4 tw Wwalaeaa ky VA. 2 ie i * Aaa se tet K et Ke ry - Pps f ; . LA » Pe) boy ae Ter} 8 ew poy a FSges PIE Ab door a5 H 7 HO PPE Sc eh pe 29 PPh Prats ih ory y PMS pipiheree A Dill Ie ed : Pees co ua DP Da ay iS en Ai a Penney jp eee rey LM pA IA WDC al dll Ae, PAVH TS Pata oh an Deane we Piniew Ur a a A Laie ae Pe! Pare 5°3 VaA Ey v0? ¥ "8% i aoe : vay ope DEP OL AY ne nek PU eT ah eo of . Pee h yh we Se x aM lial oes . RA py wd : ey , rf Lé Pandy a isi 5 : Pear a eo a ee mbricid are Poth at ata fen le f Beye op he A a ae Fig rey al. Oat A Pit 5 a hy fps Aue H HARVARD UNIVERSITY e Library of the Museum of Comparative Zoology PHVSlonoecy Of THE INVERTEBRATA ELE PHRYVetOLOGY OF tite tNVE REE BRATA A. B. GRIFFITHS, Px.D., F.R.S. (EDIN.), F.C.S. MEMBRE DE LA SOCIETE CHIMIQUE DE PARIS} MEMBER OF THE PHYSICO-CHEMICAL SOCIETY OF ST. PETERSBURG AUTHOR OF “ RESEARCHES ON MICRO-ORGANISMS,” “THE DISEASES OF CROPS,” ETCREDG, < Ve LONDON Pe EeV E AWD CoO. 5 HENRIETTA STREET, COVENT GARDEN, W.C. *“. 1892 [All rights reserved | /T92, tery (oastume of doornfs, 2006. TO PROR tf. i, AUALEY, LEDER Ss... ES, F.Z.S. Correspondant de l'Institut de France Past-President of the Royal Society, etc. etc. WHO HAS CREATED A NEW EPOCH IN BIOLOGY; AND WHOSE GENIUS HAS DONE SO MUCH TO AWAKEN THE KEENEST INTEREST IN THE STUDY AND POPULARISATION OF SCIENCE This Work is (by permission) Dedicated AS A TOKEN OF ADMIRATION AND RESPECT BY THE AUTHOR PREFACE. “* Phystology is to a great extent applied physics and chemistry.” Pror, HUXLEY. “4 true knowledge of biology must be based on a knowledge of chemistry and physics." —M. M, P, Murr. “ Biology being the science which deals with the matter and energy of living things, manifestly rests on physics and chemistry, since it involves the appli- cation of the laws and principles of these sciences to the special case of living matter.” —R. J. H, Gipson. “ Chemistry lies at the basis of physiology,’—A. BINET. “ It is impossible that physiology can ever acquire a scientific foundation without the aid of chemistry and physics.”—J. VON LIEBIG. THE branch of biology detailed in the following pages has had only a few workers, for the reason that the majority of biologists are not chemists, and consequently have not the necessary manipulative skill in applying a science like chemistry to the solution of biological problems. The true functions of the various organs of the Javertebrata have always been, until recent years, more or less prob- lematical. Morphology and histology alone could not answer correctly the questions involved ; but physiology with chemical and physical methods of research have illuminated very many obscure problems concerning the functions of the various organs and tissues of the /avertebrata ; and no doubt vill PREFACE. they are destined to play an important part in the elucidation of many problems still requiring solution. The following work gives an account of some of the most important researches on the subject, which have been published during the past fifteen or twenty years; and I have also included an account of my own researches in the present volume, more especially as these have appeared in the Proceedings of the Royal Societies of London and Kdinburgh, and have also attracted the attention of the Académie des Sciences (l'Institut de France), to the extent that its Council thought proper to award me an “honourable mention” in connection with the Prix Montyon, which is given annually for researches in experimental physiology and physiological chemistry. Besides, several well-known biologists have informed me that a work on the physiology of the /nverte- brata would be a welcome addition to biological literature. Consequently, I hope that this work (although I am fully cognisant of its many imperfections and shortcomings) may prove of some utility to those scientists and students who are desirous of investigating biological problems involving the applications of chemistry and physics. I take this opportunity of expressing my gratitude and best thanks to Sir Richard Owen, K.C.B., F.R.S., for the great interest he has always taken in my investigations, and for the many letters of friendly criticism which I have received from him. I am also grateful to Mr. I’. E. Beddard, F.R.S.E.; the Rev. W. H. Dallinger, LL.D., F.R.S.; Mr. H. H. Dixon (of the University of Dublin); Prof. J. C. Ewart (of the Univer- sity of Edinburgh); Prof. Léon Fredericq (of the University of Liege); Dr. A. Giard (of Paris); Mr. 8. T. Griffiths ; PREFACE. ix Mr. A. Johnstone, F'.G.S. (of the University of Edinburgh) ; Dr. C. A. MacMunn, F.C.S. ; Prof. P. Mantegazza (of the University of Rome); Dr. A. C. Maybury, F.G.8.; Prof. A. von Mojsisovics (of the University of Gratz); Mr. E. B. Poulton, F.R.S.; Dr. G. J. Romanes, F.R.S.; Prof. G. O. Sars (of the University of Christiania); and Dr. C. Zeiss, for valuable assistance in various parts of the book. - My obligations are due to the President and Council of the Royal Society of Edinburgh for the loan of certain wood-blocks used in illustrating my own papers on the Invertebrata, and which were originally printed in the Society’s Proceedings. In conclusion, I here record the name of my sister (Miss Mildred H. Griffiths), for her help in preparing, under my direction, certain drawings for the illustrations. Figures 32 and 33 are supplied by Dr. Carl Zeiss, optician, Jena, from his catalogue of microscopes. A. B. GRIFFITHS. EDGBASTON, Feb. 1892. ‘eh ea eB iis, > Se +. eieert ee Cipher ete ym ' « > : ‘ e ) ond Ss. - ' an Pon “ - - ig ; — yy serra ) 7 ‘ wae ¥ a in a oo ie CONTENTS. CHAPTER I. PAGE Introduction: Definition of Physiology—The Actions of Living Matter—Cells and their Functions—The Function of the Sarcode of the lowest Animals—Dual and Triple Functions of an Organ —Law of Von Baer—Classification of the Jnvertebrata—Division of Physiological Labour, &c. CHAPTER II. The Chemistry of Protoplasm: ‘‘ The Physical Basis of Life ’’— Analyses of Albumin—Chemical and Physical Properties of Albumin—Lieberkiihn’s Formula for Albumin—Schorlemmer on the Synthesis of Albumin—Loéw and Bokorny’s Researches— Researches of Reinke, Mori, Kretzschmar, Griffiths, Schiitzen- berger, Palladin, Schulze, and Kisser, on Albumin—Decomposition Products of Albumin or Protoplasm—Latham’s Formula for Albumin—Spencer’s Definition of Life, &c. CHAPTER III. Digestion in the Jnvertebrata: DIGESTION IN GENERAL—Modes of Nutrition—Digestion in the Protozoa—Phosphorescence and Digestion—Digestion in the Porifera, Cwlenterata, Echinodermata, Tr ichoscolices, Nematoscolices, Clietognatha, Arthropoda, Polyzoa, fe) Xli CONTENTS. Brachiopoda, Mollusca, Hemnichordata, and Urochordata—General Remarks concerning Digestion in the Invertebrata CHAPTER IV, Digestion continued : DIGESTION IN PARTICULAR—Digestion in the Protozoa: No specialisation of parts—Digestion in the Porifera and Celenterata : Researches of Greenwood, Lankester, Haéckel, Voigt, Cienkowski, MacMunn, Fredericq — Digestion in the Echinodermata : Researches of Fredericq, Griffiths, MacMunn— Digestion in the Trichoscolices: Experiments of Fredericq— Digestion in the Annelida: Researches of Fredericq and Griffiths ; the Pancreatic Function of the so-called “ Liver ’’—Digestion in the Insecta and Arachnida: Researches of Griffiths on the Salivary Glands and “Livers” of the Jnsecta; Lowne on the Malpighian Tubules of Calliphora; Von Planta, Leuckart, and Schonfeld on the Food Stuff of Bees; the Researches of Griffiths and Johnstone on the Salivary Glands and ‘‘ Liver ”’ of the Spider —Digestion in the Crustacea; Investigations of Griffiths on the *« Livers’’ of the Brachyura and Macroura; Stamati’s Investiga- gations on the Gastric Juice of the Crayfish—Digestion in the Lamellibranchiata: Researches of Fredericq, Griffiths, and MacMunn—Digestion in the Gasteropoda: Investigations of Griffiths, Levy, and Fredericq—Digestion in the Cephalopoda : Researches of Griffiths, Krukenberg, Fredericq, and De Bellesme on the “ Liver ’”’ (Pancreas) of Sepia—Digestion in the Tunicata— Constituents of the Secretions of the Salivary Glands and Pancreas (so-called “ liver"’) in the Invertebrata, &c. : CHAPTER V. Absorption in the Invertebrata: No Distinct Set of Vessels—The Function of the Typhlosole—Absorption by the Alimentary Canal and Blood-vessels—Absorption in the Protozoa : Protozoan Absorp- tion due to Excitability or Irritability of the Cell—Absorption in the Porifera, Colenterata, Echinodermata, Cestoidea, Annelida, Myriapoda, Insecta, Arachnida, Crustacea, Polyzoa, Brachiopoda, and Mollusca—General Remarks on Absorption, &c PAGE 20 rte) « OT CONTENTS. xill CHAPTER VI. PAGE The Blood in the Jnvertebrata: The Size of some Invertebrate Cor- puscles—Coagulation of Invertebrate Blood—The Protozoa and Porifera devoid of Blood—The Blood in the Actinozoa and Echinodermata—The Blood in the Myriapoda: Three distinct Corpuscles—The Blood in the Annelida: The Fluids of the Perivisceral Cavity and the Pseudo-hzmal System ; First appear- ance of a Coloured Corpuscle ; Researches of MacMunn, Lankester, Delle Chiaje, Schwalbe, Krukenberg, and Milne-Edwards—The Blood in the Jnsecta: Pigments of the Blood; Researches of Poulton and Fredericq ; Coagulation of Insects’ Blood—The Blood in the Crustacea: Investigations of Fredericq; Percentages of Saline Matter in Crustacean Blood; Densities of Crustacean Blood; Blood of the Mollusca: Researches of Griffiths, Cuénot, Fredericqg, and Krukenberg; Transport of Oxygen by means of Hzmocyanin; Percentages of Saline Matter in Molluscan Blood; Saline Composition of Molluscan Blood—The Chro- matology of Invertebrate Blood: Researches of MacMunn, Poulton, and others; The Hemoglobin of Lwmbricus ; Micro- spectroscopes—Griffiths’ Researches on the Gases of the Inverte- brate Blood—General Remarks, &c. . : “ : + 125 CHAPTER VII. Circulation in the Jnvertebrata: Fusion of Circulation and Digestion in the Protozoa, Porifera, and Coalenterata—Blood and Vascular Systems in the Echinodermata and Annelida—Circulation in the Trichoscolices, Arthropoda, Polyzoa, Brachiopoda, Mollusca, and Tunicata, &e. . : ; é ; : : - - : spis2 CHAPTER VIII. Respiration in the /nvertebrata : Respiration in the Protozoa, Porifera, Celenterata: Respiratory Pigments; Researches of Moseley, MacMunn, M‘Kendrick, Krukenberg, and De Negri; Internal or Tissue Respiration ; Respiration in the Echinodermata; Investi- gations of Dugés, MacMunn, and Feettinger—Respiration in the Trichoscolices and Annelida: Researches of MacMunn, Geddes, Beddard, and Vejdovsky—Respiration in the Nematoscolices : XIV CONTENTS. Bunge’s Investigations on Respiration in Ascaris—Respiration in the Myriapoda and Insecta: Griffiths and Lyonnet on the Power of certain Insects resisting Asphyxia; Trachez and Tracheal Gills; Tissue Respiration—Respiration in the Arachnida: Respira- tion by Trachez, ‘“ Lungs,” and the General Surface of the Body— Respiration by Branchiz and Pigments—Activity of Respiration— Respiration in the Polyzoa, Brachiopoda, Mollusca, and Tunicata— General Remarks on Invertebrate Respiration, &c. . : CHAPTER IX, Secretion and Excretion in the Jnvertebrata: General Remarks on Secretion and Excretion—The Protozoan Contractile Vacuole— Secretion of Lime Carbonate in the Coelenterata: Researches of Murray and Irvine—The Excretory Organs in the Hchinodermata : Investigations of Griffiths on the Renal Organs of Uraster—The Renal Organs to the Annelida and Nematoidea—The Secretion of Viscid Matter by the Prototracheata—Excretory Function of the Malpighian tubules in the M/yriapoda—Poisons secreted by Insects : Researches of Poulton; The Salivary Glands in the Lepidoptera and their Function ; Griffiths’ Researches on the Renal Function of the Malpighian Tubules in the Jnsecta—The Arachnida: Poison Glands of the Arthrogastra and Araneina ; The Arachnidium of the Araneina ; Investigations of Griffiths, Johnstone, and Weinland on the Renal Organs in the Araneina—The Crustacea: The Shell- gland a Renal Organ ; Researches of Griffiths on the Green Glands of Astacus—The SBrachiopoda: Secretion of the Shell; the Functions of the Pseudo-hearts—The Mollusca: Secretion of Lime Carbonate by these Animals; Formation of Pearls; Re- searches of Irvine and Woodhead on Shell-formation ; Researches of Griffiths and Follows on the Organ of Bojanus; Researches of MacMunn, Griffiths, and others on the Function of the Nephridia in the Mollusca; Secretion of Mucus by the Pulmo- gasteropoda—Nerves and the Phenomena of Secretion—The Invertebrate Kidney—Comparison of the Invertebrate Kidney with that of the Vertebrata, &c. CHAPTER X. Nervous Systems of the Jnvertebrata : General remarks ; Nerve-centres, Nerve-fibres ; Functions of Nerve-fibres—The Diffused Nervous PAGE 207 eat CONTENTS. XV PAGE System of the Protozoa—Ledenfeld’s Investigations on a Nervous System in the Porifera—The Nervous System of the Calenterata : Researches of Kleinenberg, Romanes, Haéckel, Hertwig, and others ; Experiments of Romanes on the Nervous System of the Meduse; Eimer’s Investigations on Ctenophora—The Nervous System of the Echinodermata: Researches of Romanes, Ewart, Fredericq, Prouho, and Hamann; Internal and External Nerve- plexuses of Hchinus—Nervous Systems of the Trichoscolices, Anne- lida, Nematoscolices, Chetognatha, Prototracheata, and Myriapoda— The Nervous Systems of the Jnsecta: The Cerebral Ganglion or Brain—The Nervous Systems of the Arachnida and Crustacea : Investigations of Sars, Fredericq, Vandevelde, and Griffiths—The Nervous Systems of the Polyzoa, Brachiopoda, Mollusca, and Tunicata, &c. . . : ‘ : : . 208 CHAPTER XI, The Organs of Special Sense, &c., in the Jnvertebrata : Tactile Sensi- bility and Sight in the Protozoa and Porifera—The Cclenterata: Rudimentary Eyes and Olfactory Organs in the Meduse—The Echinodermata : Tactile Sensibility ; Sense of Smell: Experiments of Griffiths; Sense of Hearing ; Eyes: Researches of Romanes and Ewart—The Sense-organs in the Trichoscolices, Annelida, Nematoseolices, Chetognatha, and Myriapoda—Sense-organs in the Insecta: Tactile Organs ; The Senses of Taste, Smell, and Hearing ; Simple and Compound Eyes of Insects, Mosaic Vision; The “Voices ” of Insects—Sense-organs in the Crustacea : Blind Cave- crabs, Cirripedia, Crayfishes, &¢.—Sense-organs in the Mollusca : Organs of Touch, Taste, Smell, Hearing, and Sight; The Cepha- lopod Eye—Intelligence or Reason in certain Invertebrates, kc. . 345 CHAPTER XII. Movements and Locomotion in the Jnvertebrata: In the Protozoa: Pseudopodia, Flagella, and Cilia as locomotive organs; Researches of Dallinger and Drysdale ; The Muscular Fibre in the Peduncle of Vorticella—Movements in the Porifera—Locomotion, &c., in the Calenterata: Researches of Romanes—Locomotion, &c., in the Trichoscolices, Annelida, Nematoscolices, and Myriapoda; Loco- Xvi CONTENTS. motion, &c., in the Insecta: The Flight of Insects—Locomotion, &c., in the Arachnida, Crustacea, and Mollusca, &c. CHAPTER XIII. Reproduction and Development in the Invertebrata: Spontaneous APPENDIX . Generation, Gemmation, Fission, Endogenous Cell Formation, Parthenogenesis, Sexual Reproduction, Hermaphroditism, Sexual Elements of Reproduction, Fecundation, Development of the Embryo, and Conjugation—Reproduction in the Protozoa: Investi- gations of Dallinger and Drysdale and others—Reproduction, &c., in the Porifera, Cwlenterata, Echinodermata, Trichoscolices, Anne- lida, Nematoscolices, Chetognatha, Onychophora, and Myriapoda— Reproduction, &e., in the Jnsecta: their Odours, Colours, Dances, and Music, as Agents in the Reproduction of the Jnsecta—Repro- duction in the Arachnida, Crustacea, Polyzoa, Brachiopoda, Mollusca, and Tunicata—Concluding Remarks: Pleomorphism, Origin of Life, &c. INDEX OF AUTHORITIES . SUBJECT INDEX PAGE 398 THE PHYSIOLOGY OF THE INVERTEBRATA. CHAPTER I. INTRODUCTION. ANIMAL physiology may be defined as that branch of biology which is concerned in the elucidation of the various functions which take place in the animal economy. It is a branch of study quite distinct from morphology, chorology, and = anus. ~ S ee: ERE eer) nro OR) S ees ors reas as | & bo = Se pa Ie) fe UE Sd a ec 2 © Ee QQ. ere ns | || Bx eos of the Crustacea. ‘To this order belong the lobster (Homarus), crayfish (Astacus), and shrimp (Palwmon). The alimentary canal is well defined, especially the stomach. 60 PHYSIOLOGY OF THE INVERTEBRATA. As an example of the Macroura, we describe in detail the ali- mentary canal of Astacus fluviatilis (the fresh-water crayfish). The mouth lies behind the mandibles, and is a wide aperture bounded by the labrum in front and the metastoma behind. This oral aperture leads into a wide but short cesophagus situated on the ventral side of the head. The cesophagus opens almost vertically into a large stomach divided into cardiac and pyloric portions. The pyloric portion, dilated dorsally in a ceecum, passes directly into a long tubular intestine, which dilates into a FORE GU si small rectum, and finally ter- minates in an anus (Fig. 13). MID ‘ cut The only lateral appendage to the alimentary canal of Astacus is the so-called liver (Figs. 14 pile and 16), whose ducts open on GUT : , each side of the pylorus. ‘This so-called liver is in reality a digestive gland or pancreas, and consists of numerous czecal Fic. 14.—ALIMENTARY CANAL OF tubes, whose microscopical ASTACUS. structure is represented in Fig. a = cardiac part of stomach. 4=an- 16, There are no-other cecal terior gastric muscles. c = cardiac : appendages to the alimentary ossicle. d = pyloric part of stomach. e = pyloric ossicle. canal of Astacus 5 ka this re- a teri é i les. U J = posterior _sasine —musess. spect the crayfish differs from g = so-called “liver.” 2 = caecum. 7 i = intestine. & = rectum. the Brachyura and some other Macroura. But it may be stated that ‘in many Crustacea the digestive canal is sur- rounded by cells filled with oily or fatty matter of a yellow or blue colour; they may be compared to an omentum, and probably serve as a store of nutriment, to be drawn upon during the moult, or when food is scarce.” There are no salivary glands in Astacus fluviatilis. As the stomach of the crayfish (Fig. 15) is far in advance of any PHYSIOLOGY OF THE INVERTEBRATA. 61 previously described, it is important that a full detailed description of it should be given. As already stated, the stomach of Astwcus is divided into cardiac and pyloric FIG. 15. LONGITUDINAL SECTION OF STOMACH OF ASTACUS. a@ = esophagus. é = position of gastrolith. c¢ = lateral tooth. d = ptero- cardiac ossicle. e = anterior gastric muscle. = cardiacossicle. 9» = uro- cardiac process. # = zygocardiacossicle. z = pre-pyloric ossicle. 4 = median tooth. /= pyloric ossicle. | = posterior gastric muscle. m = czecum. 0 = median pyloric valve. = aperture of ‘‘bile’’ duct. g = lateral pouch. vy = cardio-pyloric valve. s = intestine. /¢ = lateral pyloric valve wv = small inferior tooth. portions. The internal walls of the anterior half of the cardiac por- tion are membranous and are invested with numberless minute hairs ; but in the pos- terior half the walls FIG. 16.—STRUCTURE Of SO-CALLED LIVER‘ are strengthened by Baader calcified and chitinous a = epithelium cells. 4 = so-called hepatic cells. p : ¢ = ferment cells. ossicles which are so arranged as to form a gastric mill or gizzard. Professor Huxley * describes the gastric mill of Astacus in the following * The Anatomy of Invertcbrated Animals, p. 318. 62 PHYSIOLOGY OF THE INVERTEBRATA. words: ‘‘It consists, in the first place, of a transverse, slightly arcuated cardiac plate, calcified posteriorly, which extends across the whole width of the stomach, and articulates at each extremity by an oblique suture with a small curved triangular antero-lateral or pterocardiac ossicle. On each side, a large, elongated postero-lateral or zygecardiac ossicle wider posteriorly than anteriorly, is connected with the lower end of the antero-lateral ossicle, and, passing upwards and backwards, becomes continuous with a transverse arcuated plate, calcified in its anterior moiety, and situated in the roof of the anterior dilatation of the pyloric portion; this is the pyloric ossicle. These pieces form a sort of six-sided frame, the anterior and lateral angles of which are formed by mov- able joints, while the posterior angles are united by the elastic pyloric plate. ‘rom the middle of the cardiac piece a strong calcified urocardiac process extends backwards aud downwards, and, immediately under the anterior half of the pyloric ossicle, terminates in a broad, thickened extremity, which presents inferiorly two strong rounded tuberosities, or cardiac teeth. With this process is articulated obliquely upwards and forwards, in the front wall of the anterior dilatation of the pyloric portion, and articulates with the anterior edge of the pyloric ossicle, thus forming a kind of elastic diagonal brace between the urocardiac process, and the pyloric ossicle. The inferior end of this pre-pyloric ossicle is produced downwards into a strong bifid urocardiac tooth. Finally, the inner edges of the postero-lateral ossicles are flanged inwards horizontally, and, becoming greatly thickened and ridged, form the large lateral cardiac teeth. The membrane of the stomach is con- tinued from the edges of the pre-pyloric to those of the postero-lateral ossicle in such a manner as to form a kind of pouch with elastic sides, Which act, to a certain extent, as a spring, tending to approximate the inferior face of the pre- pyloric ossicle to the superior face of the median process of the cardiac ossicle.” PHYSIOLOGY OF THE INVERTEBRATA. 63 There are four principal muscles (see Figs. 54 and 15) which work this complex stomach. The two anterior gastric muscles attached to the cardiac ossicle, ascend obliquely forwards and are fixed to the inner surface of the carapace. The two posterior gastric muscles attached to the pyloric ossicle are also fixed to the carapace. The food torn to pieces by the mandibles is crushed into a fine state of division in the. cardiac portion of the stomach. The thick walls of the pyloric portion are covered internally with long hairs. These project into the interior forming a kind of strainer, which only allows the nutritive juices and finely divided particles to pass into the intestine. At the sides of the cardiac portion of the stomach, embedded in its tissues, are usually to be found in the summer two cal- careous masses or plates, known as gastroliths. At the period when the crayfish moults the gastroliths are also cast. They weigh from two to three grains; what their function may be is still unknown. Possibly, they may be simply deposits due to an excess of calcareous matter in the system.* We have now come to the end of the great class, ARTHRO- pops. The majority of its members, excepting degenerate types, have well-defined digestive apparatuses. Often, as in the Crustacea and Insecta, the intestinal epithelium is furnished with a hard layer of chitin (C,,H,,N,O,,), sometimes raised into projections destined to crush and macerate the food. The mouth is either suctorial, masticatory, or biting; and in the Crustacea certain anterior parts of the intestinal canal become buccal pieces. In some of the lower Arthropods there are present both salivary glands and so-called livers; in others, either one or the other organ is absent—e.y., both salivary glands and “livers” are present in the Orthoptera, Coleoptera, and Arthrogastra. In the Lepidoptera, Arctisca, and Dilopoda only salivary glands are present; and in the Yiphosura and Ostracoda there are only the so-called livers or digestive * See also Irvine and Woodhead in Proc. Roy. Soc. Edin., vol. 16, P. 330. 64 LHAVSIOLOGY OF THE INVERTEBRATA. glands. The “liver” in the lower Arthropods consists of ceecal prolongations of the intestine, but in the higher Crustacea it becomes an organ of considerable size. As a rule the salivary glands are better differentiated in the Insecta and Arachnida than in any of the other classes of the Arthropoda. But the large bilobed liver, or, as we prefer to call it, the pancreas, is characteristic of the Orustacea, especially the higher forms. It appears that the salivary glands and pancreas are interchangeable, sometimes one replacing the other. . It may be remarked that in many of the Arthropoda the alimentation considerably influences both the form and the dimensions of the digestive apparatus. Carnivorous animals have a digestive apparatus which is comparatively short. Caterpillars, which are most voracious, have wide intestines, while the butterflies, which eat little, and only liquid foods, have long and slender alimentary tubes. Certain genera of the Insecta (Mphemera, Bombyx, &c.) which are very voracious as larvee, are in the mature state destitute of organs of mandu- cation. Wholly destined for generation or reproduction, they cannot take any nutriment; hence the brief duration of their lives. THE POLYZOA. The IMalacoscolices, one of the Malacozoic Series, is divided into two great classes—the Polyzoa and Brachiopoda ; and the former class is subdivided into four orders. The Polyzoa have a mouth surrounded with tentacula, an enlarged alimentary canal, sometimes furnished with denti- form projections destined for mastication. Occasionally there exists a sort of stomach. - Most of the Polyzou are microscopic animals; but, living in ~ colonies, they sometimes form conspicuous masses; conse- quently they bear a resemblance to the Sertularian Hydrozoa. (1) The Podostomata.—This order is represented by the genus Lhabdopleura. The disc or lophophore is horseshoe- PHYSIOLOGY OF THE INVERTEBRATA. 65 shaped. In the Rhabdoplewra the tentacula are narrower, but longer, than any other Polyzow; in this respect they somewhat resemble the Brachiopoda. “The mouth is situated beneath the free margin of the disc, on the opposite side to the anus.” (2) The Phylactolemata are all fresh-water Polyzoa. The mouth (Fig. 17) is situated on the lophophore, and is surrounded by a num- ber of ciliated tentacula. The mouth leads into an cesophagus which passes into a muscular pharynx. “The particles of food are carried down the inner surface of each ten- tacle, and the mouth and pharynx expand to re- ceive such as are appro- priate, as if by an act of selection. The rejected particles pass out between the bases of the tentacula, or are driven off by (3 the centrifugal currents.” Fic. 17.—ALIMENTARY CANAL OF The muscular pharynx PEED ON leads into a capacious a= tentacles. 4=lophophore. c = mouth. d = cesophagus. e = pharynx. / = sto- stomach. The narrow mach. g = intestine. A = anus. intestine is continued @ = nervous ganglion. from the posterior end of the stomach, and terminates in an anus situated near the mouth. ‘The intestine is bent backwards, so that it runs almost parallel with the anterior portion of the alimentary canal. The walls of the stomach are studded with cells or follicles of a pancreatic nature ; and its orifice is surrounded by cilia. The food particles are constantly regurgitated into E 66 PHYSIOLOGY. OF THE INVERTEBRATA. the middle portion of the stomach (which is sometimes called a gizzard), and, after having undergone a further comminu- tion, are returned to the anterior portion of that organ, where they are kept in constant agitation. These particles finally pass into the intestine. The undigested portion of the food agglomerates into small pellets which are carried upwards and are expelled through the anus. The alimentary canal of the Polyzoa is devoid of salivary glands. It has been stated that the Polyzoa resemble somewhat the Sertularian Hydrozoa, but it must be distinctly understood that the Polyzoon has not merely a digestive cavity, like the Hydra and the Actinia; tor the digestive apparatus of the former is differentiated into a pharynx, stomach, and intestine provided with an anal aperture. In fact, the Polyzoon has a complex and highly developed digestive system. Then, again, the Polyzoan tentacula differ from those of the Hydrozoa and Actinozoa, in being somewhat stiff and provided with cilia. (3) The Gymnolemata are marine Polyzoa, except Paludi- cella, which is a fresh-water form. (4) The Pedicellinea.—In this order the buds, produced by gemmation, become detached from the original stock. THE BRACHIOPODA. This class is divided into two orders, the Zretenterata and the Clistenterata. They are all marine animals “provided with a bivalve shell, and are usually fixed by a peduncle, which passes between the two valves in the centre of the hinge line, or the region which answers to it in those Brachi- opods which have no proper hinge.” (1) The TZretenterata have no hinge. The mouth or oral aperture leads into an cesophagus, which passes into a stomach provided with pancreatic follicles. From the stomach passes the intestine, which opens into the cavity of the pallium or mantle on the right side of the mouth. The alimentary canal PHYSIOLOGY OF THE INVERTEBRATA. 67 is suspended in a spacious perivisceral cavity. “The walls of this cavity are provided with cilia, the working of which keeps up a circulation of the contained fluid.” In Lingula the intestine is long, and forms two bends before it terminates in the pallial cavity. (2) The Clistenterata have a hinge uniting the two valves of the shell. In the Zerebratula the mouth opens downwards into the pallial chambers, and is situated in the middle line, about one-third of the length of the shell from the hinge. The mouth of the Brachiopoda has no rudiments of a maxillary or dental apparatus. The cesophagus in Zerebratula is short, and is situated between the anterior portions of the so-called liver. The stomach is an oblong organ which is dilated at the cardiac end; the narrower may be spoken of as the pyloric portion, but there is no valvular structure at the pylorus. The cardiac portion of the stomach is surrounded by the so-called liver. The intestine is short, straight, and is continued in a line with the pylorus to the interspace between “the attachments of the adductores longi and cardi- nales to the ventral valve,” where it ends blindly. The so- called liver (pancreas) is a large organ consisting of numerous ramified follicles. There are usually two ducts from this organ, communicating with the cardiac portion of the stomach. The alimentary canal is freely suspended in the body cavity by delicate membranes which stretch from the body walls. THE Mo.Luusca. The Mollusca form the second division of the Malacozoic Series; and this division comprises seven orders. (1) The Lamellibranchiata include the Ostrea, Anodonta, Mytilus, Pecten, Cardium, Mya, Unis, &e. The mouth is bounded by lips, which are usually produced into two labial palps. These palps are ciliated, and by the action of the cilia food particles, which have passed into the branchial chamber, are driven into the mouth. The mouth of a Lamellibranch PHYSIOLOGY OF THE INVERTEBRATA. 68 1on ‘or “IOAIT BY} UL poppaquid yovuo}s jo uoljisod = s ‘wintpivo -uad = 4 ‘yavay = ~ ‘snuvfog jouvsio = 0 ‘ajosnul JOJORI}e1 JolIajsod = w= ‘ayosnw JOJONppe Joiiajsod = wz ‘snuy=y ‘suoydis=yY¥ ‘STIs = 6 ‘o[A]s YIM wMndad OUJses =y 00} = 2 "JOOJ JO VoUTI]SNs Ul sUTJSIJUI = YP “BAI[ Pay[wo-os = 2 = ‘aJOSNUI JOJONppe JOLaJUN = g ‘YyJNoUl = V teeth—for the prehens mastication of food particles. It passes by a short cesophagus. (Fig. 18) into an expanded stomach, which is embedded in. carrieS no organs—jaws or At the pyloric end of the stomach a diverticulum of that organ contains a rod-like body—the the so-called liver. The function of the crystalline style is most crystalline style. PHYSIOLOGY OF THE INVERTEBRATA. 69 likely to mix the food particles with the secretions of the stomach and those poured into it from the ducts of the large digestive gland (‘‘liver”), which surrounds the stomach. The crystalline style is well-developed in Mya, Cytherea, &c. ; but in Ostrea it only exists in a rudimentary state as a piece of cartilage; and in Pholas it is said to have the form of a folded plate. The Lamellibranch stomach leads into a long intestine, which turns downwards and makes many convolutions among the so-called liver and. genital gland, and again comes into the dorsal region, where it traverses the heart, leaving the pericardium at its posterior end, and ultimately terminates in an anus situated behind the posterior adductor muscle. The anus is placed ona projecting papilla. That portion of the intestine from where it enters the heart to the anal aperture is usually called the rectum. In a transverse section, the intestine is horseshoe-shaped, due to the folding in of its dorsal wall, consequently forming a typhlosole. The so-called liver, which is pancreatic in function, consists of numerous branched ceecal follicles. These are united into ducts which open into the stomach by several irregular apertures. There are no salivary glands in the Lamellibranchiata. (2) The Scaphopoda.—In Dentalium the mouth is sur- rounded by many filiform tentacula which play the rdle of prehensile organs. The mouth leads into a buccal chamber containing the odontophore—a prehensile rasp-like tongue. The buccal chamber passes into the cesophagus leading into the stomach. The intestine then follows, and after being coiled several times, terminates in an anus behind the root of the foot. The intestine of the Scaphopoda does not traverse the heart, as in the Lamellibranchiata, for that organ is entirely absent. The so-called liver is bilobed. (3) The Polyplacophora are vermiform Mollusca without eyes or tentacula. In Chiton the shell is unlike that of any other Mollnse. It consists of eight calcified plates arranged 70 PHYSIOLOGY OF THE INVERTEBRATA. in a segmented, imbricated manner one behind the other, The mouth is at one end of the body, and the anus at the other. (4) The Heteropoda.—tThis order, which includes Atlanta, is sometimes immersed in that of the Gasteropoda. It may be remarked in passing that, although the Zamel- libranchiata have no salivary glands, these organs are frequently present in the Odontophora, which include the Scaphopoda, Polyplacophora, Gasteropoda, Pteropoda, and Cephalopoda, (5) The Gasteropoda are subdivided into the Pulmogastero- poda and the Branchiogasteropoda. As an example of the digestive system of the Pulmo- gasteropoda we describe that of Helix (the snail). The alimentary canal, which is much coiled, bends forward to open by an anus in the mantle cavity. The mouth, situated at the base of the head-lobe in front of the foot, is bounded by lips. It leads into a buccal cavity, into which is poured the secretion from two large salivary glands (Fig. 19, A). Then follows the cesophagus, which dilates into a crop or pro ventriculus. The crop leads into the stomach (provided with a blind cecal appendage) passing into a long-coiled intestine embedded in a large many-lobed organ—the so- called liver, which opens by ducts into both the intestine and stomach. ‘The posterior portion of the intestine bends anteriorly and widens into a rectum which opens, by an anal aperture situated on the right side of the body, into the mantle or pallial cavity. The intestine of Helix is folded internally so as to form a typhlosole. The two salivary glands are on each side of the crop, but their ducts open into the buccal cavity. These glands present different degrees of development in different Gasteropods. This is due to the construction of the mouth and the nature of the food. In Heliv and Limasz the salivary glands are well-developed organs; but in Calyptrwa.they are simple tubes. . --- - - A. B. Cc. PHYSIOLOGY OF THE INVERTEBRATA. FIG. 19.—ALIMENTARY CANAL OF HELIX ASPERSA. @=mouth. &=odontophore. c=tooth. d= buccal mass. e = cesophagus. /=salivaryduct. ¢= salivary gland. #4 = rectum.. 2 =crop or proventriculus. = intestine. /= liver. = stomach. Buccal Mass. a = tentacle (optic organ). 4 = tentacle (olfactory organ?). ¢=horny jaw. a@=mouth. e = laterallip. / = cir- cular lip. Longitudinal Section of Buccal Mass. a@ = odontophore. ¢ = ra- dular membrane. c = odontophore cartilage. d@ = intrinsic muscle. 7h 72 PHYSIOLOGY OF THE INVERTEBRATA. The ducts from the large many-lobed “ liver” (pancreas) open into the stomach and anterior portion of the intestine. The secretion of this organ is pancreatic in function. The buccal cavity (Fig. 19, B and C) is furnished with hard masticatory structures. ‘The upper portion is provided with a horny jaw, and on the floor is the odontophore or radula. This odontophore (lingual ribbon) lies over a cartilaginous support (Fig. 19, Cc). Powerful muscles are attached to this support, and by the alternate expansion and contraction of these muscles the odontophore is worked backwards and forwards. By this mechanism the food taken into the mouth is ground down against the horny palate. The odontophore is a chitinous product of the radular membrane (Fig. 19, c), and is armed with tooth-like projections. The projections are constantly being replaced as they are worn away by the friction which ensues during mastication. In the Sranchiogasteropoda (which includes Buccinum, Patella, Cyprewa, &e.) the alimentary canal does not, as a rule, vary very much from that of the Pulmogusteropoda. (6) The Pteropoda are marine Molluscs. The foot, which is small, is provided with two large, muscular, wing-like fins (epipodia).* In Hyalwa the cesophagus dilates into a kind of crop or proventriculus, which is followed by a cylindrical stomach. ‘The intestine is tubular, describes two convolutions in the substance of the liver, and then terminates in an anus situated beneath the right fin. (7) The Cephalopoda.—This order is divided into the Dibranchiata and the Tetrabranchiata ; and the former order is subdivided into the Decapoda and the Octopoda. The Dibranchiata include Sepia, Octopus, Argonauta, &e. Asan example of the digestive system (Fig. 20) we describe that of Sepia officinalis. The mouth, armed with two chitinous jaws which overlap each other, is provided with an * See Cuvier’s Mémoires pour servir a UHistoire et l’ Anatomie des Mollusques. PHYSIOLOGY OF THE INVERTEBRATA. 73 odontophore. It leads into a long cesophagus, which is narrower in the Dibranchiata than in the Tetrubranchiata, and then dilates into the muscular stomach. ‘The pyloric portion of the stomach communicates with a glandular sac—the pyloric cecum. The intestine is bent somewhat upon itself, passing towards the neural (ventral) end of the body and terminating in a median - anus. One or two pairs of salivary glands are present , in the Dibranchiata, which pour the secretion into the buccal cavity or the anterior portion of the cesophagus. The so-called liver is a well- developed bilobed organ provided with two ducts, which in the Decapoda receive the ducts of a large number of cecal appendages. It has been considered that these appendages are the rudiments of a pancreas; ~. but there is no doubt that Petts if the so-called liver per se is yg, 20,—AtimeNTARY CANAL oF essentially pancreatic in SEPIA, function. This organ does a = buccal mass. 6 = salivary glands. not give rise to any of the «= esophagus. d = so-called liver. biliary acids ( lycocholic é = pancreatic follicles (so-called). . 8 y f = stomach. g = pyloric czecum. and taurocholic acids) nor »% = ink-bag. i = intestine. & = anus. glycogen. The colouring matters which the so-called liver contains, do not answer chemically to bilirubin and biliverdin. But its secretion con- tains leucin, tyrosin, and a ferment (or ferments) which con- verts starch into glucose. The ink-bag is a tough, fibrous, glandular sac. It is usually 74 PHYSIOLOGY OF THE INVERTEBRATA. of an oblong pyriform shape, and secretes a brown or black fluid, the colour of which is very durable. The Zetrabranchiata are represented by the only existing genus, Nautilus, which is provided with an external chambered siphunculated shell. Like that of the Sepia, the mouth of the Nautilus is armed with powerful jaws (Fig. 21). It leads into an cesophagus which dilates into a wide crop. The crop passes into the FIG. 21.— ALIMENTARY CANAL OF NAUTILUS. a = buccal mass. 4 = cesophagus. c =crop. d@=stomach. e = “pyloric” cecum. f= intestine. g¢ = anus. # = so-called liver. & = funnel. stomach whose internally chitinous lining is thick and ridged. The ceecum in Nautilus is small, and is attached to the anterior portion of the intestine. The intestine makes two abrupt bends and terminates in the branchial cavity. In Nautilus there are no salivary glands, unless certain small glandular bodies within the buccal cavity possess that function. The so- called liver is a racemose tetra-lobed gland, and its function is, & priori, tat of a pancreas. The Zetrabranchiata have four gills and numerous short PHYSIOLOGY OF THE INVERTEBRATA. 75 retractile tentacula without suckers ; while the Dibranchiata possess two gills and from eight to ten tentacula with suckers round the head. From what has been said, it will be seen that the Mollusca have a very complete digestive system which is comparable, in a great measure, with that of the Vertebrata. In some of the Mollusca we find a long cesophagus and enlarged stomach, an intestine with circumvolutions, and a rectum. In others, we observe the stomach arranged more or less after the plan of certain Vertebrates ; there are cardiac and pyloric portions, separated by a salient fold. ‘‘ Sometimes the stomach is furnished with triturating hooklets of varied form. But it is especially by the development of the glandular appendages that the stomach of the Mollusca is distinguished from that of the animals hierarchically inferior. These organs, in fact, go on perfecting and complicating themselves more and more in the diverse families of Molluscs, and especially in the more advanced of the Molluscs—the Cephalopods (Cuvier)—there are cesophageal salivary glands with short cca, a liver (so-called) developed, compact, divided into lobes, provided each of them with an excretory conduit or duct, and all these conduits or ducts open together or separately at the commencement of the median intestine, or into the stomach.” But this “liver” is essentially pan- creatic in function: the true Vertebrate liver is entirely absent in the Invertebrata. THE PHARYNGOPNEUSTAL SERIES. This series is divided into two orders—the Hemichordata and the Urochordata (Tunicata). (1) The Hemichordata are represented by a single example —Balanoglossus, which is “an elongated, apodal, soft-bodied worm, with the mouth at one end of the body and the anus at the other.” The mouth, surrounded by a well-marked lip, leads into a wide cesophagus which opens into a stomach, 76 PHYSIOLOGY OF THE INVERTEBRATA. From the stomach passes the intestine, which terminates in an anal aperture situated at the posterior end of the body. The mouth is provided with a proboscis. (2) The Urochordata or Tunicata.—As an example of this order we describe Phallusia mentula (Fig. 22). The oral aperture leads into the pharyngeal - respiratory chamber, from which the cesophagus, situated on the posterio-neural side of the body, selects the food particles intro- duced into thatchamber by the action of small tentacula. The walls of the pharyngeal-re- spiratory chamber are gathered into ciliated folds, which have a number of slit-like per- forations. These act as a kind of sieve. On the heemal side of the pharynx there is a FIG. 22.—ALIMENTARY CANAL OF ciliated groove bounded PHALLUSIA. by two glandular folds a= mouth, %=tentacles. c = intestine. (the endostyle). The d@ = stomach, e = heart. / = cesophagus. g =Savigny’s tubules. 2 = anus. & = atrial E aperture. an internal-folded sto- mach. ‘The intestine, which forms a loop, terminates in an anus situated opposite the atrial or cloacal aperture on the neural side of the body. The Savigny tubules lie upon, and open by a duct into, the stomach. These tubules also ramify over the wall of the intestine, and are pancreatic in function. They are present in nearly all the Zunicata.* * See Chandelon in Bull. Acad. Be'g., 1875 ; and Dr. W. A. Herdman in cesophagus leads into PHYSIOLOGY OF THE INVERTEBRATA. OF In Appedicularia there is a caudal appendage which contains a notochord; but in the Ascidians the caudal appendage is only present in the larval condition of the animal—a condition closely resembling the tadpole or larval frog. In fact, these animals are degenerated Vertebrates.* Another point in which the Ascidians approach the Vertebrata is that the pharynx is also a respiratory cavity. We have now come to the end of our chapter on Inverte- brate digestion in general. Below the Actinia the alimentary canal communicates with the body cavity, but with the excep- tion of the 7’nicata,in all those forms higher (than the Actinic) in the animal scale, the body cavity and alimentary canal are entirely separated from each other. In regard to the masticatory apparatuses; (1) a gizzard is observed in the Rotifera, Oligochwta, the higher Insecta, Polyzoa, Gasteropoda, and Cephalopoda. (2) The com- plex masticatory apparatus of Echinus, with its five jaws, each traversed by a tooth, is probably nothing more than altered epithelium which has become hardened. (3) Hardening of the membrane of the buccal mass is a further advance in the apparatus designed for mastica- tion; as these structures are at the commencement of the alimentary canal, and are separated from the stomach. In the Annelida (¢.g., Lumbricus and Hirwdo) the so-called jaws are hardened parts of the epithelium of the mouth. These structures may be functionally compared to the teeth of the Vertebrata. (4) The Arthropoda present a highly developed masticatory apparatus in the jaws, which are appendages of the body segments. ‘‘The simplest condition is met with in the Myriapoda, as the centipede. A small labrum above the oral aperture, a pair of mandibles or hard crushing jaws, a labium below the oral aperture, with side lobes. The Arachnida (spider and scorpion) have labrum and mandibles, the Challenger Reports, 1882, part i. p. 49; 1886, part ii. pp. 22, 52 and 88; part iii. pp. 22 and 42. * See Ray Lankester’s book, Degeneration, p. 41. 