is placed first a spermatheca, and near the extremity a convolute tubular sebific gland. The number of ege-tubes is subject to extraordinary variation, according to the species, and according to the age of the fertilised individual. Social Life.— Termites live in communities that consist sometimes of enormous numbers of individuals, The adult forms found in a community are (1) workers; (2) soldiers; (3) winged males and females; (4) some of these winged forms that have lost their wings. Some species have no worker caste. The individuals of the third category are only present for a few days and then leave the nest in swarms. In addition to the adult individuals there are also present various forms of young. The individuals that have lost their wings are usually limited to a single pair, king and queen; there may be more than one king and queen, but this is not usual. The king and queen may be recognised by the stumps of their cast wings, which exist in the form of small triangular pieces folded on the back of the thorax (Fig. 255). The con- tinuance of the community is effected entirely by the royal pair ; they are the centres of activity of the community, which is thrown into disorder when anything happens to them. Usually the pair are physically incapable of leaving the nest, especially the queen, and frequently they are enclosed in a cell which they cannot leave. In consequence of the disorganisation that arises in the com- munity in the absence of a royal pair, Termites keep certain individuals in such a state of advancement that they can rapidly be developed into royalties should occasion require it. These veserve individuals are called complementary by Grassi; when 362 NEUROPTERA CHAP. they become royalties they are usually immature as regards the condition of the anterior parts of the body, and are then called by Grassi and others neoteinic, as is more fully explained on p. 380. Swarms.— As a result of the Termite economy large numbers of superfluous individuals are frequently produced ; these, in the winged state, leave the community, forming swarms which are sometimes of enormous extent, and are eagerly preyed on by a variety of animals including even man. Hagen has given particulars? of a swarm of Z. flavipes in Massachusetts, where the Insects formed a dark cloud; they were accompanied by no less than fifteen species of birds, some of which so gorged themselves that they could not close their beaks. There is but little metamorphosis in Termitidae. Young Termites are very soft; they have a thin skin, a dispropor- tionately large head, and are of a peculiar white colour as if filed with milk. This condition of milkiness they retain, not- withstanding the changes of form that may occur during their growth, until they are adult. The wings first appear in the form of prolongations of the meso- and meta-nota, which increase in size, the increment probably taking place at the moults. The number of joints of the antennae increases during the develop- ment; it is effected by growth of the third joint and subsequent division thereof; hence the joints immediately beyond the second are younger than the others, and are usually shorter and altogether more imperfect. The life-histories of Termites have been by no means completely followed ; a fact we can well under- stand when we recollect that these creatures ive in communities concealed from observation, and that an isolated individual cannot thrive; besides this the growth is, for Insects, unusually slow. Natural History.—The progress of knowledge as to Ter- mites has shown that profound differences exist in the economy of different species, so that no fair general idea of their lives can be gathered from one species. We will therefore briefly sketch the economy, so far as it has been ascertained, in three species, viz. Calotermes flacicollis, Termes lucifugus, and T. bellicosus. Calotermes flavicollis inhabits the neighbourhood of the Mediterranean Sea; it is a representative of a large series of species in which the peculiarities of Termite life are exhibited 1 P. Boston Soc. xx. 1878, p. 118. XVI TERMITIDAE 363 in a comparatively simple manner. There is no special caste of workers, consequently such work as is done is carried on by the other members of the community, viz. soldiers, and the young and adolescent. The habits of this species have recently been studied in detail in Sicily by Grassi and Sandias.' The Insects dwell in the branches and stems of decaying or even dead trees, where they nourish themselves on those parts of the wood in which the process of decay is not far advanced; they live in the interior of the stems, so that frequently no sign of them can be seen outside, even though they may be heard at work by applying the ear to a branch. They form no special habitation, the interior of the branch being sufticient protec- tion, but they excavate or increase the natural cavities to suit their purposes. It is said that they line the galleries with proctodaeal cement; this is doubtful, but they form barricades and partitions where necessary, by cementing together the proctodaeal products Fia. 230.—Some individuals of Calo- with matter from the salivary termes flavicollis: A, nymph with : q partially grown wing-pads; B, glands or regurgitated from the adult soldier ; C, adult winged in- anterior parts of the alimentary ‘lividual. (After Grassi.) canal. The numbers of a com- munity only increase slowly and remain always small, rarely do they reach 1000, and usually remain very much below this. The king and queen move about, and their family increases but slowly. After fifteen months of their union they may be surrounded by fifteen or twenty young; in another twelve months the number may have increased to fifty, and by the time it has reached some five hundred or upwards the increase ceases. This is due to the fact that the fertility of the queen is at first progressive, but ceases to be so. A queen three or four years old produces at the time of maximum production four to six eggs a day. When the community is small—during its first two years—the winged individuals that depart from it are about eight or ten annually, but the numbers of the swarm augment with the increase of the B 1 4tti Acc. Gioen. vi. and vii. 1893 and 1894. 364 NEUROPTERA CHAP, population. The growth of the individuals is slow; it appears that more than a year elapses between the hatching of the egg and the development of the winged Insect. The soldier may complete its development in less than a year; the duration of its life is not known; that of the kings and queens must be four or five years, probably more. After the winged Insects leave the colony they associate themselves in pairs, each of which should, if all goes well, start a new colony. The economy of Zermes lucifugus, the only European Termite besides Culotermes flavicollis, has been studied by several observers, the most important of whom are Lespés’ and Grassi and Sandias. This species is much more advanced in social life than Calotermes is, and possesses both workers and _ soldiers (Fig. 231, 2, 3); the individuals are much smaller than those of Calotermes. Burrows are made in wood of various kinds, furni- ture being sometimes attacked. Besides making excavations this species builds galleries, so that it can move from one object to another without being exposed; it being a rule—subject to certain exceptions—that Termites will not expose themselves in the outer air. This is probably due not only to the necessity for protection against enemies, but also to the fact that they cannot bear a dry atmosphere; if exposed to a drying air they speedily succumb. Occasionally specimens may be seen at large; Grassi considers these to be merely explorers. Owing to the extent of the colonies it is difficult to estimate with accuracy the number of individuals composing a community, but it is doubtless a great many thousands. Grassi finds the economy of this species in Sicily to be different from anything that has been recorded as occurring in other species; there is never a true royal pair. He says that during a period of six years he has examined thousands of nests without ever finding such a pair. In place thereof there are a considerable number of complementary queens—that is, females that have not gone through the full development to perfect Insects, but have been arrested in various stages of development. In Fig. 231, Nos. 4 and 5 show two of these abnormal royalties; No. 4 is comparatively juvenile in form, while No. 5 is an individual that has been substituted in an orphaned nest, and is nearcr to the natural condition of perfect development. We have no information as to whether any develop- 1 Ann. Sei. Nat. Zool, (4) v. 1856, p. 227. XVI TERMITIDAE 365 ment goes on in these individuals after the state of royalty is assumed, or whether the differences between these neoteinic queens are due to the state of development they may happen to be in when adopted as royalties. Kings are not usually present in these Sicilian nests; twice only has Grassi found a king, but Fic. 231.—Some of the forms of Termes lucifugus. 1, Young larva; 2, adult worker ; 3, soldier ; 4, young complementary queen ; 5, older substitution queen ; 6, per- fect winged Insect. (After Grassi.) he thinks that had he been able to search in the months of August and September he would then have found kings. It would appear therefore that the complementary kings die, or are killed after they have fertilised the females. Parthenogenesis is not thought to occur, as Grassi has found the spermathecae of the complementary queens to contain spermatozoa. 366 NEUROPTERA CHAP. XVI The period of development apparently occupies from eighteen to twenty-three months. At intervals swarms of a great number of winged individuals leave the nest, and are usually promptly eaten up by various animals. After swarming, the wings are thrown off, and sometimes two specimens or three may be seen running off together; this has been supposed to be preliminary to pairing, but Grassi says this is not the case, but that the object is to obtain their favourite food, as we shall mention subsequently. Although these are the usual habits of Zermes lucifugus at present in Sicily, it must not be concluded that they are invari- able; we have in fact evidence to the contrary. Grassi has himself been able to procure in confinement a colony—or rather the commencement of one—accompanied by a true royal pair ; while Perris has recorded’ that in the Landes he frequently found a royal pair of ZY. lucifugus under chips; they were accompanied in nearly every case by a few eges. And Professor Perez has recently placed a winged pair of this species in a box with some wood, with the result that after some months a young colony has been founded. It appears probable therefore that this species at times establishes new colonies by means of royal pairs derived from winged individuals, but after their establish- ment maintains such colonies as long as possible by means of complementary queens. It is far from improbable that distinc- tions as to the use of true and complementary royalties may be to some extent due to climatic conditions. In some localities T. lucifugus has multiplied to such an extent as to be very injurious, while in others where it is found it has never been known to do so. The Termitidae of Africa are the most remarkable that have yet been discovered, and it is probably on that continent that the results of the Termitid economy have reached their climax. Our knowledge of the Termites of tropical Africa is chiefly due to Smeathman, who has described the habits of several species, among them 7. bellicosus. It is more than a century since Simeathman travelled in Africa and read an account of the Termites to the Royal Society. His information was the first of any importance about Termitidae that was given to the world; it is, as may be well understood, deficient in many 1 Ann, Soc. ent. France (5), vi. 1876, p. 201. ? Phil. Trans. xxi. 1781, pp. 139-192. “8 x ‘sopttaday, ay} Aq pasoyo ‘aur st "3 WW Sye0 e a q gage ieee ee 1+ Aq posoy AL SIT} UE Ceourryua ue Sy Wf [peo oY] 07 saoueryua Jo oury ‘9 ‘g ¢ ueanb ayy Jo ‘sjuepuea}je Joy pue uaenb ay} Moys 0} uado uaxyoiq Ayperjaed ‘snsoorpj0q sawmuagy Jo [pao eLoy—'"Zeg ‘ory eS EES ne SSV7 SS SAWSV ee Se ——— SS 2 = SS ———————————— ee ——— Se ee SS ee —= Ss Se 368 NEUROPTERA cHaP. details, but is nevertheless of great value. Though his state- ments have been doubted they are truthful, and have been confirmed by Savaget 7. bellicosus forms buildings compar- able to human dwellings; some of them being twenty feet in height and of great solidity. In some parts of West Africa these nests were, in Smeathman’s time, so numerous that they had the appearance of villages. Each nest was the centre of a community of countless numbers of individuals; subter- ranean passages extended from them in various directions. The variety of forms in one of these communities has not been well ascertained, but it would seem that the division of labour is carried to a great extent. The soldiers are fifteen times the size of the workers. The community is dependent on one royal couple. It is the opinion of the natives that if that couple perish so also does the community; and if this be correct we may conclude that this species has not a perfect system of replacing royal couples. The queen attains an almost incredible size and fertility. Smeathman noticed the great and gradual growth of the abdomen, and says it enlarges “to such an enormous size that an old queen will have it increased so as to be fifteen hundred or two thousand times the bulk of the rest of her body, and twenty or thirty thousand times the bulk of a labourer, as I have found by carefully weighing and computing the different states.” He also describes the rate at which the eggs are pro- duced, saying that there is a constant peristaltic movement? of the abdomen, “so that one part or other alternately is rising and sinking in perpetual succession, and the matrix seems never at rest, but is always protruding eges to the amount (as I have frequently counted in old queens) of sixty in a minute, or eighty thousand and upward in one day of twenty-four hours.” This observer, after giving an account of the great swarms of perfect winged Insects that are produced by this species, and after describing the avidity with which they are devoured by the Hymenopterous ants and other creatures, adds: “I have discoursed with several gentlemen upon the taste of the white ants; and on comparing notes we have always agreed that they are most 1 Ann. Nat. Hist. (2) v. 1850, p. 92. * Dr. G. D. Haviland informs the writer that he thinks it probable this so-called peristaltic movement is merely the result of alarm; he has not, however, had any opportunity of observing TZ. bellicosus. XVI TERMITIDAE 369 delicious and delicate eating. One gentleman compared them to sugared marrow, another to sugared cream and a paste of sweet almonds.” From the preceding brief sketch of some Termitidae we may gather the chief points of importance in which they differ from other Insects, viz. (1) the existence in the community of in- dividuals—workers and soldiers—which do not resemble their parents; (2) the limitation of the reproductive power to a single pair, or to a small number of individuals in each community, and the prolongation of the terminal period of life. There are other social Insects besides Termitidae: indeed, the majority of social Insects—ants, bees, and wasps—belong to the Order Hymen- optera, and it is interesting to note that analogous phenomena occur in them, but nevertheless with such great differences that the social life of Termites must be considered as totally distinct from that of the true ants and other social Hymenoptera. Development.—Social Insects are very different to others not only in the fact of their living in society, but in respect of peculiarities in the mode of reproduction, and in the variety of habits displayed by members of a community. The greatest confusion has arisen in reference to Termitidae in consequence of the phenomena of their lives having been assumed to be similar to those of Hymenoptera; but the two cases are. very different, Hymenoptera passing the early parts of their lives as helpless maggots, and then undergoing a sudden metamorphosis to a totally changed condition of structure, intelligence, and instinct. The development of what we may look on as the normal form of Termitidae—that is, the winged Insects male and female—is on the whole similar to that we have sketched in Orthoptera; the development in earwigs being perhaps the most similar. The individuals of Termitidae are, however, in the majority of cases if not in all, born without eyes; the wing-rudiments develop from the thoracic terga as shorter or longer lobes according to the degree of maturity; as in the earwigs the number of joints in the antennae increases as development advances. All the young are, when hatched, alike, the differences of caste appearing in the course of the subsequent development; the most important of these differences are those that result in the production of two special classes—only met with in social Insects—viz. worker and soldier. Of these the workers are individuals whose develop- VOL. V 2B 370 NEUROPTERA CHAP. ment is arrested, the sexual organs not going on to their full development, while other organs, such as the eyes, also remain undeveloped ; the alimentary canal and its adjuncts occupy nearly the whole of the abdominal cavity. The adult worker greatly resembles—except in size—the young. Grassi considers that the worker is not a case of simple arrest of development, but that some deviation accompanies the arrest. The soldier also suffers an arrest of development in certain respects similar to the worker; but the soldier differs in the im- portant fact that the arrest of the development of certain parts is correlative with an extraordinary development of the head, which ultimately differs greatly from those of either the worker or of the sexual males and females. Soldier.—All the parts of the head of the soldier undergo a greater or less change of form; even the pieces at its base, which connect it by means of the cervical sclerites with the prothorax, are altered. The parts that undergo the greatest modi- fication are the mandibles (Fig. 233, B); these become much enlarged in size and so much changed in form that in a great many species no resemblance to the original shape of these organs can be traced. It is a curious fact that the specific characters are betterexpressed in these superinduced modifications than they are in any other part of the organisation (except, perhaps, the wings). The soldiers are not alike in any two species of Termitidae so far as we know, and it seems impossible to ascribe the differences that exist between the Fic. 233.—The pairs of manai- Sldiers of different species of Termitidae bles of different adult indi- to special adaption for the work they gitnals of Termes SP F™ ave to perform. Such a suggestion is Singapore. A, Of worker ; I 5D B, of soldier ; ©, of winged justifiable only in the case of the Nasuti See (Fig. 234, 1), where the front of the head is prolonged into a point: a duct opens at the extremity of this point, from which is exuded a fluid that serves as a cement for XVI SOLDIERS 371 constructing the nest, and is perhaps also used to disable enemies. Hence the prolongation and form of the head of these Nasuti may be fairly described as adaptation to useful ends. As regards the great variety exhibited by other soldiers—-and their variety is much greater than it is in the Nasuti—it seems at present im- possible to treat it as being cases of special adaptations for useful purposes. On the whole it would be more correct to say Fic. 234,—Soldiers of different species of Termites. (After Hagen.) 1, Termes armiger ; 2, T. dirus; 3, Calotermes flavicollis; 4, T. bellicosus; 5, T. occidentis; 6, T. cingulatus (?); 7, Hodotermes quadricollis (2); 8, T. debilis(?), Brazil. that the soldiers are very dissimilar in spite of their having to perform similar work, than to state that they are dissimilar in conformity with the different tasks they carry on. The Termite soldier is a phenomenon to which it is difficult to find a parallel among Insects. The soldier in the true ants is usually not definitely distinguished from the worker, but it is possible that in the leaf-cutting ants, the so-called soldier may prove to be more similar in its nature to the Termite soldier. The soldiers of any one species of Termite are apparently ex- 372 NEUROPTERA CHAP. tremely similar to one another, and there are no intermediates between them and the other forms, except in the stages of differentiation. But we must recollect that but little is yet known of the full history of any Termite community, and it is possible that soldiers which in the stage of differentiation promise to be unsatisfactory may be killed and eaten,—aindeed there is some evidence to this effect. There is too in certain cases some difference larger or smaller size being the most important—hetween the soldiers of one species, which may possibly be due to the different stage of development at which their differentiation commenced. It would at present appear that, notwithstanding the remark- able difference in structure of the soldiers and workers of the white ants, there is not a corresponding difference of instinct. It is true that soldiers do more of certain things than workers do, and less of others, but this appears to be due solely to their possession of such very different structures; and we are repeatedly informed by Grassi that all the individuals in a community take part, so far as they are able, in any work that is going on, and we find also in the works of other writers accounts of soldiers performing acts that one would not have expected from them. The soldiers are not such effective combatants as the workers are. Dudley and Beaumont indeed describe the soldiers as merely look- ing on while the workers fight.!. So that we are entitled to con- clude that the actions of the soldiers, in so far as they differ from those of the rest of the community, do so because of the different organisation and structures of these individuals. We shall, when speaking of food, point out that the condition of the soldier in relation to food and hunger is probably different from that of the other forms. Various Forms of a Community.—The soldiers and workers are not the only anomalous forms found in Termitid communi- ties; indeed on examining a large nest a variety of forms may be found that is almost bewildering. Tables have been drawn up by Grassi and others showing that as many as fifteen kinds may be found, and most of them may under certain circumstances coexist. Such tables do not represent the results of actual examination in any one case, and they by no means ade- quately represent the number that, according to the most recent observations of Grassi, may be present; but we give one taken 1 Tr. N. York Ac. viii. 1889, pp. 85-114; and ix. 1890, pp. 157-180. E XVI TERMITIDAE 373 from Grassi, as it conveys some idea of the numerous forms that exist in certain communities. In this table the arrangement, according to A, B, C, D, E, represents successive stages of the development :— Forms of Termes lucifugus. (After Grassi.) Zool. Anz. xii. 1889, p. 360. 1. Young, undifferentiated larvae. | | | 2. Larvae that will 3. Larvae that will 4. Reserves for royal specimens: not mature the sexual mature the sexual (only present when 14, 15, and 11 organs. organs. are wanting, or when 14 and 15are | present in insufficient numbers). | | I | | 5. Larvae of 6. Larvae of 9. Nymphs of the 10. Nymphs of 11. aes for soldiers. workers. first form. the second form. royal pairs (only | | | present when 14, 15, and 4 are want- : ing, or when the | | two latter are present in insuffi- | 7. Soldiers. 8. Workers. j | cient numbers). 12. Winged 18. Reserve Insects. royal pairs ? 