78 PHYSIOLOGY OF THE INVERTEBRATA. and two pairs of more delicate jaws—the maxille. These are the side lobes of the labium of the centipede, specialised into distinct lateral jaws. In the Arachnida, the mandibles are extended into prehensile and offensive claws. The maxille in the spider are related in a remarkable manner to the function of reproduction. The specialisation is there- fore incomplete. The Crustacea have a labrum, two mandibles, four maxillee (the second pair representative of the split labium of the Myriapoda), and three pairs of maxillipedes (feet-jaws). These last represent the six legs of the Lnsecta. The somites, which in the latter bear motor organs, carry in the Crustacea organs that serve for mastication, but they are in structure closely allied to the true legs on the suc- ceeding somites.” : In the Jnsecta, the labium, labrum, mandibles and maxillze are all met with; they present numberless and complex modifications, but for all that are chiefly subservient to the functions of taking in or crushing food. (5) The odontophore or radula of the Mollusca forms a still further advance, as it appears to combine the functions of teeth and of a tongue. As far as a stomach is concerned, the first indication of it as a separate organ is observable in some of the Echinodermata, e.g., in the Asteridea, but the specialisation of the organ is in- complete, inasmuch as it forms a dual function, viz., that of a renal organ as well as being a gastric cavity. There is a true stomach (a dilatation of the alimentary canal) in the Annelida, Arthropoda, Polyzoa, Brachiopoda, and Mollusca. The crop present in the Jnsecta is simply a cavity which serves to store the food before passing into the stomach. 'The intestine is straight, and without conyolutions in many forms—as, for example, in the Asteridea, Myriapoda, Arthrogastra, &e—but also in many of the JJollusca there is a bend or flexure in the intestine. CHAPTER IV, DIGESTION IN THE INVERTEBRATA. Digestion in Particular, In the present chapter we describe in detail the physiology of the digestive function in certain selected types of all the more important branches of the Jnvertebrata. THE PROTOZOA. The Protozoa having no differentiated parts, the cell itself performs, among other functions, that of digestion. This function is diffuse in the lower animals, and only becomes specialised or differentiated as we ascend in the zodlogical scale, ) THE PORIFERA AND C@LENTERATA. Among the animals with cellular differentiation—the Porifera and the Celenterata—the internal cavity of the body (morphologically identical with the alimentary canal, and not with the somatic or body cavity of other animals) has the function of a digestive cavity. Concerning the function of digestion in Hydra fusca, Dr. Greenwood* has recently come to the following con- clusions: (#) the ingestion of solids is performed by slow advance over the prey of lip-like projections of the animal’s substance. Hntomostracea, Nais, beetle larvee, and raw meat prove the most acceptable food; innutritious matter does not act as a stimulus to digestion. (2) The digestion of * Journal of Physiolegy, vol. 9, 317. 80 PHYSIOLOGY OF THE INVERTEBRATA. enclosed food particles takes place entirely outside the endo- dermic cells which line the enteric cavity, and among these may be distinguished: (1) pyriform cells destitute of large vacuoles holding secretory spherules during hunger, and these empty during digestive activity ; (2) ciliated vacuolate cells, often pigmented: the water of the digestive fluid is probably derived from the vacuoles. (c) The pigment occurs as brown or black grains; it has an albuminoid basis. The pigment resists solution in most chemical reagents, but dissolves slowly in nitric acid. (d) A reserve substance of al albuminoid nature accumulates during digestion in the basal part of the vacuolated cells, and eventually takes the form of spheres. The excretory pigment probably takes its rise in some residue from this absorbed substance ; it is also possible that fat is similarly formed. (¢) The medium in which digestive activity goes on is probably not acid. In Hydra viridis, which contains chlorophyll,* the mode of nutrition appears to be different from that just described. Gland cells do not form a conspicuous feature in the endo- derm of Hydra viridis, and consequently digestive secretion is less active. If the vacuolated cells of the endoderm of Hydra fusca contain a nutritive fluid we may reason, @ priori, that the food vacuoles of the Protozoa probably contain a digestive fluid; at any rate the food particles nearest to these vacuoles are always becoming smaller in size, showing that digestion is proceeding. In Hydra viridis chlorophyll has probably a secretory as well as a respiratory function. The same remark applies to the chlorophyllogenous Protozoa. “ Professor Huxley first showed the presence of ‘ yellow cells” in Zhalassicolla, which have also been found in almost all Radiolarians. These bodies Haéckelt considered as secreting cells or digestive glands, comparable to the liver cells of Amphioxus, and those * The chloroplastids of Prof. E. Ray Lankester, ¥.R.S. + Die Radiolarien, p. 136. PHYSIOLOGY OF THE INVERTEBRATA. 81 of Velella and Porpita, as described by Voigt. Subsequently Haéckel found starch in these cells, and concluded that this fact supported the idea of the nutritional function previously assigned to them by himself.* ‘“* Cienkowskif in 1871 endeavoured to show that the yellow cells of Radiolarians were parasitic algee, since they survived the death of their host, and multiplied subsequently, passing through an amceboid and encysted state.” There is no doubt that the ‘yellow cells” do survive for some time in the bodies of dead Radiolarians; but in regard to Hydra and Spongilla, Prof. E. Ray Lankester{ has shown that ‘‘the chlorophyll corpuscles of these animals are not alge at all (as stated by Dr. Brandt§), but differ in no essential respect from the chlorophyll bodies of plants.” Dr. C. A. MacMunn|| has shown that “the chlorophyll bodies of Spongilla, Hydra, Paramecium, Ophrydium, Vortex viridis, and Stentor polymorphus are of different size, colour, and give different reactions, and a different spectrum, from the ‘yellow cells’ of Actiniw. With regard to size, the ‘yellow cells’ of Anthea cereus were found to measure I2u {= 12x yz¢o7 mm.), or 134 down to 10u; while in Para- mecium they measured from 64 down to 3u—tc., less than half the size of the former; in Hydra viridis mostly from 6u to 4u. The colour is a dull brownish-yellow in the ‘yellow cells’ of Anthea, &c.; while it is a fine green in the Infusoria and Hydra. The spectrum in Spongilla, in Hydra, and in the Jnfusoria is that of plant chlorophyll; while in the ‘ yellow cells’ it is that of chlorofucin.” The chief function of animal chlorophyll and allied pig- ments is that of respiration; but it is probable that these pigments play an important part in sexual selection, in * Jena Zeitsch. 1870, p. 532. 4 + Archiv. Mikro. Anat. 1871. t Quarterly Journal of Microscopical Science, vol. 22, p. 229. § Monatsh. Akad. Wiss. Berlin, 1881. || Proceedings of Birmingham Philosophical Society, vol. 5, pt. 1, p- 212. F 82 PHYSIOLOGY OF THE ANVERTESRATA. mimicry, or act as “screens” for the protection of under- lying cells, for protective purposes; and possibly, though not probably, they may have a nutritional function, as sug- gested by Haéckel. Whatever may be the true function or functions of animal chlorophyll, one thing is certain—that the pigment is manufactured in the body of the animal con- taining it. In the words of Dr. MacMunn: “I would ask investigators to pause before they decide that when an animal chlorophyll is met with, it has been simply eaten by the animal, and deposited unchanged in its tissues; they must remember that the radicle of chlorophyll, like the radicles of other pigments, may be furnished by the action of the diges-- tive juices of the animal on some substance furnished by the plant, and that the animal laboratory is capable of building’ up molecules quite as large as that of chlorophyll. Our own hemoglobin is not the unchanged hemoglobin of our food ;. what is derived from it is broken up and then regenerated ;. and it shows an ignorance of physiology to suppose that chlorophyll should be an exception toa general rule.” Reverting once more to the Porifera, Dr. Léon Fredericq* has extracted from a large number of sponges a ferment analogous to trypsin or pancreatin. This ferment acts upon starch, fats, and albuminoids. The author of the present work fully confirms Fredericq’s researches. The ferment contained in and manufactured by the cells of the Porifera converts starch into glucose. It forms an emulsion with neutral fats, and finally decomposes them into fatty acids. and glycerol (glycerine). The ferment also converts albumi- noids into peptones, which become partially converted into leucin and tyrosin. ‘There is no doubt that the cells of the Porifera secrete a ferment in every way analogous to the pancreatic ferment of higher forms. THE ECHINODERMATA. Fredericq has also obtained similar results with many * Archives de Zoologie Expérimentale, tome 7, p. 400. PHYSIOLOGY OF THE INVERTEBRATA. 83 species of the Actiniw, only the digestive ferment secreted by the cells of these animals does not appear to have the same degree of activity as that extracted from the Porifera. Its action is much slower. The digestive apparatus of Uvraster rubens (one of the Asteridea) has been examined by the author. The walls and contents of the wide sacculated stomach, and its five sacs do not contain digestive ferments; for the digestive fluid is Fic. 23.—STOMACH AND PyLoRIC C@:cA OF URASTER. derived from the pyloric ceca situated in each ray. The pyloric sac, or stomach, gives off five radial ducts, each of which divides into two tubules (Fig. 23) bearing a number of lateral follicles, whose secretions are poured into pyloric sac and intestine.* The secretion (of the ceca) was obtained from a large number of star-fishes, and gave the following reactions :— * Proceedings of Royal Society of Edinburgh, vol. 15, p. 111; and Pro- ceedings of Royal Society of London, vol. 44, p. 325. 84 PHYSIOLOGY OF THE /NVERTEBRATA. (a) The secretion forms an emulsion with oils yielding subsequently fatty acids and glycerol. (b) The secretion decomposes stearin, with the formation of stearic acid and glycerol— C,,H,,,0, + 3 H,O = 3 0,,H;,0, + C,H,0,. (c) The secretion acts upon starch paste with the formation of dextrose. The presence of dextrose was proved by the formation of brownish-red cuprous oxide, with Fehling’s solution. (d) The secretion dissolves coagulated albumin (hard white of egg). (e) Tannic acid gives a white precipitate with the secretion. (7) When a few drops of the secretion of the pyloric ceca are examined chemico-microscopically, the following re- actions are observed :—On running in, betiveen the slide and cover-glass, a solution of iodine in potassium iodide, a brown deposit is obtained; and on running in concentrated nitric acid upon another slide containing the secretion, yellow xanthoproteic acid is readily formed. These reactions show the presence of albumin in the secretion of the organ in question. (q) The presence of albumin in the secretion was further confirmed by the excellent tests of Dr. R. Palm.* (i) The soluble enzyme or ferment secreted by the cells of the pyloric ceeca was extracted by the Wittich-Kistiakowsky method.t The isolated ferment converted fibrin (from the muscles of a young mouse) into leucin and tyrosin. (7) The albumins in the secretion are not converted into taurocholic and glycocholic acids ; for not the slightest traces of these biliary acids could be detected by the Pettenkofer and other tests. (j) No glycogen was found in the organ (1.¢., the caeca) or its secretion. From these investigations, which have been repeated on * Zeitschrift fiir Analytische Chemie, vol. 24, pt. I. + Pfliger’s Archiv fiir Physiologie, vol. 9, pp. 438-459. PHYSIOLOGY OF THE INVERTEBRATA. 85 other genera besides Uvaster, the pyloric ceeca or diverticula of the Asteridea are proved to be pancreatic in function. Dr. L. Fredericq (the distinguished Professor of Physiology in the University of Liége) has obtained similar results, but by an entirely different method. Fredericq obtains various aqueous extracts (neutral, alkaline, and acid) of the ceca previously hardened in alcohol. These extracts each contain the digestive ferments. They digest cooked and raw fibrin exceedingly well in alkaline extracts. This action is less active in neutral extracts, and is almost 7/ in acid extracts. The pyloric czeca of the Asteridea are consequently diges- tive organs—their function being similar to that of the pan- creas of the Vertebrata. Dr. MacMunn* has shown that these pyloric ceca “con- tain a large quantity of enterochlorophyll, mostly dissolved in oil, which may possibly act in supplying oxygen to the tissues of the animal, perhaps from the waste carbon di- oxide.” If this be correct, the pyloric ceca perform a dual function—that ofa digestive and a respiratory organ. It may be stated that the stomach or pyloric sac of Uraster rubens is a digestive cavity and a renal organt—i.c., it has a dual function. Darwin states, in The Origin of Species (chap. vi.), that ‘numerous cases could be given among the lower animals of the same organ performing at the same time wholly distinct functions ; thus, in the larva of the dragon- fly and in the fish—Cobites—the alimentary canal respires, digests, and excretes.” THE TRICHOSCOLICES. Dr. Fredericq has investigated the nature of digestion in Tenia serrate (one of the Cestoidea), which inhabits the small intestine of the dog. His experiments were conducted in the following manner :—Three tape-worms, killed by chloro- * Proc. Birmingham Philosop. Soc. vol. 5, pt. i. p. 214. + See Dr. A. B. Griffiths’ paper in Proceedings of Royal Society of London, vol. 44, p. 326. 86 PHYSIOLOGY OF THE INVERTEBRATA. form, were washed in water, and then cleaned by means of a brush. They were cut into small pieces and left to harden, for twenty-four hours, in a large quantity of absolute alcohol. Aqueous extracts (neutral, alkaline, and acid) were made of the hardened pieces; but each extract was found to be com- pletely inactive as a digestive fluid. Fibrin remained intact in them during many days. These extracts had a milky appearance, due to an intense fluorescence, which immediately suggested the presence of glycogen. A solution of iodine (in water) converted these ex- tracts into brown-coloured liquids. They formed a precipitate in the presence of alcohol, which was dissolved by copper sul- phate and potash. Finally, the addition of saliva caused the opalescence to disappear, and at the same time the liquid became rich in glucose, as proved by Fehling’s solution. It must be dis- tinctly understood that this glycogen is not present in the internal fluids of the tape-worm’s body, but is present in the integument of that animal. Glycogen is also present in the integument of the Nematoidea. It is seen from these investigations that the Cestoidea, and possibly the Zvematoda as well, do not contain any traces of digestive ferments, either pepsin, trypsin, or diastatic ferment. The juices of the small intestine in which Tenia serrata lives are, nevertheless, rich in ferments; but: these ferments, having little diffusive power, do not pass the barrier which the external skin of these Hntozoa offers them. This was proved in the following manner :—Some Ascares marginate (belonging to the Nematoidea), obtained from the small in- testine of a dog, were placed, some intact and others cut into pieces, into an artificial pancreatic juice.* Those which were left intact remained in the juice without apparent change; but those cut into pieces were almost completely * The aqueous extract of a dog’s pancreas which had been hardened in alcohol. PHYSIOLOGY OF THE INVERTEBRATA. 87 digested or dissolved—only leaving the horny integument (hyalin). This integument did not appear to be formed of chitin, for it was rapidly attacked by a boiling solution of potash. THE ANNELIDA. (a) The Hirudinea. For this purpose Fredericq cut into pieces twelve horse-leeches (Hamophsis vorax), and from these pieces he prepared two extracts, one acid and the other alka- line. Fibrin was digested (in twelve hours) in the alkaline extract, but was unaltered in the acid extract. The author of the present volume has obtained similar results with Hirudo medicinalis. Digestion, therefore, in the Hirudinea is somewhat similar to the pancreatic digestion in the Vertebrata. (b) The Oligocheta. In this order, represented by Lumbricus terrestris, the digestive system (Fig. 24) is more highly de- FIG. 24.—DIAGRAM OF ANTERIOR PORTION OF ALIMENTARY CANAL Or LUMBRICUS. @=mouth. 4 = salivary glands (?). c¢ = cesophagus. d= pharynx. e = calciferous glands. f= crop. g¢ = gizzard. h = intestine. veloped than in any other animal already alluded to in the present chapter. If the head or anterior portion of Lwmbricus (as far as the sixth segment) is severed from the body, and that part of the alimentary canal which it contains is dissected out of the head, and is placed on starch, it will be converted into glucose, but it has no action on fibrin. From this there is no doubt that the saliva is poured into the pharynx. This secretion bathes the food (which is of a mixed nature) during its passage through the cesophagus. Attached to 88 PHYSIOLOGY OF THE INVERTEBRATA. the sides of the posterior end of the cesophagus are three pairs of calciferous glands. These glands secrete a sub- stance extremely rich in calcium carbonate. The function of these glands in secreting calcium carbonate is to neutralise the vegetable acids of the food, for the digestive fluid of Lumbricus is inactive unless alkaline. The food and fluids in the crop of the earthworm are always alkaline. In the crop the food matter is stored before it passes into the gizzard, whose powerful muscular walls and thick chitinous lining crush any food-stuffs that require mastication or grinding. The posterior portion of the gizzard has thinner walls, and leads into the long glandular intestine, which is lined with columnar cells. The intestine is almost enveloped in a yellowish glandular tissue—the so-called liver. This organ is essentially pancreatic in function.* There is no doubt that the principal digestive fluid of worms is of the same nature as the pancreatic juice of the Vertebrata. Dr. Léon Fredericg (Archives de Zoologie Kxpéri- mentale, vol. vil. p. 394) proved this in the following manner :— A large quantity of worms, chopped into small pieces, are treated with strong alcohol. The alcohol is left to act for many hours; and then decanted. The alcoholic extract is used in the examination for biliary acids. The insoluble residue is pressed between several folds of filter paper, dried in air, and finally pulverised in a mortar. The pulverised residue is divided into several parts, the object being to prepare several aqueous extracts (neutral, alkaline, and acid), The dilute acid solutions used in preparing the acid extracts are made from hydrochloric acid and water (the degrees of concentration being from six to twelve cc. of HCl per litre of water). The divided residue (previously alluded to) is allowed to macerate in the fluids for twenty-four hours ; and then filtered. The filtered liquids are placed in separate test-tubes in each of which a small piece of fibrin has been * Dr. A. B. Griffiths’ paper in Proc. Roy. Soc. Edinb., vol. 14, p. 237- PHYSIOLOGY OF THE INVERTEBRATA. 89 suspended. ‘The test-tubes are then placed in an incubator* heated to about 40° C. At the end of an hour or s80, the fibrin which is in the alkaline extract has almost en- tirely disappeared ; leaving only a small quantity of finely divided detritus. This liquid contains peptones. The neutral extract acts in a similar manner, except that the fibrin is dissolved a little more slowly ; it takes from five to six hours to complete the digestion. This liquid also contains peptones. The most concentrated acid extract has no action on the fibrin, which swells, but remains intact during many days. On the other hand, the fibrin is dissolved more or less completely in the dilute acid extracts, but to do this it requires from thirty-six to forty-eight hours. The ferment in which Zumbricus dissolves the fibrin acts well in a neutral solution, better in an alkaline solution, and badly or not at all in an acid solution; these properties entirely resemble those of trypsin or the pancreatic ferment. The neutral extract converts starch into glucose. The aqueous extract, therefore, contained a substance or ferment which acts in a similar manner to diastase. Fredericq having dissected a large earthworm (under water), removed the whole of the alimentary canal, and obtained from the intestine a fluid which is slightly alkaline and readily digests fibrin. This alkaline fluid is secreted by the glandular tissue which almost covers the intestine. The organ has been termed a “liver,” whereas it is a true pancreas. The names “bile” and “liver” have been employed at random by a great number of those who have investigated the anatomy of the Invertebrata. Nevertheless the principal characteristics of the bile (pigments and biliary acids) have never been discovered with exactitude in any animals lower than the cranial Vertebrates. There is nothing in this fact which ought to surprise us, because it is * Like the incubators used in bacteriological laboratories. See Griffiths’ Researches on Micro-Organisms, p. 17. go -PHYSIOLOGY OF THE INVERTEBRATA. established that the colouring matters of the bile are derived from one of the products of the decomposition of hemoglobin (probably of heemochromogen), a substance which is not found, except very rarely in the Invertebrata. The earthworm is one of these animals rich in hemoglobin, consequently one would suppose that liver pigments and biliary acids would be present in this Invertebrate animal. The alcoholic filtrate from the macerated worms (already referred to) would contain (if present) these pigments and acids. This filtrate is very rapidly discoloured on exposure to daylight, but, besides the colouring matter which is sensitive to light, it often contains traces of chlorophyll (from food). The alcoholic filtrate is evaporated to dryness on a water bath, and the residue treated with ether. The ethereal solution is reserved for future examination, while the insoluble residue (in ether) is dissolved in a small quantity of water. The filtered aqueous solution is now used in testing for biliary acids by the Pettenkofer test; but not the slightest trace of these acids is detected in Lumbricus. The reaction of Gmelin and Tiedemann, employed in detecting the presence of biliary pigments, was applied without success to the fresh juices and organs of Lumbricus ; also to the alcoholic extracts (from which the alcohol had been evapo- rated). The ethereal extract previously obtained was found to contain cholestrine and fatty globules. In addition to the pancreatic ferment, the author has detected indol (C,H,N) as well as leucin and tyrosin in the fresh juices and organs obtained from about 4 lbs. of earthworms. This is an additional proof of the pancreatic nature of the digestive fluid of Lumbricus. Although biliary pigments are entirely absent in the Oligocheta, other pigments are present. Most likely the pancreatic tissues, which almost envelop the intestine of Lumbricus, contain enterochlorophyll. PHYSIOLOGY OF THE INVERTEBRATA. 91 In the words of Dr. MacMunn (loc. cit., p. 189), “the radicle indol is furnished by the action of pancreatic ferments upon food proteids ; and as the so-called liver of Invertebrates is really a pancreas in at least some of its functions, possibly some such radicle may be changed by a ferment furnished by the ‘liver’ into enterochlorophyll.” Not only is the digestive fluid of Zwmbricus capable of acting upon starch (as already stated), but it readily attacks cellulose ; this fact agrees perfectly with the kind of food- stuffs which the earthworm consumes. (c) The Polycheta.—In Nereis, a pair of salivary glands are appended to the base of the proboscis. The secretion obtained from a large number of these glands readily con- verted starch into dextrose. Concerning the digestive fluid of Nereis pelagica (a marine species), Dr. L. Fredericq performed the following experi- ments :—Sixty of these worms, which had been preserved in alcohol for six months, were dried and pulverised. From the pulverised mass the various aqueous extracts (neutral, alkaline, and acid) were prepared. Fibrin was dissolved after a few minutes in the alkaline extract; at the end of a little longer time in the neutral extract; but remained intact for many days in the acid extract. The liquid resulting from the digestion gave distinctly the reactions of peptones with copper sulphate and potash. The same experiments repeated with fresh specimens of Nereis gave the same results. The digestive power of the alkaline extract is considerable; for it can digest, in less than two hours, a quantity of fibrin equal to the weight of the worms employed in making the extract. THE INSECTA AND ARACHNIDA. We now proceed to the Insecta and Arachnida, and, as examples of these two classes, we describe in detail the 92 PHYSIOLOGY OF THE INVERTEBRATA. physiology of the alimentary canal in the Orthoptera, Lepi- doptera, Hymenoptera, and the Araneina. (a) The Orthoptera.—The alimentary canal of Blatia (the cockroach) is very highly developed. The salivary glands (Fig. 25, a and b) of the cockroach are situated on each side of the cesophagus and crop, and extend posteriorly as far as the abdomen. They are about one-third of an inch in length, and composed of acini (Fig. 25, )). Accompanying the glands are two salivary receptacles, one on either side of Salivary gland. Salivary receptacle. Pe ain CT nh { A - 2 a _ Chitinous trach- b Kool ar cinus eal ducts of the ty (3 Nuclei glands. eRe a ; ny Salivary gland (under high power). Opening. FIG. 25.—(@ and 4) SALIVARY GLAND OF BLATTA. the crop. A quantity of the secretion* was extracted by crushing about sixty glands of cockroaches, which had been recently killed. The secretion was alkaline to test-papers. A portion of the secretion was added to a small quantity of starch, which was converted into glucose in twelve minutes. * Griffiths, in Proc. Roy. Soc, Edinb., vol. 14, p. 234; and Chemical News, vol. 52, p. 195. PHYSIOLOGY OF THE INVERTEBRATA. 93 The presence of glucose was proved by the formation of red cuprous oxide by the action of Fehling’s solution. Another portion of the secretion was distilled in a minia- ‘ture retort (made of glass tubing) with dilute sulphuric acid. To the distillate ferric chloride was added, which produced a red colour, indicating the presence of sulphocyanates. The secretion of these glands yields a small quantity of -ash, which contains calcium phosphate. _ The soluble ferment of this secretion may be isolated by precipitating an infusion of the glands obtained from a large ‘number of these insects with dilute phosphoric acid, adding ‘lime-water, and filtering. The precipitate is then dissolved ‘in distilled water, and re-precipitated by alcohol. This ‘precipitate converts starch into glucose, but has no action (on fibrin; in other words, it has a similar action to ptyalin -—the ferment of the saliva of the higher animals. It is ‘probable that in Blatta there are terminations of the nerves ‘In these salivary glands. It may be that these nerve- ‘endings affect the protoplasmic substance of the cells forming ithe ferment, which has the property of converting starch into _ glucose. The crop of Blatta simply acts as a receptacle to store up ‘the rapidly swallowed food until time is afforded for the food ‘to be passed on to the true stomach. The gizzard or proventriculus has been described in the ‘last chapter. It is considered by some to be an internal ‘masticatory apparatus, but M. Plateau* considers that the ‘proventriculus of Blatta acts simply as a strainer. The chylific ventriculus may be termed the true stomach (of Llatta, for it is probable that digestion is more active in ‘this than in any other part of the alimentary canal. It is \lined with epithelium, and often contains peptones. The pyloric czeca, situated in front of the chylific ventri- * See his papers on the digestion in the JMyriapoda, Insecta, and Arachnida, published in the Bulletin de, ? Académie Royale des Sciences de Be'gique, 1874-78. 94 PHYSIOLOGY OF THE INVERTEBRATA. culus, have been directly proved by the author* to be pancreatic in function. The secretion from these ceca flows into the chylific ventriculus, where digestion proceeds. | . 3 a} — CS oO E Oy ° cc ~ Cc uw a I II Ss LS ; awe Nae 6 & no sd re rs] et x € 1s 's oe : Ros - OU so a ee r= Bs thon ei e il ees AS hag ig = am e.g & f 45 95 ce, Cries es hy E oO 3 ed eee Selecta | a 4 age gs” BS aa un Co et oy = || ese Tk 2 oe ee Oo z me E So fs Shs e ‘o. | & mS 3 Bs Pa Z = J “ an 58 | & tp 2 AS pe a oF sss Sey el Sy) Q il a> 2 : 3 s 3 Ge q 5 a As < a] In the carnivorous Libellula (the dragon-fly) there is no crop or gizzard, only the chylific ventriculus is present ; the * Griffiths, in Proc. Roy. Soc. Edinb., vol. 14, p. 237. PHYSIOLOGY OF THE INVERTEBRATA. 95 fluids within this organ are always slightly alkaline, and an infusion of about twenty of these organs readily converted starch into glucose, and digested fibrin. (b) The Lepidoptera —As an example of this important order we describe the physiology of the alimentary canal of the larva and imago of Pontia brassicw (the large white cabbage butterfly). The alimentary canal of the larva (Fig. 26, 4) agrees closely with the general Lepidopterous type. The mouth opens into a pharynx lined by a dark, firm cuticula, and into the latter open two ducts from a pair of well-developed salivary glands. These glands form elongated tubes, gra- dually diminishing in diameter towards the posterior ends. The cesophagus is very narrow and short. It leads into a long chylific stomach, which opens into a short duct. Behind the stomach the intestine consists of four parts: first, a short, constricted piece; second, a dilated, oval division; third, the short rectum ; and fourth, the anal tube. The stomach has an epithelium lining, which is thrown up into folds so as to form imperfectly differentiated glandular follicles. At the posterior end of the stomach are the Malpighian tubules. Fig. 26, B, represents the alimentary canal of the imago of Pontia. The pharynx passes into a narrow, but long, ceso- phagus leading to the crop or food receptacle. This crop is entirely absent in the larval, but is developed in the pupal stage. The stomach is much smaller than in the larva, but its lining is also thrown up into glandular follicles. The posterior end of the stomach leads into a long and peculiarly coiled small intestine. The intestine passes into the wide terminal division, the rectum, from the front end of which there is a curved blind czecum or pouch. In the imago of Pontia there are also a pair of well- developed salivary glands. The secretion of the salivary glands is alkaline to test- papers, and readily converts starch into glucose. It has, 96 PHYSIOLOGY.OF THE INVERTEBRATAY however, no action on fibrin. It contains sulphocyanates, proved by the red colour produced by ferric chloride with a drop of the secretion. The stomach of both the larva and imago contains glandular follicles. These secrete a digestive fluid, which answers in every way to that of a Vertebrate pancreas. The Malpighian tubules are well-developed in the imago, as well as in the larva of Pontia. Their function is that of a renal organ, but this subject will be considered in detail in our chapter on excretion. It may be stated in passing, that according to Dr. B. T. Lowne, F.L.S.,* the Malpighian tubules of Calliphora erythrocephala (the blow-fly) are “hepatic” in function. If by hepatic he means that these tubules have the function of a Vertebrate liver, his conclusions are erroneous, for neither biliary acids nor glycogen are present in these tubules. Again, if Dr. Lowne means by “ hepatic ” that they have a pancreatic function, this is also erroneous, because these tubules do not yield any digestive ferment or ferments. On the other hand, the Malpighian tubules of the Diptera, including Calliphora, readily yield uric acid; and there is little doubt that they are physiologically the kidneys of the animal; although, concerning their place of develop- ment from the alimentary canal, as well as from other considerations, they are the homologues of hepatic organs (liver). (c) The Hymenoptera.—The structure of the alimentary canal of Apis (the bee) has already been given. The long stomach is furnished internally with small glandular follicles, and by making an alkaline extract of the stomachs obtained from a large number of bees (which had been kept for some time without food), the extract contained a ferment which hydrolyzes starch, and digests fibrin, although feebly. In fact, it answers to the characteristic tests of trypsin or pancreatin. An alcoholic extract of the bee’s stomach does * The Anatomy, Physiology, Morphology, and Development of the Blow-jly (1890). PHYSIOLOGY OF THE INVERTEBRATA. 97 not contain the smallest trace of biliary acids, pigments, or glycogen. Dr. A. yon Planta* has recently investigated the juice, or the sticky substance, which the working bees store in the cells of the larvae of the queens, drones, and workers. Leuckart? regarded it as the product of the true stomach (see Fig. 8c) of the working bees, which they vomit into the cells in the same way that honey is vomited from the honey-bag (see Fig. 8). Fisher and others regarded it as the product of the salivary glands of the bees. Schénfeld has more recently shown that Leuckart’s original view is the correct one. He showed that the saliva can be easily obtained from the salivary glands of the head and thorax, and that it is very different from the food-juice deposited in the cells by the bees; and that, moreover, the juice is similar, both chemically and microscopically, to the contents of the bee’s true stomach; he showed also, from the consideration of certain anatomical and physiological pecu- liarities of the bee, such as the position of the mouth, the inability of the bee to spit, &c., that the view of this substance being saliva is quite untenable. Certain observers have to this replied, that a bee cannot vomit the contents of its true stomach, because of a valve which intervenes between it and the honey-stomach or bag (see Fig. 87); but Schénfeld has shown that the structure, mistaken for a valve, has not the function of one, but is in reality an internal mouth, over which the animal has voluntary control, and by means of which it is able to eat and drink the contents of the honey- stomach when necessity or inclination arises. By lght pressure on the stomach, and stretching out the animal’s neck, the contents of the stomach can be easily pressed out. Dr. A. yon Planta’s investigations entirely confirm Schén- feld’s view, that the food-juice comes from the bee’s true stomach. The subject was investigated from the point of * Zeitschrift Physiol. Chemie, vol. 12, p. 327. + Deutsche Bienenzeitung, 1854-5. 98 PHYSIOLOGY OF THE INVERTEBRATA. view of its chemical composition, and care, also, was taken to investigate, individually, the juice as occurring in the cells of three varieties of bees—queens, drones, and workers. Some preliminary microscopical examinations of this sub- stance yielded the following results, which are quite in accord with the subsequent chemical analyses :— (1) The food of the queen-bee larvee is the same during the whole of the larval period; it is free from pollen grains, which have been reduced to a thickish but homogeneous juice by the digestive action of the bee’s stomach. (2) The food of the larval drones is also, during the first four days of the larval period, free from pollen, and appears to have been completely digested previously. After four days their food is rich in pollen grains, which have, however, under- gone a certain amount of digestion. The food-stuff of the larvee is probably formed from bee-bread. The following table gives the average percentages obtained from several analyses :— Food-stuff of— | rt Female or Drones or Neuters or Queen Bees. Males. Working-Bees. : -| den Water. - : : : 69.38 % 7257 5p 75 Ny o7tsO3 074 | Potalgolids 5 «i . N yaa62.,3 o7.28%, | 28 can | : | Nitrogenous matter | 45.14,, 43: 70in5 | Yieta,. | ; | In the | Fat. ; : 20 lS San, 8.325 | 6:84, | Solids |Glucose . : : 20530). 24.03 ,, 27.0505 | Ash. : : ; 4.06 ,, 2O2h a — All these food-stuffs are rich in nitrogen; all were of a greyish white colour; and that of the queen-bee was the stickiest, while that of the working-bees was the most fluid. The greater part of the nitrogenous matter of the food was proteid. The sugar present was always invert-sugar, whereas the sugar in pollen grains is invariably sucrose. ae ieee PHYSIOLOGY OF THE INVERTEBRATA. 99 The preceding table shows certain differences in the compo- sition of the different kinds of larval food, more especially in the composition of the solids present. Its composition is, moreover, quite different from that of the bee’s saliva, which contains no sugar. The difference between the proportional amount of the different solids present in the different forms of larval food is a constant one, and no doubt this variation has in view the particular requirements of the larve in question. Certain small but constant differences were also observed in the chemical composition of the food of the larval drones during the first four days and at subsequent periods. Not only is there a difference in the quality, but there is also one in the quantity of the food supplied. The juice from 100 queen-bee cells yielded 3.6028 grammes of dry matter, that from 100 drones’ cells 0.2612 gramme, and that from 100 workers’ cells, 0.0474 gramme. (7) The Araneina.—As the spider’s web has indirectly to do with digestion a few remarks on the subject may not be out of place. There is no doubt that “one of the most characteristic organs of the Avaneina is the arachnidium, or apparatus by which the fine silky threads which constitute the web are produced. H. Meckel,* who has fully described this apparatus as it occurs in Lpeira diadema, states that, in the adult, more than a thousand glands, with separate excretory ducts, secrete the viscid material, which, when exposed to the air, hardens into silk. These glands are divisible into five different kinds, and their ducts ultimately enter the six prominent arachnidial mammille, which, in this species, project from the hinder end of the abdomen. Their terminal faces are truncated, forming an area beset with the minute arachnidial papilla by which the secretion of the glands is poured out.” The secretion of these glands is insoluble in water, and has a nitrogenous basis. Web-spinning has several objects in * Miiller’s Archiv, 1846. 100 PHYSIOLOGY OF THE INVERTEBRATA. view: (1) itis a means by which the spider obtains a livelihood ; (2) it is subservient to propagation of the species *—the silk being used as a cocoon for the reception of eggs, a nest for the young, as well as forming aéronautic gossamer lines for the dispersion of the young brood on the approach of maturity; (3) in the genus Hydrachna (belonging to the Acarina) it serves to attach the moulting individual to an aquatic plant by the anterior part of the. body, when it struggles to withdraw itself from its exuvium; (4) it forms a home for the spider. The secretion of the salivary glands of Tegenaria donvestica (the common house-spider) contains a diastatic ferment and sulphocyanates. These were proved by the tests previously given. The so-called “liver ducts” of Tegenaria domestica have been investigated by Mr. A. Johnstone, F.G.S.,f and the author,{ with the following results :— When examined microscopically these ducts are seen to consist of cellular tissue; and the secretion is poured into the intestine. The secretion obtained from a large number of animals, as well as an extract made of the intestines of a very large number of spiders, gave the following reactions :— (1) The secretion and extract form emulsions with neutral oils, yielding subsequently fatty acids and glycerol. (2) The secretion and extract decompose stearin with the formation of stearic acid and glycerol :-— C,,H,,,0; +.3H,0°=' 36,0, =) CFEO.. (3) The secretion and extract act upon starch paste with the formation of dextrose. The presence of dextrose was proved by the formation of red cuprous oxide with Fehling’s solution. (4) The secretion and extract dissolve coagulated albumin with the formation of peptones, which are readily recognised * See Dr. H. C. McCook’s American Spiders and their Spinning Work. + Demonstrator in Geology in the University of Edinburgh. + Proceedings of Royal Society of Edinburgh, vol. 15, p. 113. PHYSIOLOGY OF THE INVERTEBRATA. 101 by the rose colour produced in the cold by potash and copper sulphate. (5) Tannic acid produces a white precipitate with the sec- retion. (6) When a few drops of the secretion of these ducts were examined chemico-microscopically, the following reactions were observed: on running in a solution of iodine (in potas- sium iodide) between the slide and cover-glass, a brown de- posit was obtained; and on running in concentrated nitric acid, on another slide containing the secretion, yellow xantho- proteic acid was formed. ‘These reactions prove the presence of albumin in the secretion of the organ in question. The presence of albumin was further confirmed by the tests of Palm.* (7) The soluble ferment, or enzyme, secreted by the cellular tubes was extracted, although with some difficulty, by the Wittich-Kistiakowsky method. This ferment converts fibrin into leucin and tyrosin, (8) The albumins in the secretion and extract are not converted into taurocholic or glycocholic acids, for not the slightest traces of these biliary acids could be detected by the Pettenkofer and other tests. (9) The secretion contains approximately four per cent. of solids. The slight residue (solids), which contains some com- bination of sodium, effervesced on the addition of dilute acid. (10) No glycogen was found in the secretion or extract. From these investigations, which have been repeated on several occasions, the so-called liver of the Araneina is proved to have a similar function to the pancreas of the Vertebrata. THE CRUSTACEA. (1) The Brachyura.—as a type of this order, the alimentary canal of Carcinus menus will be considered in detail. This animal is a voracious feeder; its food consists of * Zeitschrift fiir Analytische Chemie, vol. 24, pt. i. 102 PHYSIOLOGY OF THE INVERTEBRATA. animal and vegetable substances. These contain albuminoids, fatty and starchy matters, and earthy salts. The foodis torn to pieces by means of the chele. The wide and short ceso- phagus leads into a large globular stomach containing chi- tinous teeth, the object of these teeth being to sub-divide the food so that it may be acted upon by the digestive fluid poured into the intestine. The only lateral appendage of the alimentary canal of Carcinus is the so-called liver. It is an organ of considerable size, and consists of two symmetrical halves. Its secretion has the following reactions :— It decomposes fats and oils with the formation of glycerol and fatty acids. It converts starch into dextrose, and dis- solves albumin. ‘The action of the secretion upon milk is to render it transparent. The secretion contains leucin and tyrosin, no doubt produced by the metamorphoses of certain albuminous substances. In the words of Prof. M. Foster, F.R.S.,* “one result of the action of the pancreatic juice is the formation of considerable quantities of leucin and tyrosin.” ‘These organic compounds are not formed in a liver, for they are “dehydrated in a ¢ruwe liver, forming a series of cyanhydrins or cyanalcohols attached toa benzene nucleus, which then pass into the circulation.” The principal mineral ingredient found in the ashes (incin- erated at a low temperature) of the so-called liver of Careinius was sodium carbonate. In the ash of a Vertebrate liver the chief mineral constituents are potassium and phosphoric acid. The soluble ferment is readily extracted by the Wittich- Kistiakowsky method, or by the method recently introduced by Dr. N. Kravkoff.t This method consists in precipitating the soluble ferments and albuminoids by means of ammonium sulphate. By treatment with alcohol, the albuminoids become insoluble, and the ferments are then extracted with water. The ferment so extracted converts fibrin into leucin and tyrosin ; as well as hydrolyzes starch. * Text-book of Physiology, (4th ed.), 438. + Journal of Russian Chemical Society, 1887, p. 387. PHYSIOLOGY OF THE INVERTEBRATA. 103 The secretion of the so-called liver of Carcinus does not contain glycocholic and taurocholic acids, or glycogen. By using the methods of M. Zaleski* for ascertaining the presence of ferrous, ferric, and ferrosoferric compounds in a true liver, the author of the present volume could not detect the presence of iron in the organ or its secretion. From the above reactions the conclusion to be drawn is, that this bilobed organ is essentially pancreatic in function. THE MACROURA, The general details of the alimentary canal of Astacus have been described in the last chapter. The principal organs are the stomach and the “ liver.” The gastric juice of the crayfish has recently been investi- gated by M. Stamati.t By means of a gastric fistula, the gastric juice can be easily collected from the crayfish. This secretion is of a yellowish colour, somewhat opalescent, and alkaline to test-papers. It digests fibrin, rapidly forming peptones which give the ordinary reactions: it also transforms starch into glucose. It appears also that fats are emulsified and fatty acids liberated. ‘his so-called gastric juice of M. Stamati was in fact nothing more than the secretion of the “liver,” which pours its secretion into the anterior part of the intestine, and no doubt finds its way into the pyloric portion of the crayfish’s stomach. After the stomach of Astacus has been thoroughly washed out with water, an extract of the organ does not digest fibrin, nor does it act upon starch. This proves that Stamati’s gastric juice was in reality the secretion of the “ liver.” The so-called liver of Astacus fluviatilis has been proved by the author § to be pancreatic in function. Its secretion * Zeitschrift fiir Physiologische Chemie, vol. 10, ppe 453-502. + Dr. A, B. Griffiths’ paper in Proc. Roy. Soc. Edin., vol. 16, p. 178. t Comptes Rendus de la Société Biologique, (2), t. 5, p. 16. § Griffiths’ paper in Proc. Roy. Soc. Edin., vol. 14, p. 237+ 104 PHYSIOLOGY.