14. rel royal 15. Substitution couple. royal pairs. On inspecting this table it will be perceived that the variety of forms is due to three cireumstances—(1) the existence of castes that are not present in ordinary Insects; (2) the coexistence of young, of adolescents, and of adults ; and (3) the habit the Termites have of tampering with forms in their intermediate stages, the result of which may be the substitution of neoteinic individuals in place of winged forms. This latter procedure is far from being completely understood, but to it are probably due the various abnormal forms, such as soldiers with rudiments of wings, that have from time to time been discovered in Termite communities, and have given rise to much perplexity. In connexion with this subject we may call attention to the necessity, when examining Termite nests, of taking cognisance of the fact that more than one species may be present. Bates found different Termites living together in the Amazons Valley, and Mr. Haviland has found as many as five species of Termitidae and three of true ants in a single mound in South Africa. In this latter case observation showed that, though in such close proximity, there was but little further intimacy between the species. There are, however, true inquiline, or guest, Termites, 374 NEUROPTERA CHAP. of the genus Lutermes, found in various parts of the world living in the nests of other Termitidae. Origin of the Forms.—The interest attaching to the various forms that exist in Termites, more particularly to the worker and soldier, is evident when we recollect that these never, so far as we know, produce young. In the social Hymenoptera it has been ascertained that the so-called neuters (which in these Insects are always females) can, and occasionally do, produce young, but in the case of the Termites it has never been sug- gested that the sexual organs of the workers and soldiers, whether male or female, ever become fruitful; moreover, the phenomena of the production of young by the white ants are of such a nature as to render it in the highest degree improbable that either workers or soldiers ever take any direct part in it. Now the soldier is extremely different from the sexual individuals that produce the young, and seeing that its peculiarities are not, in the ordinary sense of the word, hereditary, it must be of great interest to ascertain how they arise. Before stating the little information we possess on this sub- ject, it is necessary to reiterate what we have already said to the effect that the soldiers and workers are not special to either sex, and that all the young are born alike. It would be very natural to interpret the phenomena by supposing the workers to be females arrested in their development—as is the case in social Hymenoptera—and by supposing the soldiers to be males with arrested and diverted development. The observations already made show that this is not the case. It has been thoroughly well ascertained by Lespés and Fritz Miiller that in various species of Calotermes the soldiers are both males and females. Lespés and Grassi have shown that the workers of Termes lucifugus ave of male and female sex, and that this is also true of the soldiers. Although the view of the duality of the sexes of these forms was received at first with incredulity, it appears to be beyond doubt correct. Grassi adds that in all the individuals of the workers and soldiers of Zermes lucifugus the sexual organs, either male or female, are present, and that they are in the same stage of development whatever the age of the individual. This statement of Grassi’s is of importance because it seems to render improbable the view that the difference of form of the soldier and worker arises from the arrest of the develop- XVI TERMITIDAE 375 ment of their sexual organs at different periods. The fact that sex has nothing whatever to do with the determination of the form of workers and soldiers may be considered to be well established. The statement that the young are all born alike is much more difficult to substantiate. Bates said that the various forms could be detected in the new-born. His statement was made, however, merely from inspection of the nests of species about which nothing was previously known, and as it is then very difficult to decide that a specimen is newly hatched, it is probable that all he meant was that the distinction of workers, soldiers, and sexual forms existed in very small individuals—a statement that is no doubt correct. Other observers agree that the young are in appearance all alike when hatched, and Grassi reiterates his statement to this effect. Hence it would appear that the differ- ence of form we are discussing arises from some treatment subse- quent to hatching. It may be suggested, notwithstanding the fact that the young are apparently alike when hatched, that they are not really so, but that there are recondite differences which are in the course of development rendered conspicuous. This con- clusion cannot at present be said with certainty to be out of the question, but it is rendered highly improbable by the fact ascertained by Grassi that a specimen that is already far advanced on the road to being an ordinary winged individual can be diverted from its evident destination and made into a soldier, the wings that were partially developed in such a case being afterwards more or less completely absorbed. This, as well as other facts observed by Grassi, render it probable that the young are truly, as well as apparently, born in a state undifferentiated except as regards sex. Fig. 230 (p. 363) is designed to illustrate Grassi’s view as to this modification; the individual A is already far advanced in the direction of the winged form C, but can never- theless be diverted by the Termites to form the adult soldier B. According to the facts we have stated, neither heredity nor sex nor arrest of development are the causes of the distinctions between worker and soldier, though some arrest of development is common to both; we are therefore obliged to attribute the dis- tinction between them to other influences. Grassi has no hesitation in attributing the anatomical distinctions that arise between the soldiers, workers, and winged forms to alimentation. 376 NEUROPTERA CHAP. Food, or the mode of feeding, or both combined, are, according to the Italian naturalist, the source of all the distinctions, except those of sex, that we see in the forms of any one species of Termite. Feeding.—Such knowledge as we possess of the food-habits of Termitidae is chiefly due to Grassi; it is of the very greatest importance, as giving a clue to much that was previously obscure in the Natural History of these extraordinary creatures. In the abodes of the Termites, notwithstanding the enormous numbers of individuals, cleanliness prevails; the mode by which it is attained appears to be that of eating all refuse matter. Hence the alimentary canal in Termitidae contains material of various conditions of nutritiveness. These Insects eat their cast skins and the dead bodies of individuals of the community; even the material that has passed through the alimentary canal is eaten again, until, as we may presume, it has no further nutritive power. The matter is then used for the construction of their habitations or galleries, or is carried to some unfrequented part of the nest, or is voided by the workers outside of the nests; the pellets of frass, 7.e. alimentary rejectamenta, formed by the workers frequently betraying their presence in buildings when none of the Insects themselves are to be seen. The aliments of Calotermes flavicollis are stated by Grassi and Sandias to be as follows: (1) wood; (2) material passed from the posterior part of the alimentary canal or regurgi- tated from the anterior part; (3) the matter shed during the moults; (4) the bodies of other individuals; (5) the secretion of their own salivary glands or that of their fellows; (6) water. Of these the favourite food is the matter passed from the posterior part of the alimentary canal. We will speak of this as proctodaeal food. When a Calotermes wishes food it strokes the posterior part of another individual with the antennae and palpi, and the creature thus solicited yields, if it can, some proctodaeal food, which is then devoured. Yielding the proctodaeal food is apparently a reflex action, as it can be induced by friction and slight pressure of the abdomen with a small brush. The material yielded by the anterior part of the alimentary canal may be called stomodaeal product. It makes its appearance in the mouth in the form of a microscopic globule that goes on in- creasing in size till about one millimetre in diameter, when it is as TERMITIDAE Ave either used for building or as food for another individual. The mode of eating the ecdysial products has also been described by Grassi and Sandias. When an individual is sick or disabled it is frequently eaten alive. It would appear that the soldiers are great agents in this latter event, and it should be noticed that owing to their great heads and mandibles they can obtain food by other means only with difficulty. Since they are scarcely able to gnaw wood, or to obtain the proctodaeal and stomodaeal foods, their condition may be considered to be that of permanent hunger, only to be allayed by carnivorous proceedings. When thrown into a condition of excitement the soldiers sometimes exhibit a sort of Calotermiticidal mania, destroying with a few strokes five or six of their fellows. It is, however, only proper to say that these strokes are made at random, the creature having no eyes. The carnivorous propensities of Calotermes are ap- parently limited to cannibalism, as they slaughter other white ants (Termes lucifugus) but never eat them. The salivary food is white and of alkaline nature; when excreted it makes its appearance on the upper lip. It is used either by other individuals or by the specimen that produced it; in the latter case it is transferred to the lower lip and swallowed by several visible efforts of deglutition. The aliments we have mentioned are made use of to a greater or less extent by all the individuals except the very young; these are nourished only by saliva: they commence taking proctodaeal and stomo- daeal food before they can eat triturated wood. Royal Pairs.—The restriction of the reproductive powers of a community to a single pair (or to a very restricted number of individuals) occurs in all the forms of social Insects, and in all of them it is concomitant with a prolongation of the repro- ductive period far exceeding what is natural in Insects. We are not in a position at present to say to what extent the lives of the fertile females of Termitidae are prolonged, there being great diffi- culties in the way of observing these Insects for long periods owing to their mode of life ; living, as they do, concealed from view, light and disturbance appear to be prejudicial to them. We have every reason to believe, however, that the prolongation extends as a rule over several years, and that it is much greater than that of the other individuals of the community, although the lives of even these latter are longer than is usual in Insects; but this 378 NEUROPTERA CHAP. point is not yet satisfactorily ascertained. As regards the males there is reason to think that considerable variety as to longevity prevails. But the belief is that the royal males of Termitidae also form an exception to other Insects in the prolongation of the terminal periods of their lives. In Hymenoptera, male in- dividuals are profusely produced, but their lives are short, and their sole duty is the continuation of the species by a single act. We have seen that Grassi is of opinion that a similar condition of affairs exists at present with Termes lucifugus in Sicily, but with this ex- ception it has always been considered that the life of the king Termite is, roughly speaking, con- temporaneous with that of the queen; it is said that in certain species the king increases in bulk, though not to an extent that can be at all com- pared with the queen. It must be admitted that the duration of life of the king has not been Fic, 235.