-OF THE INVERTEBRATA. contains about five per cent. of solids, and readily digests fibrin and hydrolyzes starch. Similar reactions {to the above are also produced by the so-called livers of Homarus and Palemon, There is no doubt that the “liver” of the Macroura is a true pancreas. THE LAMELLIBRANCHIATA. Dr. Léon Fredericq has investigated the alimentary canal of Mya arenaria (see Fig. 18) and Mytilus edulis (the mussel). The secretions of the ‘so-called livers of these two animals digest fibrin analogous to the pancreas of higher forms.” When neutral and alkaline extracts of the organ are prepared, they have the characteristic reactions already given under the head of Carcinus manas; but Fredericq states that he has extracted glycogen from the secretion of the ‘liver ” of Mya. It is, however, probable that glycogen is only present in this organ and other tissues of J/ya during certain periods of growth. It may be remarked that in Carcinus, where development is achieved by sudden bounds—by moultings— the “liver” contains glycogen during these periods of rapid growth, but at other times there is not the slightest trace of the carbohydrate in that organ or any part of the alimentary canal. The contents of the digestive canal of Mya are acid. This acid is chlorohydric acid, and is found chiefly in fluids obtained from the stomach. It is possible that the function of the stomach, as a separate digestive organ, becomes more differ- entiated in the Lamellibranchiata. Is it possible that it gives rise to a secretion similar to the gastric juice of higher forms ? The so-called liver of Ostrea, Pecten, Anodonta, and Cardiwm functionates as a true pancreas. Dr. (. A. MacMunnt has extracted enterochlorophyll from * Proce. Roy. Soc. Hdin., vol. 14, p. 237. t+ Philosophical Transactions of Royal Society, 1886, pt. i, p. 235. PHYSIOLOGY OF THE INVERTEBRATA. 105 the “liver” pigments of certain genera of the Mollusca, as well as from a large number of other Invertebrates. Among the Mollusca experimented on were—AIytilus, Ostirea, Ano- donta, Cardium, Unio, Octopus, Buccinum, Patella, Helix, and Limaxz. In some Molluses—as Patel/a—the “liver” contains enterohzeematin besides enterochlorophyll. It might be suggested in reference to the discovery by Fredericq of glycogen (C,H,,O,) in the “liver” of Mya that it was pro- duced by the enterochlorophyll present in the organ; as enterochlorophyll is allied to chlorophyll. But MacMunn (Joc. cit., p. 257) states that he has made ‘ various sections of Invertebrate ‘ livers’ obtained from animals feeding and fast- ing, but never obtained a trace of starch (C,H,,O,) or cellulose with iodine in iodide of potassium, Schulze’s fluid, or with iodine and sulphuric acid. These experiments were made on the ‘livers’ of Helix aspersa, Anodonta cygnea, Patella vulgata, Ostreu edulis, Mytilus edulis, Astacus fluviatilis, the ceeca of star fishes, &c. The precautions recommended by Geddes* of previously digesting the tissues in alcohol, and in caustic potash, and neutralising with acetic acid, having been adopted in each case.” It appears that the ‘ enterochlorophyll occurs dissolved in oil globules, also in granular form, and sometimes dissolved in the protoplasm of the secreting cells of the ‘liver..” The probable function of this and other pigments will be alluded to in a subsequent chapter. THE GASTEROPODA. The secretion of the salivary glands of Heli aspeisa has been examined by the author.t It contains a ferment which converts starch into glucose. The ferric chloride test failed to show the presence of sulphocyanates. ‘The mineral ingre- dients found were calcium and chlorine; but no phosphates * Proc. Roy. Soc. Edin., vol. 11, p. 377- t dbid., vol. 14, p. 235. 106 PHY STOLOGY (OF THE INVERTEBEATA. or carbonates could be detected in the salivary glands of Helix. Similar results have been obtained with the salivary glands of Limax flavus, and Limax maxinus. The so-called livers of Helix aspersa, Limax flavus, and Limax maximus are pancreatic in function. Dr. M. Levy* has recently carefully examined the so-called liver of Helix pomatia. The weight of its organic constituents is very constant, being the same in summer and winter, and in great measure they are the same in kind in all periods of the year. The alcoholic extract of the gland when examined by the spectroscope gave the spectrum of enterochlorophyll. The digestive ferments present are a diastatic, a peptic, but not a tryptic one. The peptic ferment appears to be iden- tical with the late Dr. Krukenberg’s helicopepsin. The diastatic ferment disappears during the winter sleep; it is capable of digesting raw starch, but has no action on cellulose. A fat emulsifying action is shown by the secretion in the summer-time, but this also disappears during hibernation. The ferment, by means of which this action is brought about, is not identical with the one described by Dr, Schmiede- bergt as histozyme. Histozyme, which was separated from pigs’ kidneys, is concerned in the splitting up of hippuric acid. ‘The snail’s ferment has no such action. According to Dr. Levy, glycogen with sinistrin is generally present in the organ, but all tests for bile gave a negative result. Jecorin was also absent. Dr. Levy has separated the following sub- stances from the so-called liver of Helix pomatia :— Enterochlorophyl1 Lecithin Oleic acid In the alcoholic extract ( Fatty acids ’ Chlorine Ash ~+ Phosphoric acid | Sulphuric acid. In the ethereal extract 1 A trace of fat. * Zeit. Biol., vol. 27, p- 398. +t Archiv. Exper. Path. und Pharim,, vol. 14. PHYSIOLOGY OF THE INVERTEBRATA. 107 Sugar Globulin (coagulating at 66° C.) Glycogen Sinistrin Hypoxanthine* Potassium ( Sodium Calcium Magnesium Ash Tron (traces) Manganese " Chlorine Phosphoric acid Sulphuric acid. In the aqueous extract In winter animals, silica was also found as an ash con- stituent. Dr. Fredericq has investigated the nature of the secretions of the salivary glands and “liver” of Arion rufus. The secretion of the salivary glands readily acts upon starch, but has no action upon fibrin and neutral oils. The secretion of the “liver” is a brown liquid, and can be collected in a sufficiently large quantity by killing a large number of fresh snails. It suffices to dissect them lengthways to extract the viscera, and to collect the liquid which flows from the cut end of the intestine. If the secretion is extracted after the ani- mals have just been feeding, it is most likely that the secretion will be slightly acid (acidity due to food); in that case the digestion of fibrin takes about twenty-four hours. On the other hand, if the secretion is extracted when alkaline, or if the acid secretion is rendered slightly alkaline by a small quantity of scdium carbonate, its activity is greatly increased. In an acid solution the ferment is inactive, and this is readily observed when a small quantity of acidulated water is added to the digestive fluid of the snail, for it completely stops the digestion of fibrin. The “liver” and its secretion furnish a diastatic ferment transforming starchy matters into glucose. The so-called * And other bases precipitable by phosphotungstic acid. 108 PHYSIOLOGY OF .THE INVERTEBRATA. liver of Arion rufus, as well as Helix, is a digestive gland which is comparable to the pancreas of the Vertebrata. It contains neither biliary pigments nor biliary acids. If one considers that the Vertebrate liver is not a digestive gland in the proper sense of the word, since neither bile nor an infusion ot hepatic tissues contains digestive ferments, we may conclude that the name of liver is in no way applicable to the diges- tive gland of the Gasteropoda. It is stated by Barfurth that the liver of the Gasteropoda performs the functions of a hepato-pancreas. It is certainly pancreatic in function; but there are no chemico-physio- logical reasons for saying that it also possesses a hepatic function. The salivary glands and “liver” of Patella vulgata have been investigated by the author.* The limpet (P. vulgata), with its conical shell adhering to the rocks of our coasts, 1s well known to every sea-side wanderer. This member of the Gasteropoda, has been the subject of many scientific memoirs in ancient and modern times. Amongst naturalists, Aristotle was the earliest who gave an account of some of the limpet’s habits, and Cuvier was the first to describe its anatomy. Although this interesting little animal has attracted the attention of many naturalists, it is only within the last decade that the true functions of its internal organs have been satisfactorily worked out. The *‘ liver” of Patella vulgata isa yellowish saccular gland, and the greater bulk of this organ is encircled by the super- ficial coil of the intestine. Its secretion acts upon starch- paste converting the starch into glucose, as proved by Fehling’s solution. The secretion, as well as the organ itself produces an emulsion with oils and fats, yielding subsequently glycerol and fatty acids. The soluble ferment secreted by the columnar cells of the epithelium of the gland is readily extracted by either the Wittich-Kistiakowsky or Kravkoff * Dr. Griffiths in Proceedings of Royal Society of London, vol. 42, p. 393 3 vol. 44, p. 328. PHYSIOLOGY OF THE INVERTEBRATA. 10g methods. The isolated ferment, as well as the organ and its secretion, digest fibrin. Neither the organ nor its secretion contains biliary acids or glycogen, [rom these investigations there is no doubt that the so-called liver of Patella vulgata is similar in function to the pancreas of the Vertebrate division of animal life. The two salivary glands of Putella are well-marked, and situated anteriorly to the pharynx, lying beneath the pericar- dium on one side and the renal and anal papille on the other. They are of a yellowish-brown colour, and give off four ducts. The secretion of these glands was examined by the same method applied to the salivary glands of Sepie officinalis (see later in this chapter), and with similar results. The following table represents the constituents found in the salivary secretions of the two orders of the Mollusca :— + = Present. — = Absent. | i. : | Cephalopoda. Gasteropeda. | Dibranchiata. ais ale | presi aaa ae ee cals See Sher pee | Soluble diastatic ferment + | + + Geemepae © sos | + + | _ Sulphocyanates | oa : Calcium phosphate ‘ | + 2 - Calcium . oe + + ie iene eee ? EAeaE DMCA =| The “liver” and salivary glands of Buccinwin (whelk) have similar functions as the same organs in Pifclla. THE CEPHALOPODA. In a memoir published in the Chemica! News, vol. 48, page 37, and the Journal of the Chemical Society, 1884, page 94, the author gave an account of a peculiar excretory 110 PHYSIOLOGY OF THE INVERTEBRATA. product found in the Sepia’s “liver.” This product was proved to be albumin in pseudo-crystalline aggregations when examined under the microscope. These bodies are not of a constant occurrence in this organ of Sepia officinalis. Two years after the publication of the above-mentioned memoir the author * made a thorough examination of this organ in Sepia which substantiated and extended the observa- tions of Krukenberg,t Fredericq,t and Jousset de Bellesme.§ After carefully dissecting the organ out of the cavity of the body of a fresh Sepia, the following experiments were performed :— (1) A small portion of the organ was placed on starch- paste. The starch granules disappeared, with the exception of the celluloid covering, and on treating with water, and testing the solution with Fehling’s solution, sugar in the dextrose form was found. (2) The organ gave an akaline reaction to litmus paper. (3) When a small portion of the organ was agitated with a small quantity of oil, an emulsion was produced—this emulsion had first aun alkaline reaction, and after some time became acid, owing to the formation of butyric and other acids of the fatty series. (4) The action of it on milk was to render the milk trans- parent in four hours; 15 cc. of milk were rendered trans- parent by 6 milligrammes of the organ. (5) A chemico-microscopical examination of the secretion of the organ revealed the presence of albumin. The Isolation of the Ferment.—The process used to obtain the ferment or ferments (in a crude state) from the secretion of the organ was that devised by Wittich and used by Kistiakowsky|| in his researches on pancreatic ferments. * Proceedings of Royal Society of Edinburgh, vol. 13, p. 120. + Untersuch. Physiol. Inst. Heidelberg, Bd. 1, p. 327 [1878]. + Bull. Acad. Sciences Belgique, tome 56, p. 761 [1878]; Revue Intern. Sciences, t. 3, p. 263 [1879]. § Comptes Rendus, t. 88, pp. 304, 428 [1879]. | Pfliger’s Archiv. fiir Physiologie, vol. 9, p. 438. PHYSIOLOGY OF THE INVERTEBRATA. 11 The process consists in hardening the organ in alcohol for three days, and then cutting it up into very small pieces, ex- tracting with glycerol and filtering. On the addition of alcohol to the filtrate, the ferment is precipitated. The action of this ferment or ferments on starch was the complete conversion of the latter into dextrose or right- handed glucose, which was proved by the action of Fehling’s solution ; and the formation of crystals (C,H,,0; NaCl, H,O) with a solution of sodium chloride, a distinction from levulose or left-handed glucose, which does not form these crystals with sodium chloride solution. The action of the ferment on fibrin was the formation of leucin (¢- amido- caproic acid, C,H,,NO,) and tyrosin (paraoxyphenylamido- propionic acid, C,H,,NO,); for on treating the fermented mass with hot water and filtering, a solution is obtained which contains leucin and tyrosin. When acetic acid was added to this solution, acicular crystals were deposited. These crystals are insoluble in ether, but soluble in boiling water. ‘lhe aqueous solution produced a red flocculent pre- cipitate on the addition of a neutral solution of mercuric nitrate ; this reaction is characteristic of tyrosin. The acetic acid solution, after precipitating the tyrosin, was evaporated, when leucin was deposited in white shining plates, which melt at 98°C. These crystals of leucin were heated with barium oxide, the result of the action being the formation of amylamine and carbon dioxide :— Go, NO, = N(C,H,,)H, + CO, By digesting the organ itself with boiling water and filtering, the filtrate contained leucin and tyrosin. The ferment has no action on cellulose. From these investigations, the so-called liver of Sepia officinalis is proved to be a pancreas, for the juices of the organ are purely digestive in function, digesting starch, oil, and similar bodies, and transforming fibrin into leucin and tyrosin. Then, again, albumin is present in its secretion, which is 112 PHYSIOLOGY OF THE INVERTEBRATA. characteristic of the pancreatic fluid of the higher animals— no albumin being found in the liver, for albuminoids are decomposed by that organ. No glycocholic and taurocholic acids or glycogen were obtained from the organ. Not the slightest trace of these biliary compounds could be detected in the organ or its secretion. There is no doubt that these investigations prove that this so-called liver of the Cephalopoda is a true pancreas or digestive organ. The author in his paper entitled, ‘« Further Researches on the Physiology of the Invertebrata,”* gave the following account of the salivary glands of the cuttle-fish: here are two pairs of salivary glands in Sepia officinalis. The posterior pair, which are the larger (see Fig. 20) lie on either side of the cesophagus. The secretion of the posterior glands is poured into the cesophagus, while the secretion of the smaller anterior pair of glands passes directly into the buccal cavity. A quantity of the secretion was extracted by using several freshly-killed cuttle-fishes. It was alkaline to test-papers. A portion of the secretion was added to a small quantity of starch, the starch being converted into glucose in fifteen minutes. The presence of glucose was proved by the formation of red cuprous oxide by the action of Fehling’s solution. The soluble enzyme, or ferment, contained in the secretion (which is capable of causing the hydration of starch), was isolated by precipitating the secretion with dilute normal phosphoric acid, adding lime-water and then filtering. The precipitate produced was dissolved in distilled water and reprecipitated by alcohol. This precipitate converts starch into glucose. When a drop of the clear secretion was allowed to fall into a beaker containing dilute acetic acid, stringy flakes of mucin were easily obtained. The presence of mucin was confirmed by several well-known tests. Another portion of the secretion was distilled (with the * Proceedings of Royal Society of London, vol. 44, p. 327- PHYSIOLOGY OF THE INVERTEBRATA. 113 utmost care) with dilute sulphuric acid, and to the distillate ferric chloride solution was added, which gave a red colour, indicating the presence of sulphocyanates. The inorganic constituents, as far as the author could make out, consisted only of calcium phosphate. No calcium carbonate could be detected. There is much in favour of the supposition that the diastatic ferment in these secretions is produced as the result of the action of nerve-fibres (from the inferior buccal gan- glion) upon the protoplasm of the epithelial cells of the glands. THE TUNICATA. The very fine, branched, and ampullated tubules (sometimes known as Savigny’s tubules), ramifying over the wall of the intestine in nearly all the Zunicata, form a digestive gland, which is certainly pancreatic in function. The common duct of this gland opens into the stomach. The latter organ always contains a secretion having similar chemical properties to those produced by the pancreatic tubules. The two following tables summarise our studies of the — salivary glands and the so-called livers of the Jnverte- brata :— PHYSIOLOGY OF THE INVERTEBRATA. 114 i i AF at ae cts t é + + i =f | + + | 3 af ote ap 4 =|. regergouward | .eshrqoune | -oaoyeuaoung | | *euroarry | “e1oydouom Ay] ‘rpodoyeydap “vpodo.1oysey | kal +P i ats ar i i ee oN Sh: * ayeuoqres wNTDlTeD aULIOTYD | luenntcoyi@) ayeydsoyd umr1mlep * soyeuedooyqding UION]L qUNTUIOF O1YRISPICT ‘naoydoprdoy | ‘ex0jdoyqag | “BIMYOOS YO 4quesqy = —- ‘queselg = + ‘'SGNVID AUVAITIVS AHL () 115 PHYSIOLOGY OF THE INVERTEBRATA. “sqT[A9 ANssTZ-dATJOOUTMOD ayy Aq MOSNPOTY OY} UT pamtoZIed ST UOTJOUN; O1Uad00AT3 ayy Yeyy Soywys OUOYSpUNT_ + ‘UdAts Aprorye ‘naqnuod xyazyT JO ,, OAT ,, OY} UO SUOTZVSTYSAAUT S,AAOT] OSTL 99g » + + + + + + | “eyworany, 4upodoyeydag | ‘ > + + + + + «tpodorayser) | + + + GQ). + + + + vyeryo -UvIqI[[awue'T aa *BAINOTOV]T + *eandqoevig “pUleuRly 1 al 2 oy) = +] +] +} +) - +] +] # | +] - +] +] +] + ]- t+ 1 tl oe | bok eH +] +/+] +] 4+] - is°) | ral 8 aE 12lelele g a ea eae s 5 5 s ~ & | & g Ss | = rs 8 5 = g g | st 2 = oa | 2a ; 8 (quosqy = — ‘juosolg = +) | oh — | “eyeULapouryog — a “BLQLIOg twmipog * uaso0o0dpy prow ooqooody) : . * prov oroyoorney, urmngyy uIsoad J, urone'y > souojday uljeor1ourg JUOUAIOZ O1RISLIC] (LON UO GALVIENANTAMIG UAHLIG) UAAIT GATIVO-OS AHL (4) 116 PHYSIOLOGY OF THE INVERTEBRATA. The chief digestive glands of the Invertebrata are the pancreas (the so-called liver) and the salivary glands. There appears to be no organ, from the lowest to the highest Invertebrate animal, corresponding with the Vertebrate liver. Dr. C. Letourneau, in his La Biologie, says: “ Does the pancreas exist in the Invertebrates? This is a question. of comparative physiology which still waits for a reply. We do not begin clearly to recognise the pancreas except in fishes, and then only in a rudimentary state.” After the recent researches of Krukenberg, Fredericq, Jousset de Bellesme, Plateau, Hoppe-Seyler, as well as those of the author, the problem now requiring solution is the following :—Does a true /iver exist in the Invertebrata? The pancreas appears to be the chief digestive organ of the earlier forms of animal life. On the other hand, some biologists look upon the Verte- brate liver, pancreas, and salivary glands as differentiated bodies of an original pancreas of the Jnvertebrata. But have not many forms of the lower animals similar salivary glands to those found in the Vertebrata? And is not the so-called liver of the Znvertebrata a true pancreas, capable of producing the same chemical and physiological reactions as the pancreas of higher forms ? CHAPTER V. ABSORPTION IN THE INVERTEBRATA. In Chapters III. and IV. the processes of digestion in the Invertebrata were considered in detail. The digested food becomes tissue; but before this is attained the said digested food, which is still enclosed in the alimentary canal (if present), must first pass through its walls and gain entrance into the blood or tissues. This process is known as «absorption. The function of absorption in the Vertebrata is carried on by a distinct set of vessels, but these are entirely wanting in the Jnvertebrata. In the higher animals absorption takes place partly in the stomach and partly in the intestine. “The mucous membrane of the stomach and intestine con- tains an abundant supply of capillaries ; the walls of these vessels are only one cell thick; consequently the soluble peptones and sugar will diffuse readily into their interiors.” In the intestine the area of absorption is largely increased by means of the villi in the Vertebrata, and by means of the typhlosole in those Invertebrates whose intestine is provided with such an arrangement. There are no openings in the substance of the villi and typhlosoles ; consequently the nutritive fluids pass directly through their substance by a kind of transudation or imbibi- tion (endosmosis). Every animal membrane will absorb certain fluids with greater or less facility. Thus most of them will absorb pure water more abundantly than a solution of sodium or potassium chloride ; or a solution of sugar more 118 PHYSIOLOGY OF THE INVERTEBRATA. readily than one of gum; and the same liquid will be ab- sorbed more readily by one membrane, and less so by others. Thus every membrane has a special power of absorption for certain fluids, which it will take up in greater or smaller quantity, according to their nature and composition. In all cases, however, there is a natural limit to this quantity, beyond which absorption will not continue. In the higher animals there is absorption by the blood- vessels and absorption by the lacteals ; but, as already stated, there are no distinct vessels in the Jnvertebrata set apart for the function of absorption. In the lower Mollusca, Echino- dermata, &c., the digested food is absorbed by the walls of the alimentary canal. In the higher Mollusca and Arthropoda, the digested tood or nutritive fluids are absorbed by the blood- vessels in the walls of the alimentary canal. In both of the above cases, the two functions of absorption and digestion are not completely differentiated from each other. In the Lnvertebrata the digested food is brought into con- tact or close relationship with the various tissues in three ways: (1) The food particles (as in Ameba), during the process of digestion, are brought into contact with the tissues (using the term in its widest sense), that are to be nourished or renovated by them. In this case there is a fusion of the two functions of absorption and digestion. ‘The digested food immediately becomes tissue. (2) The digested food or nutritive fluid transudes through the walls of the alimentary canal into the somatic or body cavity, and is consequently absorbed by the walls of, and the organs suspended in, that cavity. In this case, the nutritive fluid passes through a transitory condition, in such a state being known as the “chylaqueous” fluid. The so-called chylaqueous fluid is found in the body cavity, and is never enclosed in any distinct vessels; it undoubtedly represents the blood of the higher animals. (3) The digested food contained in the alimentary canal is PHYSIOLOGY OF THE INVERTEBRATA. 119 absorbed by the blood-vessels distributed on the walls of the digestive system.. Through the medium of blood-vessels the products of digestion are carried to all parts of the body. In this case there is a fusion of the functions of absorption and circulation; the products of digestion become incorpo- rated with the blood ere they reach the tissues for which they are destined. Therefore, in the Jnvertebrata the function of absorption does not exist as an entirely separate function, as one finds in the Vertebrata. It is either fused with the function of digestion or the function of circulation. THE PROTOZOA. The Gregarinida, being parasitic organisms, pass their existence in the chyle or nutritive fluid of the higher animals. They absorb by the whole surface of their bodies the nutritive fluids of their hosts; such fluids are already in such a state as to form a nutritive material for these low organisms. Probably the nutritive material does not undergo any fur- ther change after passing into the body of a Gregarina. ‘* Perhaps no other animals present such a complete want of differentiation between the functions of digestion and ab- sorption ” as do the Greyarinida. In the Lhizopoda (e.g., Ameba) food is taken in at any part of the cell, but only at one region of the cell at one given time—i.c., the whole surface of the cell can ingest food, but only one portion of it ingests at atime. In these animals the intimate contact of the food particles, absorbed within the living substance, is aided by the contractions of the sarcode, by the emission and retraction of the pseudopodia. The sarcode of these organisms absorbs nutrient matter from the food particles. There is no distinct channel through which the food particles pass. What causes the sarcode to absorb nutrient matter from the heterogeneous materials introduced into the cells by the pseudopodia ? There is no doubt that 120 PHYSIOLOGY OF THE INVERTEBRATA. itis due to the excitability* or irritabilityt of the cell, caused indirectly by the presence of food particles. Speaking of the Rhizopoda, M. Richet says that “irritability is their life complete.” The presence of food particles excites digestion and absorption, but only the digested particles are absorbed. This power of selection is possessed by the protoplasm of the cell; it is a physiological property of that complex substance whose composition has already been alluded to in the early part of the work. In the compound Lhizopoda, only certain regions of the sarcode take in food particles. ‘The food so ingested passes through more or less of a compound Lhizopoda in a similar fashion to that met with in the simple forms.” In the Jnfusoria the tood particles may possibly undergo a preliminary digestion in the short cesophagus (¢.g. Para- mecium). After this the food gives rise to food vacuoles in the sarcode. These food vacuoles undergo a rotatory move- ment round the cell, just below the cuticular layer. “Only the sarcode immediately in contact with the food vacuoles, as they pass round, can be regarded as truly absorptive. Here is, then, the first marking off of a region (only a region) of the sarcode, whose work is that of absorbing nutrient materials from the food, and transferring them to other parts of the sarcodic body.” THE PORIFERA. In the Porifera the food particles, along with water, enter through the inhalent apertures, and pass into the gastro- vascular cavity, which is lined with flagellate cells; but the functions of digestion and absorption in the Porifera do not differ very much from those occurring in the Rhizopoda. THE CGLENTERATA. In the Hydrozoa the function of absorption is somewhat * See Dr. Romanes’ Vental Evolution. + Richet’s Hssai de Psychologie Générale. PHYSIOLOGY OF THE INVERTEBRATA. 121 more complicated than in the Lhizopodu. The digestive and somatic cavities are not differentiated, for they form one common cavity. The digested food is absorbed by the cells of the endoderm. In the Protozoa the function of absorption is effected by the sarcode, whereas in the Hydrozoa the “sarcode” becomes differentiated into cellular membranes, the internal one (endoderm), lining the digestive cavity. The endoderm of the Hydrozow is the absorptive layer and is the means of transferring the absorbed fluids to the ectoderm. Although there are many points in the mode of absorption in the Hydrozow comparable to those of the Rhizopoda, yet the former class marks a distinct advance on that of the latter; for the food is first digested in the “chylaqueous ” fluid contained in the digestive and somatic cavity, whereas in the Rhizopoda the food particles are brought into actual contact with the sarcode, which performs both the functions of digestion and absorption. In the Actinozow the function of absorption comes under the second method already described. The digested food transudes through the linings of the digestive cavity, or passes directly through the posterior aperture into the somatic cavity. The somatic cavity, which is distinct from the digestive cavity,* contains a ‘‘chylaqueous” fluid. This fluid consists largely of water, and contains albuminoid spherules, which are possibly the precursors of the white corpuscles of chyle and of blood in the higher animals. The nutrient matter of the digested food, having passed into the somatic cavity, is absorbed by the endodermic cells of that cavity and by the mesenteries. THE ECHINODERMATA. As far as the function of absorption in the Lehinodermata is concerned, there is very little difference from that of the * In Actinozoa the digestive cavity is suspended in the somatic cavity. 122 PHYSIOLOGY OF THE INVERTEBRATA. Actinozoa. The alimentary canal, or digestive system, is sus- pended in the somatic cavity ; and the digested food transudes through the walls of the former into the latter. The nutrient fluid is then absorbed by the walls of the somatic cavity, as well as by the various organs suspended therein. The somatic or peritoneal cavity in the Asteridew contains a watery cor- pusculated fluid. The corpuscles are nucleated cells; this fluid therefore represents the blood of the higher animals. It will be noticed that in the Actinozoa, as well as in the Echinodermata, the function of absorption is distinct from that of digestion, but it is not performed by any special organs. | THE CESTOIDEA, As already stated, the Cestoidea are reversions to a lower or simpler type. They are immersed in the chyle or the tissues of the higher animals; consequentiy they absorb the digested food, &c., by the whole of the external surface. Although these animals are much higher in the zoological scale than the Gregarinida, there is in the functions of digestion and absorption a close analogy between these two orders. In both, the processes of absorption and digestion are not differentiated. THE ANNELIDA. The digestive tube is suspended in the perivisceral cavity. The digested food transudes into this cavity, and there becomes mixed with a colourless corpusculated fluid. This fluid fills the perivisceral cavity, and is analogous to the blood of other Invertebrates.. This colourless fluid is not contained in any vessels, although there is in Lwmbricus, for example, a red fluid contained in a well-developed system of vessels, in addition to the colourless fluid already mentioned. The nutrient matters, after having passed into the peri- visceral cavity or chambers—as the perivisceral cavity is generally divided into chambers by means of thin muscular PHYSIOLOGY OF THE INVERTEBRATA. 123 mesenteries—are absorbed by the pseudo-hemal vessels, as well as by the various tissues, &c., suspended in the peri- visceral cavity. THE MyYRIAPODA AND INSECTA. In these two classes of the Znvertebrata there is a distinct advance, in the mode of absorption, on all the forms alluded to in the present chapter. Over the external surface of the alimentary canal there are distributed blood-vessels ; and the nutrient matter of the food is chiefly absorbed by these vessels, and more especially by those carrying venous blood. Here the digested food is absorbed by distinct vessels, although there may be some transudation directly into the somatic or body cavity, especially in some of the lower orders of these two classes. The vessels which absorb the digested food are not special vessels (like the lymphatics of the Vertebrata) set apart for the function of absorption, for they perform the ordinary func- tion of veins, as well as ** carrying away from the tissues of the alimentary canal the effete products resulting from the work of those tissues. But in addition to this there is laid upon them the office of receiving the fresh material introduced into the system through the alimentary canal. These vessels are not only transmitting blood, but are absorbing ‘ chyle’; there is a fusion of the functions of absorption and circulation.” ‘THE ARACHNIDA. The function of absorption in this class is performed in a similar manner to that of the Myriapoda and Insecta. The digested food passes into the veins, and is conveyed to the dorsal vasiform heart. THE CRUSTACEA. The digested food passes from the intestine into the blood- vessels or veins. which are distributed on its walls. No other 124 PHYSIOLOGY OF THE INVERTEBRATA: vessels are known to convey the digested food into the circu- latory system ‘“‘than the irregular venous receptacles which are in contact with the parietes of the intestine.” THE PoOLYZOA AND BRACHIOPODA. The function of absorption in the Polyzoa and the brachio- poda is not so highly differentiated as the Myriapoda, Insecta, Arachnida, and Crustacea. In the latter, the digested food passes into vessels, or, in other words, into the circulatory system ; but as there are no vessels in the Polyzow and the Brachiopoda, the function of absorption is analogous to that of the Actinozow. There is an alimentary canal suspended in a somatic or body cavity. The digested food transudes through the walls of the digestive system, and is then absorbed by the external endoderm of the body cavity, as well as by the organs suspended therein. THE MOLLUSCA. The function of absorption in the Jol/usca is placed under the head of our third category. The digested matter is absorbed by vessels, but these perform the dual functions of absorption and circulation. There are no special absorbent vessels in the Jnvertebrata, But although there is no special apparatus set apart for absorption, the nutrient fluids, absorbed by either the sarcode, somatic linings, or blood-vessels, are spread wherever they are required, the distribution being in some animals effected slowly, in a way analogous to absorption. In others the distribution of the nutrient fluids is accomplished rapidly by the establishment of currents, which serve also to remove the excretory products eliminated from the organs. This originates another function, the circulation of the blood, and another set of organs by which this is performed. CHAPTER VI. THE BLOOD IN THE INVERTEBRATA. In animals of the simplest structure all the fluids of animal economy resemble one another. “ It seems, indeed, to be only water charged with a certain amount of organic particles ; but in animals higher in the scale of being, the humours cease to be of the same nature, and there is one, distinct from all the others, destined to nourish the body ; this fluid is the blood. It not only nourishes the body, but is the source whence are drawn all the secretions, such as the saliva, urine, bile, and tears.” In the Mammalia, Aves, Reptilia, Amphibia, Pisces, and in most of the Annelida, the blood isofa red colour. But in the greater number of the Invertebrata the blood presents various colours and densities, being often thin or watery, and slightly yellow or green, brown, rose-coloured, or lilac. The majority of the Jnver- tebrata have white blood; ¢.g., the Insecta, Crustacea, Mol- lusca, &e. The blood of the Znvertebrata, like that of the Vertebrata, is not homogeneous, for it consists of a transparent or semi-trans- parent liquid, and a number of small, solid corpuscles, which float in this liquid. In the higher animals the corpuscles are of two kinds, red and colourless ; but in the Jnvertebrata there are, as a rule, only colourless corpuscles. The red blood of Annelides is different from the red blood of the Vertebrata, inasmuch as the plasma is coloured, and the corpuscles are colourless in the former, while in the latter the plasma is colourless, 126 PHYSIOLOGY OF THE INVERTEBRATA. and there are present coloured and colourless corpuscles. The perivisceral fluid of the Annelida is colourless, and contains colourless nucleated corpuscles. The corpuscles in the blood of the Jiwertebrata are of different sizes, and the size varies much in the same in- dividual. The size of the corpuscles in the earthworm and leech are as follows :— LInumbricus A . - _yiv inch in diameter. Hirudo . : : - zsoo inch in diameter. Their form, however, is generally spherical; and their surface has a raspberry appearance. In the higher Jnvertebrata the blood clots after a variable period of time. Drs. J. B. Haycraft and E. W. Carlier* have recently examined the coagulation of the blood in certain forms of the Invertebrata. According to their investigations, ‘‘in Inverte- brate blood the clot is formed, at any rate for the greater part, by the welding together of blood-corpuscles. These throw out processes, which interlace to form a solid mass.” Haycraft and Carlier have examined the blood of a crab and a sea-urchin. ‘‘Crab’s blood clots in about five minutes, when the opaque pinkish fluid becomes water-clear, with a branching clot within it. During and after coagulation the clot becomes of a brown-black colour, from the development within the corpuscles of a pigment.” “The blood of the sea-urchin varies very much in the number of corpuscles present in the different specimens. In most cases, when allowed to coagulate, the clot is very small, and not easy to demonstrate in a few drops of blood.” The blood of the higher Invertebrates generally darkens rapidly on exposure toair. For example, Mr. E. B. Poulton, F.R.S.,f has shown that the blood of Lepidopterous larva and * Proc. Roy. Soc. Edinh., vole 15, Ps» 423. + Proceedings of Royal Society, 1885, p. 294. PHYSIOLOGY OF THE INVERTEBRATA. 127 pupee becomes black: and Dr. C. A. MacMunn* has shown that the blood of Helix pomatia assumes a blue tinge on ex- posure to air. Concerning the composition and nature of the Invertebrate blood generally, further remarks will be given later in this chapter. THE PROTOZOA AND PORIFERA, These animals are without blood, for no part of the sarcode can be regarded as blood. The sarcodic substance lining the canals, which traverse the skeleton of the Porifera, is also devoid of any fluid analogous to the blood of the higher Invertebrata. In some of the Cestoidea and allied forms the blood or nutritive fluid found “in those interstices of the mesoderm that represent the somatic cavity of other animals, is said to be free from corpuscles.” The simplest form of Invertebrate blood is present in the Nemuatoidea. In the Polyzoa the fluid contained in the perivisceral cavity consists largely of water, and has but few, if any, corpuscles. This nutritive fluid (the chylaqueous fluid of some writers), derived in the first instance from the food that has been digested in the alimentary canal, and which has transuded through the walls of that canal, is, without doubt, analogous to the blood of higher forms. In the Hydrozoa, which are provided with blood, the blood is of a very watery nature. The amount of fibrin is extremely small; consequently the fluid is non-coagulable, and it is almost devoid of corpuscles. That the so-called chylaqueous fluid is analogous to the blood of higher forms is demonstrated by the fact that the perivisceral fluid of the Annelida yields on investigation “not only albumin and fibrin, but crystals which are derived from the water that constitutes so large a part of the nutritive fluid.” From the above remarks it will be observed that the blood * Quarterly Journal of Microscopical Science, 1885. 128 PHYSIOLOGY OF THE INVERTEBRATA of many of the Jnvertebrata is devoid of corpuscles; and the young of many of these animals (which in the adult form have corpusculated blood) have blood without corpuscles. This is another fact which proves that ‘“ development is a progress from the general to the special, from the lower to the higher form, and that the earlier stages of the history of higher animals are similar to the adult forms of lower ones.” Although many forms of the Invertebrata have blood devoid, or nearly devoid, of corpuscles, other forms have corpusculated blood, _, THe AcTINOzZOA AND ECHINODERMATA. 4 The ‘“‘ chYlaqueous” fluid in the Actinozoa and Echinodermata is analogous to the blood of higher forms. In both these classes the blood is corpusculated; some of these corpuscles are distinct cells with wall and nucleus, but the majority of the corpuscles in the blood of the Actinozoa and Echinoder- mata are of a very rudimentary nature. “They are probably small masses of matter with no definite limiting membrane on their exterior, akin, perhaps, to the albuminous molecules in our chyle.” THE MyrIAPopaA. In this class the blood is contained in some part of its course in blood-vessels. It contains three distinct corpuscles, which are devoid of cell-walls. ‘The simplest kind are pellucid central nuclei invested by a few granules. Next rank the oat-shaped corpuscles, where the nucleus is still very evident. The third and most perfect form presents a central nucleus, surrounded and almost obscured by a large number of granules. As yet no definite cell-wall is to be seen on the exterior of the granules.” PHYSIOLOGY OF THE INVERTEBRATA. 129 THE ANNELIDA. The perivisceral cavity, communicating with the excretory or segmental organs, contains a corpusculated fluid which is nutritive. The corpuscles are oval, flat, granular, colourless bodies without a limiting membrane. Besides these corpuscles, the blood of the Annelida contains “ actual cell corpuscles of fusiform shape, and devoid of granules. Here, then, are some corpuscles with a true wall, but all the solid, floating particles of the blood are not yet of that high order of structure.” The fiuid present in the pseudo-heemal system or vessels of the Annelida contains a substance allied to hemoglobin ; and according to Dr.MacMunn, this red colouring niatter func- tionates in a similar manner to the histohematins of other Invertebrates, 7.¢., it has a respiratory function. It will be noticed, that there is in the case of the pseudo-hzmal system of the Annelida a fusion of the functions of circulation and respiration. This hemoglobin is dissolved in the fluid and does not belong tothe corpuseles. It is questionable whether this ‘‘ respiratory blood,” as Prof. Huxley* calls it, possesses any nutritive properties ; it sppears to be entirely devoted to the function of respiration. In the Gephyrea, represented by Sipunculus, the blood corpuscles contain a coloured fluid between the external wall and the central nucleus. ‘This is the first appearance of a coloured corpuscle, but it differs essentially from the coloured corpuscles of the Mammalia, for in the latter the colouring matter is distributed throughout the corpuscle. Prof. E. Ray Lankester, F.R.S.,f has shown that the perivisceral cavity of Sipunculus nudus contains a_ pale madder-like colouring matter, “which is due to a large number of coloured corpuscles from sz55 tO qyo Of an * The Anatomy of the Invertebrated Animals, p. 57. t+ Proceedings of Royal Society, vol. 21, p. 71. 130 PHYSIOLOGY OF THE INVERTEBRATA. inch in diameter, and that this colouring matter, also found in other parts of the worm, is not hemoglobin.” Delle Chiaje showed that in Sipwneulus balanorophus and S. echinorhynchus “the arterial blood is red, the venous brown. G. Schwalbe* found that the body fluid of Phascolo- soma elongatum (a Gephyrean) is a bright-rose or greyish-red colour, and is cloudy owing to the presence of morphological elements, and that on standing in the air it gets darker and darker until it assumes an intense Burgundy-red colour. By long standing in the air this colour goes into a dirty brown owing to decomposition, and in drying the whole assumes a dirty green colour. Krukenbergt found the blood of Sipunculus nudus to contain the same colouring matter as that observed by Schwalbe ; he finds that it is the oxygen of the air which brings about the colour change, and that the colour is removed by CO,. This colouring matter gives no absorption band either in the oxidised or reduced condition. Krukenberg calls this pigment hemerythrin, and the chro- mogen belonging to it hemerythrogen. The colouring matter is decomposed by H,S. The oxygen in the oxidised blood-pigment seems, according to Krukenberg, to be more firmly fixed than in oxyhemoglobin. Milne-Edwards{ in 1838 discovered that certain Annelids possessed green blood, his observations being made on Subella. ‘Prof. Ray Lankester § on examining the blood of Sabella ventrulabrum and Siphonostoma (sp. ?) with the spectroscope discovered the interesting fact that it only gives a banded absorption spectrum, but is capable of being oxidised and reduced, and it behaved in such a way with potassium cyanide and ammonium sulphide, as to have led him to conclude that hemoglobin and this colouring matter (chloro- cruorin) ‘ have a common base in cyanosulphem, and perhaps * Archiv. fiir Mikr. Anat., vol. 5, p. 248, et seq. + Vergleich. Physiol. Studien, p. 85. t{ Annales des Sciences Naturelles, 1838, vol. 10, p. 190. § Journal of Anatomy and Physiology, 1868, p. 114 ; 1870, p. 119. PHYSIOLOGY OF THE INVERTEBRATA. 131 in Stokes’ reduced hamatin.’* . . . . Prof. Lankester could not obtain derivatives of chlorocruorin, owing, as he has stated, to the apparent instability of this body, which decomposes rapidly.” Dr. MacMunn has recently examined spectroscopically the behaviour of chlorocruorin with certain reagents, but his investigations will be de- scribed later in this chap- ter, when we consider in detail the chromatology of the Invertebrate blood. The red blood of Lwin- bricus can be made to yield crystals of oxyhe- moglobin (Fig. 27), and a solution of these crystals gives an absorption spec- trum (Fig. 28). Heemoglobin is also pre- sent in special corpuscles FiG. 27.—CRYSTALS OF OXYHASMOGLOBIN of the blood of Glycera FROM BLOOD OF LUMBRICUS. (one of the Polychta) ; as well as in the vascular fluid of Nephelis and Hirudo. lt t | iy Ie Mi} PV A Hil 60 70 80 90 100 110 120 130 140 150 Fic. 28.—ABSORPTION SPECTRUM OF OXYH-EMOGLOBIN FROM BLoopD OF LUMBRICUS. appears that this particular colouring matter is spectro- scopically identical with Vertebrate hemoglobin. Tue INSECTA. In a large number of insects the blood is colourless ; although sometimes it is of a green, yellow, or red hue. ‘This colour * Hamochromogen. 132 PHYSIOLOGY OF THE INVERTESRATA. is not due to the flat, oat-shaped, granular corpuscles with their well-defined walls and nuclei, but is due to the liquid in which they float. In the case of Phytophagous larve, Mr. E. B. Poulton, F.R.S.,* has shown that they owe their colour and markings to two causes:—(1). “Pigments derived from their food- plants, chlorophyll and xanthophyll, and probably others ; (2) pigments proper to the larvee or larval tissues made use of because of some (merely incidental) aid by either or both of these groups of factors. It may be generally stated that all green colouration without exception, is due to xantho- phyll. All other colours (including black and white) and some yellows, especially those with an orange tinge, are due to the second class of causes. .... Derived pigments often occur dissolved in the blood, or segregated in the subcuticular tissues (probablyythe hypodermic cells), or even in a chitinous layer, closely acsdemred with the cuticle itself.” In some cases, the colour of the blood changes before the pupal stage is reached, while in others it remains the same as in the larval condition. On this point Mr. Poulton (/oc. cit. p. 277) says:—‘‘the superficial derived pigments of Sphinx Ligustri become brown in the dorsal region, before pupation, while the colour of the blood is unchanged. In Dicranura Vinula the whole larva becomes reddish-brown, and in this case the green blood changes to brownish-yellow. The true larval pigment also changes before pupation, except: when it is cuticular. Thus the larva of #. Angularia becomes transparent by the disappearance of dark pigment, and the green blood gives its colour to the larva. The green colour of the blood is generally retained in the pupal state, and it is often of great importance.” According to Mr. Poulton, the blood of Phytophagous larvee and pup is acid to litmus-paper, with the exception of that of Zphyra punctaria, which seemed to be neutral. This acid, which is volatile, is readily extracted with ether; but its * Proc. Hoy. Soc., 1885, p. 270. PHYSIOLOGY OF THE INVERTEBRATA, 133 nature has not been determined, The corpuscles of Phyto- phagous blood are amceboid. Coagulation.—* The blood clots after a very variable period of time, but generally darkens in about five minutes, ultimately forming a solid black clot which is due to oxida- tion. If blood be sealed in a tube, the small quantity of oxygen present will form a thin black film on the surface of the blood, and the action then ceases.” Mr. Poulton has shown “ how blood can be kept indefinitely without clotting in a section of tube with a cover-glass over one end, and the other cemented to a glass slide.” He has kept “ the blood otf Pygera Bucephalus in this way for a month, quite unchanged, and on then breaking off part of the cover-glass a thick black crust was formed on the surface, while the blood beneath became translucent instead of clear and transparent. On removing the crust a second thin one was formed, but on removing this, no further coagulation “took place. If in sealing up blood, or placing it in a tube section, a bubble of air is accidentally included, coagulation takes place round the bubble, but not elsewhere. This black substance is the normal clot, for the injured places on larvee which have healed are always black, notably the horns of Sphinv larvie which have been nibbled off by others of the same species. The coagulation takes place after the addition of water, or of a saturated solution of neutral salt (sodium sulphate). The occurrence of a reducing agent in the blood appears to be very remarkable, but it is possible that the substance is capable of again yielding up its oxygen, and so acting as a earrier. It has been observed that if fresh blood be added to that which is turning black on the surface, the black clouds are redissolved. If this be not so, it is difficult to see how the blood can be the internal medium for the supply of oxygen in these animals, and one is tempted to the supposi- tion that in the tracheal system we have a means for the supply of oxygen direct to the tissues.” Another suggestion which occurred to Poulton was that “the coagulation is a 134 PHYSIOLOGY OF THE INVERTEBRATA. very similar process to the darkening of cuticular pigment on larvee, and the darkening of the pupal covering. It has always been assumed that this darkening is due to light, but it takes place rapidly and completely in pupz buried several inches under ground, in compact and opaque cocoons, or sometimes in the heart of a tree.” Furthermore, Poulton has never observed that darkness made the least difference to the darkening of pup. It is, therefore, ‘‘ very probable that this will also prove to be due to oxidation, and possibly to the formation of a substance similar to the black clot of the blood.” Poulton has observed that “the brown and colourless blood darkens as well as the green.” The Action of Reagents——The action of (7) alcohol (fifty per cent.) on the blood of P. Bucephalus was to precipitate proteids ; and if the mixture is shaken, “the proteids and pigments are precipitated as yellowish-green clouds, and in a few minutes the upper part of the liquid becomes blue, and ultimately black, from the formation of coagulum. ‘The proteids are decolourised and sink, the alcohol remaining yellow with xanthophyll (the chlorophyll disappearing). Absolute alcohol does not lie on the top of the blood (like diluted alcohol), but mixes with it at once. (%) Chloroform behaves in the same manner as ether, but it dissolves nothing coloured from the green coagulum ; the latter contracts in a few hours, and a clear blue liquid appears between it and the sides of the tube. The exposed surface of the coagulum (the chloroform having sunk to the bottom) rapidly becomes black. (c) Distilled water, like weak spirit, lies on the top of the blood with a cloud of precipitated proteid (probably globulin) above the junction. On shaking, the cloud disap- pears, and the blood only seems diluted; if now more water be added (altogether many times the volume of the blood), in a few minutes the whole fluid becomes cloudy, remaining dark-greenish. On filtering, a blue solution comes through, which slightly darkens for some hours. With less water the PHYSIOLOGY OF THE INVERTEBRATA. 135 blood coagulates normally, although after a longer interval of time. (d) Carbon disulphide had no effect for a consid- erable time. Hventually the blood was coagulated (green) but nothing coloured was dissolved out.” The Action of Heat.— The blood of the pupa of Sphinx Ligustri was heated in a glass tube in a water-bath; no change was seen till the temperature reached 132° F., when part of the blood became slightly dim. By 141° the whole of the blood was distinctly cloudy, but it was not till 180° that the blood became quite coagulated—solid-looking and opaque, the proteids being yellow with xanthophyll. In the interstices of the clot was a clear yellow fluid. The xantho- phyll in the coagulum was easily extracted by ether or alcohol.” Dr. L. Fredericq* has also investigated the nature of the blood in the Jnsecta. He experimented upon the blood of the larva of Oryctes nasicornis (belonging to the Coleoptera). The blood was extracted by making a small slit (with fine scissors) across the skin of the back and the walls of the dorsal vessel ; into this slit a slender glass canula was inserted when the blood of the animal immediately rose in the tube. The blood is a colourless liquid having somewhat the aspect of the lymph of the Mammalia, and holding in suspension a large number of colourless globules which slightly interfere with its transparency. ‘The blood of Oryctes quickly coagu- lates. This coagulation is not arrested by the addition of sodium chloride, magnesium sulphate, &c. But a slightly elevated temperature (54° C.) sufficed to prevent coagula- tion. When exposed to the air the blood of this insect becomes a dark brown colour; but the brown colour has not the same intensity throughout the fluid ; it is of a deeper colour in the vicinity of the mass of globules. Light has no action in changing the colour; the change being due to oxidation. After being coagulated with hot water, the blood of Oryctes * Bulletins del Académie Royale de Belgizue, 3° série, tome i, 136 PHYSIOLOGY .OF THE INVERTEBRATA. changes to a brown colour in contact with air. But the coagulum produced by alcohol is not acted upon by air. When the oxidised or brown blood is examined by the spectroscope, it does not show any characteristic absorption bands. At first sight the blood of Oryctes appears to contain a substance acting under the influence of oxygen in a similar manner to hemoglobin or hemocyanin. ‘The substance which becomes brown in air, does not probably play any 7dle in the respiration of the animal. ‘The blood in the vessels is perfectly colourless; the brown colour which is produced after it has been extracted from the body is probably a cadaveric or post mortem phenomenon comparable to the spontaneous coagulation which equally occurs in this liquid. In fact, the colourless substance, which becomes brown on exposure to air is not contained in the blood which circulates, but is formed at the moment of spontaneous coagulation. If one carefully plunges the larvee of Oryctes into warm water (so to 55° C.) for a quarter of an hour before opening it, the blood extracted from the dorsal vessel neither coagulates nor colours in air. The production of the colourless substance (susceptible of becoming brown in contact with air) has probably been prevented by the temperature of 50° to 55° C. For when once this substance has been produced, the temperature of boiling is incapable of preventing its combination with oxygen, and a change of colour which it indicates. Finally, the most important fact which proves that the phenomenon of colouration does not play any réle in the respiration of the animal, is that the brown substance once formed constitutes a stable combination, which is not decom- posed by acids or alkalies, and is not decolourised when placed in vacuo or in a sealed tube. The phenomenon of colouration which the blood of the larvee of Oryctes presents when it is exposed to air, appears to be a cadaveric phenomenon, and as already stated, com- PHYSIOLOGY OF THE INVERTEBRATA, 137 parable to spontaneous coagulation. The substance which becomes brown in air does not form any intermediate vehicle between the exterior air and the tissues which require it. The existence of such an intermediate vehicle is most doubtful, especially when one bears in mind the anatomical disposition of the respiratory apparatus in the Jnsecta, 1.¢., the air penetrates by the tracheee among all the living tissues. By means of the trachez the function of respiration is carried on in every part of the body. THE CRUSTACEA. Dr. Léon Fredericq* has examined the blood of various Crustacea. The blood of crabs, lobsters, &c., which live in the sea, has exactly the same taste as sea water; which leads one to suppose that the blood or nourishing fluid of these animals has the same saline composition as the waters in which they live. According to an analysis of Backs, and cited by Pelouze and Fremy,f the water of the North Sea contains a little more than three per cent. of soluble salts :— Sodium chloride : + 2.358 Potassium chloride . . 0.101 Magnesium chloride. ee OL 2a Magnesium sulphate. . 0.199 Calcium sulphate . sy POSLEE 3.046 It tastes strongly salt and bitter. In support of the idea that the blood of certain Crustaceu living in the North Sea, has the same saline composition as the medium in which they live, Fredericq obtained the following result after analysing the blood of an Ostend lobster (Homarus vulgaris) :— 3.040 per cent. of soluble ashes. * Bulletins de ? Académie Roya'e de Belgique, 3° série, tome iv. + Traité de Chimie, 3° éd., tome 1, p. 252. 138 PHYSIOLOGY OF THE INVERTEBRATA. The blood of a large female lobster (bled by making a cut in the claws) weighed 26.49 grammes. This blood was dried at a moderate heat in a covered crucible; then heated to complete carbonisation. The porous carbon was exhausted with warm water. The filtered solution was evaporated to dryness, the residue allowed to cool in a dessicator, and weighed with the usual care. The 26.49 grammes of blood yielded 0.8055 gramme of soluble salts, equal to 3.040 per cent. 23.01 grammes of the blood of the crabs (Carcinus manas) of Roscoff yielded 0.708 gramme of soluble salts, equal to 3.07 per cent. The crabs (C. menas) of Roscoff living in sea water of a density of 1.026 were also examined; 14.78 grammes of the blood of these animals yielded 0.445 gramme of soluble salts, equal to 3.001 per cent. The hermit crab (Platycarcinus pagurus) of Roscoff, whose blood had a density of 1.037, was examined by Fredericq ; 13.54 grammes of this blood yielded 0.419 gramme of soluble salts or equal to 3.101 per cent. In the case of another hermit crab the blood had a density of 1.036, and 31.08 grammes of it yielded 0.965 gramme of soluble salts, equal to 3.104 per cent. In the case of the sea crayfish (Palinurus vulgaris) of Roscoff, 22.94 grammes of blood yielded 0.666 grammes of soluble salts, equal to 2.9 per cent. In the case of Maja squinado of Roscoff, 15.60 grammes of blood yielded 0.476 gramme of soluble salts, equal to 3.045 per cent. The sea water of Roscoff in which the above Crustaceans lived was also analysed with the following results :—27.312 grammes of sea water yielded on evaporation 0.929 gramme of saline residue which is equal to 3.401 per cent. In another determination 26.266 grammes of the same water yielded 0.894 gramme of saline residue, which is equal to 3.407 per cent. PHYSIOLOGY OF THE INVERTEBRATA. 139 The Maja squinado of Naples lives in sea water which is exceptionally rich in saline matter ; 20.669 grammes of this water yielded 0.821 gramme of saline residue, equal to 3.9 per cent; 14.807 grammes of the blood of Maja yielded 0.498 gramme of soluble salts, equal to 3.37 per cent. Not ouly has Fredericq examined the blood of various Crustaceans inhabiting sea water but he has also examined the blood from those living in brackish and fresh water. 6.48 grammes of the blood of Carcinus menas inhabiting brackish water yielded 0.096 gramme of soluble salts, equal to 1.48 per cent. To examine the blood of fresh water Crustaceans seven crayfishes (Astacus fluviatilis) were used in the experiments. A large quantity of blood was obtained by making an incision in the claws. Its taste was only slightly saline; 23.453 grammes of it yielded 0.221 gramme of soluble salts, that is less than one per cent. (0.94 per cent.) The following table gives a summary of the results obtained concerning the saline matter of the blood of various Crustaceans and the medium in which they live :— PROPORTION OF SALINE MATTER IN THE BLOOD OF CRUSTACEANS. Ee ee aieieieea | Per- Density. Bice Density. gece of salts. Astacus fluviatilis . : : — | 0.940 — fresh water Carcinus manas . : -| 1.480 2 brackish water. ” 9 . . Sahel roe 1y) tlcneeegO 1.007 | about 0.9 ” op : F A — 1.560 | 1.010 sea peles ‘ % ' F i — | 1.990 | 1.015 esc ” 99 ; ; 2 aH 3.001 1.026 2°40 ii % : ; : — | 3.007 —- 3.40 Homarus vulgaris . 3 3 — | 3.040 1.026 aAr Platycarcinus pagurus . = |, 02027 3-101 1.026 3-40 3 Fs : 1.036 3.104 1.026 3-40 Palinurus vulgaris . — 2.900 1.026 3-40 Maja squinudo. : ; os 3-045 1.026 3-40 » ” . F -| — 3-370 ? 3-90 140 PHYSIOLOGY OF THE INVERTEBRATA, The blood of crabs living in brackish water contains a smaller percentage of saline matter than those living in sea water; and the blood of crayfishes living in rivers contains only a very small amount of saline matter—generally less than one per cent. According to the above investigations it appears that there is an exchange of salts, forming a kind of equilibrium between the composition of the blood and the external medium in which these Crustaceans live. This equilibrium is the result of the simple laws of diffusion. Among the fresh water Crustaceans the albuminoid substances of the blood probably retain a little more of the soluble salts than is contained in the external medium. It is probable that this exchange of dissolved salts is established by the respiratory organs—the branchie. ‘The delicate walls of the branchia, which separate the blood from the external medium, allow the respiratory gases to pass by simple diffusion: and most likely these delicate walls act in a similar manner to a dialyzer with easily diffusible salts. The albuminoid substances of the blood do not pass into the external medium. The nourishing fluids, to which the illustrious physiologist —Claude Bernard—gave the name of “milieu intérieur,” have not (with the animals previously mentioned) the constant chemical composition and independence of the conditions of the “ milieu extérieur ” which characterises the blood of the higher animals. Among fishes (Pisces) the branchial walls allow equally to pass the oxygen and carbonic anhydride of respiration. One can therefore understand that there is a similar exchange of salts between the blood and the external medium. But experience proves that it is the inverse of that which takes place among the Crustaceans and other Invertebrates ; for the blood of marine fishes has a saline composition which is entirely different from that of sea water. he blood of a sole, a PHYSIOLOGY OF THE INVERTEBRATA. 141 haddock, and a weever does not contain more soluble salts than the blood of fresh water fishes. Among fishes the interior fluid constituting the blood is isolated more or less from the external medium in which the animal lives. In regard to this there is an advance on that which occurs among Invertebrates. The blood of the Crustacea contains corpuscles which are very well defined. They are oval in shape, granular, and present a very distinct wall externally and nucleus within. THE MOoLuusca. The blood of the lower Mollusca (Lamellibranchiata and Gasteropoda) is corpusculated, but the nuclei (which are generally present) are sometimes very indistinct. The percentages of saline matter contained in the blood of Anodonta and Mytilus were found to be the following* :— Te Mie Ill. IVs Average. Anodonta cygnea . : . | 1.002 | 0.998 | 1.006 | 0.996 1.000 Mytilus edulis 2 z . | 1-796 | 1.799 | 1.810 | 1.800 1.80! It will be observed that the blood of the fresh water mussel contains a smaller amount of saline matter than that of the marine form. The blood of the Mollusca is principally colourless, but Dr. L. Cuénott has recently shown that the blood from the heart of Aplysia depilans (one of the Gasteropoda) has a distinct rose colour, due to the presence of 0.636 per cent. of an albuminoid which is precipitated by alcohol, acids, mercuric chloride, and the usual reagents. Its colour has no relation to the presence of oxygen, and it seems improbable that it plays any part in respiration. When the blood is dialyzed, * See Dr. Griffiths’ paper read before the Royal Society of Edinburgh on June 1, 1891 (P. 7. S. £., vol. 18, p. 288). + Comptes Rendus, vol. 110, p. 724. 142 PHYSIOLOGY OF THE INVERTEBRATA. or exposed for a long time to air, it decomposes spontaneously, part of the albuminoid remaining in solution and_ part separating in a white, flocculent form. This albuminoid is entirely distinct from hemocyanin, and has been called hemorhodin. If the blood is concentrated im vacuo and heated, it becomes opalescent at 58° C., and coagulates completely at about 70° C. The blood of Aplysia punctata is quite different, and contains 1.77 per cent. of a perfectly colourless haemocyanin which is not affected by air, and coagulates at about 76° C. This albuminoid probably plays no part in the absorption of oxygen. In the Gasteropoda, Cephalopoda, as well as in the Crustacea and Arachnida, the function of respiration is brought about by an albuminoid substance analogous to hemoglobin, but contains copper instead of iron. This substance, which Fredericq* named heemocyanin, combines with oxygen, form- ing a very unstable combination. The blue colouring matter of the blood of Octopus vulgaris is due to the absorption of oxygen, for if the blood is placed in vacuo it loses its colour, but regains it in the presence of air or oxygen. Hzemocyanin occurs in the arteries of the living Octopus. Krukenbergt examined the blood of Sepia officinalis, Carcinus menas, Homarus vulgaris, Squilla mantis, as well as other species of the Mollusca and Crustacea, and observed that the blood becomes blue by shaking with oxygen or air ; and that the blue colour disappears more or less with carbonic anhydride. ‘ Krukenberg also found great differences in the blood of individual Gasteropod Molluscs, which led him to assume that perhaps the oxygen in such cases is in a firmer combination with the hemocyanin than is the case in Crabs and Cephalopods. He also made the interesting observation * Archives de Zoologie Lxpérimentale, 1878; see also Fredericq’s La Lutte pour l Existence, p. 84. + Vergleich. Physiol. Studien, 1st R.,-3 Abh., 1880, 8. 72. PHYSIOLOGY OF THE INVERTEBRATA. 143 that the blood of Crabs and Cephalopods on treatment with carbonic oxide became colourless, but regained its blue colour on shaking with air. This behaviour is different from that of hemoglobin when similarly treated. It was further found that blood which had become blue by the reception of oxygen if allowed to stand in a test-tube exposed to the air did not lose its blue colour from above downwards, but from below upwards, whence he concludes that the blueing is not due to suspended particles, but to the presence of a chromogen which becomes blue by the reception of oxygen. .... He could find no hemocyanin in the blood of several Molluscs (e.g., Tethys fimbria, Doris tuberculata, Aplysia depilans, &c).” Although the blood of the higher Invertebrates, as a rule, contains copper, in some this element is replaced by man- gapese. Krukenberg has shown that the blood of Pinna squamosa (one of the Lamellibranchiata) as well as the organ of Bojanus are rich in manganese. If a borax bead is dipped into the blood of Pinna and then heated in the oxidising blowpipe flame, the bead becomes a distinct violet colour, and in the reducing flame it remains colourless. It is probable that copper, manganese, and possibly other ‘metals play the same part in the blood of the Invertebrata as iron plays in the Vertebrata. The author* of the present volume has also extracted copper from the blood and organs of Sepia officinalis ; but the process was entirely different from those of Fredericq and Krukenberg. In the majority of the Jnvertebrata the carrier of oxygen to the tissues is hemocyanin contained in the blood ; but in many of the Annelida, as well as in nearly all Vertebrates, the transport of oxygen from the surrounding medium (air or water) to the living tissues is made by means of the hemoglobin of the blood. * See Dr. Griffiths’ paper in Chemical News, vol. 48, p. 37; Journal of Chemical Society, 1884, p. 94. 144 PHYSIOLOGY OF THE INVERTEBRATA. This substance (as is well known) forms an oxygenised combination which is very unstable, and which is carried by the blood across the tissues of the animal, and is there dissociated, yielding its oxygen to the elements of those tissues which require it. Prof. Ray Lankester discovered that in some Annelids the hemoglobin is replaced by a green-colouring matter (chloro- cruorin). Reverting once more to the saline matter contained in the blood of the Mollusca, the author* obtained the following results (i.e, percentages) :— | fe Il. Tit, | Average. | | = |———— | a Helix pomatia . 2] 12065 1.072 1.069 | 1.068 } f a Helix aspersa . : 1.07 1.080 1.062 | 1.0 ‘S) vi | iS | o . . 2 Limneus stagnalis . | 1.200 1.203 1.210 1.204 1) 5 Limax flavus. yi Tarias2) |. ero6, bana geal eae iB. = . | a Dimas maximus . oP | atest 0) 1-027 1.114 | 1.120 O48 | / \'a 2 g | Buccinum undatum .| 1.699 | 1.710 | 1.698 | 1.702 |g2s | s a Patella vulgata . =. | ‘1.706 | 1.721 | 1.719 Tyas =a) | | | Ihigte? : Ane | | < oi Sepia officinalis . = | 21840" | °2.862>"|/ Sgr 21 Means | SiS : | | om Octopus vulgaris ‘ | 3.004 | 3.032 | 3.020 3.018 oO | Dr. L. Fredericqt found 3.016 per cent. of soluble and insoluble salts in the blood of Octopus vulgaris. The author of the present volume has submitted to analysis the ashes of the blood of several Invertebrate animals. ‘The ashes were obtained by incinerating the blood, partially covered in a platinum dish, at a very low tempera- * A paper read before the Royal Society of Edinburgh on June 1, 1891. + Bulletins de V Académie Royale de Belgique, 3° série, tome iv. PHYSIOLOGY OF THE INVERTEBRATA. 145 ture. By so doing the alkaline metals are not volatilised as they are when a high temperature is used. The following results represent the averages of three analyses in each case :— Cancer | Carcinus| Astacus Palinurus | Homarus pagurus.| menas. | fluviatilis. vulgaris. | vulgaris. Copper oxide (CuO) . 0.22 0.19 0.20 0.18 0.18 Iron oxide (Fe,O,) .| trace | trace — — trace Lime (CaO). 3-55 | 3-57 3.58 3-79 3-54 Magnesia (MgO) : 1.91 1.89 1.88 1.90 1.89 Potash (K,O) . : 4.97 4.78 4.82 4.92 4-77 Soda (Na,O) . : 43-90 | 44.91 44.96 43.98 44.99 | Phosphoric acid (iB; es 4.90 4.86 4.81 4.87 4.84 Sulphuric acid (80) 2.90 2.81 2.75 2.86 2.81 Chlorine . : 37-65 | 36.98 37-00 37-50 36.96 100.00 | 99.99 100.00 100.00 99.98 Anodonta| Mytilus Pinna Sepia Octopus cygnea. edulis. squamosa,. | officinalis. | vulgaris. Copper oxide (CuO) . 0.23 0.22 trace 0.24 0.21 Manganese oxide (Mn0O,) . : P — trace 0.19 _— = | Iron oxide (Fe,0O,) .- — — trace — = Lime (CaO) . 5 ||) Han a2 3.70 2.31 2.40 Magnesia (MgO) . 1.82 1.86 1.83 I.51 1.55 Potash (K,O) . -| 4.90 4.80 4.86 4.92 4.90 Soda (Na,0) . | 44.18 | 43.90| 44.02 45-40 | 45-31 *Lithium . a .| trace — | — — —_ phy toric acid | (P,0,) 4.89 4.82 4-79 4.90 4.88 Sulphuric acid (SO,) | 2.80 2.76 29s 2.81 2.83 Chlorine... | 37-55 37-92 | 37-88 37-90 37-92 nae Me i ol ss ae hl / 99.98 | 100.00 | 100.00 99.99 100.00 There is no doubt, from the above analyses, that copper plays an important part in the blood of the Jnvertebrata ; in fact it plays a similar 7é/e to that of iron in the blood of the higher Vertebrata.t * Detected by the spectroscope. + See Dr. Griffiths’ paper read before the Royal Society of Edinburgh on June 1, 1891. K 146 PHYSIOLOGY OF THE INVERTEBRATA. THE CHROMATOLOGY OF THE BLOOD OF THE INVERTEBRATA. We have already alluded to some of the colouring matters contained in the blood of the Jnvertebrata, but as a consider- able amount of work has been done in this direction, we propose to describe more fully the results obtained in this important subject. In England the two great authorities on the colouring matter of the Invertebrate blood are Dr. C. A. MacMunn, and Mr. E. B. Poulton, F.R.S. Both of these scientists have presented us with a valuable series of investigations which we now proceed to describe. | The colour of the blood in the Jnvertebrata “ does not as a rule belong to the corpuscles, but to what in them answers to the liquor sanguinis of Vertebrates, although there are many exceptions. In some hemoglobin occurs. ‘Thus, Prof. Lankester has shown* that in Glycera, Capitella, and Phoronis, and in Solen legumen, it is found in special corpuscles ; while in the vascular fluid of others it is found dissolved, ¢.g., with cer- tain exceptions in some chetopod Annelids, in some Leeches (Nephelis, Hirudo), in Polia sanguirubra (a Turbellarian), in the special vascular system of a marine parasitic Crustacean observed by E. van Beneden, in the general blood-system of the larva of the Midge (Chironomus), in the general blood- system of the Molluse Planorbis, and in the general blood- system of the Crustaceans, Daphnia and Cheirocephalus.” Hemoglobin is also present in the blood of Lumbricus Arenicola, and Eunice ; and it has already been stated that this haemoglobin is spectroscopically the same as that found in Vertebrate blood. The blood obtained from five hundred earth-worms (Lwm- bricus terrestris) was treated with benzene, which readily dissolves the colouring matter. The mixture was allowed to stand for twenty-four hours at o° C.; when it separated into two distinct layers. The one containing the colouring * Proceedings of Royal Society, vol. 21, p. 71. PHYSIOLOGY OF THE INVERTEBRATA. 147 matter was then separated from the other; and about one- sixth of its volume of pure absolute alcohol was added. After filtration the alcoholic extract was exposed to —12° C., when red crystals were obtained. These crystals yielded the following results on analysis :-— Blood of Lumbricus. | ta | Blood of Dog. I Il. lll | vs ; dorsal ma | Carbon . : : : 53-91 53:86 _ 52:55 | Hydrogen : : ; 7.02 710 — | These Nitrogen i , ; -— = _ TGsN74 |) | Sulphur . : ; , 0.41 0.37 — 0.39 | | Iron ie Ee 85 9.5 — — | Oseh lt loa | Oxygen . 3 5 zi _. — | — 2 SA) | | The above analyses prove that the colouring matter of the blood of Zumbricus is comparable chemically to that of a Vertebrate animal, like the dog.* Although hemoglobin is present in the blood of certain Invertebrates, the chief constituent in the blood of the majority of these animals is HEMOCYANIN, a compound said to be analogous to hemoglobin, but containing copper instead of iron. lt is well known that ‘‘the blood of many Molluscs and Arthropods is of a blue colour after exposure to the air, and this is in most cases due to the presence of hemocyanin.” (1) The Lchinodermata.—Dr. MacMunnf has examined the blood of Holothuria nigra. It does not contain hemo- globin, but when examined with the spectroscope it strongly absorbed the violet end of the spectrum but gave no bands. The colouring matter of the blood “is soluble in absolute * Griffiths in Proc. Roy. Soc. Edinb., 1891 (June 1). + Quarterly Journal of Micro:copical Science, vol. 30, p. 60. 148 PHYSIOLOGY OF THE INVERTEBRATA. alcohol, forming a deep yellow solution, giving an ill-defined band at the blue end of the green, beginning to be feebly shaded at about \ 526, darker at 4507, and extending to about A474. On evaporation it left a reddish residue soluble in ether, in chloroform, and other lipochrome solvents, and when in the solid state it became a transient blue with nitric acid, blue, green, and brownish with sulphuric acid, and greenish-yellow with iodine in potassic iodide. Therefore, the blood of Holothwria nigra contains a red lipochrome like that of certain Crustaceans, as Dr. Halliburton* has discovered.” Dr. MacMunn also found this red lipochrome or lutein — in the digestive gland of H. nigra; and states that he has no doubt that it “is built up in the digestive gland and carried in the blood current to be deposited in other parts of the body, though what its réle may be when deposited there, it is difficult to say. It is not easy to see of what use so much brilliant coloration as exists within the body of Holothuria nigra can be, except that the lipochrome is changed into some other constituent. If it be respiratory, as tetronerythrin is believed by Merejkowskyt to be, we could see some reason for its existence,” but as Dr. MacMunn has repeatedly shown, “‘ what has been called tetronerythin does not exist in two states of oxidation. Merejkowsky would doubtless call the red lipochrome of H. nigra tetron- erythrin without hesitation ; but since he published his results our knowledge of these fat pigments has undergone achange, » for we now know that there are a great number of pigments, formerly, with regard to their supposed respiratory properties, included under the name tetronerythrin, which are distin- guishable from each other, and which cannot any longer be called tetronerythrin, the rhodophan of the retinat is not respiratory, nor is the true tetronerythrin in the so-called ‘roses’ around the eyes of certain birds, respiratory.” The * Journal of Physiology, vol. 6. + Bulletin de la Société Zoologique de France, 1883, p. 81. + Kiihne in Untersuchungen a. d. Physiol. Instit. d. Univ. Heidelberg, Bd. 1, Heft 4, und Bd. 4, s. 169-248. PHYSIOLOGY OF THE INVERTEBRATA. 149 lipochromes included under the name _ tetronerythrin by Merejkowsky “ fail to respond to the test used in determining whether any pigment is respiratory or not, namely, change of colour and spectrum under the influence of reducing agents.” Dr. MacMunn* has also investigated the brown colouring matter of the perivisceral fluid of Hcehinus (esculentus ?) and sphera. This colouring matter gave two bands, one between D and E covering EH, and the other between ) and F, the first of which became decidedly darker after the addition of ammo- nium sulphide. MacMunn named this pigment echinochrome, and it has a respiratory function. Since his discovery of echinochrome, MacMunn has made some valuable observations on the perivisceral fluid of Strongylocentrotus lividus. On opening a specimen a pale red fluid exudes from the perivisceral cavity. ‘‘ In a short time a clot forms; this becomes gradually darker in colour and it contracts more and more, until all its connections with the side of the containing vessel are broken, and it finally shrinks into a small brown-red mass. The corpuscles are carried down by this clot, and it is to them, not to the plasma, that the colouring matter belongs.” Prof. P. Geddes f (who has worked out the morphology of the corpuscles of the perivisceral fluid of various Echinoderms) has shown that the finely granular, pale corpuscles run together to form plas- modia, and that it is to their fusion that the clotting is due. “ The corpuscles present all degrees of coloration, from a brilliant red, through a pale orange, to colourless. ‘The red ones are nucleated and of irregular shape, and rapidly throw out amoeboid processes, so also do the others. The nucleus is strongly refracting and gives the corpuscles the appearance of a round hole having been punched in it. ‘The red corpuscles measure from ;;'55 inch in long diameter x 5,55 inch in short, down to 355 in long x ggg, in short, while several * Preceedings of Birmingham Philosophical Society, vol. 3, p. 380. + Proc. Roy. Soc., 1880. 150 PHYSIOLOGY OF THE INVERTEBRATA. measure zz/55 in both diameters. The pale ones zs'50 * zo00 down to sg55 * goa; the latter are multinucleated. “The pigment itself in the fresh state showed no distinct bands, but treated with caustic potash in the solid condition 15h XG: D E.b 1 G Echinochrome +KHO, iresh clot. Echinochrome in ‘* Serum.”’ Do. + Stan- nous chloride. Echinochrome in blood clot. Do. + NaHO. Do. in absolute alcohol. Do. with acetic acid. Do. with stan- nous chloride. Dried clot in ether. Do. in chloro- form. Do. in carbon bisulphide. Do. in benzene Fresh clot in glycerine. Do. with stan- nous chloride. FIG. 29.—SPECTRA OF PERIVISCERAL FLUID OF STRONGYLOCENTROTUS LIVIDUS. (After C. A. MACMunN.) the colour changed to dark purple” and showed the bands in ~ as the spectrum « (Fig. 29). MacMunn says that the deepening of colour which echinochrome undergoes on exposure to the air must be in PHYSIOLOGY OF THE INVERTEBRATA. 151 part due to the oxidation of a chromogen, if so we may infer the existence of such, and name it echinochromogen. Echinochrome differs from the blood pigments of most Invertebrates, as it is readily dissolved by a great number of solvents. It can be obtained in solution and isolated by two methods :—‘‘(a) The fresh blood-clot can be extracted with the solvents mentioned before, or (0) the clot may be separated from the serum by filtering, the pigment dried at the tempera- ture of the air (as it changes by using heat) and the dried pigment thus obtained treated by solvents. By the adoption of the latter method it can be obtained in a purer condition.” “The ‘serum’ after separation of the clot is a faint yellow colour and shows two faint bands in the green, but if allowed to stand some time in contact with the clot it becomes a faint violet red,” and then gives the spectrum seen in Fig. 29,0. On the addition of stannous chloride to the serum dark bands (Fig. 29, ¢) make their appearance. These bands have the following positions, A 541.5 to A 532 and A 506 to \ 486.5. Inthe oxidised condition the serum has a spectrum of the same kind but the bands are feebler. The serum is “faintly acid or neutral, faintly opalescent on heating, opalescent with absolute alcohol, and faintly so with ether.” Spectra Fig. 29, d and e are those of the brownish-red clot, after standing in contact with the serum and with sodium hydroxide respectively. The red alcoholic solution of the clot gives the spectrum represented in Fig. 29,7. These bands read: first, X 557 to 545-53 second, A 524.5 to A5o1; third, X 494.5 to’ 475. On the addition of ammonium sulphide two new bands make their appearance. The first is from A 531 to A507; and the second, 494.5 to (475, the colour of this solution being changed to yellow, and on shaking with air remained the same. On the addition of acetic acid to an alcoholic solution of the fresh clot, the spectrum given in Fig. 29,g is seen. “The spectrum of the original absolute alcohol solution is that 152 PHYSIOLOGY OF THE INVERTEBRATA. of the neutral pigment, as can be proved. Hydrogen peroxide did not affect the bands. Hydrochloric acid produced the same effect as acetic acid; the bands reading: first, A 545.5 to X 529.5; second, A 511.5 to A 488. When the alcohol solution is treated with stannous chloride the colour changes to yellow, and two very well-marked bands appear (Fig. 29, 7). Dark part of the first band, A 535 to A 511.5; second, A 496.5 to’ 477. Sodium hyposulphite changed the colour to yellow, but the original bands could be seen, although faint.” Dr. MacMunn has also examined solutions of echinochrome in chloroform, water, ether, carbon disulphide; some of the spectra of these solutions are given in Fig. 29. Kchinochrome is only partially soluble in water and alcohol, but is soluble in chloroform, ether, beuzene, glycerol, carbon disulphide, and petroleum ether. It is capable of existing in two states of oxidation, therefore its function is of a respiratory nature. Echinochrome has not been obtained in the crystalline condition. (2) The Annelida.—The blood of many Annelids contains hemoglobin; some contain pigments allied to chlorophyll, while others contain lipochromes. The blood of Arenicola piscatorum (one of the Polycheeta) contains, besides hemoglobin, a lipochrome or lipochromes. Dr. MacMunn obtained a dark brown-green extract by treating this worm with a solution of caustic potash. This solution gave no bands. But he has extracted from the digestive system and the integument of Avenicola certain lipochromes, which have well-defined absorption spectra. The spectrum of the blood of Nereis Dumerillii consists of a single band like that of reduced heemoglobin. The spectrum of an aqueous solution of the blood of this worm consisted of two feeble bands; ‘the first was like that of the first of oxyhzemoglobin, but the second was rather narrower than is the second blood-band. ‘These bands read approximately : the first, from A 584.5 to A574, the second, about XA 550.5 to 536, anda third one at the blue end of the green, from about PHYSIOLOGY OF THE INVERTEBRATA. 153 A 507 to A 474 (2) was visible. Sulphide of ammonium caused these bands to disappear,” but Dr. MacMunn could not then detect that of reduced hemoglobin. The various colouring matters contained in the blood and organs of certain worms are given in the following table :— | | Chlorocruorin, | Lipochromes. ced cleats Hemoglobin. | Polynie . ait -- | present — absent | Aphrodite . : — Ss — present | Nereis. : — | present — — _Sabella . «| present | —- — - | Siphonostoma . present — -- _— | Serpula. : present — — _ | Cirratulus . , — present — present Terebella . : _ present — present | Lumbricus : _ | present = present | Hirudo .. : = ar — present | Chatopterus Pi - absent present = | Arenicola . : -- | present = — Pontobdella | — | = present = Glycera | — | = — present Phoronis . : | _— | _ —- present Dr. MacMunn has examined the green fluid (containing chlorocruorin) of Sabella by means of the microspectroscope. The spectrum (Fig. 30,@) consists of a dark band before D, and a feeble one between D and E. The green blood has “a reddish tinge with reflected gaslight, and in most cases is green with transmitted daylight, and reddish with transmitted gaslight. On dilution with water this fluid gave two bands: b h Ut 7 154 PHYSIOLOGY OF THE INVERTEBRATA. the first from X 618 to A 593, the second from A 576 to A 554.5.” On adding ammonium sulphide, the spectrum Fig. 30, 0 is produced. The first of these bands extends from A 625 to d 596.5 (?), but this, and also the second band, says MacMunn, BC D Eb 1 G Oxychloro- cruorin. The same + NH4HS. Do. + NaHO. Aq. sol. + NaHO, then NH4HS. Blood of Ser- pula, living animal. Blood of another Serpula. Do. from a dilated part of blood-vessel. Do. from same part, a third specimen. Do. from same part, a fourth specimen. Aqueous solu- uion of blood of Serpula. Do. other specimens. Do. + NaHO, then NH4HS. Gills of Serpula. Operculum of Serpula. Fic. 30.—SPECTRA OF THE BLOOD OF SABELLA AND SERPULA, (After C. A. MACMUNN.) “were very faint.” After the addition of sodium hydroxide to this solution, a dark band is seen covering D, “ which recalls to mind the band of alkaline hematin (Fig. 30, ¢), and this band extends from X 595 to A 576.” PHYSIOLOGY OF THE INVERTEBRATA, 155 When the blood is treated with alcohol and potassium hydroxide and filtered, a yellow-coloured solution is obtained “free from bands, but on adding ammonium sulphide a band appears covering D” (Fig. 30,d). “On treating aqueous solutions with acetic acid the bands faded away, and the colour of the solution changed to a brownish colour (gaslight).” MacMunn tried the action of alcohol acidulated with sulphuric acid on chlorocruorin, and obtained a greenish solution, which showed a faint shading in the green, too indistinct to map. “ Hence none of the decomposition products of haemoglobin or hematin could be obtained, the pigment, as Prof. Lan- kester had already shown, being destroyed by the reagents required to produce acid hematin and hematoporphyrin. The blood of the pseudo-hzmal system of Serpula contortu- plicata presents some resemblance to that of Sabella. There are slight differences in the blood spectra of some specimens, which doubtless are due to the pigment being present in different states of oxidation, and on comparing some of these spectra with those of the histohematins and with the decomposition products of hemoglobin, a striking likeness is apparent.” “On putting a Serpu/a into the compressorium, and bring- ing gentle pressure to bear on the upper surface of the animal, and examining with the microspectroscope, using a good achromatic substage condenser, a series of spectra are obtained when the various parts of the animal are moved under the objective ; what these parts are is seen by looking down the left-hand tube of the microscope. In this way we can differentiate the blood-vessels, intestine, gills, opercu- lum, and other parts, and study the spectrum of each.” With the pseudo-hemal system of Serpula, MacMunn obtained a spectrum represented in Fig. 30,c. The band before D is like that of Lankester’s chlorocruorin, but the first after D and also the second are different. An aqueous solution of the blood from the pseudo-heemal system is yellow by daylight, reddish-yellow by gaslight, and 156 PHYSIOLOGY OF THE INVERTEBRATA. its spectrum is represented in Fig. 30,e. The band before D was from 620.5 to A 593, the second about A 583.5 to A 572, the third uncertain (about A 551 toA 532). After the addi- tion of ammonium sulphide, “‘the only band seen with cer- tainty was that before D, which seemed slightly nearer the violet.” In an alcoholic solution only a faint band was visible from about X 501 to A 477. In a specimen in which the blood appeared a_ bright carmine-red colour, MacMunn obtained the spectrum repre- sented in Fig. 30,/ The second band of this spectrum resembles the first band of hemochromogen, and is really the same as Fig. 30, 0. Fig. 30,g represents the spectrum of the blood from a dilated part of the principal blood-vessel of Serpula. ‘The darkness of the second band at once distinguishes the pigment from chlorocrurorin.” Fig. 30, and also represent the spectra of the blood from the same part of a third and fourth specimen. “An aqueous solution of blood obtained from a dozen specimens, whose blood gave the above spectra, was yellow, and showed the three bands represented in Fig. 30, 7, and these gave the following readings :—First band, X618 to A 593; second, A582 to A 570.5; third, A551 to X529.5 (?) On treatment with sulphide of ammonium the solution became slightly greener ; no bands could then be seen after D, and that before it was very faint. Hence it would appear that the two- and three-banded spectrum denotes the oxidised state. “In some Serpule@, whose blood was not red but brown, the bands before and after D reminded one of chlorocruorin (Fig. 30,%). An aqueous solution of the blood of these speci- mens had a reddish tint by gaslight, and gave three bands, which read as follows:—First, \ 620.5 to 595; second, . A 538.5 torA 570.5; third,’ 551 to A532. On adding sul- phide of ammonium, the band before D read 620.5 to \ 598, and a second band was visible after D, which could not be measured. On adding to this reduced fluid some caustic soda, at first the only change produced was the disappearance PHYSIOLOGY OF THE INVERTEBRATA. 157 of the faint band after D; but, after standing, the spectrum given in Fig. 30,/ appeared, of which the bands read: first, A623 to (607; second, A 596.5 toA579. This shows that the blood of these Serpule did not contain the same kind of chlorocruorin as Sabella, but a pigment very closely related to it, probably nearer to hematin than it.” MacMunn has also investigated spectroscopically the gills and opercula of Serpula. The pigment present is allied to, if not identical with, tetronerythrin. The use of this pigment is not of a respiratory nature. “It is not unlikely that, especially when its likeness to Kiihne’s chromophanes is taken into consideration, it may be of use in absorbing rays of light concerned in some obscure photochemical process.” * From what has been said, it will be seen that the blood of the Annelida contains various pigments; and that hamo- globin and the lipochromes are uniformly distributed among these animals. Krukenbergt observes: ‘“ Chlorophane und rhodophane tragen auch bei Wiirmern in manchen Fiillen viel zu einer lebhaften pigmentirung bei.” (3) The Jnsecta.—Mr. E. B. Poulton, F.R.S., has examined spectroscopically the blood of Lepidopterous larvee and pupe. He used Zeiss’ microspectroscope in these researches, which was found ‘to be extremely delicate and convenient on all occasions.” As a means of illumination a paraffin lamp was at first used, ‘‘ and it acted very well for the less refrangible half of the spectrum, but in all later work bright sunlight was alone employed, because of its immense superiority at the violet end.” Concerning Zeiss’ and other microspectroscopes used in researches on the chromatology of the Invertebrate blood, a description of these instruments will be given later in the present chapter. The greatest care is required in obtaining the blood of insects so as to prevent any admixture with food particles of * Quarterly Journal of Microscopical Science, 1885. + Grundziige einer vergl. Physiol. d. Farbstoffe und der Farben, 1884, p. 137. 