—Royal pair of Termes sp. from Singa- sufficiently established, for pore, taken out of royal cell. A, A, King, the coexistence of a king Rides iam, MN queen im “the royal cell is not incon- sistent with the life of the king being short, and with his replace- ment by another. Much that is imaginary exists in the litera- ture respecting Termites, and it is possible that the life of the king may prove to be not so prolonged as has been assumed. Returning to the subject of the limitation of the reproduction of the community to a single pair, we may remark that « priora one would suppose such a limitation to be excessively unfavour- able to the continuation of the species; and as it nevertheless is the fact that this feature is almost, if not quite, without exception XVI TERMITIDAE 379 in Insect societies, we may conclude that it is for some reason absolutely essential to Insect social life. It is true that there are in Termitidae certain partial exceptions, and these are so interesting that we may briefly note them. When a royal cell is opened it usually contains but a single female and male, and when a community in which royal cells are not used is inspected it is usually found that here also there are present only a single fertile female and a single king. Occasionally, however, it happens that numerous females are present, and it has been noticed that in such cases they are not fully matured females, but are imperfect, the condition of the wings and the form of the anterior parts of the body being that of adolescent, not adult Insects. It will be recollected that the activity of a community of Termites centres round the great fertility of the female ; without her the whole community is, as Grassi graphically puts it, orphaned; and the observations of the Italian naturalist make it clear that these imperfect royalties are substitution queens, derived from specimens that have not undergone the natural development, but have been brought into use to meet the calamity of orphanage of the community, The Termites appar- ently have the power of either checking or stimulating the reproduc- tive organs apart from other organs of the body, and they appear to keep a certain number of individuals in such a condition that in case of anything going wrong with the queen, the reserves may be brought as soon as possible into a state of reproductive activity. The in- dividuals that are in such a condition that they can become pseudo- royalties are called complementary or reserve royalties, and when actually brought into use they become substitution royalties. It is not at present quite clear why the substitution royalties should he in such excess of numbers as we have stated they were in the case we have figured (Fig. 236), but it may be due to the fact that when the power or the community is at a certain capacity for supporting young a single substitution royalty would not supply the requisite producing power, and consequently the conmnunity adopts a greater number of the substitution forms. Termites are utterly regardless of the individual lives of the members of the community, anid when the reproductive powers of the company of substitution royalties become too great, then their number is reduced by the effective method of killing and eating them. According to Grassi’s observations, the communities of Termes 380 NEUROPTERA CHAP. lucifugus are now kept up in Sicily almost entirely by substitution royalties ; the inference being that the age of each com- munity has gone beyond the capacity for life of any single royal queen. The substitution royal- ties are, as we have said, called neoteinic (véos, youth- ful, te(vw, to belong to), be- cause, though they carry on the functions of adult Insects, they retain the juvenile con- dition in certain respects, and ultimately die without having completed the normal development. The pheno- menon is not quite peculiar to Insects, but occurs in Fic. 236.—Pair of neoteinic royalties, taken Some other animals having from the royal chamber of Termes sp. at , “ ate o Singapore by Mr. G. D. Haviland. The a well-marked —metamor queen was one of thirteen, all in a nearly phosis, notably in the Mexi- similar state. A, king; B, C, queen. can Axoloti2 A point of great importance in connexion with the neoteinic royalties is that they are not obtained from the instar im- mediately preceding the adult state, but are made from Insects in an earlier stage of development. The condition immediately preceding the adult state is that of a nymph with long wing- pads; such specimens are not made into neoteinic royalties, but nymphs of an earlier stage, or even larvae, are preferred. It is apparently by an interference with one of these earlier stages of development that the “nymphs of the second form,” which have for long been an enigma to zoologists, are produced. Post-metamorphic Growth.—The increase of the fertility of the royal female is accompanied by remarkable phenomena of growth. Post-metamorphic growth is a phenomenon almost unknown in Insect life, except in these Termitidae; distension not infrequently occurs to a certain extent in other Insects, and ? Camerano, Bull. Soc. ent. Ital. xvii. 1885, p. 89; and Kollmann, Verh. Ges. Basel, vii. 1883, p. 391. XVI TERMITIDAE 381 is usually due to the growth of eggs inside the body, or to the repletion of other parts. But in Termitidae there exists post- metamorphic growth of an extensive and complex nature; this growth does not affect the sclerites (i.e. the hard chitinous parts of the exo-skeleton), which remain of the size they were when the post-metamorphic growth commenced, and are consequently mere islands in the distended abdomen (Fig. 236, B,C). The growth is chiefly due to a great increase in number and size of the ege- tubes, but there is believed to be a correlative increase of various other parts of the abdominal as distinguished from the anterior regions of the body. A sketch of the distinctions existing between a female of a species at the time of completion of the metamorphosis and at the period of maximum fertility does not appear to have been yet made. New Communities.—The progress of knowledge in respect of Termitidae is bringing to light a quite unexpected diversity of habits and constitution. Hence it is premature to generalise on important matters, but we may refer to certain points that have been ascertained in connexion with the formation of new communities. The duration of particular communities and the modes in which new ones are founded are still very obscure. It was formerly considered that swarming took place in order to increase the number of communities, and likewise for promoting crossing between the individuals of different com- munities. Grassi, however, finds as the result of his prolonged observations on Termes lucifugus that the swarms have no further result than that the individuals composing them are eaten up. And Fritz Miiller states’ that in the case of the great majority of forms known to him the founding of a colony by means of a pair from a swarm would be just about as practicable as to establish a new colony of human beings by placing a couple of newly-born babes on an uninhabited island. It was also thought that pairs, after swarming, re-entered the nests and became royal couples. It does not, however, appear that any one is able to produce evidence of such an occurrence. The account given by Smeathman of the election of a royal couple of Lermes bellicosus is imperfect, as, indeed, has already been pointed out by Hagen. It suggests, however, that a winged pair after leaving the nest do again enter it to become king 1 Jena. Zeitschr. Naturw. vii. 1873, p. 458. 382 NEUROPTERA CHAP. and queen. The huge edifices of this species described by Smeathman are clearly the result of many years of labour, and at present substitution royalties are not known to occur in them, so that it is not improbable Smeathman may prove to be correct even on this point, and that in the case of some species mature individuals may re-enter the nest after swarming and may become royal couples. On the whole, however, it appears probable that communities of long standing are kept up by the substitution royalty system, and that new communities when established are usually founded by a pair from a swarm, which at first are not in that completely helpless condition to which they come when they afterwards reach the state of so-called royalty. Grassi’s observations as to the sources of food remove in fact one of the difficulties that existed previously in regard to the founding of new colonies, for we now know that a couple may possibly bear with them a sufficient supply of proctodaeal and stomodaeal aliment to last them till workers are hatched to feed them, and till soldiers are developed and the community gradually assumes a complex condition. Professor Perez has recently obtained! the early stages of a community from a winged pair after they had been placed in captivity, unattended by workers. Miiller’s observation, previously quoted, is no doubt correct in relation to the complete helplessness of royal pairs after they have been such for some time; but that helplessness is itself only gradually acquired by the royal pair, who at first are able to shift for themselves, and produce a few workers without any assistance. Anomalous Forms.—Miiller has described a Calotermes under the name of C. rugosus, which is interesting on account of the peculiar form of the young larva, and of the changes by which it subsequently becomes similar in form to other species of the genus. We represent the development of this larva in Fig. 237. We may call attention to the fact that this figure illus- trates the large size of the paunch, which is so extraordinary in some of the states of the Termitidae. Tt will be recollected that the genus Calotermes is destitute of workers. There is another genus, Anoplotermes, in which the reverse condition prevails, and the soldier is absent; this is the only case yet known in which such a state of affairs exists. 1 OR. Ae, Paris, exix, 1894, p. 804. XVI TERMITIDAE 383 The species is called d. pacificus by Fritz Miiller ; it differs from other Termitidae in possessing a proventriculus destitute of tritu- rating ridges. The nests of this species are utilised by a little Hutermes (£. inquilinus Miller) for its own advantage ; whether by first destroying the Anoplotermes or whether by merely taking possession of the nests abandoned by their owners is not known. It is a most remarkable fact that the Hutermes resembles the that the organ by which the blood is propelled into the setae is a terminal chamber of the dorsal vessel ; Verlooren,? who first observed this accessory system of circulation, thought the contractile chamber was quite separate from the heart. The nature of the connexion between this terminal chamber that drives the blood backwards and the other chambers that propel the fluid forwards appears still to want elucidation. The nymphs of the Ephemeridae being creatures adapted for existence in water, the details of their transformation into creatures having an entirely aerial existence cannot but be of much interest. In the nymphs the tracheal system is well developed, but differs from that of air-breathing Insects in the total absence of any spiracles. Palmén has inves- tigated this subject,* and finds that the main longitudinal tracheal trunks of the body of 2 the nymph are not connected i with the skin of the body by i 4 E tracheae, but are attached ad i 4 8 thereto by ten pairs of slender paw strings extending between the + 289. A. Ny Fe henierella Maine = 1% ‘ : Fic, 282.—A, Nymph of Ephemerella wnita ohitinous integument and the with gills of left side removed ; y, gills : 5 B, nymph ot Tricorythus sp. with gill tracheal trunks. When the an (hae vee silleovers Skin is shed these strings—or rather a chitinous axis in each one—are drawn out of the body, and bring with them the chitinous linings of the tracheae. Thus notwithstanding the absence of spir- acles, the body wall is at each moult pierced by openings that extend to the tracheae. After the ordinary moults these orifices close iminediately, but at the change to the winged state they remain open and form the spiracles. At the same time the tracheal gills are com- 1 Zeitschr, wiss. Zool. xxxiv. 1880, p. 404. 2 dan. Nat, Hist. (5) xv. 1885, p. 494. 3 Mem. Cour, Ac. Belg. 4to, xix. 1847, p.1. 4 Zur Morphologie des Tracheensystems, Helsingfors, 1877, pp. 1-20. XIX MAY-FLIES 437 pletely shed, and the creature is thus transformed from a water- breather to an Insect breathing air as usual. In addition to this change there are others of great importance, such as the develop- ment of the great eyes and the complete atrophy of the mouth- parts. The precise manner of these changes is not known ; they occur, however, within the nymph skin. | The sudden emergence of the winged Insect from the nymph is one of the most remarkable facts in the life-history of the may-tly; it has been observed by Sir John Lubbock,’ who describes it as almost in- stantaneous. The nymph floats on the water, the skin of the back opens, and the winged Insect flies out, upwards and away; “from the moment when the skin first cracks not ten seconds are over before the Insect has flown away.” The creature that thus escapes has not, however, quite completed its transformation. It is still enveloped in a skin that compresses and embarrasses it ; this it therefore rapidly gets rid of, and thus becomes the imago, or final instar of the life-cycle. The instar in which the creature exists winged and active, though covered with a skin, is called the sub-imago. The parts of the body in the sub-imago are as a whole smaller than they are in the imago, and the colour is more dingy; the appendages—wings, legs, and caudal setae—are generally considerably shorter than they are in the imago, but attain their full length during the process of extraction. The creatures being, according to Riley, very impatient and eager to take to the wing, the completion of the shedding of the skin of the sub-imago is sometimes performed while the Insect is flying in the air, The food of young Ephemeridae is apparently of a varied and mixed nature. Eaton says” that though sometimes the stronger larvae devour the weaker, yet the diet is even in these cases partly vege- table. The alimentary canal frequently contains much mud ; very” small organisms, Fra, 283.—Lingua of Heptagenia longicauda, such as diatoms and con- x16. m, Central; /, lateral pieces. (After . Vayssiere. fervae, are thought to form : a large part of the bill of fare of Ephemerid nymphs. Although 1 Tr, Linn, Soc, xxv. 1866, p. 488. 2 Ann. Nut. Hist. (3) xviii. 1866, p. 145. 438 NEUROPTERA CHAP. the mouth is atrophied in the imago, yet it is highly developed in the nymphs. This is especially notable in the case of the lingua or hypopharynx (Fig. 283); indeed Vayssiere * seems to ineline to the opinion that this part of the mouth may be looked on in these Insects as a pair of appendages of a head- segment (see p. 96 ante), like the labium or maxillae. The life-history has not been fully ascertained in the case of any species of may-fly ; it is known, however, that the develop- ment of the nymph sometimes occupies a considerable period, and it is thought that in the case of some species this extends to as much as three years. It is rare to find the post-embryonic development of an Insect occupying so long a period, so that we are justified in saying that brief as may be the life of the may- fly itself, the period of preparation for it is longer than usual. Réaumur says, speaking of the winged fly, that its life is so short that some species never see the sun. Their emergence from the nymph-skin taking place at sunset, the duties of the generation have been, so far as these individuals are concerned, completed before the morning, and they die before sunrise. He thinks, indeed, that individuals living thus long are to be looked on as Methuselahs among their fellows, most of whom, he says, live only an hour or half an hour? It is by no means clear to which species these remarks of Réaumur refer; they are doubtless correct in certain cases, but in others the life of the adult is not so very short, and in some species may, in all probability, extend over three or four days; indeed, if the weather undergo an unfavourable change so as to keep them motionless, the life of the flies may be prolonged for a fortnight. The life of the imago of the may-fly is as remarkable as it is brief; in order to comprehend it we must refer to certain peculi- arities of the anatomy with which the vital phenomena are con- nected. The more important of these are the large eyes of the males, the structure of the alimentary canal, and that of the reproductive organs. We have already remarked that the parts of the mouth in the imago are atrophied, yet the canal itself not only exists but is even of greater capacity than usual; it appears to have much the same general arrangement of parts as it had in thenymph. Its coats are, however, of great tenuity, and according » Ann. Sci. Nat. Zool. (6) xiii. 1882, p. 118. ° Réeaumur, Afem. vi. 1742, p. 457. XIX MAY-FLIES 439 to Palmén? the divisions of the canal are separated by changes in the direction of certain portions anterior to, and of others posterior to, its central and greater part—the stomach—in such a manner that the portions with diverted positions act as valves. The stomach, in fact, forms in the interior of the body a delicate capacious sac; when movement tends to increase the capacity of the body cavity then air enters into the stomachic sac by the mouth orifice, but when muscular contractions result in pressure on the sac they close the orifices of its extremities by the valve- like structures we have mentioned above; the result is, that as complex movements of the body are made the stomach becomes more and more distended by air. It was known even to the old naturalists that the dancing may-fly is a sort of balloon, but they were not acquainted with the exact mode of inflation. Palmén says that in addition to the valve-like arrangements we have described, the entry to the canal is controled by a circular muscle, with which are connected radiating muscles attached to the walls of the head. Palmén’s views are adopted, and to a certain extent confirmed, by Fritze,” who has examined the alimentary canal of the may-fly, and considers that though the normal parts of the canal exist, the function is changed in the imago, in which the canal serves as a sort of balloon, and aids the function of the reproductive organs. The change in the canal takes place in an anticipatory manner during the nymph and sub-imago stages. The sexual organs of Ephemeridae are remarkable for their simplicity ; they are destitute of the accessory glands and diver- ticula that, in some form or other, are present in most other Insects. Still more remarkable is the fact that the ducts by which they communicate with the exterior continue as a pair to the extremity of the body, and do not, as in other Insects, unite into a common duct. Thus in the female there is neither bursa copu- latrix, receptaculum seminis, nor uterine portion of oviduct, and there is no trace of an ovipositor; the terminations of the ducts are placed at the hind margin of the seventh ventral plate, just in front of which they are connected by a fold of the integu- ment. The ovary consists of a very large number of small egg- tubes seated on one side of a sac, which forms their calyx, and one of whose extremities is continued backwards as one of the 1 Uber vaarige Ausfihrsgiinge, etc., Helsingfors, 1884, p. 53. 2 Ber, Ges. Freiburg, iv. p. 5; cf. J. &. Mier. Soc. 1889, p. 206. 440 NEUROPTERA CHAP. pair of oviducts. The male has neither vesiculae seminales, acces- sory glands, nor ductus ejaculatorius. The testes are elongate sacs, whose extremities are prolonged backwards forming the vasa deferentia ; these open separately at the extremity of the body, each on a separate intromittent projection of more or less complex character, the two organs being, however, connected by means of the ninth ventral plate, of which they are, according to Palmén, appendages. We should remark that this authority considers Heptugenia to form, to some extent, an exception as regards the structures of the female; while Polymitarcys is in the male sex strongly aberrant, as the two vasa deferentia, instead of being approximately straight, are bent inwards at right angles near their extremities so as to meet, and form in the middle a common cavity, which then again becomes double to pass into the pair of intromittent organs. According to the views of Exner and others, the compound eyes of Insects are chiefly organs for the perception of movement ; if this view be correct, movements such as those made during the dances of may-flies may, by the number of the separate eyes, by their curved surfaces and innumerable facets, be multiplied and correlated in a manner of which our own sense of sight allows us to form no conception. We can see on a summer's evening how beautifully and gracefully a crowd of may-flies dance, and we may well believe that to the marvellous ocular organs of the flies them- selves (Fig. 274) these movements form a veritable ballet. We have pointed out that by this dancing the peculiarly formed aliment- ary canal becomes distended, and may now add that Palmén and Fritze believe that the unique structure of the reproductive organs is also correlated with the other anatomical peculiarities, the con- tents of the sexual glands being driven along the simple and direct ducts by the expansion of the balloon-like stomach. During these dances the momentary conjugation of the sexes occurs, and immediately thereafter the female, according to Eaton, resorts to the waters appropriate for the deposition of her eggs. As regards this, Eaton says:* “Some short-lived species discharge the contents of their ovaries completely en masse, and the pair of fusiform or subeylindrical egg-clusters laid upon the water rapidly disintegrate, so as to let the eggs sink broadcast upon the river-bed. The less perishable species extrude their e Sss * Tr. Linn, Soc, 2nd ser. Zool. iti, 1883, p. 11. XIX MAY-FLIES 441 gradually, part at a time, and deposit them in one or other of the following manners: either the mother alights upon the water at intervals to wash off the eggs that have issued from the mouths of the oviducts during her flight, or else she creeps down into the water to lay her eggs upon the under-side of stones, disposing them in rounded patches, in a single layer evenly spread, and in mutual contiguity.” The eggs are very numerous, and it is thought may sometimes remain in the water as much as six or seven months before they hatch. The number of individuals produced by some kinds of may- flies is remarkable. Swarms consisting of millions of individuals are occasionally witnessed. D’Albertis observed Palingenia papuana in countless myriads on the Fly River in New Guinea: “For miles the surface of the river, from side to side, was white with them as they hung over it on gauzy wings; at certain moments, obeying some mysterious signal, they would rise in the air, and then sink down anew like a fall of snow.’ He further states that the two sexes were in very disproportionate numbers, and estimates that there was but a single female to every five or six thousand males. Ephemeridae in the perfect state are a favourite food of fishes, and it is said that on some waters it is useless for the fly-fisher to try any other lure when these flies are swarming. Most of the “duns” and “spinners” of the angler are Ephemeridae ; so are several of the “ drakes,” our large £. danica and £&. vulgata being known as the green drake and the gray drake. Ronalds says! that the term “dun” refers to the pseud-imago condition, “spinner” to the perfect Insect. #. danica and £. vulgata ave perhaps not distinguished by fishers; Eaton says that the former is abundant in rapid, cool streams, while £. vulgata prefers warmer and more tranquil rivers. These sensitive creatures are unable to resist the attractions of artificial lights. Réaumur noticed this fact many years ago, and since the introduction of the electric light, notes may frequently be seen in journals recording that myriads of these Insects have been lured by it to destruction. Their dances may frequently he observed to take place in peculiar states of light and shade, in twilight, or where the sinking sun has its light rendered broken by bushes or trees; possibly the broken lights 1 Fly-Fisher’s Entomology, 4th ed. 1849, p. 49. 