158 PHYSIOLOGY OF THE INVERTEBRATA. the alimentary canal or any secretions. As the blood in Lepidopterous larve exists under considerable pressure, it is readily obtained by making a minute prick in the hypodermis. In larvee, Mr. Poulton generally pricked the distal parts of the claspers; and then examined a drop of the blood under the microscope to see if any food particles were mixed with it. The blood should be perfectly clear, containing only colourless corpuscles, fat-cells, and minute spherules of fat. The blood of pups was obtained by making a prick in the cuticle of the wings. The blood at once issues, being under considerable pressure. ‘‘ The whole of the blood was obtained by pushing the abdominal segments inwards, and ultimately by gradually increasing compression of the pupa. Owing to histolytic changes, the weak and thin-walled digestive tract is broken, and a red fluid escapes, which is mixed with the last of the blood. By carefully watching for the first appear- ance of the red fluid, the blood may be obtained in a perfectly pure state, exactly resembling that of the larva in clearness and in microscopic contents. The blood is received into sections of glass tubes of various lengths, with the ends care- fully ground. One end is cemented with Dammar varnish to a glass slide, and when the tube is filled with blood a cover-glass is placed upon the open end, and becomes fixed by the drying of the blood. In most cases the blood so pre- pared will keep for months without change. If, however, air be admitted, an opaque black clot is formed on the sur- face, and the rest of the blood becomes cloudy. It will also keep indefinitely in sealed tubes.” * Mr. Poulton has examined the blood of the larve ot Phlogophora meticulosa, These larvee assume various shades of colour between green and brown. The green blood was taken up by a capillary tube (0.75 mm. internal diameter) ; and allowed to stand four days, during which time it was reduced to about half its volume (due to evaporation). The tube was then sealed. The spectrum produced by using a _ * Proc. Roy. Soc., vol. 38, p. 283. PHYSIOLOGY OF THE INVERTEBRATA. 159 paraffin lamp was the following: ‘‘a broad band in the red, of which the extreme edges extended from 64.5-—68.5, and when this band was best seen the violet end was cut off at 51, und the green was darkened to 52. ‘There was no absorption of the red end. When the blood was fresh and less concentrated, the blue came through on the violet side of the darkening at 51, thus showing a broad dark band between this part and the green. A more concentrated sample of similar blood, prepared in the same way and at the same time, gave a darker band in the red with the same limits, but with more defined edges. The violet end was similarly absorbed. There were indistinct traces of a broad dim band about 59-61.5.” “The fresh blood of another individual of the same species which was dark greenish-brown, due to a combination of subcuticular pigment and green blood, was examined in a capillary tube. The compound character of the larval colour- ing was proved by gentle pressure. The pale green blood with a thickness of about I mm. gave the band in the red from 65-68, the violet end, being completely absorbed at 45, darkened to 51 (when the slit was narrowed so as to render the band distinct). A greater thickness of blood darkened the band, and cut off the violet end at 50, darkening to 52 (when the band was distinct). | 13.26 12.91 | 13.14 | 14.62 14.21 | 14.34 | | Carbonic anhydride . =) 30.12 | 31.21 | 32.10 | 30.14 | 29.12 | 29.89 Nitrogen . 0 é : 1.60 | 2.00] 1.51 | 1.41 | 17/3) lees | | The nitrogen is simply dissolved in the blood, but the oxygen and carbonic anhydride are partly dissolved and partly in a state of loose chemical combination with certain constituents of the blood. The oxygen, with the hemocyanin, and possibly the greater part of the carbonic anhydride, is united to certain salts contained in the blood. (b) Blood of Cancer pagurus. The blood was obtained from very large individuals by opening the carapace, and passing the capillary point of the canula directly into the heart. A hundred volumes of the blood yielded the following volumes of oxygen, carbonic anhydride, and nitrogen after being reduced to o° C. and 760 mm. :— | I. |#9 S0Ieaee stalls lv. | 2M Oxygen ; ; j ‘ reall eas GC) | 14.88 | 14.96 | 14.85 |Carbonicanhydride . . . | 28.62 | 27.21 | 27.14 | 28.39 | | | | | Nitrowen . . ; ¢ | om |), ne@od|) Saree ego (c) Blood of Palinurus vulgaris. A hundred volumes of the blood of this animal gave the following results :— PHYSIOLOGY OF THE INVERTEBRATA. 179 Oxygen . : ‘ : : : 14.62 14.71 14.29 14.76 | Carbonic anhydride : 2 = |* 30.00) || 29:62) |) 28.92) | 29579 | Nitrogen : : > 4. ‘ 1.82 | 1.60 1.20 1.34 (d) Blood of Homarus vulgaris. A hundred volumes of the blood obtained from several large lobsters yielded the following results :-— | | | 1. 11. Il. | Oxygen . - : : =| 14.99 14.81 14.85 Carbonic anhydride ; ‘ Snatt 28.84 29.26 Nitrogen A> th tan me 1.76 1.82 85 | (e) Blood of Octopus vulgaris, A hundred volumes of the blood yielded the following results :— | DIT; == _ 3 fie ee a — {Nees 2 Le | | Oxygen . = - : ; 13.33 | 13.28 | 13.65 Carbonic anhydride : : 30.23 31.29 31.22 eee + 4 Clk 1.45 nae | 1.29 (f) Blood of Acherontia atropos. A hundred volumes of the blood of the larvee of this moth yielded the following results :— 180 PHVSTOLOGY OF THE INVERTERRATA: IT ite | Oxygen ; ‘ : : ; 16.21 | 16.79 Carbonic anhydride. : : 32.92 | 34.24 | | | Nitrogen. 4 ; ; : 1.09 | 1.98 It may be stated that the oxygen and carbonic anhydride in the blood of the Jnvertebrata do not behave according to the law of Dalton (the law of partial pressures) in regard to the absorption of a mixture of gases by a simple fluid. A portion of each gas combines chemically with some con- stituent or constituents of the blood. It was Magnus* who first demonstrated that the oxygen and carbonic anhydride of the Vertebrate blood did not obey the law of Dalton; and the same is true concerning the gases of the blood of the Invertebrata. Surveying the Jnvertebrata as a whole, we find animals like the Pyvotozoa devoid of blood; next, animals, as some Trematoda and Cestoidea, with blood devoid of corpuscles or solid particles; then such creatures as the Echinodermata, where the blood is corpusculated. In some of these forms, the corpuscles merely consist of solid particles of proto- plasm, devoid of cell walls and nuclei; while in others the blood contains walled and nucleated corpuscles. In the Myriapoda the blood contains three distinct corpuscles, and during a portion of its course is contained in blood-vessels. In the Crustacea the corpuscles are walled and nucleated, but are colourless, or nearly so; while in the Gephyrea the cor- puscles have a limiting membrane, nucleus, and coloured contents. As a rule, the colouring matter of the Invertebrate blood belongs to the plasma, and not to the corpuscles; but there are exceptions to this rule, which have already been alluded * Poggendorfi’s Annalen, vol. 40, p. 583. PHYSIOLOGY OF THE INVERTEBRATA, 181 to in this chapter. Concerning the colouring matter itself, it offers a greater diversity of individual pigments than the blood of the Vertebrata. In some forms we find chlorophyll and allied pigments ; while others contain one or more of the following pigments:—Hchinochrome, chlorocruorin, heemo- cyanin, hemoglobin, and the lipochromes. “To contrast the various conditions of the blood corpuscles of the Invertebrata with the stages in the development of our own red corpuscles is not without interest. There is a time in the history of the highest mammal when there is no blood developed; there is a time when only fluid blood, destitute of corpuscles, is to be seen; possibly our blood corpuscles commence as minute fragments or protoplasm derived from the digested food. These minute granules may coalesce in the absorbent vessels and form free nuclei; the nuclei may become surrounded by granules, a wall be de- veloped on the exterior of these, and a white corpuscle (leu- cocyte) would result.” The colourless corpuscle, in its turn, is transformed into a red corpuscle; but the history of this transformation belongs to the physiology of the Vertebrata rather than to that of the Jivertebrata. CHAPTER VII. CIRCULATION IN THE INVERTEBRATA. THE circulation of the blood in the higher animals was dis- covered by Harvey in 16109. In order to nourish all the parts of the body, it is necessary that the blood should be conveyed to these parts; but the mode in which it is conveyed differs considerably in the lower animals. Among the Invertebrates we find that the mode of circulation becomes more and more specialised as they rise in the zoological scale. Irom the Protozoa to the ‘elenterata, the circulatory and digestive systems are still fused together, for they are not differentiated. In the Echinodermata and Annelida we find the first true blood or vascular system. In most worms one of the blood-vessels forms a pulsating tube, or so-called heart, by which the blood is driven towards the periphery of the body through certain vessels, returning by others. In the Jo/lusca there is a contractile vessel, which has a much closer resemblance to the Vertebrate heart than the above. This heart consists of two or three chambers ;—(@) One or two auricles, which serve for the reception of the blood, brought to them by the veins; (0) the ventricle which serves for the propulsion of the blood into the arteries. It will be noticed from the above remarks that the circulatory system, like all others, was not perfected at once. Nature made numberless attempts, adding successively new pieces to the system, or complicating little by little those which existed already. In other words, the circulatory system became more and more PHYSIOLOGY OF THE INVERTEBRATA. 183 differentiated under the influence of natural selection and the struggle for existence. As already stated, in the lowest Invertebrates the digestive and circulatory systems are not differentiated, but among the higher Invertebrates these two systems become distinct. The circulatory system only shapes itself after the digestive system; consequently one may look upon the former as an appendage to the latter. In the higher animals the blood is made to pass through the respiratory organs in order to expose it to the oxidizing action of the air. In certain of the lower animals the air penetrates into the body; but in all the higher animals, and in many of the lower, there exists a complex apparatus for the circulation of the blood: (1) A system of blood-vessels to convey the blood into the various parts of the body. (2) An organ (called the heart) destined to put this fluid in motion. Most animals, from man to the Annelida, have a heart. THE PROTOZOA. In these creatures there is no true blood, yet there is a curious foreshadowing of a circulation. In the Rhizopoda* the only structures which may be said to have a circulatory function are the contractile vacuoles. The spaces are filled with a clear fluid, and exhibit fairly regular and rhythmic expansion and contraction (diastole and systole). During the systoles radiating canals or vessels extend from these vacuoles; these widen as the vacuole lessens in diameter. Presently the vacuole begins to expand, whilst the radiating canals become narrower in diameter and ultimately disappear. The contractile vacuole performs more than one function, and among these is probably that of circulation. ‘There is a pulsating central “organ” with conducting canals proceed- ing therefrom. Does not this look very much like a primitive circulatory system ? * The Rhizopoda includes the Protoplasta, Foruminifera, and the Ladic- laria, 184 PHYSIOLOGY OF THE INVERTEBRATA. “In the Znfusoria, contractile vacuoles ure present, and there is also a curious movement of the outer layer of the sarcode in company with the food vacuoles. It will be remembered that these food vacuoles pass, after quitting the abrupt termination of the cesophagus, through the sarcode along a very definite line. They trace the outline of the in- fusorial body as they pass along just within the contractile layer of the animal. With them the outer layer of the sar- code is said to move.” THE PORIFERA. In the Porifera or Spongida, there is no true blood, but there is a circulation of water carrying food particles and air for respiration. This circulation is brought about by the action of cilia, which cause the currents of water to enter the inhalent pores, and after traversing the internal canals, finaily take their exit through the exhalent pores. These currents of water containing nutritive matter act as carriers of tissue- forming materials as well as of waste products, consequently we may regard them as representing the circulatory system among these Invertebrates. Although the water currents in the Porifera have a circulatory function, they also perform the functions of respiration and digestion. THE CcazLENTERATA. In these animals the blood or nutritive fluid is not con- tained in any vessels, but is free in the somatic cavity or enteroccele. This fluid is moved by ‘the contractions of the body, and, generally, by cilia developed on the endodermal lining of the enteroccele.” By this means a kind of circula- tion is constantly maintained. ‘The movements of the body of the animals belonging to the Cw/lenterata cause a movye- ment of the corpusculated blood in the body cavities, a flux and reflux, a flowing and an ebbing of the nutritive fluid. Here is the most general form of circulation. There are no PHYSIOLOGY OF THE INVERTEBRATA. 185 vessels and no special pumping apparatus, for the whole body is concerned in the performance of this function. ‘“ In the compound Cwlenterata, this motion of the corpusculated fluid of the body cavity affects also the fluid in those extensions of FIG. 35.—CIRCULATION IN MEDUS®. the body cavities, through the common flesh or ccenosarc, that place in communication the interiors of the various members of the compound animal.” Fig. 35 represents the circulatory system in the Meduse. THE ECHINODERMATA. All the Hcehinodermata are furnished with distinct organs of circulation, consisting of a ‘“‘ heart or corresponding organ, and a complicated system of vessels. This circulatory system consists of two vascular rings surrounding the orifice of the digestive tube. These rings are connected with each other, they emit radiating ramifications, and one of them receives vessels proceeding from the intestine.” Such is a general description of the circulatory apparatus in the Lchinodermata, but since the time of Cuvier and Tiedemann ‘the presence or absence of a blood-vascular system in the Asferidea has been alternately asserted and denied.” The investigations of Greef,* Hoffmann,t and Teuschert are in favour of “the * Marburg Sitzungsberichte, 1871-2. + Niederliindisches Archiv, vol. 2. t Jenaische Zeitschrift, vol. 10. 186 PHYSIOLOGY OF THE “INVERTEBRATA, existence of the anal ring, and of an extensively ramified system of canals, connected with it and with the neural canals.” But according to Prof. Huxley, “ the facts, as they are now known, do not appear to justify the assumption that these canals constitute a distinct system of blood-vessels.” Prof. Huxley doubts the special circulatory function of the neural canals, and he does not consider that the sinus which accompanies the madreporic canal is in reality a heart. He states that this sinus and canals ‘‘are mere sub-divisions of the interval between the parietes of the body and those of FIG, 36.—CIRCULATION IN ECHINODERMATA (Sea-urchin). the alimentary cana!, arising from the disposition of the ambulacral vessels and that of the walls of the peritoneal cavity ; both of which, as their development shows, are the result of the metamorphosis of saccular diverticula of the alimentary canal, which have encroached upon, and largely diminished, the primitive perivisceral cavity which exists in the embryo. The peritoneal cavity of the body and rays is filled with a watery corpusculated fluid (blood); a similar fluid is found in the ambulacral vessels, and probably fills all the canals.” Fig. 36 represents the circulatory system in Avhinus. PHYSIOLOGY OF THE INVERTEBRATA. 187 THE ‘T'RICHOSCOLICES. “In the Zurbellaria, Trematoda, and Cestoidea, the lacunie of the mesoderm and the interstitial fluid of its tissues are the only representatives of a blood-vascular system. It is probable that these communicate directly with the terminal ramifications of the water-vascular (respiratory) system. In the fotifera, a spacious perivisceral cavity separates the mesoderm into two layers, the splanchnopleure, which forms the enderon of the alimentary canal, and the somatopleure, which constitutes the enderon of the integument. The ter- minations of the water vessels open into this cavity.”* THE ANNELIDA. In the Annelida there is a perivisceral cavity (perienteric space) communicating with the segmental or excretory organs. This cavity contains a colourless fluid consisting of a coagul- able albuminous plasma and numerous colourless corpuscles. The perivisceral fluid is not only nutritive, but acts as a liquid fulcrum to the muscular movements of the body. If this fluid is let out the power of voluntary motion is lost. It has been stated that “the vermicular motions of the intestine are aided or determined by its resistance and support; it favours circulation by obviating the pressure upon the blood-vessels, which follow the contact of the intestine with the integument, and is, perhaps, the source, or one of the sources, of the blood itself.” This fluid con- tains albumin, fibrin, and certain salts. In addition to the perivisceral cavity and its fluid, there is in most of the Annelida a system of vessels with contractile walls. These vessels, known as the pseudo-hemal system, are filled with a fluid, which may be red or green, and corpusculated or non- corpusculated. In some Annelids the pseudo-heemal system communicates with the perivisceral cavity ; but in the majority of these animals it is shut off from it. * Huxley’s Anatomy of Invertebrata, p. 57. - 188 PHYSIOLOGY OF THE INVERTEBRATA. Professor Huxley considers that the perivisceral fluid represents ordinary blood as far as being a carrier of nutri- ment to the tissues; and that the pseudo-hemal fluid is 8) AS d = supra-neural ‘Transverse section. lateral neural vessels. D transverse vessels. h = hearts. oO 5 Cc sub-neural vessel. 6 = dorsal vessel. — FG. 37.—THE CiRCULATORY SysTEM CF LUMBRICUS. e = nerve. alimentary canal. vessel. & = segmental organ. B = Looking down on nerve with supra-neural vessel removed. a \ = Dissection from dorsal side, with the alimentary canal turned on one side. probably only engaged in the function of respiration ; hence the reason that he calls it ‘‘ respiratory blood.” After these general remarks we proceed to detail at length the pseudo-hzemal systems of Lumbricus and Hirudo. («) In Lumbricus, there are three principal vessels which PHYSIOLOGY OF THE INVERTEBRATA. 189 traverse the body in a longitudinal direction (Fig. 37, A, B, C, D). The dorsal or supra-intestinal vessel is situated on the dorsal side of the alimentary canal. The supra-neural or sub-intestinal vessel is situated along the ventral side of the alimentary canal; and the sub-neural vessel les directly beneath the great ventral ganglionic nerve cord. Besides the three principal vessels, there are two lateral neural vessels situated on either side of the nerve (Fig. 37, B). The dorsal vessel (which is contractile, and consequently drives the blood from behind forward) is connected with the supra- neural vessel in nearly every segment by pairs of transverse vessels—i.¢., one vessel on each side of the body connects the dorsal to the ventral trunk. In the anterior portion of the’ body the longitudinal vessels break up into a blood plexus, consequently in this region (7.¢., first seven segments) there are no distinct transverse vessels. Between the seventh and tenth segments, the dorsal vessel becomes dilated into what is known as the “ hearts” of LIumbricus. These “ hearts” contract so as to force the blood from the dorsal to the ventral side of the body. The dorsal vessel also sends out branches to the body wall, mesenteries, and to the walls of the alimentary canal. The supra-neural vessel sends out branches to the nervous system, and also transverse vessels which unite with the sub-neural trunk (Fig. 37, D). Certain transverse vessels also unite the dorsal to the sub-neural vessel ; these vessels supply the segmental organs and integument with blood. (b) The body or perivisceral cavity in Hirudo is only im- perfectly differentiated from the vascular system. It is filled with loose connective tissue in which are dorsal, ventral, and lateral spaces (sinuses) containing blood. The vascular system (Fig. 38) consists of a ventral blood- vessel or sinus, and two wide lateral vessels which run along the sides of the body. There is also a median dorsal vessel. All these vessels anastomose with each other, and send off 196 PHYSIOLOGY OF THE INVERTEBRATA. branches which also anastomose and give rise to a fine net- work of blood-vessels situated on the organs of generation, nephridia, and in the muscular mesodermic layer. The red blood contained in these vessels has already been described. In the Polychwta the perivisceral cavity is continued into all the important appendages of the body, consequently they are filled with blood. ‘The circulation of this fluid is effected partly by the contraction of the body and its appendages, partly by the vibratile cilia, with which a greater FIG, 38.—DIAGRAM OF THE PSEUDO-H-EMAL VESSELS OF HIRUDO. (After GRATIOLET.) a = dorsal vessel and branches. 4 = lateral vessel and branches, c = ventral vessel and branches. d = branches. or less extent of the walls of the perivisceral cavity is covered. In a great number of Polychaeta no part of the body is specially adapted to perform the function of respiration, the aération of the blood probably taking place wherever the integument is sufficiently thin; and, even when distinct branchiee ordinarily exist, members of the same family may be deprived of them.” PHYSIOLOGY OF THE INVERTEBRATA. 1gl In many of the Polychata, the pseudo-hemal system is entirely absent (¢.g., Polynoé squamata), while in others it varies greatly in the arrangement of the principal vessels ; ‘** but they commonly consist of one or two principal longitu- dinal dorsal and ventral vessels, which are connected in each somite by transverse branches. Where branchie exist, loops or processes of one or other of the great trunks enter them.” The dorsal and ventral vessels are generally con- tractile ; and the direction of the contractions “is usually such that the blood is propelled from behind forwards in the dorsal vessel, and in the opposite direction in the ventral vessel ; but the course which it pursues in the lateral trunks is probably very irregular,” THE ARTHROPODA, The various classes belonging to the Arthropoda present a system of vessels, partially at least, shut off from the somatic or body cavity. But the blood-vascular system is not com- plete in any Invertebrate animal. In some part or parts of the body the vessels will be found to terminate, and the blood will flow through lacunz or spaces not bounded by any limiting membrane. From this remark it will be observed that the old form of circulation once more comes uppermost— i.e., the blood passes into the general body cavity. This primitive form of circulation is met with in all Invertebrates, but the higher forms have partially developed a system of blood-vessels, which is, however, incomplete, consequently the lower the animal, the more extensive is the lacunar circulation. In the Jnvertebrata, the arteries have not the three coats, such as are met with in the higher animals. The heart is generally situated in a dorsal position ; and its pulsations drive the blood at once over the body generally, and not to the organs of respiration first. ‘‘The word ‘pericardium,’ used by some writers in describing the blood systems of the Jnver- tebvata, 1s an unfortunate and a misleading one. The pericardium of the Jnsecta and Crustacea has no homology 192 PHYSIOLOGY OF THE INVERTEBRATA. with the serous membrane, that invests the heart of the Vertebrate animals. It is, in truth, a large venous sinus, surrounding that long segmented vessel in the dorsal region of the body that is generally called the heart. From this sinus, blood passes into the heart by certain lateral openings provided with valves opening inwards. Yet another unfor- tunate name has been used in this connection. Certain parts of the venous system in the Jnsecta and Myriapoda have been designated portal. They represent, however, in no manner the portal system peculiar to the Vertebrata.” In the Arthropoda, there are no pseudo-hzmal vessels ; and “the blood-vascular system varies from a mere perivisceral cavity without any heart (Ostracoda, Cirripedia) up to a complete, usually many-chambered heart with well-developed arterial vessels. The venous channels, however, always have the nature of, more or less, definite lacune. The blood cor- puscles are colourless, nucleated cells.” * In all those Arthropods where a heart is present, the blood returns to that organ by the lacunar spaces situated between the organs. These conduits, without special walls, debouch into a so-called pericardiacal reservoir, and the blood pene- trates afterwards into the heart by cardiacal clefts. In the Brachyura and Macroura (Fig. 39) the blood, before returning to the heart, is oxidised in passing through the branchie. In the Myriapoda, the heart has many chambers, and it is nearly as long as the body. The blood enters this organ by a pair of clefts, and leaves it partly by the communication with the adjacent chamber, and partly by the lateral arteries. “A median aortic trunk continues the heart forwards, and the lateral trunks encircle the cesophagus and unite into an artery which lies upon the ganglionic chain. The arterial system in the Chilopodw is, in fact, as complete as that of the Scorpions.” In the Jnsecta, circulation is chiefly effected by means of * Huxley’s Anatomy of the Invertebrata, p. 252. + See Newport in the Philosophical Transactions of the Royal Society, 1863. PHYSIOLOGY OF THE INVERTEBRATA. 193 the heart, which is a tubular organ running along the back of the insect, and hence called the dorsal vessel (Fig. 40). This ey) «8 es S ¢ ga = 8 38 Eo > i= o £ 5 i=} « YO Fe un gis See Y in me vi ve = S [a (3) a = im a = = Qe & ) ag & a ee" ene oF ts we "Se Ao Ss ea gg Ble 8 Bw td li Yn 2 Ao & Ss by i is] yw f o & qu 8 72 oO w 2,8 2,0 Ae caer a, oat pee ah =| Eat bs ee ae 62 ron Ua a M_— eo lop) od iS) a Ps — cl a B22: ee oS § il aS) = o NS eae. a "Soy .S _8 38 ~ a qo =s @ Il =i ae ll .€& & is formed of a series of sacs opening one into the other, from behind forwards, in such a manner that the folds formed by the junction of the sacs serve as valves to prevent the reflux N 194 PHYSIOLOGY OF THE INVERTEBRATA. of the blood. The blood enters the heart from the cavity of the body by a series of valvular openings, when it is gradually driven forwards by the successive contraction of the divisions of the heart, until it escapes in the neighbourhood of the head. After this it is no longer confined within vessels, as neither arteries nor veins have been observed in the Jnsccta; Fic. 40.—CIRCULATION IN THE INSECTA, a = dorsal vessel or heart. & = principal lateral currents. but the blood or nourishing fluid is spread about in the lacunze and interstices of the organs. Even in these lacune the blood is still animated by the action of the heart, and is ultimately forced back until it again reaches that organ. These lacunze all communicate with a sinus or vessel on the ventral side of the body. ‘Thence the blood passes to the respiratory organs, and then to the so-called pericardium or venous sinus surrounding the heart. It may be mentioned that in the Lepidoptera, Orthoptera, &c., a ventral vessel has been observed. Dr. V. Graber * discovered a ventral vessel in Stetheophyma grossum (grass- hopper) and various species of Libellula, and states that it should be regarded in the light of an artery to a dorsal vein. * Ie Insecten, 1877, vol. 1, pp. 328-345. PHYSIOLOGY OF THE INVERTEBRATA. 195 Mr. A. H. Swinton* has also observed a ventral vessel (Fig. 41) beneath the intestines-in Sphina Ligustri. This vessel is contractile like the dorsal vessel, and unites with the latter at the junction of the thorax with the abdomen. At this junction there is a dilatation of a flat-roundish form. Swinton states that there is a twofold alternating pulsation in this dilatation, that indicated a circular flow of the fluid, wee Dorsal vessel ee ace "EE RL: = d oy ' . FiG. 41.—CIRCULATION IN THE ABDOMEN OF SPHINX. (After SWINTON.) A = heart. #& = dorsal vessel. C = ventral vessel. a = afferents. S = intestines. ¢ = trachez, as shown by the double-headed arrows (Fig. 41); and which appears to be a rudimentary heart, composed of an auricle and a ventricle, such as exists in the Mollusca. The two main vessels have, besides, several afferents, a, a, and those to the lower one seemed to open each time the flap or fold spasmodically moves upwards; while a central cylin- drical duct (B) passes from the heart (A) ventrally into the thorax, where its rhythmical action, says Mr. Swinton, “ could be at intervals seen extending as far as the second annulation, although the forms of its vessels were obscured, from the fact that circulation was already partially stayed in this position of the body. Lastly, the ventral and flat-roundish vessels continued to palpitate vigorously long after the valves of the dorsal vessel had ceased to move.” Mr. Swinton considers that he has discovered, in this pulsating flat-roundish vessel and its afferents, the ¢rwe heart in the Lepidoptera. * Insect Variety: its Propagation and Distribution, 1880, p. 39. 196 PHYSIOLOGY OF THE INVERTEBRATA. The Arachnida (pulmonary) have a circulatory apparatus, which is to a certain extent well developed. The heart (Fig. 42), situated dorsally, has the form of an elongated vessel, and gives rise to various arte- ries. The blood having traversed the organs, passes to the lungs, and from thence reaches the heart, following a course similar to that observed in the Crustacea. In those Arachnida which breathe only by trachez (¢.g., the mites), the circulatory apparatus is rudimentary ; for there appears to be merely a simple dorsal vessel without arteries or veins; and it may be re- marked, that in some species the heart or dorsal vessel appears to be entirely Fic. 42. wanting. HEART OF A SPIDER. In some of the lower Crustacea a = abdomen. 4=Ilateral the heart is entirely absent. For in- pulmonary vessels. ¢=ante- stance, in the Copepoda there is no rior aorta. d = transverse : - ? branches. e=genitalarteries. heart; while in the Ostracoda there is either no heart (Cypris and Cythere), or it is only in a rudimentary form. According to Claus, the heart in Cypridina, Halocryptis, and Conchecia consists only of a short saccular organ with one anterior and two lateral appendages. The Cirripedia have no heart or other circulatory apparatus—that is, as far as is known in the present state of biological science. Dr. G. O. Sars* has recently investigated the circulatory apparatus in Cyclestheria hislopi (see Fig. 11), one of the Phyllopoda. The heart of this Phyllopod is located in the dorsal part of the body, and is easily observed in living specimens through the transparent shell. It has the form of an elongated tube traversing no less than four segments of the body, viz., the maxillary segment and the * Ohristiania Videnskabs-Selskabs Forhandlinger, 1887. PHYSIOLOGY OF THE INVERTEBRATA. 197 three first segments of the trunk, its posterior part being, moreover, extended to the middle of the succeeding segment, and its anterior extremity slightly projected within the man- dibular segment. It is provided with four pairs of distinctly defined lateral valvular openings, each pair occurring exactly in the middle of the corresponding segment. Here, the heart is connected to the body wall by slender fibres, the intervening parts being slightly instricted, whereby the dorsal as well as the lateral edges of the heart acquire a regular undulated appearance. ‘The heart of Cyclestheria has its greatest width across the anterior part, located within the dorsal prolongation of the cervical division, whence it tapers somewhat posteriorly. Its posterior extremity is abruptly truncated and furnished with a rather wide medial opening, whereas the anterior extremity contracts to a short aorta through which the blood introduced into the heart is expelled. The lateral openings of the heart are each surrounded by delicate concentric muscular fibres, and limited by two distinctly defined valvular lips. Likewise at the posterior extremity of the heart a valvular arrangement would seem to occur, and the origin of the aorta is marked off by two narrow lips closing and opening at regular intervals. Of any other distinctly defined blood-vessels, Dr. Sars could not find any trace, the blood circulating simply within the lacunar interstices between the muscles and the connective tissues. In the shell, these lacunar interstices have a very complicated arrangement, forming a richly anastomosing network of what Dr. Sars calls ‘ blood- rooms.” Along the dorsal line, however, the presence of a well-defined longitudinal blood-sinus may be readily de- termined. The blood of Cyclestheria is colourless, and contains numerous small rounded corpuscles, the course of which may be traced with comparative ease, especially in young trans- parent specimens. By the contraction of the heart (about 150 per minute) the blood is expelled exclusively from its 198 PHVSTOLOGY OF THE INVERTEBRATA .«, anterior extremity, which is prolonged so as to form a short aorta, which has at its base a valvular apparatus. This apparatus opens and closes at regular intervals. On leaving the open end of the aorta, the blood flows in two different directions, one part anteriorly, the other posteriorly. The considerable quantity of blood conducted to the anterior part of the body is seen to flow down the sides of the head, partly supplying its several appendages, partly running straight back along its ventral side to the region of the adductor muscle of the shell. Here the blood enters the valves, being received within the complicated system of canals occurring between their two lamelle. The other principal arterial cur- rent is seen running from the heart backwards along the dorsal side of the trunk, immediately above the intestine; and, on reaching the tail, it bends round and flows anteriorly along the ventral side, sending off, in each segment, lateral currents to the branchial legs. The blood thus conducted to the various parts of the body and shell returns to the heart by two different ways. The considerable quantity of blood introduced within the canal-system of the shell is at last received by two longitudinal sinuses passing along its dorsal side, the anterior rather short, the posterior occupying the greater part of the dorsal line. In the anterior sinus the blood flows backward, in the posterior, forward ; the two currents meeting at the place where the body is connected with the shell dorsally. Here both currents suddenly bend down, the one on the anterior, the other on the posterior side, and pour out the blood into the pericardial sinus, whence it passes into the heart through the lateral valvular openings. The remaining part of the blood, introduced into the trunk and the tail, is at last received within a large sinus, occupy- ing the upper part of the dorsal side of the trunk and divided from the arterial dorsal sinus by a longitudinal ligament extending from the lower side of the heart to the tail. This blood-sinus is apparently fed in each segment of the trunk by a pair of ascending currents from the branchial PHYSIOLOGY OF THE INVERTEBRATA. 199 legs. The blood contained in the above-mentioned sinus flows from behind forward, or in an opposite direction to that contained in the arterial sinus, and for the most part is introduced into the heart through its posterior extremity, though some would also seem to enter the posterior pair of the lateral valvular openings. Sars says that the course of the blood within the several limbs is not easy to examine in Cyclestheria hislopr, for they (the limbs) are concealed for the greater part by the shell. In the antenne, however, which at times are more or less completely exserted beyond the shell, the blood can be dis- tinctly seen passing along the upper edge of each branch to the extremity, then turning round, and flowing back along the lower edge to the scape (Sars). In the higher Crustacea, the heart and circulatory appa- ratus are far better defined than in the lower orders of this class. The heart of Ho- Fic. 43. — VERTICAL SECTION OF A MAUS 1S a powerful quadrate CRUSTACEAN, SHOWING THE COURSE : OF THE BLOOD. organ, and the arteries are large, Oe ee | = gill. & = vessels which ollect the aérated blood from gills. c= vessels in distribution. There are conducting venous blood to gills. Pemtrichileexpansions|(“ pills, 7 = Heart, .¢ =carapace. (= bran- “ chiocardiac vessels. ¢ = sternum. hearts”) at the base of the 4 = venoussinus. blood-vessels conducting the blood to the branchiz. The heart consists of a single con- tractile cavity, and the arteries in the higher Crustacea are closed tubes; but the venous blood passes back through the interstices between the organs of the body, until it reaches certain cavities or reservoirs situated at the bases of the limbs (Fig. 43); therefore the venous blood bathes all the organs. From the reservoirs or sinuses the blood passes to the bran- chize, where it becomes aérated by contact with the water, 200 PHYSIOLOGY OF THE INVERTEBRATA. and then passes through proper vessels to the heart. It will be seen that the circulation in the higher forms is semi- vascular and semi-lacunar. The circulatory apparatus of Astacus is well defined. The heart is situated dorsally and behind the stomach. It is surrounded by the so-called pericardium, which is in reality a blood-sinus ; consequently the heart is suspended in a blood- sinus. There are six apertures in this organ provided with valves which open inwards. These allow the blood to enter the heart during the diastole, and prevent its egress, except by the arteries, during the systole. There are six arterial trunks provided with valves at their commencement, their object being to prevent the regurgitation of the blood. These arteries ramify minutely, but the capillary system has not been investigated with anything like satisfaction. So far as is known, the blood passes from the arteries into the lacunee and into the perivisceral cavity. From these lacunz it ultimately finds its way to the branchiz and heart. Reverting once more to the heart of the Crustacea, Sir tichard Owen, I’.R.S., says that ‘‘ we may trace in the heart of these animals a gradational series of forms, from the elongated median dorsal vessel of Limulus, to the short, broad, and compact muscular ventricle in the lobster and the crab. In all the Crustacea the heart is situated immediately beneath the skin of the back, above the intestinal tube, and is retained in situ by lateral pyramidal muscles. “In the Entomostraca,* and in the lower, elongated, slender, many-jointed species of the Edriophthalmous Crustacea, the heart presents its vasiform character. It is broadest and most compact in the crab.” THE POLYZOA. The perivisceral cavity contains a nutritive fluid. This is kept in constant motion by the action of cilia with which the * The Entomostraca include the Phyllapoda, Cladocera, Ostracoda, and the Copepoda. PHYSIOLOGY OF THE INVERTEBRATA. 201 inner surface of the cavity and the outer surface of the intestine are covered. This movement, which extends into the tube of the common stock, is equivalent to a true circu- lation of the blood. Consequently, the function of circulation in these animals is comparable to that in the Coelenterata, for the blood is not, during any part of its course, contained in any system of vessels, but is free in the body cavity. THE BRACHIOPODA. The sinuses met with in the Brachiopoda are the result of partial limitation of the general cavity of the body, for a special purpose. These sinuses “extend into each lobe of the mantle, and end cecally at its margins. The lobes of the mantle are probably, together with the ciliated tentacula, the seat of the respiratory function. The sinuses of the pallial lobes of Zingula give rise to numerous highly con- tractile, teat-like processes, or ampulle. During life the circulating fluid can be seen-rapidly coursing into and out of each ampulla in turn.” Between the ectoderm and the lining membrane of the sinus-like “‘prolongations of the perivisceral cavity in the mantle, and between the endoderm, the ectoderm, and the liming membrane of the perivisceral cavity itself, there is an interspace, broken up into many anastomosing canals,” which Prof. Huxley considers, “to represent a large part of the proper blood systems.” Dilatations of these canals have been erroneously described as hearts, but they are not contractile. “ Although the existence of a direct communication between the perivisceral chamber and the blood canals has not been demonstrated, it is very probable that the perivisceral chamber really forms part of the blood-vascular system.” THE MOLLUSCA. In the Mollusca the circulatory system is more highly differentiated, and “in very many, if not all, the blood cavities 202 PHYSIOLOGY OF THE INVERTEBRATA. communicate directly with the exterior by the organs of Bojanus,” or kidneys. The higher Mollusca have all of them well-defined hearts, generally with auricles and ventricles (Fig. 44), arteries and veins, though the capillary system is still absent. The hearts of the Gasteropoda and Cephalopoda have valves and columnz carne; there are also contractile expansions at the base of the vessels conducting the blood to the branchiee. We now describe the circulatory system in three orders of the Mollusca. FIG. 44.—DIAGRAM SHOWING THE MODIFICATIONS OF THE HEART IN THE INVERTEBRATA. 1 = part of dorsal trunk of aworm. 2 = heart of Nautilus. 5 = heart of a Lamellibranch. 4 = heart of Octopus. 5 = heart of a Gasteropod. v = ventricle. a@=auricle. = ccephalicartery. ¢ = abdominal artery. The arrows indicate the direction of the blood-current. (1) The Lamellibranchiata.—The vascular system consists of a heart, anterior and posterior aorte, and other blood- vessels and sinuses. In Anodonta the heart lies in the middle line of the body, and is surrounded by the pericardium or blood sinus. It consists of a median ventricle, which is perforated by the intestine (see Fig. 18), and of two auricles which are situated on each side of the ventricle. The ventricle gives rise to the anterior and posterior aortze. The auricles are muscular sacs, and communicate with the ventricle by the auriculo-ventricular openings. These open- PHYSIOLOGY OF THE INVERTEBRATA, 203 ings are each provided with a pair of valves, which project into the ventricle, and there meet in front of the openings. These valves allow the blood to pass from the auricle to the ventricle, but prevent its return from the ventricle to the auricle. By the contraction of the auricles the blood is forced into the ventricle. After the contraction of the auricles have ceased, the ventricle contracts and forces the blood forwards and backwards through the two aorte. The blood passes through the ramifications of these vessels into the system of lacune or sinuses situated in-the mantle and between the viscera. From these lacunze the blood passes FIG. 45.—CIRCULATORY SYSTEM OF HELIX. a@=heart. 46 = vessels carrying blood from lung to heart. c = lung. d=aorta. e= gastricartery. f= ‘‘hepatic” artery. ¢ = pedal artery. A = abdominal cavity, supplying the place of a venous sinus. ¢ = irregular canal communicating with 4, and carrying blood to lung. into a large median venous sinus termed the vena cava, which extends between the anterior and posterior adductor muscles. At the base of the branchiz are two lateral sinuses. The main portion of the blood passes into the renal organ (the organ of Bojanus) and ultimately to the branchia, and from thence is returned as arterial blood to the auricular portion of the heart. (2) The Gasteropoda.—In Helix the heart (Fig. 45) is 204 PHYSIOLOGY OF THE INVERTEBRATA, close to the pulmonary sac. It consists of an auricle and a ventricle. The aorta proceeds from the ventricle, and divides into two branches: one of these passes forward and ramifies in the head and foot, while the other passes back- wards and dorsally to the viscera, where it also ramifies. The arterial branches terminate by opening into lacune; from these the blood passes through the pulmonary arteries to the lung, and thence through the pulmonary veins, which ultimately join to form a large pulmonary vein which leads into the auricle. The organ of Bojanus, or kidney, “lies close to the pulmonary sac in the course of the current of the returning blood.” Antr. vena - Antr. aorta. cava, — Efferent branchial vessels. > Gill. Nephridium Afferent (kidney). branchial vessels. Auricle. Ventricle. Vein. = Post. vena cava. “SA Capillaries. Post. aorta. Fic. 46.—BLoop SystT—EM AND NEPHRIDIA OF SEPIA. (3) The Cephalopoda.—The circulatory system of Sepia is seen in Fig. 46. “The heart is placed upon the posterior face of the body, on the hzemal side of the intestine, and receives the blood by branchio-cardiac vessels, which correspond in number with the gills ; and, as they are contractile, might be regarded as auricles. The gills themselves have no cilia, and PHYSIOLOGY OF THE INVERTEBRATA. 