442 NEUROPTERA CHAP. are enhanced in effect by the ocular structures of the Insects. It has recently been ascertained that a species of Teleganodes is itself luminous. Mr. Lewis) who observed this Insect in Ceylon, states that in life the whole of the abdomen was lumin- ous, not brightly so, but sufficient to serve as a guide for captur- ing the Insect on a dark night. It has also been recorded that the male of Caenis dimidiata gives a faint blue light at night. Nearly 300 species of Ephemeridae are known, but this e may be only a fragment of what | actually exist, very little being known of may-flies of other parts of the world than Europe and North America. One of the more curious forms of the family is Oniscigaster wakefieldi; the body of the imago is unusually rotund and furnished with lateral processes. In Britain we have about forty species of may-fly. The family is treated as a distinct Order by Brauer and Packard, and is called Plectoptera by the latter. That Insects so fragile, so highly organised, with a host of powerful enemies, but themselves destitute of means of attack or Fic. 284.—Oniscigaster wakefieldi. New defence, should contrive to exist Zealand. (After M‘Lachlan.) . é at all is remarkable; and it appears still more unlikely that such delicate Insects as Ephemeridae should leave implanted in the rocks their traces in such a manner that they can he recognised; nevertheless, such is the case,—indeed, the may-fly palaeontological record is both rich and remarkable. Several forms are preserved in amber. In the Tertiary bed of the old lake at Florissant, Scudder has been able to distinguish the remains of no less than six species; while in the Jurassic layers of the Secondary epoch, in more than one locality, the remains of several other species have been detected and described. Still more remarkable is the fact that in the Devonian and Carboniferous layers of the 1 P. ent. Soc. London, 1882, p. xiii. XIX MAY-FLIES 443 Palaeozoic period, remains are found that appear to be akin to our existing Ephemeridae. Pulingenia feistmantelii from the Carboniferous of Bohemia is actually referred to a still existing genus; it is said to have been of gigantic size for a may-tly. The families Megasecopterides, Platypterides, and Stenodicty- opterides of the Carboniferous epoch (see p. 343) are all more or less closely allied to the Ephemeridae, and in addition to these Broneniart has established the family Protephemerides for some Insects that he considers to have been the precursors in the Carboniferous epoch of our existing may-flies. These ancient Insects differed in having the wings of another form from those of exist- ing Ephemeridae, and in having the hind wings equal in size to the front pair. Besides this, these Insects had, as shown in Fig. 285, prothoracic dorsal appendages ; some had also projections from the abdominal segments, considered by Brongniart to be of the nature of gills. Some doubt must exist as to this point, for we find in the imago of one of our existing Ephemeridae, Oniscigaster wakefieldi, Fig. 284, abdominal processes that are not gills. It is remarkable that may- flies, which now form a com- paratively unimportant part of the Insect tribe, should in far distant times have been represented Fic. 285.—Homaloneura bonniert ; Car- by so great a variety of allied forms. — boniferous of Commentry. (After a ‘ ‘ Brongniart.) Our fragile, short-lived may-flies ‘i appear to be, as Scudder says, the lingering fragments of an expiring group. CHAPTER XX NEUROPTERA PLANIPENNIA——SIALIDAE, ALDER-FLIES, SNAKE-FLIES— PANORPIDAE, SCORPION-FLIES —- HEMEROBIIDAE, ANT-LIONS, LACEWINGS, ETC. Fam, VIII. Sialidae—Alder-flies and Snake-flies. Four wings of moderate size, meeting in repose over the back at an angle; the hinder of the two pairs slightly the smaller ; the anal area small or nearly absent, not plicate. Nervures moderately numerous, transverse veinlets moderately numerous, Jorming irregularly disposed cells. The metamorphosis 1s great; there is a quiescent pupa. The larva has the mandibles Jormed for biting, urmed with strong teeth. THE Sialidae, though but a small family of only some six or eight genera, comprise a considerable variety of forms and two sub- families — Sialides and Raphidiides. The former group has larvae with aquatic habits possessed of branchiae but no spiracles. Stalis lutaria is one of the commoner British Insects frequenting the vegetation about the banks of tranquilstreams; ogn | tt See bas si . . Fic. 286.—The alder-fly, Sialis lutaria. Britain. it is well known to A, With wings expanded ; B, in profile. ; anglers, being used by them for a bait. According to Ronalds it is called the alder or CHAP. XX SIALIDAE 445 orl-tly, and in Wales the humpback. It is very unattractive in appearance, being of a blackish colour, with wings of a yellow-brown tinge, and makes but a poor show when flying. The female deposits patches of elongate eggs, placed on end and packed together in a very clever manner (Fig. 287). These patches of egvs, of a stone-gray colour, are common objects on rushes or stems of grass near water, and it is stated that there may be no less than 2000 or 3000 eggs in one of them. Our figure gives some idea of the mode in which the eggs are arranged, Fic. 287.—Portion of a row of eggs of Fia. 288.—Sialis lutaria, Sialis lutaria. (Atter Evans.) larva. and the curious narrow process that exists at the end of each. The eggs are said to be sometimes placed at a considerable distance from water, so that when the tiny larvae are hatched they must begin their lives by finding the way to a suitable pool or stream. The larvae (Fig. 288) are objects of very great interest owing to each of segments 1 to 7 of the hind body being furnished on each side with a jointed filament, while the last segment ends in a still longer, but unjointed process. These filaments are branchiae by means of which the Insect obtains air, being, as we have said, destitute of spiracles. It is an active creature and waves its filaments in a very graceful manner; this process no doubt aids the branchiae in their respiratory work. These larvae are well able to exist out of water if they have a sufficiently damp environment. They live on animal matter, but their life- history has not been followed in much detail and it is not known 446 NEUROPTERA CHAP. how many moults they make. The young larva has the head disproportionately large and the branchial filaments longer. When the growth is completed the larva returns to land, seeks a suitable situation in the soil, and after an interval changes to a pupa, in which the characters of the perfect Insect are plainly visible. Subsequently, without becoming again active, it changes to the perfect Insect, and enjoys, for a few days only, an aerial life. The anatomy of the larva has been treated by Dufour.’ The supra-oesophageal ganglion is remarkably small; nothing is said as to the existence of an infra-oesophageal ganglion; there are . three thoracic and eight abdominal ganglia; the first pair of these latter are nearer together than the others, and this is also the case with the last three. The alimentary canal in the adult is provided with a large paunch attached to the crop by a narrow neck,’ but Dufour could find no trace of this in the larva. The structure of the bran- chiae has also been described by the indefatigable French entomotomist. A tracheal tube sends a branch into one of the appendages (Fig. 289); the branch gives off numerous smaller tracheae, which at their extremities break up into branchlets close to the integument. The tracheal tube that receives each main branchial trachea, sends off from near the point of entry Fic. 289.—Structure of tracheal gill Of the latter another trachea, that i distributes its branchlets on the ali- trunk with which it is con- mentary canal, The margins of each fe poet given olf a ypendage are set with swimming hairs, so that the branchiae act as organs of locomotion as well as of respiration, and by their activity in the former capacity increase the efficiency of their primary function. The genus Sialis occurs in a few species only, throughout the * Ana. Sci, Nat. series 8, ix. Zool. 1848, p. 91, pl. 1. ” Newport, Zr, Linn. Soc. xx, 1851, pl. 21, fig. 13. Loew, however, who also describes and figures the anatomy of S. dutwria, states that there is no paunch. Linnaes entomologica, iii, 1848, p. 354. XX SIALIDAE 447 whole of the Palaearctic and Nearctic regions, and reappears in Chili,” though absent in all the intervening area. Several other genera of Insects exhibit the same peculiarity of distribution. The genera Corydalis and Chauliodes form a group distinct from Salis, and are totally differ- ent in appearance, being gigantic Insects, sometimes with the man- dibles of the male enormously elongated (Fig. 290). The species ot Corydalis are called in North America Hellgrammites; Riley has described and figured the metamorphosis of C. cornutus,” the life-history being very similar to that of our little Svadis. A mass consisting of two or three thousand eggs is formed by the female, and the young larva has long fila- ments at the sides of the body like Stalis, These in the later larval life are comparatively shorter, but the Insect is then provided with another set of gills in the Fre, 290.—Corydalis crassicornis, male, form of spongy masses on the MM guste pons of the ving under-side of the body. Riley, however, considers that these organs serve the purpose of attach- ment rather than of respiration. The larvae are known to the Mississippi fishermen as crawlers, and are greatly esteemed as bait. The Raphidiides or snake-flies form the second tribe of Sialidae. There are only two genera, Raphidia and Inocellia, peculiar to the Palaearctic and Nearctic Fic. 291.—Raphidia notata, fe- yeoions. The perfect Insects are chiefly male. Britain. (After Curtis.) ‘ remarkable for the elongation of the prothorax and back of the head to form a long neck, and for the existence in the female of an elongate exserted ovipositor. 1 M‘Lachlan, Hnt. Month. Mfag. vii. 1870, p. 145. 2 Rep. Ins. Missourt, ix. 1877, p. 125. 448 NEUROPTERA CHAP. The species are rather numerous, and have been recently monographed by Albarda.'| The three or four British species of the genus are all rare Insects, and occur only in wooded regions. The Raphidiides, like the Sialides, have a carnivorous larva, which, however, is terrestrial in habits, feeding, it would appear, chiefly on Insects that harbour in old timber. The snake-fly larvae (Fig. 292) are very ingenious in their manner of escaping, which is done by an extremely rapid wriggling backwards. They are capable of undergoing very prolonged fasts, and then alter in form a good deal, becoming shorter and more shrivelled ; Fig. 292 is taken from a specimen that had been fasting for several weeks. They are excessively voracious, and hunt after the fashion of beasts of prey; their habits have been described by Stein,’ who states that he kept a larva from August to the end of May of the following year without food ; it then died in a shrivelled-up state. The larva of the snake-fly changes to a pupa that is remarkably intermediate in form between the perfect Insect and the larva; the eyes, legs, wing-pads, and ovi- positor being but little different from those of the imago, while the general form is he fen aehidia nots that of the larva, and the peculiar elonga- es tion of the neck of the imago is absent. This pupa differs from that of Sialis in the important particular that before undergoing its final ecdysis it regains its activity and is able to run about. The internal anatomy of Raphidia has been treated by Loew, and is of a very remarkable character; we can here only mention that the salivary glands consist of a pair of extremely elongate tubes, that there is a very definite paunch attached as an ap- pendage to one side of the crop, and that the most peculiar character consists of the fact that, according to Loew, four of the six Malpighian tubes have not a free extremity, being attached 1 Tijdschr. Ent. vol. xxxiv. 1891. ” Arch. f. Nutury. iv. i. 1888, p. 315. * Linnaea entomologica, iii. p. 1848, 346, pl. i. xe SIALIDAE AND SCORPION-FLIES 449 at each end so as to form elongate loops; the mesenteron is very complex in character. A considerable number of fossil re- mains from both Tertiary and Mesozoic strata are referred to Sialidae; and a larval form from the red sandstone of Connecticut has been considered by Scudder to be a Sialid, and named Mormolucoides articulatus, but the cor- rectness of this determination is very doubtful (Fig. 293). These fossils are, however, of special interest as being the most ancient Insect larvae yet brought to light. A still older fossil, from the Car- boniferous strata of Illinois called Jamia bronsoni, is considered by Scudder to have several points of resemblance to Sialidae. Fia. 293. — Mormolucoides articulatus, larva. Trias of Connecticut. (After Scudder.) Fam, IX. Panorpidae—Scorpion-flies. Head prolonged to form a deflexed beak, provided with palpi near Fic. 294.