205 are, in some cases, if not always, contractile. The arteries end in an extensively developed capillary system, but the venous channels retain, to a greater or less extent, the charac- ter of sinuses. The venous blood, on its way back to the heart, is gathered into a large longitudinal sinus—the vena cava—which lies on the posterior face of the body, close to the anterior wall of the branchial chamber, and divides into as many afferent branchial vessels as there are gills. Each of these vessels traverses a chamber, which communicates directly with the mantle cavity, and the wall of the vessel, which comes into contact with the water in this chamber, is sacculated and glandular.” In Loligo media “ the sacculated afferent veins and branchial hearts contract about sixty times a minute. The pulsations of these veins and of the branchial hearts are not synchronous. The branchial veins and the lamellz of the branchize also contract rhythmically,” but the branchial arteries do not contract. ‘‘ The portion of the branchial vein which lies between the base of the gill and the systemic ventricle is very short, and it is hard to say whether it contracts independently or not. Mechanical irritation causes contraction both of the afferent branchial veins and of the branchial hearts.” (Huxley.) In Lledone cirrhosus Professor Huxley has “ observed regu- lar rhythmical contractions of the vena cava itself, as well as of its divisions, the sacculated afferent branchial veins, of the branchial hearts, and of the branchio-cardiac vessels.” THE TUNICATA. In the Ascidians the function of circulation differs entirely from other Invertebrates. The peculiarity of this circulation is the reversal at regular intervals of the direction of the blood current. The heart is devoid of valves, and contracts with a wave-like movement. If the wave is from below upwards, “the blood passes into an abdominal vessel, thence into transverse ascending canals that lead to the extraordinary 206 PHYSIOLOGY OF THE INVERTEBRATA. network of vessels connected with the respiratory structures, into a dorsal vessel, and thence by a connecting branch to the posterior end of the heart. After a certain period, the wave of contraction through the heart, and the course of the blood, are generally reversed in direction; and the blood now flows from the ventral heart into the dorsal vessel, down through the branching network into the abdominal or ven- tral vessel, and so to the anterior end of the heart.” The blood consists of a clear plasma containing colourless corpuscles. In Appendicularia flabellum, Professor Huxley states that there are no corpuscles, and “the direction of the pulsations of the heart is not reversed at intervals, as it is in the Ascidians in general. M. Fol,* however, states that, in other Appendicularie the reversal of the contractions of the heart takes, placeit.: 24's There are no distinct vessels, but the colourless fluid which takes the place of blood makes its way through the interspaces between the ectoderm and endoderm and the various viscera,” Concerning the velocity of the circulation in the Znwver'te- brata very little is known; but it may be stated that the blood in these animals is animated by a much slower move- ment of translation than occurs in the Vertebrata. * Etudes sur les Appendiculaires, 1872. CHAPTER VIII. RESPIRATION IN THE INVERTEBRATA. Ir is well known that the presence and absorption of oxygen is essential to the life of every tissue, and that one of the products of the action of oxygen on the tissues, &c., is the production of carbonic anhydride, a gas which is inimical to life. Even the lowest members of the animal kingdom re- quire oxygen—without oxygen, no animal life. The Amba and Parameciwn, when introduced into a medium contain- ing no oxygen, or containing an excess of carbonic anhydride, very soon die. In all animals there is an interchange be- tween the gases of the organism and the gases of the medium in which they live; and this interchange, which is known as respiration, 1s continuous throughout life. In the lowest forms no special mechanism is necessary for facilitating the gaseous interchange ; for they absorb fluids containing oxygen in solution. In higher forms, canals, along which the air passes, seem to be necessary ; and in still higher forms respiration is performed by the movement of the branchizwe, or by trachez (air-tubes) and lungs. The absorption or respiration of oxygen is one of the first con- ditions of nutrition. All organised beings absorb oxygen, and this absorption goes on in all stages of the existence of living matter. The organs (using the word in its widest sense) of respira- tion differ considerably in different animals, but they have all the same physiological function to perform—that of sup- plying oxygen to the tissues and blood; and the elimination 208 PHYSIOLOGY OF THE INVERTEBRATA. of the gaseous products of decay. In fact we may define respiration as “the elimination of the gaseous products of tissue-combustion, and the introduction of the oxygen neces- sary for that combustion.” The lower forms of the animal kingdom respire directly by changes between the general surface of the body and the medium in which they live; but in the higher forms, respira- tion is a twofold process: (#) internal respiration, or the interchanges between the gases of the blood and the tissues ; and (>) external respiration, or the interchanges between the eases of the blood and the gases in the air-cells of the lungs. These interchanges, however, are not always confined to the lungs; thus there is a true cutaneous respiration in the skin, an intestinal respiration in the intestines, and most probably interchanges of a like nature take place in other organs; for it may be remarked that many organs of the Invertebrata contain various pigments, which have a res- piratory function. The respiratory apparatus is always in intimate relation with the organs of circulation. THE PROTOZOA. In most of the Protozoa, respiration takes place all over the general surface of the body ; but these animals differ somewhat in the mechanism of respiration. In the Gregarimda the interchange of gases takes place all over the body. In the majority of the Znfusoria and Rhizopoda there is a differentiation of the function of respiration, for even in these low forms the interchange of oxygen and carbonic anhydride takes place at certain specialised regions (con- tractile vacuoles), but the air is not brought into direct con- tact with the circulating fluid. The oxygen or air for res- piration is dissolved in water. The contractile vacuoles of these organisms perform several functions, among these being that of respiration. The contractile vacuoles contain PHYSIOLOGY OF THE INVERTEBRATA. 209 liquids, and during contraction send out radiating canals. This system probably communicates with the exterior. By this primitive respiratory organ the working tissues are brought into contact with oxygen dissolved in water. THE PORIFERA. In the Porifera (Spongida) respiration is effected by means of the oxygen dissolved in the water, which permeates through the various canals, and thereby brings it into intimate relation with the whole mass. In the circulation of this water through the ordinary fresh-water sponge (Spongilla) there is a fusion of the functions of digestion, circulation, and respiration. ‘Sponges absorb oxygen and give off carbonic anhydride with great rapidity ; and the manner in which they render the water in which they live impure, and injurious to other organisms, suggests the elimination of nitrogenous waste matter.” It is possible that the oxygen is retained in the substance of a sponge by certain respiratory pigments—probably a histohematin. Sponges are rich in chlorophyll, but this pigment has another function—viz., the formation of fatty matter.* THE CGELENTERATA. In the lower Cewlenterata the function of respiration is performed by the general surface of the body. The fluids in these animals are in close relationship to the water in which they live ; and consequently the ectodermic lining serves as an organ of respiration. In other words the lower Coelenterates respire by the skin. In some of the higher orders of this group the respiratory function is performed in the water- vascular tubes along with other functions performed by the same vessels. But there is no doubt that the chief mode of respiration in * MacMunn in Journal of Physiology, vol. 9. 210 PHYSIOLOGY OF THE INVERTEBRATA. the Ccelenterates is by means of the ectodermic lining, for this lining is very largely impregnated with respiratory and other pigments, as shown by Prof. Moseley* and Dr. MacMunn.t The respiratory pigments are capable of existing in a state of oxidation and reduction, and no doubt play an important part in the funetion of respiration. Professor Moseley discovered a pigment called poly- perythrin in various Ccelenterates, and Dr. MacMunn has carefully examined the brown colouring matter of jelly-fishes, and various pigments in the Actinie. In Chrysaora hysocella a brown pigment is present in ‘“‘the radiating triangular areas on the upper surface of the umbrella, and in dark patches, thirty-two in number, ali round the margin of the disc, also in the tentacles; but in each of these situations it possesses the same properties. It also occurs dotted on the surface of the umbrella between the triangular pigmented areas. Microscopically, it occurs in granules, and is limited to the surface ; these granules are yellowish in colour under a high power.” Dr. MacMunn could not extract the brown pigment with alcohol, ether, chloroform, alcohol and sulphuric acid, and alcohol and potassium hydroxide. But he obtained an extract by allow- ing portions of Chrysaora to stand, ‘the sea-water contained in the tissues dissolved the pigment, forming an orange- brown solution, showing a broad dark band at the blue end of the green. When more pigment went into solution, the fluid became a dark brown colour. Boiled in fresh and sea- water the colour went into solution, but showed no bands except the shading at the blue end of the green. A deep layer of this solution only transmitted red and some green. Ammonia and caustic potash precipitated the colouring * Quarterly Journal of Microscopical Society, vol. 17; and Journal of Physiology, vols. 7 and 8. + Quarteriy Journal of Microscop‘cal Science, vol. 30; and Journal of Marine Biological Association, 1889. PHYSIOLOGY OF THE INVERTEBRATA. 211 matter. Hydrochloric acid did not discharge the colour at first, although it became much lighter; strong sulphuric acid and nitric acid discharged it after some time. Absolute alcohol also precipitated the pigment, the fluid becoming flocculent after a while. The colouring matter in the fresh state showed no bands except some shading at the blue end of the green; it also absorbed the violet end of the spectrum.” Dr. MacMunn’s investigations on the respiratory pigment of Chrysaora confirms those of Dr. J. G. M‘Kendrick, F.R.S.,* who has also investigated the pigments from Cyanew and Aurelia by allowing fragments. of these organisms to macerate in sea-water for about thirty-six hours. ‘In these cases ammonia precipitated the colouring matter from its solutions, and it dissolved in acids.” Dr. M‘Kendrick states that after death “the body becomes slightly acid, the protoplasm disintegrates, and the colouring matter diffuses out.” When examined by the microspectroscope the fresh pig- ment from Cyanea, as well as an infusion of the organism, gave two bands, one in the orange and the other in the red. The spectrum of the blue pigment of Ahizostoma Cuviert consists of three bands, one in the red, a dark one at D, and an extremely faint band in the green. There is little doubt that the same colouring matter occurs in Rhizostoma as in Cyanea. This pigment has been termed cyanein by the late Dr. Krukenberg,t and he compared it with the blue pigment found in Velella limbosa by A. and G. De Negri.t Cyanein is soluble in water, insoluble in benzene, ether, carbon disulphide, and chloroform. On the addition of alkalies, cyanein is changed into an amethyst colour, while acids colour it red. * Journal of Anatomy and Physiology, vol. 15, p. 261. + Vergl. Physiol. Studien, zweite Reihe, dritte Abth., 1882, s. 68. t Gazetta Chimica Italiana, vol. 7 [1877]. 212 PHYSIOLOGY OF THE INVERTEBRATA. In 1884, Krukenberg stated that cyanein occurs in Velella, Aurelia, Cyanea, and Rhizostoma. Dr. MacMunn* has examined the pigments from the following | 248 = 22 a 5 In grammes, | In parts of sea g ea lime carbonate water. Pa gQ per litre. One part in Coral sand . P » 27 12 0.0320 32,000 Harbour mud, Bermuda . 27 12 0°O410 25,000 Tsophyllia dipsacea wy Ph 2z 12 0.0410 25,000 Millepora ramosa 4 « 27 ne 0.0360 28,000 | Madrepora aspera - a ee 12 0.0730 14,000 Montipora foliosa ‘ Beez I2 0.0430 23,000 Goniastrwa multilobata 3 fe) 12 0.0730 14,000 Porites clavaria . ; é II 12 0.0930 11,000 Oculina coronalis . A : fe) 96 0.0237 42,600 Their experiments prove that ‘there is very great diversity as to the amount of carbonate of lime that will pass into solu- tion in sea water from various calcareous structures in a given time.” The more dense varieties of coral are less soluble than the porous varieties. ‘The rate of solution is also much greater when the water is constantly renewed than when the same water remains in contact with the coral, and the solution approaches to saturation.” (7) From the investigations and observations of Murray and Irvine ‘it is evident that a very large quantity of car- bonate of lime is in a continual state of flux in the ocean, now existing in the form of shells and corals, but after the death of the animals passing slowly into solution, to go again through the same cycle.” “On the whole, however, the quantity of carbonate of lime that is secreted by animals must exceed what is re-dissolved by the action of sea-water, and at the present time there is a vast accumulation of carbonate of lime going on in the ocean. It has been the same in the past, for with a few insignificant exceptions all the carbonate of lime in the geological series of the rocks has been secreted from sea water, and owes its origin to organisms in the same way as the carbon of the car- boniferous formations. The extent of these deposits appears 254 PHYSIOLOGY OF THE “INVERTEBRATA. to have increased from the earliest down to the present geological period.” THE ECHINODERMATA. We have already alluded to the secretion of the protective skeleton in these animals; consequently we proceed to describe the excretory organs of the Asteridea, being an im- portant order of the Hchinodermata. The author * has shown that the five sacs of the stomach of Uraster rubens sometimes act as renal organs. With a quantity of the fluid obtained from a large number of star- fishes the following experiments were performed :— (1) The clear liquid from these sacs was treated with a hot dilute solution of sodium hydroxide. On the addition of pure hydrochloric acid a slight flaky precipitate was obtained, after standing seven anda half hours. These flakes, when examined beneath the microscope (4 in. obj.) were seen to consist of various crystalline forms, the predominant forms being those of the rhomb. On treating the excretion alone with alcohol, rhombic crystals were deposited which were soluble in water. When treated with nitric acid and then gently heated with ammonia, these crystals yielded reddish- purple murexide crystallised in microscopic prisms. (2) Another method was used for testing the fluid contents of the sacs of the stomach of Uraster. These fluid contents were boiled in distilled water, and evaporated carefully to dryness. The residue obtained was treated with absolute alcohol and filtered. Boiling water was poured upon the residue, and to the aqueous filtrate an excess of acetic acid was added. After standing some hours, crystals of write acid were deposited, and easily recognised by the chemio-micro- scopical tests mentioned above. The above-mentioned alcoholic filtrate was tested for urea. * See Dr. A. B. Griffiths’ paper in Proceedings of Royal Society, vol. 44, p- 325. : PHYSIOLOGY OF THE INVERTEBRATA. 255 To do this, the alcoholic solution was diluted with distilled water, and boiled over a water-bath until all the alcohol had vaporised. The warm aqueous solution (A) remaining was now tested for urea in the following manner :— (a) On the addition of mercuric nitrate to a portion of the aboye solution, no white precipitate was obtained. (>) To another portion of the solution (A), a solution of sodium hypochlorite was added. No bubbles of nitrogen were disengaged. (c) No crystals of urea nitrate were formed in a small quantity of the solution (A) [concentrated by evaporation | after the addition of nitric acid. (d) The distillation of a small quantity of the solution (A) with pure sodium carbonate in a chemically clean Wiirtz’s flask attached to a small Liebig’s condenser, failed to produce in the distillate any coloration with Nessler’s reagent. The above tests clearly prove the entire absence of urea in the excretion under examination. No guanin or calcium phesphate could be detected in the excretion, although the author has found the latter compound as an ingredient in the renal excretions of the Cephalopoda and the Lamelli- branchiata.* From these investigations, the isolation of uric acid proves the renal function of the five pouches or sacs of the stomach of the Asteridea.t There is no doubt that the stomach of starfishes performs a dual function: it is an excretory organ as well as a digestive gland, and separates the nitro- genous products of the waste of the tissues, &c., from the blood or nutritive fluid in the form of uric acid, which is at certain times to be found in the five pouches of that organ. In the Jnvertebrata there are numerous examples where an organ performs a dual and even a triple function. * Proceedings of Royal Society of Edinburgh, vol. 14, p. 230. + See also Durham in Quart, Journ. Micros. Science, 1891. 256 PHYSIOLOGY OF THE INVERTEBRATA. THE ANNELIDA. (1) The Hirudinean—The author* has examined the nephridia of Hirudo medicinalis. These nephridia are in pairs, extending from the second to the eighteenth segments (somites). Hach nephridiumf consists of a much-convoluted cellular tube. The cells of the tube are perforated by small ducts. The nephridia (segmental organs) open externally on the ventral side of the body. In Lumbricus the nephridium communicates internally by a wide funnel-shaped aperture (which is ciliated) with the perivisceral cavity, but in Hirudo it opens internally by a “cauliflower-headed” portion (the analogue of the funnel-shaped aperture in Lumbricus) into the perinephros- tomial sinus. Hach nephridium consists of five principal parts—(a) posterior lobe, (2) anterior lobe, (c) apical lobe, (d) the testis lobe, (¢) the vesicle, with its duct, which opens externally. The nephridia of Hirudo are covered with a pigmented connective tissue. These pigments are no doubt the histoheematins of Dr. C. A. MacMunn, for he says: “I have found that throughout the whole animal kingdom in each tissue and organ there are present colouring matters.” { In examining the physiology of the nephridia or segmental organs of the Hirudinea, the. author obtained the excretions from a large number of freshly killed leeches. These excre- tions were examined by the same chemical and microscopical methods used in the examination of the segmental organs of the Oligochwta and the renal organs of the Asteridea. The nephridia of Hirudo contain uric acid and sodium ; and it may be that the uric acid is in combination with sodium as sodium urate. * Proceedings of Royal Society of Edinburgh, vol. 14, p. 346. + From vegpds, a kidney. t Proc. Birmingham Philosophical Society, vol. 5, p. 211; Proc. Roy. Soc., 1886; and Philosoph. Trans., 1886. PHYSIOLOGY OF THE INVERTEBRATA. 257 (2) The Oligochwta.—The renal system of Lwmbricus consists of a large number of coiled tubes (Fig. 47) distributed in pairs, one pairin each somite of the body. Hach tube or segmental organ (nephridium) consists of three distinct parts—(a) A much-conyoluted thin portion, terminating in a funnel-shaped opening ; (2) a thick-walled glandular portion; (¢) a thick icle. Cuticle Dorsal vessel. Epidermis. Circular mus- cular layer. 4 Middle loop of nephridium. Typhosole. Longitudinal < muscular /s.’\ layer. 43 Hepatic cells, 4 so-called il SS livers: Outer loop of nephridium. Inner loop of nephridium. rh th he sae bie Q) Epithelium of intestine. Ventral v. Ccelom. ., Internal open- ing of neph. / , Vent. nerve cord. ~————> Subneural vessel. External \ opening of nephridium. Fic. 47.—NEPHRIDIUM OF LUMBRICUS. muscular portion (the outer loop), which opens externally by an aperture near the ventral side of the body. The nephri- dium as a whole lies on the posterior side of the septum, but the funnel-shaped aperture opens on the anterior surface ; that is to say, into the cavity of the segment in front of that in which the main body of the nephridium lies. This is the case in every segment containing these organs. The septa, or mesenteries dividing the body into segments, are richly R 258 PHYSIOLOGY OF THE INVERTEBRATA. supplied with blood-vessels, many of which are intimately con- nected with the folds of the nephridia. There is little doubt that the nitrogenous waste matters are absorbed by the glandular portions of these coiled tubes, and ejected by the contractile parts to the exterior. The author * has isolated uric acid from the excretion ot the nephridia or segmental organs of Lumbricus terrestris. The contents of these organs do not contain guanin, urea, or calcium phosphate. The segmental organs in the Oligochwta are therefore renal in function, eliminating the nitrogenous waste matters con- tained in the blood, in the perivisceral cavity. The largest: amount of uric acid was found in the excretion contained in the muscular part of the segmental organ (Fig. 47, outer loop of nephridium). The following table is a summary of the constituents of the nephridia or segmental organs of the Annelida :— Hirudinea, Oligochata, Polychaeta. Uric acid . é : : present present (2) Urea « ; : 5 2 absent | absent — Guanin . ‘ : : : absent absent —- Calcium phosphate : : absent absent — Sodium : : . t present — — The minute structure of the excretory organs in the Oligo- cheta, especially those of Lwmbricus terrestris, have been worked out by Dr. E. Claparéde, and detailed in his “ Histo- logische Untersuchungen iiber den Regenwurm,” ft and also by Prof. C. Gegenbaur. t * Proceedings of Royal Society of Edinburgh, vol. 14, p. 233. t Zeitschrift fir Wissenschaftliche Zoologie, vol. 19. + Ibid, vol. 4, PHYSIOLOGY OF THE INVERTEBRATA. 259 THe NEMATOIDEA. In a paper read before the Royal Society of Edinburgh on July 1, 1889, the author stated the results of his examina- tion of the renal organs of the Nematoidea. The body of the “thread-worms” is elongated, round, and thread-like, tapering (more or less) towards the anterior and posterior ends. The Vematoidca are not divided into segments, and they have no segmental organs. In the species (Angwillula brevispinus) selected for investi- gation the renal organ is a glandular mass situated in front of the gizzard. This organ has a well-developed excretory duct, which opens externally by a tranverse slit (the vascular pore) on the ventral side of the body. When a section of the glandular organ of Anguillula is examined under the microscope, the epithelial lining is seen to consist of nucleated cells, similar to those of the Malpighian tubules of the Jnsecta (see later in this chapter). The organ contains a clear fluid, which can be made to yield microscopic crystals of uric acid. The author has extracted uric acid from a large number of these organs (obtained by dissection under the microscope) by boiling them in distilled water. The filtrate, tested by the methods already described, yielded uric acid and murexide crystals. A fresh “ glandular organ” was placed upon a microscope slide and crushed ; then a drop of dilute acetic acid added, and the whole covered by a cover-glass. On examining with the microscope it was observed that rhombic plates and other crystalline forms had deposited. The cover-glass was slightly raised, and on the addition of a drop of nitric acid, followed by ammonia and gently heating over a spirit lamp, prismatic crystals of murexide were formed. No urea, guanin, calcium phosphate, &c., could be de- tected in the excretion of this organ. These reactions prove that the so-called ‘“‘ glandular organ” of the Nematoidea is physiologically a kidney. 260 PHYSIOLOGY OF THE INVERTEBRATA. THE PROTOTRACHEATA. This order is represented by the genus Peripatus, which contains several species. These animals have the power of “throwing out a web of viscid filaments when handled or otherwise irritated.” This viscid matter is secreted by two large ramified tubular glands situated on the sides of the digestive tube, and open externally by the perforations of the oral papillae. Peripatus breathes by means of trachez, hence the reason that Prof. Huxley has referred the order to which Peripatus belongs to the Arthropoda. From these remarks it will be observed that respiration in Peripatus is on the insect-type—ie., by means of tracheal tubes; but the other excretory organs differ from those of the Insecta. In the Insecta the renal organs are the Malpighian tubules, but no such appendages to the alimentary canal are present in Peripatus. The kidneys are segmental organs or nephridia, like those of the worms, but of a more highly complex type. ‘There is a pair of these organs in each segment. They open in- ternally into the body cavity, and externally at the base of the limbs. THe Myrtapropa. The intestines of the animals belonging to this class are provided with Malpighian tubules which perform an ex- cretory function ; in other words, they are physiologically the kidneys. THE INSECTA. Before describing the excretory organs, it is perhaps desirable that we mention certain secretions, and the organs (as far as possible) which give rise to them. (a) The poison which certain insects secrete is a fluid strongly impregnated with formic acid. In many cases this fluid is secreted by a special gland, and poured into a re- ceptacle connected with the sting (¢.g., in Apis and Vespa). PHYSIOLOGY OF THE INVERTEBRATA. 261 The larva of Dicranura vinula possesses a gland which secretes formic acid. The duct of this gland opens in a horizontal slit on the red margin below the true head, and is thus placed in such a position that its contents are ejected in an anterior direction. Disturbance causes the larva to withdraw its head still further, and to inflate the red margin, especially in the region of the gland duct, and at the same time the head is always turned in the direction of the dis- turbance. Thus the fluid is thrown towards the cause of the irritation, and the terrifying appearance of the larval full- face is also brought to bear upon it (Poulton). The acid ejected by the larva of D. vinula is a defensive fluid, and no doubt is a means of protection against enemies. _ This defensive fluid is ejected from a transversely placed aperture on the ventral surface of the prothorax, immediately below the head.- Mr. E. B. Poulton, F.R.S., Prof. R. Mel- dola, F.R.S., and Prof. W. R. Dunstan have proved by chemical tests that this fluid secreted by the larva of D. vinula is formic acid. ‘The smell is also quite characteristic, and affords an indication of the large proportion of acid present in the secretion. It is also an interesting fact that the freshly-made and moist cocoon of D. vinwla is powerfully acid to test-paper.” The secretion consists of a pure aqueons solution of formic acid, containing an average of 33 per cent. of anhydrous acid. A mature larva will eject 0.05 gramme of the secretion, con- taining 40 per cent. of acid. The rate of secretion is slow; starvation lessens its amount and decreases the quantity of acid; but there is no difference in the nature of the acid when the larva is fed on poplar instead of willow.* “The larva appears to depend entirely upon ¢actile stimuli for the direction in which to move its terrifying full-face, and towards which to eject the irritant acid secretion. Visual sensations appear to play no part as guides in the assumption of the defensive attitude.” * See Report of British Association, 1887, p. 765. 262 PHYSIOLOGY OF THE INVERTEBRATA, The larva of Dicranura furcula does not eject an irritant secretion, but it possesses an eversible “gland” as a defensive organ. A similar structure is present in the larva of D. vinula, but it is unable to evert its prothoracic ‘“ gland ” voluntarily. This structure is eversible in the larve of Melitwa artemis, Orgyia pudibunda, Orgyia antiqua, and Liparis auriflua ; and there is no doubt that these defensive structures are of con- stant occurrence in Lepidopterous larvee. The power of everting the “ gland” in the larva of D. vinula has been lost, due to the fact that the “larva has acquired the remarkable power of ejecting the intensely irritant secretion | to a considerable distance by forcing it through the narrow chink, with its closely approximated lips, which constitutes the mouth of the duct leading to the sac. Such a formidable means of defence may readily have supplemented the more usual method of eversion, a method which can only give rise to the discharge of vapour into the air, instead of a well- directed stream of fluid, which, if volatile, as it is in these larvee, of course produces abundance of vapour.” The eversible glands of the larva of Liparis auriflua are not often completely everted, but they are very sensitive to tactile impressions, and on “stimulation a clear, transparent secretion appears in the lumen, being probably raised by partial eversion. The secretion is not acid to litmus paper, but it possesses a peculiar and penetrating odour.” The ejection of defensive fluids and vapours are not con- fined to the anterior parts of insects, for in the Bombardier Beetles, according to Dr. Léon Dufour, a pungent vapour, resembling nitric acid in its properties, is ejected from the anus. rachinus displosor will furnish twelve such discharges, but subsequently explosion with noise is replaced by the emission of a yellowish or brownish fluid, which readily vaporises. ‘These discharges are meant to arrest the onset of larger predacious beetles. Brachinus crepitans is sometimes gregarious, and when one individual is disturbed the whole PHYSIOLOGY OF THE INVERTEBRATA, 263 discharge in unison, but after about twenty explosions they only emit a white fluid. M. F. Pouchet * says :—‘ L’instinct de la défense est telle- ment inhérent 4 la tribu:des Bombardiers, qu’au seul coup de canon d’alarme de l’un d’eux, tous les autres crépitent en méme temps: c’est un feu roulant sur toute la ligne.” There is something in these insects discharging the fluid in unison which seems to point out that they are guided not merely by instinct, but by that which is the equivalent of mind. The chief enemy of &. crepitans, which inhabits Great Britain, is Calosoma inquisitor (Fig. 48). FiG. 48.—BOMBARDIER BEETLE AND ITS ENEMY. (After F. A. POUCHET.) The secretory glands of the Bugs are situated exterior to the insertion of the posterior legs, and emit fcetid effluvia on seizure. The ground bettles of the genus Carabus, when disturbed, eject a fluid which is caustic if applied to the skin. In conclusion, it may be remarked that a very large number of insects eject liquids or vapours as a means of * L' Univers, pv 137- 264 PHYSIOLOGY OF THE INVERTEBRATA. protecting themselves, more or less, from the attacks of various enemies.* (6) There are two pairs of salivary glands of the larval Lepidoptera (see Fig. 7). The posterior or second pair secrete the viscous substance, which hardens on exposure to the atmosphere and forms silk. This silk is the material in which the larve or caterpillars invest themselves. The vis- cous substance from these glands is made into threads and spun into cocoons by means of a slender tubular organ called a spinneret, which is situated on the labium. Most caterpillars spin silken threads to secure themselves from falling, and many of them, as already stated, spin a cocoon in which to pass the pupal state. In Myrmecoles and the Hemerobide the silk is furnished by the rectum. (c) The glow-worm, or Lampyris splendidula, and many other insects have the power of emitting light. According to Schulze,f the males of the glow-worm have a pair of photogenic organs, ‘‘ which lie on the sternal aspects of the penultimate and ante-penultimate abdominal somites. Hach is a thin, whitish plate, one face of which is in contact with the transparent chitinous cuticula, while the other is in rela- tion with the abdominal nerve-cord and the viscera. The sternal gives out much more light than the tergal face. The photogenic plate is distinguishable into two layers, one occupying its sternal and the other its tergal half. The former is yellowish and transparent, the latter white and Opaque, in consequence of the multitude of strongly refract- ing granules which it contains. Trachez and nerves enter the tergal layer, and for the most part traverse it to terminate in the sternal layer, which alone is luminous. * For further information on the defensive fluids and the eversible glands of Lepidopterous larvze, see the papers by Mr. E. B. Poulton, F.R.S., in the Transactions of Entomological Society of London, 1885, p. 322 ; ibid., 1886, p. 1565 zbid., 1887, p. 295; Report of British Association, 1887, p. 765 ; and his excellent book, The Colours of Animals. + Archiv fiir Mikroskopische Anatomie, 1855. PHYSIOLOGY OF THE INVERTEBRATA. 265 Each layer is composed of polygonal nucleated cells. The granules are doubly refractive, contain uric acid, and probably consist of urate of ammonia. Hence the cells of the layer which contain them are termed by Schulze the ‘urate cells,’ while he calls the others the ‘parenchyma cells.. The branches of the trachezee which ramify among the parenchyma cells end, like those of other parts of the body, in stellate nucleated corpuscles, one process of the corpuscle passing into a ramification of the trachea. Schulze is inclined to think that the other processes end in paren- chyma cells. The nerves of the photogenic plates are derived from the last abdominal ganglion ; they branch out between the parenchyma cells into finer and finer branches, which eventually escape observation.” (Huxley.) Lampyris can vary at will the intensity of the phosphoric light. It has been stated that the light is connected with the action of oxygen upon a fatty material secreted by the photogenic organs, and the light so produced is reflected by means of the granules already alluded to. The function of the Malpighian tubules of insects were not definitely established until a few years ago. Some zoologists stated that they represented the ‘‘ liver,” while others main- tained that they were renal in function. The Malpighian tubules of Blatta (Periplancta) have been shown by the author* to contain uric acid and urea. Dr. C. A. MacMunnf has confirmed the author’s investiga- tions, for he has extracted uric acid from the Malpighian tubules of Periplaneta orientalis. These tubules were crushed, boiled with distilled water, the extract evaporated to dryness, washed with hot alcohol, and again dissolved in boiling water and filtered. ‘To the filtrate excess of acetic acid was added, and in some hours uric acid crystals of various forms, and giving the murexide test, were formed. * Chemical News, vol. 52, p. 195. + Journal of Physioloyy, vol. 7, p. 128. 266 PHYSIOLOGY OF THE INVERTEBRATA, The author* has also examined the Malpighian tubules of Libellula depressa (Figs. 49 and 50), and has proved that they have a renal function. yassnane: ay Teeaae zene ~ISS —— SESE Fe Ne Marre STS = Nears mn = \y Coes ~ eS ey Ae Fae iN co] x as See SEG tL pr i 7 aN LEED PO NENG NI aah (Ee Malpighian tubules FIG. 49.—MALPIGHIAN TUBULES OF LIBELLULA. Libellula depressa (the dragon-fly) is a voracious insect, which lives in water, during its earlier stages, where it undergoes an imperfect metamorphosis, the pupa finally creeping out of the water, and chang- ing intothe imago. By ex- perimenting with a large number of the larval forms of Libellula, the author has extracted (from the larvee) uric acid crystals, by using similar methods to those already described in this chapter. FIG. 50.—MALPIGHIAN TUBULES OF LIBELLULA. A = Longitudinal section showing the va- rious states of the epithelial lining. F B = Transverse section of tubule. xX 230. In the imago or mature form of the dragon-fly the Malpighian tubules number from sixty to seventy, and are branched. Under the microscope, a Malpighian tubule is * Proc. Roy. Soc. Edinb., vol. 15, p. 401. PHYSIOLOGY OF THE INVERTEBRATA. 267 seen to consist of a connective tissue layer, a delicate “tracheal tube,” a basement membrane, and an epithelial layer of comparatively large nucleated cells (Fig. 50). The internal cavity of one of these tubules is very irregular, as is seen by examining various parts of it in a_ transverse section. The uric acid contained in these tubules can be extracted by boiling a large number of them in water, filtering, and then evaporating the filtrate to dryness, The residue is treated with alcohol, filtered, and the residue so formed is dissolved in boiling water to which acetic acid is added. After standing for several hours, crystals of uric acid (C,H,N,O,) are deposited. These crystals are readily con- verted into murexide, Then, again, if a fresh Malpighian tubule is placed upon a slide under the microscope, and crushed, a drop of dilute acetic acid added, and the whole covered by a cover-glass, rhombic and other crystalline forms are deposited. These crystals are also readily converted into murexide by the action of nitric acid and ammonia, No other substance besides uric acid could be detected in the Malpighian tubules of Libellula depressa. From the above-mentioned reactions it is evident that the Malpighian tubules of the Jnsecta are physiologically true renal organs. As already mentioned some zoologists of the older school stated that these appendages of the alimentary canal repre- sented the “liver,” and this statement has been recently revived by Dr. B. T. Lowne in his work on Calliphora. But the Malpighian tubules of the Diptera (including Calliphora) readily yield uric acid when the proper tests are skilfully applied; and they do not contain the least trace of biliary acids, glycogen, or even ferments. The Malpighian tubules of the Jnsecta are undoubtedly true kidneys, although they are developed from the alimentary canal. 268 PHYSIOLOGY OF THE INVERTEBRATA. THE ARACHNIDA. (a) In the Scorpion the posterior extremity of the abdomen is armed with a sort of hooked claw, which, when the animal is in motion, is always carried over the back in a most threatening attitude. This claw-like organ is the sting, and at its base are situated two poison-glands whose ducts pass into the point of the sting, so that when the animal strikes with its weapon, a small portion of the poison or vemon is instilled into the wound. ‘The sting is a weapon of offence. (6) In the Avaneina the poison gland is lodged in the cephalo-thorax, and the duct of it opens at the summit of the terminal joint. It will be noticed that in the Arancina the poison gland is situated in the anterior part of the body, whereas in the malpighian tubes . ¥ ne iS) 3 & is | OH ile [ oO // (im / £ If > Ww {2 Cc ae liver ducts* malpighian tubes E 3 8) x Fic. 51, A AND B.—MALPIGHIAN TUBES OF TEGENARIA. construction of dwellings, and of webs for the capture of prey, but isconstantly employed in securing them from falls whilst in motion, or in descending in a direct line from an elevated position to some object below them. Many spiders papers. 270 PHYSIOLOGY OF THE) INVERTEBRATA. have the power of emitting this secretion in the form of threads, one end of which floats freely in the air until it meets with some object to which it adheres. By this means spiders often form natural bridges, by means of which they can pass over brooks and rivers, in some cases twenty and even fifty feet wide. Another purpose to which this secretion is applied by all spiders is the formation of silken cocoons for the reception of the ova, which a few species (7.¢., wandering spiders) carry about with them. Hl i H 1 FIG. 52, @ AND 6.—CRYSTALS OF UrRIC ACID AND MUREXIDE. a = the uric acid crystals. 4 = murexide crystals. Concerning the excretory apparatus in the Araneina, Mr. A. Johnstone, F.G.S., and the author* have examined the Malpighian tubules of Zegenaria domestica (Fig. 51, A and B). The intestines of this species form a tube-like body, which dilates into a short rectum, and into this rectum the Mal- pighian tubules open. An aqueous extract of a large number of these tubules yielded uric acid (Fig. 52). The secretion is neutral to test * Proc. Roy. Soc, Edinb., vol. 15, p. 111. PHYSIOLOGY OF THE INVERTEBRATA. 275 The uric acid was extracted by both of the methods used for testing the pylorie sacs of Uraster (see p.) 254. The uric acid is present as sodium urate, for sodium is easily detected in the secretions of these organs. No doubt some sodium compound is a normal constituent of the blood of Tegenaria. No urea, guanin, or calcium phosphate could be de- tected in the secretion. But it may~ be stated that Dr. C. Weinland* has recently extracted crystals of guanin from the excrements of certain spiders. The guanin so extracted is stated to have answered to all the reactions of that substance as described by Capranica.t There is no doubt that the Malpighian tubules of the Arachnida are renal in function. THE CRUSTACEA. Among the lower Crustacea the renal organ is represented by the so-called shell-gland. It consists of a coiled tube with clear contents. In Apus (belonging to the Phyllopoda) this gland opens by a duct ‘‘on the base of the first pair of thoracic appendages, immediately behind the second maxillee.” In his paper on Cyclestheria hislopit Dr. G. O. Sars says that the only organ to which an excretory function has been attributed is the so-called shell-gland (see Fig. 11). Its structure is glandular, but of what nature the secretion is, and in what manner performed in this species, has not yet been satisfactorily ascertained. Some naturalists state that this peculiar organ secretes the material of which the shell is built up, but it is far from evident that such is its real function. On examining the organ, Dr. Sars failed to detect in this species any secreting orifice, the whole organ appear- ing to constitute a convoluted canal or duct recurring in itself. * Zeitschrift fiir Biologie, vol. 25, p. 390. t+ Zeitschrift fiir Physiologische Chemie, vol. 4, p. 233. $ Christiania Videnskabs-Selskabs Forhandlinger, 1887, p 43- 272 PHYSIOLOGY OF THE INVERTEBRATA. But there is no doubt that in other forms of the lower orders of the Crustacea the secretion ‘of the shell-gland does contain uric acid, proving the renal function of the organ in question. In the Decapod Crustacea * the excretory organs are re- presented by the so-called green glands. Dr. Rawitz has recently examined the anatomical structure of these glands in Astacus fluviatilis, and his results may be summarised as follows :—The gland is uniformly green on the ventral side, but on the dorsal side only at the periphery ; elsewhere white, with a round yellow-brown speck in the centre. When examined microscopically the gland is seen to consist of two tubules closely interwoven. The cells of the green part contain a round grass-green drop of protoplasm, and the yellow-brown cells a uniformly yellow-brown coloured nucleus. The tubules anastomose, the yellow-brown cells being the terminal portions of tubules and secretory. a = glandular portion. 6 = sac- The author} has made a com- like portion. ¢ = opening of plete study of the function of duct. § @= nerve with ramif- the sreen.glands of Astacus ee ae fluviatilis, and the results of these researches may be stated as follows:—The so-called ereen glands of the fresh-water crayfish lie in the cavity of the head below the front part of the cardiac division of the stomach (see Fig. 13). The openings of these organs are situated at the base of each antenna. ‘The organ, carefully dissected out of the head of a fresh-killed crayfish, is seen to consist of two principal parts (Fig. 53): a dorsal or upper- PIG. 53: GREEN GLAND OF ASTACUS. * The Decapoda includes the Brachyura and the Macroura. + See Dr. Rawitz’s paper, read before the Berlin Physiological Society on January 28, 1887. t Dr. Griffiths’ paper in Proceedings of Royal Society of London, vol. 38 (1885), p. 187. 273 PHYSIOLOGY OF THE INVERTEBRATA. ‘apixoinjWy = *‘plov oN = VW ‘HSIZAVUD AO GNVTD NAAN WOW SIVISAYD AIOY OlaQ—'PS “Oy 274 PHYSIOLOGY OF THE INVERTEBRATA. most one which is a transparent and delicate sac-like body filled with a clear fluid, and a ventral or an underlying portion of a green colour, glandularin appearance, containing granular cells. As is well known, these green glands were formerly believed to be the auditory organs of Astacus ; but in 1848 Drs. Will and Gorup-Besanez* stated that this organ probably contained guanin, and from this supposition the green glands have been considered as excretory organs. The secretion of these glands is acid to litmus paper, and on treating the secretions, obtained from a large number of green glands, with hot dilute sodium hydroxide solution, and then adding hydrochloric acid, a slight flaky precipitate was obtained, and on examining these flakes under the microscope they were seen to consist of small crystals in rhombic plates. On treating the secretion with alcohol these rhombic crystals (Fig. 54 A) were deposited; they were soluble in boiling water. When these crystals were moistened with dilute nitric acid, alloxanthine (C,H,N,O,) was produced, and on heating this substance with ammonia, reddish-purple murexide (Fig. 54 B) or the “ammonium purpurate ” [C,H,(NH,)N,0, | of Prout was obtained. The murexide so obtained crystallises in prisms, which by reflected light exhibit a splendid green metallic lustre, and by transmitted light are a deep reddish- purple. On running in a solution of potassium hydroxide upon a microscopic slide containing some of the murexide crystals they were dissolved. It is evident (from the above reactions) that these rhombic crystals are deposits of uric acid (C;H,N,O,) from the secretion of the green gland of the crayfish. ‘These deposits of uric acid crystals were covered more or less with a very thin and superficial coating of some brown colouring matter, probably one of the pigments already described. * See DMiinchen Gelehrie Anzeigen, No. 233, 1848. PHYSIOLOGY OF THE INVERTEBRATA. 275 - The secretion of the green gland of Asfacivs contains guanin, which is proved by treating the secretion with boiling hydro- chloric acid. A solution is obtained containing flakes of uric acid in suspension, these are filtered off, and the filtrate set aside to cool, when a few crystals (guanin hydrochlorate) separate which are soluble in hot water. On the addition of ammonia to this hot aqueous solution a precipitate is obtained of guanin (C,H,N,O), the precipitated guanin being composed of a number of minute microscopic crystals. On running in warm dilute nitric acid (on to the slide), these crystals dis- appeared, but they where precipitated again on the addition of a drop of silver nitrate in the form of the nitrate of silver compound (C,H,N,O,AgNO,) of guanin. This investigation proves that the so-called green gland of Astacus fluviatilis is a true urinary organ, its secretion containing uric acid and traces of the base guanin. The green gland is, therefore, physiologically the kidney of the animal.* The nerve, which comes off from the supra-cesophageal gan- glion, passes to the neck of this gland (see Figs. 13 and 53), and ramifies over its surface between the outer and inner membranes of which it is composed. In the Edriophthalmic Crustacea, there are occasionally present one or two tubules which open into the posterior part of the alimentary canal. These are renal organs and contain uric acid. They are analogous to the Malpighian tubules of the Znsecta. In this respect the Amphipoda and Isopoda differ from other Crustacea. THE BRACHIOPODA. The shell of these animals is “a cuticular structure secreted by the ectoderm, and consists of a membranous basis, hardened * For further details see Dr. Griffiths’ papers in Proceedings of Royal Society, vol. 38, p. 187 ; Chemical News, vol. 51, p. 121; Journal of Chemical Society, 1885, p. 680 ; Science Gossip, 1886, p. 57. 276 PHYSIOLOGY OF THE INVERTEBRATA. by the deposit of calcareous salts, sometimes containing a large proportion of phosphate of lime (Lingula).” In Waldheimia and other Brachiopods, “the perivisceral cavity communicates with the pallial chamber by at least two, and sometimes four, tubular organs, which have been described as hearts, but are now known to have no such nature.” These organs are funnel-shaped, the wide parts of which open into the perivisceral cavity. The narrower parts of these organs pass through the anterior wall of the visceral chamber, and terminate in small openings in the pallial cavity. According to Dr. Morse, the ova pass through these organs in Terebratulina septentrionalis. The so-called pseudo-hearts have a double function, being renal organs and genital ducts. They are the homologues of the organs of Bojanus of the Mollusca, and of the segmental organs of worms. THe MOLLUSCA. The excretion of carbonate of lime is an important function in a large number of Molluscs. In Anodonta, which is taken as a typical example of the Lamellibranchiata, the shell is a ‘‘ cuticular excretion from the surface of the mantle,” and consists of variously disposed lamellee of organic matter impregnated and hardened by the deposition of calcareous salts (chiefly carbonate of lime, mineralised as arragonite). The shell has no cellular struc- ture; “but from the disposition of its lamelle, and from the manner in which the calcareous deposit takes place in them, it may present varieties of structure which have been distin- euished as nacreus, prismatic, and epidermic ” (Fig. 55). In the young Lamellibranch shell there is a much larger percentage of calcium phosphate present than in the adult shell: the calcium phosphate being gradually replaced by calcium carbonate as the animal arrives at maturity. The ligament which unites the valves together is an uncal- cified chitinous material. This material is continuous with ~ PHYSIOLOGY OF THE INVERTEBRATA. 277 the horny cuticle which spreads over the external surface of the valves, and is reflected over the ventral edges into the mantle or pallium. The pearly or nacreus layer has a laminated texture, and is secreted by the mantle. The production of pearls (¢.7., in Meleagrina margaritifera, the “pearl oyster”) is as follows: A grain of sand, or other hard substance, gets in between the pallium and the shell. Con- sequently the external surface of the pallium becomes uri- tated, and the laminated mo- ther-of-pearl layer (nacreus EIG. 55s layer) is secreted by the pal- — secrion or SHELL or GAPER. lium, during the remainder of «a =cuticula. 4 = prismatic layer. the animal’s life, around this ¢ = @creus layer. d = epithelium. wos eé = mantle. irritant nucleus.* The exoskeletons of the Brachywra and Macroura have a similar structure to the Lamellibranch shells;f and it has been shown that the particular combinations of lime requisite for the formation of these shells, &c., are calcium chloride, calcium carbonate, or calcium phosphate. The sulphate of lime present in sea water cannot be utilised for shell formation unless it is first converted into one of the above forms. The researches of Irvine and Woodhead+ prove that “ shell forma- tion in, the crab is somewhat different from egg-sheli formation in the hen, and occupies an intermediate position between * According to Dr. G. Harley, F.R.S. (Proc. Roy. Soc., 1888) pearls have the following composition :— Calcium carbonate . : : Ol. 72 Organic matter (animal) . = S 5.04 Water . : : . ; “ ae Ae 99.89 + See Vitzou’s paper in Archiv de Biologie, tome 10, p. 659. + Proc. Roy. Soc. Edin., vol. 15, p. 308 ; vol. 16, p. 324. 278 PHYSIOLOGY OF THE INVERTEBRATA. such egg-shell formation and bone formation, as the carbonate of lime is deposited in the chitinous portion of growing epithelial cells in the crab shell.” “In the secreting layer of the mantle of certain Molluscs the lime in the epithelial cells is principally phosphate, whilst the fluid bathing its outer surface and the shells them- selves contain the lime, principally in the form of a carbonate. If there is a definite interval between the secreting surface and the area of deposition, or if much chitin or other tissue is developed between the actively secreting cells and the tissue in which the lime is deposited, there is always a greater tendency to the formation and deposition of carbonate of lime.” Phosphates of the alkalies and alkaline earths occur in the blood or nutritive fluid, and the latter acts as a carrier of lime, &c., to every part of the body where carbonic anhydride may be given off; thus carbonate of lime is formed, and the phosphoric acid re-enters the circulation. As already stated, the embryonic and young shells of the Lamellibranchiata are richer in phosphate of lime than the Shells of the fully-grown animal. No doubt as greater activity goes on a larger amount of carbonic anhydride is produced, and by this means more carbonate of lime is de- posited than phosphate of lime. When alkaline phosphates, associated with lime and albumin, preponderate in the blood, the lime so separated is in the form of phosphate, as in bone formation; when these are partially replaced by an excess of alkaline carbonates, as in the majority of marine animals, the lime is secreted as car- bonate. | ? The corals have a secreting layer of cells which, according to Irvine and Woodhead, produce chitin—chitin infiltrated with calcium carbonate, and almost pure calcium carbonate, with a small quantity of cementing organic material. The carbonate of lime is formed by the ammonium car- bonate produced by the decomposition of the effete products PHYSIOLOGY OF THE INVERTEBRATA. 279 of animals, as urea, &c., decomposing the calcium sulphate in the sea water with the formation of calcium carbonate. In the blood of the lime-secreting Invertebrates there are phosphates of lime and soda, along with alkaline chlorides, carbonates, and sulphates associated with albuminous matter, carbonic anhydride and oxygen being also present in varying quantities. This blood is alkaline, which is due to the pre- sence of alkaline phosphates and carbonates. Dr. Schmidt found that the blood of Anodonta cygnea was slightly alkaline; and on evaporation it yielded crystals of calcium carbonate resembling gaylussite. ‘“ These could not have been present originally in the alkaline fluid, and it is probable that they were produced by the formation of ammo- nium carbonate from the decomposition of urea* and nitro- genous organic matter.” The membrane which secretes chitin also brings lime to the surface, and in performing its protoplasmic function car- bonic anhydride is set free; this readily forms calcium car- bonate after decomposing certain lime salts. ‘ But it must be noted that the chitin is directly in contact with the upper secreting cells, in fact, the younger layers of chitin still form the upper or older portion of the cell.” Irvine and Wood- head “maintain that the direct contact allows of the dialysis into the chitin of a portion of the phosphate of lime before it is completely transformed into the carbonate. As the car- bonate of lime is formed the free phosphoric acid is apparently reabsorbed and utilised afresh. In proof of this fact, and as bearing on the whole question of lime secretion, we refer to the investigations of Schmidt, who, in speaking of Unio, Anodonta, and Helix, describes the structure of the secreting membrane of the mantle as a layer of hexagonal cells on which is a structureless transparent membrane in which the lime is deposited, and ascribes to it the function of decomposing the blood, of secreting a compound of albumin with phosphate of * Urea and uric acid are present in the excreta of Anodonta, see the author’s paper in the Chemical News, vol. 51, p. 241. 280 PHYSIOLOGY OF THE INVERTEBRATA. lime next the shell, which is decomposable even by the carbonic anhydride of the air or of the water, but of retaining the phosphoric acid and returning it to the organs which require it for the process of cell formation. In proof of this he gives the following analysis of the ash of the secreting layer of the mantle: I Ul. Calcium phosphate . 5 : 14°85 14°91 Calcium carbonate, sodium phosphate, 2.71 3.45 sodium chloride,and calcium sulphate ; , showing how large a proportion of the lime salts must, in this secreting layer, be in the form of phosphates. As further proof he gives analysis of the mucus which is found between the shell and the mantle, in which he finds much albuminate (basic) of lime, a small proportion of carbonic anhydride, but not a trace of phosphate. In the delicate membrane in which the lime is deposited we have an analo- gous membrane to that of egg-shell membrane (of birds), separated from the secreting layer of cells by a fluid containing albumin, carbonic anhydride, and lime salts, in whatever way combined, and deposited in the structureless membrane. According to analysis of the ash, the lime salts present are in the following proportion : Anadonta, Helix, Calcium carbonate : : 5 99.45 ..- 99.06 Calcium phosphate. : : O55) ees 0.94 So that Schmidt was able to trace the transition stages through the excess of phosphate in the mantle, the albu- minate in the intermediate bathing mucus, and the carbonate in the shell.” Irvine and Woodhead believe that the carbonic anhydride in this case was the result of metabolic processes going on in the mantle, and that the carbonate of lime formed was gradually passed on in this condition from the lime-mucous solution (if present in that condition) into the membrane again by dialysis. PHYSIOLOGY OF THE INVERTEBRATA. 281 “ As the process of shell-formation must necessarily go on slowly, it is not at all astonishing that such a small propor- tion of carbonic anhydride should be found in the mucous material. It is used up as it is formed in laying down the carbonate of lime of the shell. “ As regards the proportion of the lime salts and chitin, Schmidt found that the amount of earthy phosphate increases in proportion to the quantity of chitinous tissue present in the basement structure : Crayfish. , Squilla. Lobster. Chitin . ‘ a ore aos 62.84 ae 22.94 Lime salts. S32 ase S7aL7. Bre 77.06 100.00 100.00 100.00 Calcium phosphate 13.17 gic 47-52 We 12.06 Calcium carbonate 86.83 52.48 87.94 100.00 AP 100.00 sie 100.00 “He argued from this that the calcium (lime) phosphate is in intimate relation with cell-formation.” But Irvine and Woodhead think that as the chitin becomes older and thicker the cellular layer becomes less active, less carbonate is formed, and that there is thus a more direct passage out- wards of the phosphate. In their papers already mentioned, Irvine and Woodhead give the following analyses as showing the comparative amount of calcareous and organic matter in the common edible crab : Water, blood, salts, &c. . : . 6,646 grains Flesh (gave 14.56 of ash containing 4.94 te phosphate. 295 Outer calcareous structure . ‘ © 29565 J33 Inner calcareous structure Z - : : r 103 ” TO.GOOms as . The caicareous structure consisted of : 282 PHYSIOLOGY OF THE INVERTEBRATA. Lime tiene Total. | Chitin. | ..-ponate. Lae Percentage. Carapace . E 817 | 150.32 | 656.80 | 9.87 Sie Chelze : . | 1184 | 236.80 | 933.00 | 14.20 Gitén | teas See oy ambe 736 | 147.20 | 579.97 | 8.83 CaCO, . 78.80 Abdominal ) ( 156 31.20 |, 122,034) ox Ca,P,0, . 1.20 segments } { 63 12.60 | 49.64 | 0.76 | ceo eee 100.00 Outer struc-) - — - 1, + | 2956 | 587.12 | 2342.34 | 35-53 ture weight ) | |= | he | INNER. Inner struc-) are phe « 103 | 35.00 | 66.98 | 1.02 | Chitin . 34.00 8 | CaCO, . 65.00' Teeth (mandibles) weighed . 17 grains. | Ca,P,0, . 1.00 Stomachical teeth (horny mat- 100.00 ter) weighed : : leap a The nutritive fluid (blood) of an edible crab weighing about 8000 grains contained :— Calcium phosphate . . - : : - 11.10 grains Phosphoric acid) =. 2) Ge 9a) ee anya Having alluded to the secretion of the shells and exo- skeletons in the Mollusca and Crustacea, we now proceed to describe the organ of Bojanus in Anodonta cygnea and other Lamellibranchiata. The function of this organ has been investigated by Mr. Harold Follows, F.C.S., and the author.* It is a paired, elongated, oval, glandular sac with folded walls. It is situated beneath and behind the pericardium, and in front of the posterior adductor muscle (see Fig. 18). This organ is composed of a yellowish or brownish spongy tissue, which is covered with a closely ciliated cellular layer. Its secretion is acid to litmus paper, and it contains uric acid, urea, and calcium phosphate. The presence of these com- pounds were proved by the methods already described in this chapter. * Chemical News, vol. 51, p. 241; Journal of Chemical Society, 1885, p. 921 ; Proceedings of Royal Society of Edinburgh, vol. 14, p. 233- PHYSIOLOGY OF THE INVERTEBRATA. 283 Mr. Follows and the author also examined the blood (of Anodonta) contained in the vena cava before it enters the organ of Bojanus, and it was proved that the blood contains uric acid and urea. After leaving the vena cava the blood passes into the organ of Bojanus and thence to the branchie. The blood in the branchize does not contain uric acid or urea. The investigation proves—(w) that the organ of Bojanus is physiologically the kidney of the animal, eliminating the nitrogenous waste matters (in the form of uric acid and urea) contained in the impure blood as it is brought to this organ by the vena cava; (0) that after the blood has passed through the organ of Bojanus, it is freed from urea and uric acid. The secretion of the organ of Bojanus in Mya arenaria (see Fig. 18) contains uric acid, urea, and calcium phosphate. Drs. Will and Gorup-Besanez* stated that they found guanin in the organ of Bojanus of the fresh-water mussel, but subsequently Voit could not detect the least trace of this base in the organ in question. Mr. Follows and the author entirely agree with the conclusions of Voit, for we also could not detect guanin in the organ of Bojanus in Anodonta cygnea, although it may be remarked that guanin is present in the green glands of Astacus and Homarus.T The organ of Bojanus appears to be well-developed in the majority of the Lamellibranchiata, but in Ostrea and Teredo it seems to be present in only a very rudimentary form.t The nephridia of Helix aspersa and Limax flavus contain uric acid, and were proved by MacMunn $ to have a renal function. * Ann. der Chem. und Pharm., vol. 59, p. 117; and Diinchen Gelehrte Anzeigen, 1848. + See Dr. Griffiths’ papers in Proc. Roy. Soc. of London, vol. 38, p. 187 ; and Proc. Roy. Soc. of Edinburgh, vol. 14, p. 233: + See the papers of Lacaze-Duthiers in Annales des Sciences Naturelles, 1854-1861. § Journal of Physivlogy, vol. 7, p. 128. 284 PHYSIOLOGY OF THE INVERTEBRATA. The author has confirmed MacMunn’s investigations, and he has also proved the renal function of the nephridia in Limax maximus, Helix pomatia, Limax variegatus, Arion ater, and other Gasteropods. They contain, in addition to uric acid, urea and calcium phosphate. Many of these organs also contain some of the histohzematins; and in the case of “ Arion ater the nephridium showed a spectrum resembling that of myohzematin, and this spectrum is remarkable for its resemblance to that of the kidney of Vertebrates.” (MacMunn.) The Gasteropoda are provided with numerous glands which secrete mucus. The epiphragm of Helix is secreted by mucous glands, but it becomes hardened and strengthened by the deposition of calcareous matters. This epiphragm (perforated) is secreted before hybernation (i.., the winter sleep), and closes the shell-opening when the animal is retracted. The epiphragm is cast off in the spring when the animal awakes. The secretion of the mucous glands of slugs is of value to the animals as a means of protection against the attacks of enemies. The mucus secreted is often pigmented, and it gives a polished appearance to the pigments which resemble certain metallic hues; such pigments are spoken of as protec- tive colours. Having referred to certain secretions of the Pulmogustero- yoda, we have now to consider those of the Branchiogasteropoda. The author* has investigated the nephridia of Patella vulyata. These organs consist of two parts—left and right lobes. The left nephridium is very small in comparison to the right. The anatomy and histology of these organs have been fully described by Professor E. Ray Lankester, F'.R.S.,f J.T. Cunningham,t{ and Harvey Gibson.§$ * Proceedings of Royal Society, vol. 42, p. 392. + Annals and Magazine of Natural History, vols. 20 (1867), and 7 (1881). ~ Quarterly Journal of Microscopical Science, vol. 22, p. 369. § Transactions of Loyal Society uf Edinburgh, vol. 32, p. 617. PHYSIOLOGY OF THE INVERTEBRATA. 285 After dissecting the nephridia from the bodies of a large number of fresh limpets, the secretions of the left nephridia were examined separately from those of the right nephridia. Both secretions were examined chemically by two separate methods as follows: (a) The clear liquid from the nephridia was treated with a hot dilute solution of sodium hydroxide. On the addition of HCl a slight flaky precipitate was obtained after standing for some time. ‘These flakes when examined microscopically were seen to consist of small rhombic plates and other forms. On treating the secretion alone with alcohol, rhombic crystals were deposited, which were soluble in water. When these crystals were treated with nitric acid and then gently heated with ammonia, reddish-purple murexide was obtained. (>) The second method for testing the secretion of the nephridia of Patella was as follows: The secretion was boiled in distilled water, and then evaporated carefully to dryness. The residue so obtained was treated with absolute alcohol and filtered. Boiling water was poured upon the residue, and to the aqueous filtrate an excess of pure acetic acid was added. After standing about seven hours, crystals of uric acid (C;H,N,O,) were deposited, and readily recognised by the chemico-microscopical tests mentioned above. The secretions of both the left and right nephridia yield uric acid. It has been suggested by Professor R. J. Harvey Gibson (in his masterly memoir on the “ Anatomy and Phy- siology of Patella vulgata”*) that the secretions of the two nephridia may be chemically distinct, The author could not extract or detect (after a most searching investigation) the presence of any other substance besides uric acid in the secretion of either nephridium. ‘The isolation of uric acid proves the renal function of the nephridia of Patella vul- gata. The nephridia of the Cephalopoda have also been examined * Transactions of Royal Society of Edinburgh, vol. 32, p. 601. 286 PHYSIOLOGY OF THE INVERTEBRATA. by the author.* Taking Sepia officinalis as a type of the Cephalopoda, it was proved that the nephridia of the animal are true renal organs. The venous blood, as it passes from the vena cava, is distributed by a number of afferent branchial vessels which communicate with the sacculated and glandular nephridia; it then passes into the branchie, and hence it is sent back to the heart. The secretion of the nephridia contains uric acid and calcium phosphate, but urea, guanin, calcium carbonate, and magnesium carbonate are absent. Uric acid is also present in the blood of the vena cava before it enters the nephridia, but the blood after passing into the branchie contains no uric acid. The nephridia of the Cephalopoda are true renal organs, eliminating the nitrogenous waste matters in the form of uric acid, contained in the impure blood as it is brought to these organs by the vena cava. As already stated no urea could be detected in the nephridia of Sepia, and the same remark applies to those of Octopus. The muscular tissues of these animals do not yield urea; but it may be remarked that the muscular tissues of certain Lamellibranchs do contain this base. For instance, 100 grammes each of the adductor muscles and foot of Mya arenaria (large individuals) were chopped into small frag- ments and were allowed to remain in contact with alcohol for twelve hours. ‘The alcohol was then squeezed out and evaporated on a water-bath. The residue obtained was dissolved in water, placed in the receiver of a mercury pump, and treated with sodium hypobromite. By this method the following results were obtained :— Ti. II. Ill. Adductor muscles ‘ : 42.6 xe 56.2 tN 56.8 Foot . : : : : 48.9 ee 52.0 are 58.6 * Proc. Roy. Soc. Edin., vol. 14, p. 230. PHYSIOLOGY OF THE INVERTEBRATA, 287 These results are expressed in milligrammes of urea per 100 grammes of muscular tissue.* It is most probable that the formation of urea takes place in the muscles. It is certainly present in the blood of Mya and Anodonta. Milne-Edwards states that ‘it is probable that in all cases the secreted matter exists in the blood already formed. It was thought, for example, that the urea found in urine must be formed by and in the kidneys, since it could not be detected by chemical analysis in the blood; but if these organs be destroyed in a living animal, or re- moved, urea will, after a certain time, be formed in the blood, thus clearly proving that the kidneys do not form it.” In the higher animals an abundant alimentation gives rise to a greater excretion of uric acid and urates. On the con- trary, in abstinence the uric acid and its salts disappear, but urea is excreted in greater quantity. This applies not only to Vertebrates but also to many Invertebrates. Urea is a product of more or less complete oxidation of organic sub- stances, and is formed, as already stated, in muscular tissues, by the disintegration of the anatomical elements. Uric acid, on the other hand, is the result of an incomplete oxidation, and is produced for the most part in the bood or its equivalent, when such fluid is surcharged with peptones which the tissues are unable to assimilate. Secretion and excretion can be traced back to the phenomena of nutrition—that is to say, to the molecular acts effected in the midst of glandular cells, which means that it can be accomplished without the inter- vention of the nervous system. Such is the case with the lowest Invertebrates; but in the higher forms, possessing a more or less complete nervous system, secretion and excretion are largely influenced by nerves. It may be probable that if the commissural cords connecting the supra-cesophageal with the sub-cesophageal ganglion were severed nervous stimulus would not be supplied to the green glands of * See also Smith’s new method for estimating urea in the Pharm. Journ. Trans. [3], vol. 21, p. 294. 288 PHYSIOLOGY OF THE INVERTEBRATA. Astacus, and consequently the secretion of urine would be most probably influenced. At any rate, this is a question for research. In the Vertebrata there is no doubt that the nervous centres do greatly modify the secretions. Forty-six years ago, Schiff demonstrated that lesions of the cerebral peduncles rendered the urine albuminous and acid. Claude Bernard* proved that punctures of the roof of the fourth cerebral ventricle gave rise to the formation of glucose sugar in the urine. Lesions of the isthmus and of the lower part of the cervical marrow can prevent the urinary excretion, or in other words, produce anuria. There is no doubt that in the Jnvertebrata the nerves play an important part in the phenomena of secretion, and even in the lower orders, where there are no traces of nervous elements, the protoplasm of the cells, being irritable, is capable of bringing into play the phenomena which we have been discussing in the present chapter. Experimental evi- dence shows that the Amba, for instance, excretes, digests, and respires; but so far at least as present microscopic expedients reach, this organism appears to be simply a small mass of protoplasm, nevertheless it has the power of adjust- ing its low organisation to the environment. “In the organism lies the principle of life; in the environment are the conditions of life. Without the fulfilment of these con- ditions, which are wholly supplied by environment, there can be no life.” The wonderful adaptations of each organism, and of each part of every organism to its environment, inspire us with a sense of the boundless resource and skill of Nature in perfect- ing her arrangements for each single life. The causes of these adaptations are to be sought in the numberless structural modifications brought about by means of natural selection and by the direct action of the environment. As already stated, not only an organism as a whole, but each organ is also capable of undergoing modification. Hence © * Lecons de Physiologie Opératoire. PHYSIOLOGY OF THE INVERTEBRATA. 289 the reason that there are strange facts to confront in deter- mining the nature of anorgan. For instance, the Malpighian tubules of the /nsecta are diverticula of the alimentary canal, consequently they have been described as livers, and morpho- logically they ought to have the function of a liver. But when physiology, aided by chemical methods, steps in, we find that these organs have solely a renal function. Is it possible that the Malpighian tubules had originally the function of a liver? ‘This is improbable, but it is well known that an organ may lose its original function, and yet persist because it is of use for some other purpose: one of these predominate at one time, another at another, and the organ undergo structural modification in consequence.* The variety of modifications or forms of the renal organs in the Jnvertebrata may be illustrated by the table on pp. 290-1. The table on p. 292 is a summary of the constituents (present and absent) in the renal organs of the higher Invertebrata. In the lower Jnvertebrata the kidney performs other functions besides that of a renal organ; but in the higher forms a special organ is set apart for that function, and it resembles in many respects the Vertebrate kidney. On this point Prof. Huxley says: ‘In the Vertebrata, the renal apparatus is constructed on the same principle [as the renal organs of the Mollusca] . ... The Vertebrate kidney ‘is an extreme modification of an organ, the primitive type of which is to be found in the organ of Bojanus in the Molluse, and in the segmental organ of the Annelid ; and, to go still lower, in the water-vascular system of the Turbellarian. And this, in its lowest form, is so similar to the more com- plex conditions of the contractile vacuole of a Protozoon, that it is hardly straining analogy too far to regard the latter as the primary form of uropoietic as well as of internal respiratory apparatus.” * In the higher animals, for example, we have the formation of a lung from a swimming bladder, and of the ear passage from a gill cleft. T —_ PHYSIOLOGY OF THE INVERTEBRATA. 290 “plow O11) pre ony “prow ol ‘prov O11 (i) “prov oly) ‘(0}v1N TANTpos sv) plow OQ ‘prow og (i) — ~ ~— ‘prov oy) “UvS10 [BUI B JO FLY} SU [JOA Sv sUOTJOUNZ IayyO UWIOJIod osoqT, , . . ( “ “ec ) “c “ ) . : * (saqny uerysrdyeyy) sepuqny 1en{[ag j : c : : : : suvs.o TeJUaUISaG : : : : . * sueS10 avjnpuryy ,, : . . ( we oe ) be ce . (sueS1o Teyuomsos) “ es * (erpuydou) soqny repny[a9 Var YoRutoys) YORUIojs ayy Jo sayonod say oy, ) ,Wd4sAS IB[NOSVA-197B AY : * ,SofONoRA d[IJORIQUOD : * ,SaTONOVA JITJORIZUOD v194do.1n9 NY E) *vraydoyqyig (q)- * epodoayyary VYvIYOVIJOJOIg w! voployemMoN (v) sad1[ooso}vulaN * vyeyodjog “ vyeyoostg (4) - * vprpuuy * eoulpaitH (»)) ‘ vapieysy (v) eyeurepouryog * vqyeIaqzUudToO . . . eplsuodg 10 vilazII0g * weriosnjuy (9) : * B0Z0J0OIg eysve[doyoig (”), “Uo1ja100g UI yuasord syonporlg —fq pozuosaider oupry ‘ow ‘sxopig ‘sossv[pO (‘sayoumasan s.woyynp ayy wolf papdwop ) ‘AUNGIM ALVUCALYAANT AL 291 PHYSIOLOGY OF THE INVERTEBRATA. ‘(j) prow or, ‘ayeyd -soyd umntopeo ‘prow ong ‘ploe O11) ( Tanoyeo ‘vam ‘prow og | ‘aqyeydsoyd { tantoreo “vain ‘prov ong | ‘uluend pue prov og ( ‘plo’ ony) ‘uluens J ‘(oye WANIpos sv) prov org plow ony, | suvSIO AV[NpULTS pue paywpNooes jo IPG | \ [ (erpraqdon) SUBSIO Iv[UpUR[S pue paye[nooes jo Ueg * .,snuvlog jo suvsio ,, Ina * (suBSIO Iupnqny) syrvay-opnosg (,,Spueps uda.s ,,) « a ( spurs aepnqyag | . . ( “ ia ) as “ . . ( “ “c ) “ “ | (soqny uvIqsidjey_) soynqny aepnyjap * (etpriydou) | | vyerqouraqraqay, (z) * eByerouriqig (1) | epodoyeydag (2) vpodo.1a4 | “sesorqourig (Z) | a * epod -O.104S¥.d0WTN ‘| : ‘ vpodosajsey (q) * eqerqouriqiyjomey (2) ; 3 ByBlayUayst[y (2) * ewimororyy (i) * winayorig (/) vrmeqyydoupg (/’) vulourly (a) . vi9}doalog (yp) * BOSNI[OTL | * vpodorporig * epodoiyyay ‘morpotiny A10j910X9 UB OAT “930 ‘wpnUusapoundy YY UT ,, S[[9O SutLopuUeA,, OY} FVYY SaAdTjog (16gI ‘auUaagG *souoly “Umnor *zwNg) WegING “Wf *H “I (Z) ‘jeuvo Areqyuourye oy} Jo sT[VM oy Aq pue onssty oatyoouuod ayy Aq yuayxo 90S 09 puL ‘s][90 OLtAeposetM deaf A UO polio st vozhjoy SULLY OY} UL UOTJoIOXa yey} UMOYS sey (16gI ‘aauarg ‘souny ‘Ulnor yuoN¢)) JOWAV]T “WG “AW (1) “wywaqazavuy ay} Ul UOT}eIoxa uo pervodde savy saoded omy ‘siaqutmd ay} Jo spuey oy} ul peovd svMm YIOM sIy} IOUIG—'ALON (06€ ‘d ‘Sz *foa ‘ahojog nf yruyospnag ) puerure A, 0} Surpzooor ‘st yey, + ‘ppodosajspbououvig ayy UL JUEsqY , ss \ < fe RQ Q N tS aN S | | | | ai) ee “i ae oe i i else i wurpog | | | = ¢ | es | " a a eae aff ‘ aqeydsoyd wintoe9 | | | | S. 2 - = | eee + | = = ; * * urmens S | _ > s ie = See alin ged eet = a 1) S + + + ee + +e} =k a " * prow om N : | = Ss | On | | “ryeTyouRrq “epod “zpod x ‘nourpnatyy] | “VpaqoosyoO | ‘vaproyemoyy | “eyoosuy | ‘epluyorry | ‘vaorqsnag “ypauery -019}805) -opeyday ou ; Ts eee = quesqy = quasoig te 292 CHAPTER X. THE NERVOUS SYSTEMS OF THE INVERTEBRATA. NERVOUS tissue consists of two distinct structural parts: (a) nerve-cells and (0) nerve-fibres. The nerve-cells are usually found in aggregates termed ganglia or nerve-centres ; and ganglia are united to ganglia by nerve-cords or bundles, which consist of many delicate nerve-fibres. The latter act as the conductors of nervous force; in fact, ‘“ the characteristic function of nerve-fibres is that of conducting stimuli to a distance. The function of nerve-cells is different, viz., that of accumulating nervous energy, and, at fitting times, of dis- charging this energy into the attached nerve-fibres. The nervous energy, when thus discharged, acts as a stimulus to the nerve-fibre ; so that if a muscle is attached to the end of a fibre, it contracts on receiving this stimulus. When nerve- cells are collected into ganglia, they often appear to discharge their energy spontaneously; so that in all but the very lowest animals, whenever we see apparently spontaneous action, we infer that ganglia are probably present.” ‘There is another important point, viz., the difference between muscles and nerves under the influence of a stimulus. ‘A stimulus applied toa nerveless muscle can only course through the muscle by giving rise to a visible wave of contraction, which spreads in all directions from the seat of disturbance as from a centre. A nerve, on the other hand, conducts the stimulus without sensibly moving or undergoing any change of shape. Therefore muscle-fibres convey a visible wave of contraction, and nerve-fibres convey an tnvisible, or 294 PHYSIOLOGY OF THE INVERTEBRATA. molecular, wave of stimulation, Nerve-fibres, then, are functionally distinguished from muscle-fibres—and also from protoplasm—by displaying the property of conducting in- visible, or molecular, waves of stimulation from one part of an organism to another, so establishing physiological con- tinuity between such parts, without the necessary passage of waves of contraction.” (Romanes.) Nerve-fibres may be functionally divided into five groups —motor, sensory, vascular, secretory, and inhibitory. When a nerve-fibre is stimulated from some nerve-centre, it may give rise to the contraction of a muscle or a blood-vessel, in- creased secretion from a gland, or a diminution or arrest of some other kind of nervous action. In all these cases, ‘‘ the nervous influence travels outwards from a ganglion or nerve-centre towards the periphery, thus presenting an analogy to ordinary motor nerves.” Perhaps the best classification of nerve-fibres, from a physiological point of view, is the following ; = i (a) Motor (efferent), excite contraction of muscles. mM el (b) Vascular (vaso-motor), excite contraction of blood-vessels. = Q : : * ae (c) Secretory, excite secretion. Ee (d) Inhibitory, affect other nerve-centres so as to moderate or Bie destroy their action. 8 (e) Connecting, which connect motor-cells in nerve-centres. ie) (1) General, “convey to nerve-centres in brain influences which cause sensations of a vague character (not permanent).” (a) Sensory + (2) Special, ‘convey to nerve-centres in brain influences which cause visual, auditory, gustatory, olfactory, or tactile sensa- tions.” (b) Afferent, convey to nerve-centres influences which cause no sensation, and which may or may not be followed by further nervous activity.” (c) Connecting, ‘‘ which connect sensory cells in nervous centres.” Centripetal (sensory) nerve-fibres. The centrifugal nerve-fibres convey influences outwards from a nerve-centre ; while the centripetal nerve-fibres con- vey influences inwards towards a nerve-centre. It should be PHYSIOLOGY OF THE INVERTEBRATA. 295 borne in mind that the different nerve-fibres merely act as conductors, the effects depend upon the arrangements or apparatuses at the end of the fibres. It is the totality of the properties which nerve-cells and nerve-fibres are capable of giving rise to, which constitutes innervation. When nerve-centres or ganglia are excited the activity or energy produced is not the same in each case. Some produce the sensations of light, sound, pain, &c. ; others are the cause of secretion or locomotion; others are associated with psychical states; while a fourth exerts an influence over other nerve-centres. These nerve-centres may be classified as follows: (a) ‘‘ Receptive centres, to which inflnences arrive which may excite sensations or some kind of activity not associated with consciousness. (b) Discharging centres, whence emanate influences which, according to structures at the other ends of the nerves connected with them, may cause movements (muscles), secretion (glands), or contractions of vessels. (c) Psychical centres, connected with sensation, in the sense of conscious perception, feeling, volition, intel- lectual acts, and will. (d@) Jnhibitory centres, which inhibit, restrain, or even arrest the action of other centres.” In the majority of cases there are terminal organs at the commencement of sensory, and the terminations of motor nerves. Such organs are seen in the rods and cones of the retina and the terminal plates of muscle ; but in some few cases nerve-fibres may terminate in loops towards the periphery of the body or in the interior of organs. We now proceed to describe the nervous systems in the Invertebrata. THE PRoTOzOA. In none of these animals has any trace of a nervous system been discovered; nevertheless, as nervous elements are nothing more than the products of the differentiation of protoplasm, it is logical to assume that certain parts of the protoplasmic 296 PHYSIOLOGY OF THE INVERTEBRATA. cells of the Protozoa, are the means of conveying nervous energy. If no nervous system is anatomically differentiated, there is every reason to believe that the protoplasm contains a ‘diffused nervous system ” (Gruber). In these organisms innervation is rudimentary ; and the nervous function devolves upon the protoplasm, which is the cause of the phenomena of contraction, secretion, &c., and according to M. Binet, of certain psychical acts. Certainly no definite nerve-tracts have been discovered in these animals; ‘“‘but any one who has attentively watched the ways of a Colpoda, or still more of a Vorticella, will probably hesitate to deny that they possess some apparatus by which external agencies give rise to localised and co- ordinated movements. And when we reflect that the essential elements of the highest nervous system—the fibrils into which the axis fibres break up—are filaments of the extremest tenuity devoid of any definite structural or other characters, and that the nervous system of animals only becomes con- spicuous by the gathering together of these filaments into nerve-fibres and nerves, it will be obvious that there are as strong morphological, as there are physiological, grounds for suspecting that a nervous system may exist very low down in the animal scale, and possibly even in plants.” (Huxley.) THE PORIFERA. No differentiated nervous system has been discovered, but there is little doubt that nervous function is traceable in the protoplasm of these animals. The nervous system of the horny sponges has been recently examined by Dr. R. von Ledenfeld.* He gives an account of Huspongia anfractuosa, which differs in some particulars from Huspongia officinalis (the bath sponge). The fine membrane which extends from the tips of the horny * Sitzungsberichte der Kgl. Preussischen Akademie der Wisrenschaften in Berlin, 1885, p. 1015. PHYSIOLOGY OF THE INVERTEBRATA. 2097 fibres consists of parallel spindle-shaped cells, which are set perpendicularly to the outer surface of the sponge; they end in extraordinarily fine tips. ‘The protoplasm contains small, but highly and doubly refractive, granules embedded in a single refractive substance. ‘The granules are so arranged as to give the appearance of a kind of transverse striation. ‘These are muscle-fibres. If the investigations of Ledenfeld are correct, we have in these animals the beginning of a true nervous system. THE CQ@LENTERATA. Kleinenberg has shown that in Hydra the cells of the ectoderm terminate internally in delicate processes from which fine longitudinal filaments are’ produced. ‘These fila- ments form a layer between the ectoderm and endoderm. According to Kleinenberg, these filaments are the represen- tatives of both muscle and nerve; in fact, he regards them as neuro-muscular elements in an undifferentiated state. But Prof. Huxley believes that Kleinenberg’s fibres “ are solely internuncial in function, and therefore the primary form of nerve. The prolongations of the ectodermal cells have indeed a strangely close resemblance to those of the cells of the olfactory and other sense-organs in the Vertebrata ; and it seems probable that they are the channels by which impulses affecting any of the cells of the ectoderm are con- veyed to other cells and excite their contraction.” Dr. G. J. Romanes, F.R.S.,* has shown that in the Meduse. we find phenomena similar to nervous transmission sent along definite tracks, or sometimes diffused from one part of the body to the other, without any histological trace of differen- tiated nerve-fibre. As in the Protoza, we have in these animals the early stages of the evolution of a nervous system. * Philosophical Transactions of Royal Society, 1875, p. 269 ; ibid. 1877, p. 659; ibid. 1879, p. 161; and his book, Jellyfish, Starfish and Sea Urchins. 298 PHYSIOLOGY OF THE INVERTEBRATA. Prof. E. Haeckel* has described the nervous system of the Geryonide. It forms a circle all round the margin of the nectocalyx (umbrella), ‘following the course of the radial (nutrient) tubes throughout their entire length, and pro- ceeding also to the tentacles and marginal bodies.” ‘There is a ganglion at the base of each tentacle from which the above-mentioned nerves take their origin. These ganglia contain fusiform and nucleated cells of high refractive power. . “The nerves that emanate from the ganglia are composed of a delicate and transparent tissue, in which no cellular elements can be distinguished, but which is longitu- dinally striated in a manner very suggestive of fibrillation. Treatment with acetic acid, however, brings out distinct nuclei in the case of the nerves that are situated in the marginal vesicles, while in those that accompany the radial canals, ganglion-cells are sometimes met with.” Haeckel’s researches have been confirmed by Allman, Claus, Harting, Romanes, and others, According to Drs. O. and R. Hertwig,t the nervous system of the naked-eyed Medusw consists of two parts, a central and a peripheral. ‘The central part is localised in the margin of the swimming-bell, and there forms a nerve-ring, which is divided by the insertion of the veil into an upper and a lower nerve-ring..... In all species the upper nerve-ring lies entirely in the ectoderm. Its principal mass is composed of nerve-fibres of wonderful tenuity, among which are to be found sparsely scattered ganglion-cells, -... The fibres which emanate from them are very deli- cate, and, becoming mixed with others, do not admit of being further traced.” “Beneath the upper nerve-ring lies the lower nerve-ring. It is inserted between the muscle-tissue of the veil and umbrella, in the midst of a broad strand wherein muscle- fibres are entirely absent.” The lower nerve-ring belongs * Beiti dge zur Naturgeschichte der Hydromedusen, 1865. + Das Nervensystem und die Sinnesorgane der Medusen. PHYSIOLOGY OF THE INVERTEBRATA. 299 to the ectoderm, and consists also of nerve-fibres and ganglion-cells. In these respects there is no difference between the lower and upper nerve-rings; but it may be remarked that a difference is distinguishable between the two. In the former there are many nerve-fibres of con- siderable thickness, whereas in the latter the nerve-fibres are exceedingly slender, and there are few ganglion-cells. ‘The two nerve-rings are separated from one another by a very thin membrane, which, in some species at all events, is bored through by strands of nerve-fibres which serve to connect the two nerve-rings with one another.” “The peripheral nervous system is also situated in the ectoderm, and springs from the central nervous system, not by any observable nerve-trunks, but directly as a nervous plexus composed both of cells and fibres. Such a nervous plexus | admits of being detected in the sub-umbrella of all Meduse, and in some species may be traced also into the tentacles.” This nerve-plexus is situated between the muscle-fibres and the epithelium. ‘There are also described peculiar tissue elements, such as, in the umbrella, nerve-fibres which pro- bably stand in connection with epithelium-cells; nerve-cells which pass into muscle-fibres, similar to those which Kleinen- berg has called neuro-muscular cells; and in the tentacles neuro-muscular cells joined with cells of special sensation. No nervous elements could be detected in the convex surface of the umbrella, and it is doubtful whether they occur in the veil.” (Romanes.) The nervous system of the covered-eyed differs from that of the naked-eyed Medusw. In the former the central nervous system consists of separate centres unconnected with commissural cords. ‘There are eight, twelve, or sixteen (but generally eight) of these nerve-centres situated in the margin of the umbrella. ‘They consist of cells of special sensation and a thick layer of delicate nerve-fibres. These nerve-fibres are merely prolongations of epithelial cells, as true ganglion-cells are entirely absent. 300 PHYSIOLOGY OF THE INVERTEBRATA. Professor E. A. Schiifer, F.R.S.,* has shown the presence of “ an intricate plexus of cells and fibres overspreading the sub-umbrella tissue” of Aurelia awrita. Dr. Claus has also described the presence of numerous ganglion-cells in the sub-umbrella of Chrysaora. It appears that as far as the nervous system is concerned, the naked-eyed are more highly developed than the covered- eyed Meduse. It is now our intention to briefly allude to the important researches of Dr. G. J. Romanes,t which have been made from the stand-point of experimental physiology. He has studied—(a) the effects of excising the entire margins of the nectocalyces of both the naked-eyed and the covered-eyed Medusee ; (b) the effects of excising certain portions of the margins of the nectocalyces ; (c) the effects upon the manu- brium of excising the margin of a nectocalyx (swimming organ); and he has arrived at the following conclusions :— ‘With a single exception to hundreds of observations upon six widely divergent genera of naked-eyed Medusa, I find it to be uniformly true that the removal of the extreme periphery of the animal causes instantaneous, complete, and permanent paralysis of the locomotor system. In the genus Sarsia, wy observations point very decidedly to the conclu- sion that the principal locomotor centres are the marginal bodies, but that, nevertheless every microscopical portion of the intertentacular spaces of the margin is likewise endowed with the property of originating locomotor impulses. ‘In the covered-eyed division of the Medusw, I find that the principal seat of spontaneity is the margin, but that the latter is not, as in the naked-eyed Medusa, the exclusive seat of spontaneity. Although in the vast majority of cases I have found that excision of the margin impairs or destroys the spontaneity of the animal for a time, I have also found that the paralysis so produced is very seldom of a permanent * Philosophical Transactions, 1878. + Ibid. 1875, p. 279. PHYSIOLOGY OF THE INVERTEBRATA. 