—Panorpa communis, male. Cambridge. of the mouth-parts. its apex; wings elongate and narrow, shining and destitute of hair, with numerous, slightly divergent veins and moderately numerous transverse veinlets (in one genus the wings are absent). Larvae provided with legs, and usually with numerous prolegs like the saw-flies: habits car- NIVOTOUS. The majority of the members of this family are very readily distinguished by the beak-lke front of the head, this being chiefly due to enlargement of parts of the head itself, and in a less degree to prolongation The upper (or front) face of the beak is formed entirely by the clypeus, the labrum being scarcely VOL. V 2G 450 NEUROPTERA CHAP. visible, though it may be detected at the sides of the tip of the beak; the sutures between the various parts of the head are nearly or quite obliterated, but it is probable that the sides of the beak are formed by the genae and by the stipites of the maxillae, and its under-surface chiefly by the submentum: the mentum itself is but small, the ligula is small, bifid at the ex- tremity, and each branch bears a two-jointed palpus, the basal article being of very peculiar structure in Panorpa. The mandibles are but small, and are placed at the apex of the beak ; they have each the form of an oblong plate armed with two very sharp teeth, and they cross freely. The maxillae are the only parts of the mouth-pieces that are very elongated; each cardo is articulated at the base of the head, and the stipes extends all the length of the side of the beak; each maxilla bears a five- jointed palpus and two small but very densely ciliated lobes. The antennae are long, very slender, and flexible, and are many- jointed; they are inserted between the eyes in large foramina; there are three ocelli, or none, and the compound eyes are moderately large. The prothorax is small, its notum is quite small or moderate in size, and the prothoracic stigma is placed behind it; the side-pieces are small, and there is no chitinous pro- sternum except a small longitudinal strip placed in the mem- brane between the coxae; these latter are of only moderate size, and are free and dependent. The meso- and meta-thorax are large, their side-pieces are of considerable dimensions and bear large, dependent coxae and supporting-pieces (Fig. 58); there is a stigma placed between the meso- and meta-thorax at the hind margin of the upper part of the meso-trochantin ; both meso- and meta-notum are transversely divided. The abdomen is elongate, slender, conico-cylindrical, consisting of nine segments; the basal segment is membranous and concealed; the terminal appendages are of variable nature according to the species and sex. The legs are elongate and slender, the tarsi five-jointed. The internal anatomy of Panorpa communis has been examined by Dufour? and Loew.” They agree in describing the alimentary canal as being of peculiar structure: there is a short, slender oesophagus leading to an organ in which there is seated a remarkable arrangement of elongate hairs; this structure might be looked on as the proventriculus, but Loew considers it to be rather a ' Mem. Ac. Sci. érang. vii. 1841, p. 582. * Linnaea entom. iii. 1848, p. 363. XX PANORPIDAE 451 division of the true stomach. The particulars given by these two anatomists as to some other parts of the internal anatomy are very discrepant. The Panorpidae form a small family of only nine or ten genera, two or three of these being exotic and only imperfectly known ; the three genera found in Europe are composed of very curious Insects. The scorpion-flies—Panorpa proper—are very common Insects, and have received their vernacular name from the fact that the males have the terminal segments elongate and slender and very mobile, and carry them curved up somewhat after the fashion of the scorpions (Fig. 294). It is said that Aristotle was acquainted with these Insects, and considered them to be really winged scorpions. A second European genus, Boreus, is still more peculiar; it is destitute of wings, and has the appearance of a minute wingless grasshopper; it is found from late autumn to early spring in moss and under stones,andis said to be some- times found disporting itself on the surface of the snow : the female of this Insect _ has an exserted ovipositor. 2 508 — Bowes isinatis, The writer has found this little creature in Scotland among moss in November, and under stones early in March (Fig. 295). The third European genus, Bittacus, does not occur in our islands, but is common on many parts of the Continent; the perfect Insect has a great resemblance to a Tipula, or “daddy-long-legs” fly, and attaches itself to the stems of grasses, and preys on flies; according to Brauer it has the peculiar habit of using the hind pair of legs as hands (Fig. 296), instead of the front pair, as is usual in Insects. This remark- able genus is widely distributed, and species of it are found even in the Antipodes. A species inhabiting caves has been mentioned by M‘Lachlan.' The early stages of the Panorpidae were for long unknown, but have recently been discovered by Brauer: he obtained eggs of Panorpa by confining a number of the perfect flies in a vessel containing some damp earth on which was placed a piece of meat; when 1 Ent. Month. Mag. 1894, p. 39. female. Dumfriesshire. i533 NEUROPTERA cHaP, the young larvae were hatched they buried themselves in the earth and nourished themselves with the meat or its juices. These larvae (Fig. 297) bear a great resemblance to those of the Hymenop- terous family Tenthredinidae; they have biting mandibles and palp-bearing maxillae, and show no approach to the peculiar mouth structure found in the Hemerobiidae; there are three pairs of feet placed on the three thoracic segments, and there is also a pair of less perfect feet on each of the first eight abdominal segments, those behind being the larger. The upper surface of Fic, 296.—Bittacus tipularius holding Fic. 297. Young larva of a fly in its hind legs, Austria, Panorpa communis. (After Brauer.) (After Brauer.) the body hears spines, which, however, disappear after the first change of skin, with the exception of the larger processes on the posterior segment, which persist throughout the life of the larva. The larvae are active for about one month; after this they become quiescent, but do not change to the pupa state for several weeks ; when this happens they change in form and cannot creep, although their limbs are not enclosed in any pupa case. Brauer also dis- covered larvae of Panorpa communis at large in numbers in an old tree stump that was quite covered with moss, and contained many ants in the mouldering wood. The ants appeared to be on friendly terms with the Panorpa larvae. The earlier stages of XX PANORPIDAE—-HEMEROBIIDAE 453 Boreus and Bittacus were also observed by Brauer; they are essentially similar to those of Panorpa, but the larva in Boreus is not provided with abdominal prolegs. The Panorpidae have been separated from the other Neuroptera by certain naturalists as a distinct Order, called Panorpatae by Brauer, Mecaptera by Packard; but in their structure as well as in their metamorphoses they are not so distinct from the Phryganeidae and the Hemero- biidae as to justify this step. Fossil forms of Bittacus and of Panorpa have been found in amber and in the Tertiary strata, and Scudder has described some forms from Florissant in which there are no cross-veinlets in the wings. Some remains from the English Lias have been referred to Panorpidae by Westwood under the name Orthophlebia, but it is by no means certain that they really belong to the family. Fam. X. Hemerobiidae—Ant-lions, Lacewing-flies, etc. Head vertical ; mawillae free, with five-jointed palpi ; labial palpi three-jointed. Wings subequal in size, with much reticula- tion, without anal area. Tarsi five-jointed. Metamorphosis great; the larvae with mandibles and mazxillae coadapted to form spear-like organs that are suctorial in function. Pupa, similar in general form to the imago, enclosed in & cocoon. SE LS Oe S552 KOS ANS RN AYQAA Ws) Fic. 298.—Drepanepteryx phalaenoides. Scotland. The Hemerobiidae are an extremely varied assemblage of Neuroptera; the perfect Insects of the various sub- famnilica are very different in appearance, but the family as a whole is naturally defined by the very peculiar structure of the mouth- organs of the larvae. These Insects have, in fact, a suctorial 454 NEUROPTERA cHap. mouth in their early life, and one of the ordinary biting type in adult life. This is a very unusual condition, being the reverse of what we find in Lepidoptera and some other of the large Orders, where the mouth is mandibulate in the young and suctorial in the adult. The suctorial condition is in Hemerobiidae chiefly due to modification of the mandibles; but this is never the case in the Insects that have a suctorial mouth in the imaginal instar. Nearly all the Hemerobiidae are terrestrial Insects in all their stages; a small number of them are, to a certain extent, amphibious in the larval life, while one or two genera possess truly aquatic larvae. The metamorphosis is, so far as the changes of external form are concerned, quite complete. There are no wingless forms in the adult stage. The classification given by Hagen? and generally adopted recognises seven sub-families. These we shall mention seriatim. Sub-Fam. 1. Myrmeleonides or Ant-lions.— Antennae short, clubbed, the apical space of the wing with regular, oblong cellules, Fic. 299.—Tomateres citrinus, 8, E. Africa. (After Hagen.) The ant-lions in their perfect state are usually unattractive Insects, and many are nocturnal in their habits ; the species of the genus Palpares and allies (Fig. 299) are, however, of more handsome appearance, and attain a large expanse of wing. No member of the sub-family is an inhabitant of Britain, though species of the typical genus Myrmeleon are common in Central and Northern Europe. The 1 Stettin. ent. Zeit. xxvii. 1866, p. 369 ; this author has also sketched a classifi- cation of the larvae in P. Boston Soc. xv. 1873, p. 243. xx ANT-LIONS 455 remarkable habits of their larvae attracted the attention of natur- alists so long ago as two hundred years. We owe to Réaumur an accurate and interesting account of Jf formicarius, the species found in the neighbourhood of Paris. The larvae are predaceous, and secure their prey by means of pitfalls they excavate in the earth, and at the bottom of which they bury themselves, leaving only their elongate jaws projecting out of the sand at the bottom of the pit. They move only backwards, and in forming their pit use their broad body as a plough, and throw out the sand by placing it on the head and then sending it to a distance with a sudden jerk. When about to construct its trap the larva does not commence at the centre, but makes first a circular groove of the full circumference of the future pit. Burying its abdomen in the surface of the earth, the Insect collects on to its head, by means of the front leg, the sand from the side which is nearest to the centre, and then jerks the sand to a distance. By making a second circuit within the first one, and then another, the soil is gradu- ally removed, and a conical pit is formed, at the bottom of which the ant-lion lurks, burying its body but leaving its formidable mandibles widely extended and projecting from the sand. In this position the young ant-lion waits patiently till some wandering Insect trespasses on its domains. An ant or fly coming over the edge of the pitfall finds the sand of the sloping sides yielding beneath its body, and in its effort to secure itself probably dislodges some more of the sand, which, descending to the bottom of the pit, brings the lurking lion into activity. Availing himself of his. power of throwing sand with his head, the ant-lion jerks some in the neighbourhood of the trespasser, and continues to do so until the victim is brought to the bottom of the pit and into the very jaws of its destroyer; then there is no further hope of escape; the mandibles close, empale their prey, and do not relax their hold till the body of the victim is exhausted of its juices. The position chosen is in a place that will keep dry, as the larva cannot carry on its operations when the sand is wet or damp, hence the soil at the base of a high wall or a rock frequently harbours these Insects. The parts of the mouth of the Myrmeleon are perfectly adapted for enabling it to empty the victim without for a moment relaxing its hold. There is no mouth-orifice of the usual character, and the contents of the victim are brought into the buccal cavity by means of a groove extending along 456 NEUROPTERA ‘ CHAP. the under side of each mandible; in this groove the elongate and slender lobe that replaces the maxilla —there being no maxillary palpi — plays backwards and forwards, probably raking or dragging backwards to the bueeal cavity at each movement a small quantity of the contents of the empaled victim. The small lower lip is peculiar, consisting in greater part of the two lobes that support the labial palpi. The pharynx is provided with a complex set of muscles, and, together with the buccal cavity, func- tions as an instrument of suction. After the prey has been sucked dry the carcass is jerked away to a distance. When the ant-lion larva is full grown it forms a globular cocoon by fastening together grains of sand with fine silk from a slender spinneret placed at the posterior extremity of the body; in this cocoon it Fic. 300.—Larva of Myrme- changes to an lmago of very elongate leon pallidipennis. (Atter “yo: : Meinert. ) form, and does not emerge until its meta- morphosis is quite completed, the skin of the pupa being, when the Insect emerges, left behind in the cocoon. The names by which the European ant-lion has been known are very numerous. It was called Formicajo and Formicario by Vallis- neri about two hundred years ago; Réaumur called it Formica-leo, and this was adopted by some modern authors as a generic name for some other of the ant-lions. The French people call these Insects Fourmilions, of which ant-lion is our English equivalent. The Latinised form of the term ant-lion, Formicaleo, is not now appled to the common ant-lion as a generic term, it having been proposed to replace it by Myrmecoleon, Myrmeleo, or Myrmeleon ; this latter name at present seems likely to become generally adopted. There are several species of the genus found in Europe, and their trivial names have been confounded by various authors in such a way as to make it quite uncertain, without reference to a synonymie list, what species is intended by any particular writer. The species found in the neighbourhood of Paris, and to which it may be presumed Réaumur's history refers, is now called Myrme- XX MYRMELEONIDES 457 leon formicarium by Hagen and others; M‘Lachlan renamed. it Af. curopaeus, but now considers it to be the JZ nostras of Fourcroy. The popular name appears to be due to the fact that ants—Formica in Latin, Fourmi in French—forin a large part of the victims; while lion—the other part of the name—is doubt- less due to its prowess as a destroyer of animal life, though, as Réaumur long ago remarked, it is a mistake to apply the term lion to an Insect that captures its prey by strategy and by snares rather than by rapidity and strength. The imago of Myrmeleon is of shy disposition, and is rarely seen even in localities where the larva is abundant. It is of nocturnal habits, and is considered by Dufour to be carnivorous. Considerable difference of opinion has existed as to the structure of the mouth and of the alimentary canal in these larvae. Réaumur was of opinion that there exists no posterior orifice to the alimentary canal, but Dufour ridiculed this idea, and stated positively that such an orifice undoubtedly exists. It is also usually said that the mouth is closed by a membrane. Meinert has recently exam- ined these points,! and he states that the mouth is not closed by any membrane, but is merely compressed. He finds that there is no posterior exit from the stomach; that there is a compact mass without any cavity between the stomach and the point where the Malpighian tubes connect with the small intestine. The portions of aliment that are not assimilated by the larva collect in the stomach and are expelled as a mass, but only after the Insect has become an imago. This peculiar excrementitious mass consists externally of uric acid, and from its form and appearance has been mistaken for an egg by several naturalists. The posterior portions of the alimentary canal are, according to Meinert, of a remark- able nature. The small intestine is elongate, slender, and is coiled. There are eight very long and slender Malpighian tubes ; a pair of these have free extremities, but the other six in the posterior part of their course are surrounded by a common mem- brane, and, following the course of the intestine, form ultimately a dilated body seated on a coecum. These six Malpighian tubes are considered to be partially, if not entirely, organs for the secre- tion of silk for forming the cocoon, the coecum being a reservoir. The canal terminates as a slender tube, which acts as a spinneret and is surrounded by a sheath. A complex set of muscles com- 1 Ov, Danske Selsk. 1889, p. 43. 458 NEUROPTERA CHAP. pletes this remarkable spinning apparatus. The alimentary canal of the imago has been described and figured by Dufour’; it is very different from that of the larva. The ant-lion is capable of sustaining prolonged fasts. Dufour kept specimens for six months without any food. These In- sects are said to give off a peculiar ant-like odour, due, it is thought, to their ant- eating habits. Although no species in- habits Great Britain, yet one is found in Southern Sweden. Introduced specimens get on very well in confinement in our country,? and would probably flourish at large for some years if they were liber- ated. Although the number of known species and genera of Myrmeleonides is consider- able —that of the species being now upwards of 300—the members of the sinall genus Myrmeleon are the only forms that are known to make pits of the kind we have described. Other larvae® are known similar in general form to the Fig. 301.—Upper aspect of common ant-lion, but they walk forwards sen eg te in the normal manner, and apparently stomach ; ¢, free extremi- hunt their prey by lurking in a hidden ties of two Malpighian tubes; c’, terminal common Place and, when a chance occurs, rush- portion of other six tubes; Ing on the victim with rapidity. Brauer @ -coccum s & spinneret’s has observed this habit in the case of J, Ff, muscles for protruding its sheath 5 y, g, maxillary Dendroleon pantherinus in the Prater at glands. (After Meinert.) Wien ia The most remarkable forms of Myrmeleonides are contained in the genus Palpares. We figure Tomateres citrinus (Fig. 299), an allied genus found in Eastern Africa as far south as Natal. These Insects have conspicuous blotches and marks on their wings. The species of Myrmeleon are similar in form, but are smaller, more feeble, and less ornate in appearance, 1 Ann, Sei. étrang. vii. 1834, pl. 12. ° M‘Lachlan, Hut. Afonth. Alag. ii. 1865, p. 73. ® Redtenbacher, Denk. Ak. Wien, xviii. 1884, p. 335, Xx HEMEROBIIDAE 459 Pitfalls, formed in all probability by ant-lions, have been noticed in the Galapagos islands and in Patagonia, though none of the Insects forming them have been found. Sub-Fam. 2. Ascalaphides,— Antennae elongate, with a knob at the tip; the apical area of the wing with irregular cellules, ER egketere nash nene ae Bary = QS7 Lr eo z LOT OT SEES Rm \SXiS KSA RP CER N i ste SR Sto A he rs Ee gue Fic. 302.—Ascalaphus coccajus. East Pyrenees. The sub-family Ascalaphides is not represented by any species in Britain, though being a narrow space on the hind part of the front wing from which the colour is absent, while the nervures appear to he interrupted ; they are, however, really present, though transparent ; the nature of this peculiar mark is quite unknown, but is of considerable interest in connexion with the small trans- parent spaces that exist on the wings of some butterflies, 1 Tr, ent. Soc. London, 1868, p. 189. XX HEMEROBIIDAE 469 Sub-Fam. 6. Chrysopides, Lacewing-flies.—/rayile Insects with elongate, setaceous antennae. The lacewing-flies—also called stink-flies and golden-eyes—are excessively delicate Insects, of which we possess about 15 species in Britain. Their antennae are more slender and less dis- tinctly jointed than they are in Hemero- biides, and the Chry- sopides are more elongate Insects. The peculiar = metallic colour of their eyes is frequently very conspicuous, the eyes looking, indeed, as if they were composed of shining metal; this fades very much after Fig. 313.—Chrysopa flava. Cambridge. BS Fic, 314.—Eggs of Chrysopa. A, Five Fic. 315.—Larva of Chrysopa sp. Cambridge. eggs on a leaf; B, one egg, more A, The Insect magnified; B, foot more magnified. (After Schneider.) magnifiel ; ©, terminal apparatus of the claws, highly magnified. death. Although not very frequently noticed, the Chrysopides are really common Insects, and are of considerable importance 470 NEUROPTERA CHAP. ? owing to their keeping “ greenfly” in check. The eggs are very remarkable objects (Fig. 314), each one being supported at the top of a stalk many times as long as itself; in some species (C. aspersa) the eggs are laid in groups, those of each group being supported on a common stalk. The larvae (Fig. 315) are of a very voracious disposition, and destroy large quantities of plant-lice by piercing them with sucking-spears, the bodies of the victims being afterwards quickly exhausted of their contents by the action of the apparatus connected with the spears. The larvae of two or three species of Chrysopa cover themselves with the skins of their victims after the manner of the larvae of Hemerobius ; but most of the larvae of Chrysopa are unclothed, and hunt their victims after the fashion of the larvae of Coccinellidae, to which these Chrysopa larvae bear a considerable general resemblance. These larvae have a remarkable structure at the extremity of their feet, but its use is quite un- known (Fig. 315, B, C). Some larvae of the genus make use of various sub- stances as a means of dis- guise or protection. Dewitz noticed’ thatsomespecimens he denuded of their clothing and placed in a glass, seized small pieces of paper with their mandibles and, bend- ing the head, placed the morsels on their backs; here the pieces remained in consequence of the exist- ence of hooked hairs on the skin. Green algae or eryptogams are much used for clothing, and Fic. 316.—Chrysopa (Hypochrysa) pallida, A lava ee ) )2 Dewitz supposes that the Insect spins them together with webs to facilitate their retention. According to Constant and Lucas” the larvae of Chrysopa attack and kill the larvae ) Biol. Centralbl. iv. 1885, p. 722. * Bull. Soc. ent. France (6), i. 1881, pp. xxi. and xxxi. Xx HEMEROBIIDAE 471 of Lepidoptera and Phytophagous Hymenoptera. The curious form we figure (Fig. 316) has been hatched from eggs found by Brauer on Pinus abies in Austria. The eggs were of the stalked kind we have described; the young escaped from them in the autumn, twelve days after deposition, but did not take any food till the following spring. The Chrysopides are widely distributed over the earth’s sur- face. They form an important part of the fauna of the Hawaiian islands. Sub-Fam. 7. Coniopterygides—Jfinute Insects with very few transverse nervules in the wings; having the body and wings covered by a powdery efflorescence. These little Insects are the smallest of the Order Neuroptera, and have the appearance of winged Coccidae; their claim to be considered members of the Neuroptera was formerly doubted, but their natural history is quite concordant with that of the Hemerobiid groups, near which they are now always placed. Low has made us acquainted with the habits and structure of an Austrian species, Coniopteryx lutea Wallg., but for which he has proposed the new generic name