301 nature. After a variable period occasional contractions are usually given, or, in some cases, the contractions may be resumed with but little apparent detriment. Considerable differences, however, in these respects are manifested in different species, and also by different individuals of the same species. Hence, in comparing the covered-eyed group as a whole with the naked-eyed group as a whole, I should say that the former resembles the latter in that its repre- sentatives usually have their main supply of locomotor centres situated in their margins, but that it differs from the latter in that its representatives usually have a greater or less supply of their locomotor centres scattered through the general contractile tissue of their organs. But although the locomotor centres of a covered-eyed Medusa are thus, generally speaking, more diffused than are those of a naked-eyed Medusa, if we consider the organism as a whole, the locomotor centres in the margin of a covered-eyed Medusa are less diffused than are those in the margin of a naked-eyed Medusa. In no case does the excision of the margin of a swimming organ produce any effect upon the movements of the manubrium.” Romanes has proved the effects of various stimuli upon the Meduse. After the removal of the locomotor centres (ganglia) all these animals invariably respond to stimulation, but the degrees of irritability in responding to stimuli differ con- siderably in different species. The covered-eyed, and a few of the naked-eyed Medusw respond with one or more contractions to the action of light. In the case of Sarsia tubulosa, a flash of light causes it to respond ; in fact, light acts as a stimulus. It has been ob- served that the marginal bodies of Swrsia are organs of special sense, adapted to respond to luminous stimulation; in other words, they perform the function of sight—in fact, the marginal bodies are rudimentary eyes. Romanes has shown that when these marginal bodies are excised, the mutilated animals did not seek the lhght, “ but 302 PHYSIOLOGY OF THE: INVERTEBRATA. swam hither and thither without paying it any regard.” Sarsia tubulosa and Tiaropsis polydiademata are probably the only two naked-eyed Meduse sensitive to light. But the action of light on Sarsia and Tiaropsis differs considerably. In the case of the latter, sunlight causes it to go into a kind of tonic spasm—the whole of the nectocalyx being drawn to- gether. The period of latency* in Swrsia is instantaneous with all stimulations (mechanical, electrical, luminous, &c.) ; but in Ziaropsis the period of latency is not instantaneous with luminous stimulation, for a little more than a second elapses after the first occurrence of the stimulus. With all other stimulations, in 7%aropsis, the period of latency is in- stantaneous. Romanes has shown “that the enormously long period of latent excitation in response to luminous stimuli was not, properly speaking, a period of latent excitation at all; but that it represented the time during which a certain summation of stimulating influence was taking place in the ganglia, which required somewhat more than a second to accumulate, and which then caused the ganglia to originate an abnormally powerful discharge.” The ganglionic matter of Tiaropsis represents, according to Romanes, the most rudi- mentary type of visual organ. All the excitable parts of the I/edusw are highly sensitive to electrical stimulation, but the most sensitive parts are those which correspond with the distribution of the main nerve- trunks. The external or convex surface of the nectocalyx, and the whole of the “gelatinous substance to which the neuro-muscular sheet is attached,” are insensitive to stimulation. ; ‘The extreme sensitiveness of the tissues to electrical stimula- tion suggested to Romanes the idea of ascertaining whether there is any localization of definite excitable tracts in these animals. In the case of Sarsia, “the apex of the swimming- bell is much the least excitable portion of the animal; and * 'The time which elapses between the application of a stimulus and the response to that stimulus. PHYSIOLOGY OF THE INVERTEBRATA. 303 from this point downwards to the margin there is a beautiful and uninterrupted progression of excitability, the latter being greatest of all when the electrodes are placed upon the string of cells described by Agassiz as nerve-cells.” In regard to ‘‘the marginal tract of excitable tissue, the degree of ex- citability differs slightly in different parts.” In other parts of the nectocalyx there is “a marked difference between the excitability of this organ when the electrodes are placed upon any one of the four radiating canals (and so upon the ascend- ing nerve-chains described by Agassiz), and when the electrodes are placed upon the tissue between any of the canals. The ratio is generally about 9 centims. to 6} centims.” Concerning the action of electrical stimulation the following conclusions have been arrived at by Romanes :— (1) “The excitable tissues of the Weduse, in their behaviour towards electrical stimulation, conform in all respects to the rules which are followed by the excitable tissues of other animals. Thus closure of the constant current acts as a much stronger stimulus than does opening of the same, while the reverse is true of the induction-shock. (2) “ Different species of the Medusw manifest different degrees of sensitiveness to electrical stimulation, though in all cases the degree of sensitiveness is wonderfully high, (3) ‘‘ When the constant current is passing in a portion of the strip of a severed margin, the nectocalyx sometimes manifests uneasy motions during the time the current is passing. It is possible, however, that these motions may be merely due to accidental variations in the intensity of the current, (4) “When the intrapolar portion of the severed margin of Staurophora laciniata happens to be spontaneously contract- ing prior to the passage of the constant current, the moment this current is thrown in, these spontaneous contractions often cease, and are then seldom resumed until the current again is broken, when they are almost sure to recommence. 304 PHYSIOLOGY OF THE INVERTEBRATA. This effect may be produced a great number of times in succession. : (5) “ Exhaustion of the excitable tissue of the nectocaly may be easily shown by the ordinary methods. Exhausted tissue is much less sensitive to stimulation than is fresh tissue. Moreover, so far as the eye can judge, the contrac- tion is slower, and the period of latent stimulation prolonged. (6) “The tetanus produced by faradaic electricity is not of the nature of an apparently single prolonged contraction (except, of course, such among the naked-eyed Medusw as respond to all kinds of stimuli in this way), but that of a number of contractions rapidly succeeding one another—as in the heart under similar excitation.” Romanes, in his important papers (oc. cit.), has shown the amount of section which the neuro-muscular tissues of the Meduse will endure without suffering loss of their physiolo- gical continuity ; and this isin the highest degree astonishing. He has also investigated the rate of transmission of stimuli ; as well as the regeneration of excitable tissues in these animals (%.¢c., after injury). It may be remarked that if the contractile sheet, which lines the nectocalyx is completely severed throughout its whole diameter, it again reunites, or heals up, in from four to eight hours after the operation. The nervous system of the naked-eyed Medusw is more highly developed than it is in the covered-eyed Meduse ; and tomanes has demonstrated the occurrence of reflex action in the Medusw. This reflex action occurs “‘ only between the marginal ganglia (in Sarsiv) and the point of the bell from which the manubrium is suspended—it being only the pull which is exerted upon this point when the manubrium con- tracts and acts as a stimulus to the marginal ganglia.” Romanes has brought much physiological evidence to bear on the distribution of nerves in Sarsia and it may be stated that his researches prove ‘‘ that nervous connections unite the tentacles with one another and also with the manubrium ; or perhaps more precisely, that each marginal body acts as a PHYSIOLOGY OF THE INVERTEBRATA. 305 co-ordinating centre between nerves proceeding from it in four directions—viz., to the attached tentacle, to the margin on either side, and to the manubrium.” “The nervous connections between the tentacles and the manubrium are of a more general character than those between the tentacles themselves; that is to say, severing the main radial nerve-trunks produces no appreciable effect upon the sympathy between the tentacles and the manubrium, **The neryous connections between the whole excitable surface of the nectocalyx and the manubrium are likewise of this general character, so that, whether or not the radial nerve-trunks are divided, the manubrium will respond to irritation applied anywhere over the internal surface of the nectocalyx. The manubrium, however, shows itself more sensitive to stimuli applied at some parts of this surface than it is to stimuli applied at other parts, although in different specimens there is no constancy as to the position occupied by these excitable tracts.” Romanes has examined the distribution of nerves in Tiaropsis (especially 7. indicans*), Staurophora, Aurelia, and other Meduse. In all these forms prinvitive nerves are well developed. By the word “nerves” is meant certain physio- logically differentiated tracts of tissue, which either stimu- lation or section prove to perform the function of conveying impressions to a distance. Romanes has also studied the subjects of co-ordination and natural and artificial rhythm in the Meduse ; but it is not our object to detail these important investigations, as a full account of them will be found in the Philosophical Trans- actions of the Royal Society, to which our readers are referred. Nevertheless, the following may be taken as a general summary of the results :— (1) That in the covered-eyed Medusw the lithocysts are * This species was first described by Romanes; see Journ. Linn. Soe. (Zool.), vol. 12, p. 524. U 306 PHYSIOLOGY OF THE !1NVERTEBRATA. the exclusive seats of spontaneity, so far as the “ primary movements ” are concerned. (2) The rate of the natural rhythm has a tendency to bear an inverse ratio to the size of the individual, though, it may be remarked, that size is not the only factor in determining such rate. (3) The cutting off the manubrium (polyprite) or a portion of the. nectocalyx (swimming-bell), causes, first acceleration of the rhythm, and then a progressive decline to a certain point below the original rate. The rate then remains stationary at this point, but may again be made temporarily to rise and permanently to fall by removing another portion of the nectocalyx. ‘In these experiments the rhythm, besides becoming permanently slowed, is also often rendered permanently irregular. Again, paring down the contractile tissues from around a single lithocyst* has the effect, when the tissue is greatly reduced, of giving rise to enormously long periods of inactivity. During such period, however, stimulation may initiate a bout of rhythmical contractions, to be followed by another prolonged pause. These facts tend to show that the apparently automatic action of the lithocysts is really due to a constant stimulation supplied by other parts of the organism.” (4) ‘Temperature exerts a profound influence on the rate of rhythm. This influence may be best observed within moderate limits of variation ; for water below 20° C. suspends spontaneity and even irritability, while water above 70° C. permanently slows the rhythm after having temporarily quickened it. But water between 50° and 60° C. permanently quickens the rhythm during the time that the Wedusw, which haye been removed from colder water, are exposed to its influence. In very cold water the loss of spontaneity is a gradual though rapid process, as is also its return in warmer water. After having been frozen solid, Awrelia will recover * The marginal bodies in the covered-eyed Medusa occur in the form of little bags of crystals ; hence they have been termed lithocysts. PHYSIOLOGY /OF THE INVERTEBRATA. 307 on being thawed out, but the original rate of rhythm was not observed fully to return.” (5) Oxygen accelerates the rhythm, while carbonic anhy- dride retards it, and in strong doses destroys both sponta- neity and irritability. Deficient aération of the water in which the JMeduse are living, causes irregularity of their rhythm, as well as the occurrence of pauses; until at last spontaneity altogether ceases; but on now removing the animals to fresh sea-water, their recovery is surprisingly sudden. (6) As regards stimulation, Romanes has shown that a few drops of hot water allowed to run over the excitable tissues of these animals cause a responsive contraction. Single mechanical or chemical stimuli applied to paralyse the nectocalyces of covered-eyed Medusw frequently produces in response a small series of rhythmical contractions. (7) Light acts as a powerful stimulus to some species of Meduse ; and it may be stated that the stimulus has been proved to be light per se, and not the sudden transition from darkness to light. (8) The period of latent stimulation in the case of Awrelia aurita is greatly modified by certain conditions. Of these, temperature exerts the greatest influence, but the most im- portant influence, from a physiological point of view, is that of the summation of stimuli. At the bottom of a “stair- case” the latent period is 3 of a second, while at the top of a ‘‘staircase” it is only 2 of a second. Summation of stimuli also greatly increases the amplitude of the contrac- tions; so that it both develops in the tissue a state of ex- pectancy and arouses it into a state of increased activity. (9) The excitable tissues of Aurelia may be thrown into tetanus by means of strong faradaic stimuiation ; and Romanes has proved that the the tetanus is due to the summation of contractions. (10) Reflex action occurs in various species of Medusa. In Sarsia definite nervous connections of constant occurrence 308 PHYSIOLOGY OF THE’ INVERTEBRATA, have been shown to exist between the tentacula, but not between the tentacula and polypite. Section of the neuro- muscular sheet proves that in the case of this genus physio- logical harmony may, as a rule, be easily destroyed, although it occasionally happens that such is not the case. (11) Romanes has shown that the essentially nervous function of maintaining excitationul continuity is able to persist in these primitive nervous tissues after they have been subjected to the severest forms of section. This fact “cannot be explained by Kleinenberg’s theory of double- function cells; for sometimes contractile waves will become blocked by section before the tentacular waves, and sometimes vice versd. We seem, therefore, driven upon the theory of a nerve-plexus, whose constituent elements are capable of vicarious action in almost any degree.” (12) Contractile waves in Awrelia travel at the rate of 18 inches per second, if the temperature of the water is normal; but the rate is greatly modified by temperature, straining, anesthetics, and various foreign substances. Stim- ulus-waves only travel at the rate of 9 inches per second, if the stimulus which starts such a wave is not strong enough at the same time to start a contractile wave; but if the stimulus is strong enough to start both waves, they both travel at about the same rate. (13) There appears to be no further co-ordination among the lithocysts of the covered-eyed Medusw than such as arises from contractile waves coursing rapidly from one of the number, and, as it passes the others, causing them succes- sively to discharge; but, in the case of the naked-eyed Meduse, true co-ordination has been proved to occur between the marginal ganglia, and the tracts through which it is effected have been proved to be the marginal nerves. Slightly cutting the margin of a naked-eyed Medusa exerts a very deleterious influence upon the vigour of the animal; and violent nervous shock, while it always suspends both spontaneity and irritability, will sometimes also destroy PHYSIOLOGY OF THE INVERTEBRATA. 309 co-ordination for a considerable time after spontaneity returns. (14) Romanes has ascertained the effects of the following poisons—chloroform, amylic nitrite, caffein, strychnia, mor- phia, curare, veratrium, digitalin, atropin, nicotin, alcohol, and potassium cyanide—upon the Meduse.* He has shown that there is a wonderful degree of resemblance between the actions of the above-mentioned poisons on the Medusw and on the higher animals. This is a most important discovery, especially ‘‘when we remember that in these nerve-poisons we possess so many tests wherewith to ascertain whether nerve-tissue, where it first appears upon the scene of life, presents the same fundamental properties as it does in the higher animals.” In fact the primitive nervous tissues of the Meduse adhere to the rules of toxicology that are followed by nervous tissues in general. ‘In one respect, indeed, there is a conspicuous and uniform deviation from these rules; for it has been observed that in the case of every poison mentioned, more or less complete recovery takes place when * Fresh water acts as a deadly poison to the MWedusw; and brine acts as an anesthetic. The fresh-water Medusa (Limnocodium Sorbii) is even more intolerant of sea water than are the marine species of fresh water; and brine acts as a poison to the fresh-water form. ‘“ We have thus a curious set of cross relations. It would appear that a much less profound physio- logical change would be required to transmute a sea-water jellyfish to a jellyfish adapted to inhabit brine, than would be required to enable it to inhabit fresh water. Yet the latter is the direction in which the modifica- tion has taken place, and taken place so completely that the sea water is now more poisonous to the modified species than is the fresh water to the unmodified. There can be no doubt that the modification was gradual— probably brought about by the ancestors of the fresh water J/edusa pene- trating higher and higher through the brackish waters of estuaries into the fresh water of rivers—and it would be hard to point to a more remarkable case of profound physiological modification in adaptation to changed con- ditions of life. If an animal so exceedingly intolerant of fresh water as is a marine jellyfish, may yet have all its tissue changed so as to adapt them to thrive in fresh water, and even die after an exposure of one minute to their ancestral element, assuredly we can see no reason why any animal in earth or sea or anywhere else may not in time become fitted to change its element.” (Romanes.) 310 PHYSIOLOGY OF THE INVERTEBRATA. the influence of the poison has been removed, even though this has acted to the extent of totally suspending irritability. In other words, there is no poison in the above list, which has the property, when applied to the Meduse, of destroying life till long after it has destroyed all signs of irritability.” As an explanation of this peculiarity it should be borne in mind “that in the Meduse there are no nervous centres of such vital importance to the organism that any temporary sus- pension of their functions is followed by immediate death. Therefore, in these animals, the various central nerve-poisons are at liberty, so to speak, to exert their full influence on all the excitable tissues without having the course of their action interrupted by premature death of the organism, which in higher animals necessarily follows the early attack of the poison on a vital nerve-centre.” Then, again, the mode of administering the poisons to the Medusw was different from that which is generally used when administering them to the higher animals. (15) Romanes’ researches prove that the phenomena of muscular tonus, as they occur in Sasia, tend more in favour of the exhaustion, than of the resistance, theory of ganglionic action. “The exhaustion theory supposes that the rhythm is largely due to the periodic process of exhaustion and recovery on the part of the responding tissues.” 3esides the researches on the nervous systems of the Meduse, Dr. Kimer* has investigated the nervous system of the Ctenophora. In these animals the mesoderm contains numberless fibrils, varying in diameter from spo tO zato5 of aninch. ‘These fibrils present numerous minute varico- sities, and, at intervals, larger swellings which contain nuclei, each with a large and refracting nucleolus. These fibrils take a straight course, branch dichotomously, and end in still finer filaments, which also divide, but become no smaller. They terminate partly in ganglionic cells, partly in muscular fibres, partly in the cells of the ectoderm and endoderm, Many of * Zoologische Studien auf Capri, 1873. PHYSIOLOGY OF THE INVERTEBRATA. 311 the nerve fibrils take a longitudinal course beneath the centre of each series of paddles, and these are accompanied by ganglionic cells, which become particularly abundant towards the aboral end of each series. The eight bands meet in a central tract at the aboral pole of the body; but Eimer doubts the nervous nature of the cellular mass, which lies beneath the lithocyst, and supports the eye spots.” Professor Huxley says that “the nervous system of the Ctenophoran is, therefore, just such as would arise in Hydra, if the development of a thick mesoderm gave rise to the separation and elongation of Kleinenberg’s fibres; and if special bands of such fibres, developed in relation with the chief organs of locomotion, united in a central tract directly connected with the higher sensory organs. We have here, in short, virtual, though incompletely differentiated brain and nerves.” In the Actinozoa, there is a plexus of fusiform ganglionic cells connected by nerve-fibres at the base of the body; and at the base of the tentacula of the Actiniv, near the pigment- cells (eyes ?) isolated nerve-cells have been discovered. THE ECHINODERMATA. Among these animals the nervous system consists of a number of ganglia, connected by commissural cords, so as to form a ring, from which nerve-fibres pass to various parts of the body. “The internal nervous system of Hchinus consists of five radial trunks, which may be traced from the ocular plates along the ambulacral areas, external to the radial canals to the oral floor, where they bifurcate and unite with each other, so as to form a pentagonal nerve-ring. This ring lies between the cesophagus and the tips of the teeth, which project from the lantern. Small branches leave the ring and supply the cesophagus, and lateral branches arise from the several trunks to escape with the pedicels through the apertures of the pore 312 PHYSIOLOGY OF THE INVERTEBRATA. plates. Each trunk lies in a sinus (Fig. 56, ¢) situated between the lining membrane of the shell (Fig. 56, 7) and the ambulacral radial canal (Fig. 56, ¢); the lateral branches, e—— AT SS XN 1 ‘kim MW i i If " q SN S---- RR re y BoE FiG. 56.—DIAGRAM SHOWING PORTIONS OF AMBULACRAL AND NERVOUS SYSTEMS OF ECHINUS. (After ROMANES and EWART.) a=ampulle. #=radial nerve. c=neuralradial sinus. d= lining membrane of shell. ¢ = radial ambulacral canal. f= lateral branch of radial canal. g = pedicel. # = spine. z = pedicellaria. & = layer of fibres external to shell. Z = subepidermic nerve-plexus. 7’ = plexus extending over base of spine. 2’ = plexus extending over pedicellaria towards base of mandibles. = epider- mis. 2 = lateral branch from nerve-trunk. o = continuation of lateral branch. ~ = portion of lateral branch. 7» = ambulacral plate. which accompany the first series of pedicels through the oral floor are large and deeply pigmented; the other branches within the auricles are small; those external to the auricles PHYSIOLOGY OF THE INVERTEBRATA. 313 gradually increase in size until the equator is reached, and from the equator to the ocular plates they again -diminish.” The nerve-trunk is enveloped by a fibrous sheath containing FIG. 57-—STRUCTURE OF A NERVE-TRUNK OF ECHINUS. (4fter ROMANES and EWART.) pigmented cells. The nerve-trunk consists of delicate fibres, and of fusiform cells (Fig. 57). The cells are nucleated. ‘The lateral branches of the nerve-trunk escape along with, and are partly distributed to, the pedicels; the remainder breaks up into delicate filaments, which radiate from the base of the pedicel under the surface epithelium (Fig. 56, /). When one of the large branches is traced through the oral floor after sending a branch to the foot, it breaks up into delicate fibres, some of which run towards the bases of the adjacent spines and pedicellarie, while others run inwards a short distance towards the oral aperture.” There is also an external plexus situated under the surface epithelium, and extending from the shell to the spines and pedicellariz. ‘The fibres (Fig. 58) of this plexus closely resemble those of the lateral branches of the trunk; but generally they are smaller in size, and have a distinct con- nexion with nerve-cells. The cells consist of an oval nucleus and of a layer of protoplasm, which is generally seen to project in two, or sometimes in three, directions—the several processes often uniting with similar processes from adjacent cells, so as to form a fibro-cellular chain or network.” Romanes and Ewart * have succeeded in tracing the plexus over the surface of the shell between the spines and pedi- * Philosophical Transactions, 1881, pt. iii. p. 836. 314 PHYSIOLOGY OF THE INVERTEBRATA. cellariz ; and from the surface of the shell to the capsular muscles at the bases of the spines (Fig. 59). Fic. 58.—EXTERNAL NERVE-PLEXUS OF ECHINUS. (After ROMANES and EWART.) ‘““In the case of the pedicellariz, the plexus on reaching the stem runs along between the calcareous axis and the FIG. 59.—NERVE-CELLS LYING AMONG MUSCULAR FIBRES AT THE BASE OF A SPINE IN ECHINUS, (After ROMANES and Ewart.) surface epithelium, to reach and extend over and between the muscular and connective tissue-fibres between the calcareous PHYSIOLOGY OF THE INVERTEBRATA. 315 axis and the bases of the mandibles (Fig. 56, /’, and Fig. 60). The plexus, now in the form of exceedingly delicate fibres connecting small bipolar cells, reaches the special muscles of the mandibles. .... Although this plexus is especially Ss Raa niente ae a er =a FiG. 60.—NERVE-PLEXUS LYING OVER MUSCULAR FIBRES NEAR BASE OF MANDIBLES OF PEDICELLARIA. (After ROMANES and EWART.) related to the muscular fibres—lying over and dipping in between them—it is also related to the surface epithelium, and delicate fibres often extend from it to end under or between the epithelial cells.” Romanes and Ewart have shown that the Echinodermata respond to all kinds of stimulation. The period of latency varies considerably in different species, and in different parts of the same animal. “The external nerve-plexus supplies innervation to three sets of organs—the pedicels, the spines, and the pedicellarie ; for when any part of the external surface of Echinus is touched, all the pedicels, spines, and pedicellarize within reach of the point that is touched immediately approximate and close in upon the point, so holding fast to whatever body may be used as the instrument of stimulation. In executing this combined movement the pedicellarize are the most active, the spines somewhat slower, and the pedicels very much slower. If the shape of the stimulating body admits of it, the forceps of the pedicellariz seize the body and hold it till the spines and pedicels come up to assist.” The function of the pedicellariz is to aid locomotion by 316 PHYSIOLOGY OF THE INVERTEBRATA. grasping hold of sea-weeds, &c., when an Echinus is climbing perpendicular or inclined surfaces of rock. Starfishes (with the exception of Brittle-stars) and Echint are attracted by light, but when their eye-spots are removed, they no longer are so. Romanes and Ewart have demon- strated that severing the ray-nerve destroys all physiological continuity between the pedicels on either side of the division. Severing the nerve at the origin of each ray, or severing the Fic. 61.—NERVOUS SYSTEM OF STARFISH. @ = nerve-ring. 4 = ambulacral nerve. c = eyes. nerve-ring (Fig. 61) between each ray, has the effect of totally destroying all co-ordination among the rays; ‘‘ there- fore the animal can no longer crawl away from injuries, and when inverted it forms no definite plan for righting itself— each ray acting for itself without reference to the others, there is, as a result, a promiscuous distribution of spirals and doublings, which as often as not are acting in antagonism to. one another. This division of the nerves, although so com- PHYSIOLOGY OF THE INVERTEBRATA. 317 pletely destroying physiological continuity in the rows of pedicels and muscular system of the rays, does not destroy, or perceptibly impair, physiological continuity in the external nerve-plexus ; for however much the nerve-ring and nerve- trunks may be injured, stimulation of the dorsal surface of the animal throws all the pedicels and muscular system of the rays into active movement. This fact proves that the pedicels and muscles are all held in nervous connexion with one another by the external plexus, without reference to the integrity of the main trunks.” The function of the spines and pedicellariz in Echinus are dependent upon the external nerve-plexus ; for if the latter is injured they have not the power of localising and closing, round a seat of stimulation. But “ other nervous connexions, upon which another function of the spines depends, are not in the smallest degree impaired by such injury. This other function is that which brings about the general co-ordinated action of all the spines for the purposes of locomotion. That this function is not impaired by injury of the external plexus is proved by severely stimulating an area within a closed line of injury on the surface of the shell; all the spines over the whole surface of the animal then manifest their bristling movements, and by their co-ordinated action move the animal in a straight line of escape from the source of irri- tation.” It will be apparent from the above remarks that there is a local reflex function of the spines and pedicellariz, which is entirely dependent upon the external nerve-plexus. There is also the universal reflex function of the spines, which con- sists in their general co-ordinated action for the purposes of locomotion, and which is entirely independent of the external nerve-plexus. The nerves which give rise to the universal reflex function are distributed over the internal surface of the shell—that is they form an internal nerve-plexus. The internal nerve-plexus of Hchinus has been recently 318 PHYSIOLOGY OF THE INVERTEBRATA. discovered by Dr. J .C. Ewart, of Edinburgh University. He has found that this “internal plexus spreads all over the inside of the shell, and is everywhere in communication with the external plexus by means of fibres, which pass between the sides of the hexagonal plates of which the shell of the animal is composed.” The nerve-centres in Lchinus are to be found in the nerve- ring, for as soon as the latter was removed, the animal lost, completely and permanently, all power of co-ordination among its spines—.e., the function of locomotion was entirely lost. Although locomotion was destroyed, the spines were not entirely paralysed or motionless, for they still retained the power of closing round a seat of irritation on the external surface of the shell. This is due to the fact that all the spines and pedicellariz are connected with the external plexus, and when it is irritated, all the spines and pedicellariz in the vicinity move over to the seat of irritation. ‘On the other hand, it is the internal plexus which serves to unite all the spines to the nerve-centre which surrounds the mouth, and which alone is competent to co-ordinate the action of all the spines for the purposes of locomotion.” Dr. Romanes* has shown experimentally that the am- bulacral feet of Echinus are co-ordinated by the nerve-centre, quite as much as are the spines. The nervous system of Echinus consists of the following parts (Table, p. 319). Dr. L. Fredericqt has also investigated the nervous system of Echinus. He finds that the pentagonal nerve-ring and its five radial nerve-trunks are contained in as many sheaths, which are expansions of the lining membrane of the shell. The lateral branches of these nerves are also contained in a similar sheath ; the latter pass out of the ambulacral pores in company with the pedicels, which they serve to enervate, a delicate nerve running along the whole length of each pedicel to terminate at its distal end in a tactile organ. The * See Jellyfish, Starfish, and Sea-Urchins, pp. 307-317. + Archiv. de Zool. Experi. et Générale, tome 5, pp. 429-440. PHYSIOLOGY OF THE INVERTEBRATA. 319 J Nervous System. Situation, Function, | Unites feet, spines, and Wisi 1 ay pedicellariz together, so xterna! nerve_|| External to shell. ‘\| . that they all move over plexus. } | to a seat of irritation in that plexus. _ Over internal sur- | By f ’ : | fakeiat sholl cad | Brings feet, spines, anc Internal nerve- | is in communica- | é : AE re tion with co-ordinating pedicellariz into rela- plexus. | tion with external nerve-centre. plexus. Presides over co-ordinated action of spines and feet. Nerve-centre. | Mainly round mouth It gives rise to nerve- trunks. pentagonal nerve-ring sends off, in addition to the am- bulacral trunks, the nerve-cords to the intestine. The physiological experiments of Fredericq (see p. 436 of his paper, loc. cit.) are almost entirely in accordance with those of Romanes and Ewart. Dr. H. Prouho* has investigated the nature of the external nerve-plexus in Lehinus acutus; and Dr. O. Hamann} has found and traced nerves in the various pedicellariz of the Lchinidea, and he finds that from the main nerves branches are given off to sense organs and glandular sacs. All the pedicellariz are tactile organs, as the nerve-terminations indicate; the tri- foliate ones seem to remove sand, Protozoa, &c. The large pedicellariz serve to keep off layers of living bodies—e.y., worms, and therefore act as weapons, as well as for organs of attachment when the animal is moving about. There is no doubt that the latter function is the most important; in other words, the pedicellariz aid locomotion. In Echinus microtuberculatus the gemmiform gland-bearing pedicellariz hold fast sea-weeds, &c., when the animal is at * Comptes Rendus, tome 102, p. 444. + Sitzungsberichte Jenaisch. Gesel’, fiir Med, und Naturwiss. 1886. 320 PHYSIOLOGY OF THE INVERTEBRATA. rest; these help to hide it, and the secretion from the glands is therefore of the greatest service. It will be noticed that the nervous system of the Hchino- dermata is much more highly developed than that of the Coelenterata. THE 'T'RICHOSCOLICES. According to De Quatrefages the nervous system of the Turbellaria consists of two ganglia situated in the anterior end of the body, from which, in addition to other branches, a longitudinal nerve-cord extends backwards on each side of the body. As a general rule, the lateral trunks exhibit ganglionic masses, and from these ganglia nerves are given off. These ‘may become approximated on the ventral side of the body, thereby showing a tendency to the formation of the double ganglionated chain characteristic of higher worms.” In the Rotifera, the nervous system consists of a large ganglion situated on one side of the body near the trochal. disc. This ganglion, sometimes divided into two portions, gives off nervous filaments. The nervous system of the Cestoidea consists of two longitudinal lateral nerve-trunks, which run down the body externally to the main canals of the excretory system. In the so-called head of the animal, where they are swollen (ganglia), they are united by a transverse commissure, Dr. G. Joseph * has recently examined the nervous system of the Cestoidea. The results arrived at are—(a) That the two cerebral ganglia are in many cases (Tania transversalis, T. rophalocera) connected, not by a single dorsal commissure, but by two, separated by a matrix and muscle-processes ; (0) that each cerebral ganglion is triple, consisting of a median and two smaller (dorsal and ventral) ganglia separated by muscle-processes, as is best seen in Zwenia crassicollis ; (c) that in the bladder-worm, before evagination of the hooks, the * Biologisches Centralblatt, vol. 6, p. 733 PHYSIOLOGY OF THE INVERTEBRATA. 321 central system exhibits six equatorial ganglionic masses, which afterwards form a nerve-ring by the growth of bipolar processes. THE ANNELIDA. The nervous system of the Gephyrea surrounds the ceso- phagus, and from it a simple or ganglionated nerve-cord proceeds backwards in the ventral median line. This nerve- cord gives off branches, The nerve-ring surrounding the cesophagus usually has a ganglionic mass. This mass is connected with rudimentary eyes. The nervous system of the Hirudinea, and of Hirudo in particular, is highly developed. It consists of large supra- cesophageal ganglia, which send off five pairs of nerves to the five pairs of eyes. These ganglia are connected with a sub- cesophageal ganglion by a circum-cesophageal nerve-ring. They also communicate with the buccal ganglia situated over and in front of the mouth. From the sub-cesophageal ganglion two longitudinal, ventral, and ganglionated cords proceed along the median line of the ventral aspect of the body. The ganglia of the two ventral longitudinal cords are united together in pairs by transverse commissures. Hach pair of ganglia sends off, to the right and left, two nerves. There are twenty-three pairs of ganglia on the ventral cords, in addition to the sub-cesophageal ganglion, which is com- posed of three or four pairs which have coalesced, and the caudal ganglion, which lies in the region of the posterior sucker, and is composed of seven coalesced ganglia. There is also a system of visceral nerves, consisting of a nerye, which proceeds from the supra-cesophageal ganglia, and runs above the ventral ganglionated nerve-chain, giving off along its course branches to the ceeca of the stomach. The nervous system of the Oligocheta, as represented by Lumbricus, consists of two cerebral ganglia situated on the dorsal side of the pharynx in the third segment. These x 322 PHYSIOLOGY OF THE INVERTEBRATA. ganglia are connected by two nerves, which embrace the pharynx, with the sub-cesophageal ganglia. The latter ganglia are the first of the ventral ganglionated nerve-cord. ‘This ventral nerve has a double ganglionic enlargement in every segment posterior to the third. A large nerve, which divides and sub-divides, proceeds forward from each of the cerebral ganglia. Four or five nerves run backward from the upper part of each half of the cireum-pharyngeal ring, and are distributed in the muscular walls of the pharynx. Nerves are also given off from the lower portion of this ring to the muscles of the fourth segment. ‘Two pairs of nerves from each bilateral ganglionic enlargement of the ventral cord, proceed to the viscera and muscles of each segment. Two nerves, one from each side, pass off from the ventral nerve at a point nearly half-way between the double ganglionic masses. These supply the posterior sides of the mesenteric septa. When examined under high power the nerve-rods of A B FIG, 62.—NERVOUS SYSTEMS OF POLYCH#TA. A = Polyniée squamata, B = Satella flabellata. C = Nereis regia. @ = cerebral ganglia. = cesophageal commissures., ¢ = longitudinal commissures of ventral ganglia. Lumbricus are seen to contain a large number of nerve- cells along with the nerve-fibres, This is a characteristic feature of Lwmbricus and Peripatus. In Hirudo the nerve- PHYSIOLOGY OF THE INVERTEBRATA. 323 cells are confined to the ganglia; in this respect the nerves of the leech are like those of Astacus and the spinal cord of the Vertebrata. “The nervous system of the Polycheta usually consists of a chain of ganglia—one pair for each somite—connected together by longitudinal and transverse commissures, which diverge between the cerebral ganglia and the succeeding pair, to allow of the passage of the cesophagus. The most important differences presented by the nervous systems of the Polychaeta result from the varying length of the transverse commissures. In Vermilia, Serpula, Sabella, these commis- sures are very long, so that two distinct and distant series of ganglia appear to run through the body, while, in Nepthys, the two series of ganglia are fused into a single cord enlarged at intervals. .... In most Polycheta a very extensive series of visceral nerves supples the alimentary canal.” THE NEMATOSCOLICES. In the Nematoidea the nervous system consists of a nerve- ring surrounding the cesophagus. From this ring proceed six nerves in an anterior, and two in a posterior direction. Two of the anterior nerves proceed in the lateral lines—that is, one in each—and four in the interspaces between the lateral and median lines. The posterior nerves proceed to the tip of the tail—one in the dorsal, and the other in the ventral median line of the body. Near to the nerve-ring, in front and behind it, arranged in dorsal, ventral, and lateral groups, lie certain ganglia. These are respectively known as dorsal or supra-cesophageal, ventral or sub-cesophageal, and lateral ganglia. In addition to these, there are groups of ganglia in the median and lateral lines, in the posterior part of the body ; these are known as caudal ganglia. In the Acanthocephala, represented by Echinorhyncus, the nervous system consists of a simple ganglion, which is situated 324 PHYSIOLOGY OF THE INVERTEBRATA. at the base of the proboscis. Nerves are given off from this ganglion to the proboscis, and through the retinacla to the muscular wall of the body. THE CHATOGNATHA. This class contains only one genus—Sagitta. The nervous system consists of a cerebral ganglion (brain) on which the eyes are placed, and a ventral ganglion situated near the middle of the body. These two ganglia are united by commissures. Near the mouth there are a pair of sub- cesophageal ganglia, which are united to each other, and to the cerebral ganglion by commissures which embrace the cesophagus. THE PROTOTRACHEATA. The nervous system of Peripatus consists of two large supra-cesophageal ganglia, and two imperfectly-ganglionated, widely-separated nerve-trunks, which proceed to the posterior part of the body. From these two trunks many lateral nerves pass outwards and inwards; and, according to Grube,* the latter act as commissures between the two nerve-trunks. THe MyYRIAPoDA. The nervous system of these animals forms a ventral chain, with a pair of ganglionic enlargements for each segment of the body. The anterior pair is united by commissures with the cerebral ganglia. The ventral chain gives off on each side a number of lateral nerves. The nervous system of the Myriapoda has been compared to that of the larve of the Jnsecta. The cerebral ganglia furnish nerves to certain sense organs, such as the eyes. The ganglia are constituted of cells, and the cords of nerve- fibres. * Archiv fiir Anatomie, 1853. PHYSIOLOGY OF THE INVERTEBRATA. 325 THE INSECTA. Tn these animals there is always a well-developed cerebral ganglion or brain connected by nerve-trunks with a series of ventral ganglia. One of the reasons of the great develop- ment of the brain is assuredly the greater perfection and the more important office of the organs of the special senses in the Insecta. According to Gegenbaur, many Diptera, Hymenoptera, Lepidoptera, and the large-eyed Libellule, have powerful cerebral ganglia. The cerebral ganglion or brain of the ants, of bees, and of the spinning spiders (among the Arachnida), is remarkable for its size, and even for its conformation. Though Apis is a much smaller insect than Melolontha, it possesses a cerebral ganglion more highly developed, and relatively three times larger, if we take into consideration the difference of size. The cerebral ganglion of the ant is proportionally larger still. Besides, the surface of these ganglia or brains is mammillated; and there are conyolutions. According to M. Dujardin,* the brain of Apis has avery singular form. “We perceive a disc with stel- lated strize surmounting like a hood the superior ganglion ; and from certain experiments of M. Faivre,t the cerebral ganglion has, like the cerebral hemispheres of the Vertebrates, the property of being insensible to punctures and lacerations.” The nervous system of the Jnsecta (speaking in general terms) consists of a cerebral ganglion connected to a gan- glionated nerve-trunk or trunks, which passes backwards along the ventral surface of the animal. Lateral nerves are given off from these ganglia to the organs of sense, limbs, viscera, &e. Fig. 63 represents the nervous systems of various in- sects; and numbers 4 and 5 of the same figure represent the nervous system of Periplaneta. The nervous system of Periplancta consists of supra- cesophageal ganglia (brain), which are connected by short, * Annales des Sciences Naturelles, 1850. + Ibid. 4 s., tomes 8 et 9. 326 PHYSIOLOGY OF THE INVERTEBRATA. thick commissures with the sub-cesophageal ganglion, which corresponds to several pairs of ganglia fused together. This d = eye. é = gizzard. ¢ = crop. 3 = Musca (Diptera). 4 = the brain and visceral nerves of Ferzpluneta. 5 = Periplaneta (Orthoptera). é = visceral nerves. Fic, 63.—NERVOUS SYSTEMS OF THE INSECTA. THORACIC GANGLIA 2= Dytiscus ( Coleoptera) = ram. Aa, Formica. I sub-cesophageal ganglion leads into a ventral ganglionated chain, which has three pairs of coalesced ganglia in the thorax, and six pairs of closely connected and smaller ganglia PHYSIOLOGY OF THE INVERTEBRATA. 327 in the abdomen. The brain gives off nerves to the sense organs (eyes, antennze), the sub-cesophageal ganglion supplies the mouth, and the other ganglia the rest of the body. The visceral neryous system is well developed in the Jnsecta. (Fig. 63, 4). In the Insecta, ‘‘the ner- vous system varies very much ip. the extent to which its com- ponent ganglia are united to- gether. In most Orthoptera and Newroptera, and in many Coleoptera, the thoracic and abdominal ganglia remain dis- tinct and are united by double commussures as in Dlatta (Peri- planeta). In the Lepidoptera, See eee the thoracic ganglia have coa- 4@=opticnerve. 4 = antennary lesced into two masses united = ae de ete nerve. d= fused thoracic ganglia. by double commissures; while e¢ = nerve-cord of abdomen. in the abdomen there are five ganglia, with single or partially separated commissural cords. The concentration goes furthest in some Diptera and in the Strepsiptera, in which the thoracic and abdominal ganglia are fused intoa common mass.” In many insects there are respira- tory nerves, whose branches are distributed to the muscles of the stigmata. The inner ends of these nerves form a plexus, which is situated “over the interval between two of the ganglia of the central nervous cord, and they are connected by longitudinal cords with one another, and with these ganglia.” a. t FIG, 64, THE ARACHNIDA. In the Arthrogastra, there is a bilobed cerebral ganglion or brain connected by commissures with the sub-cesophageal ganglion: from this passes a nerve-trunk (consisting of two 328 PHYSIOLOGY OF THE INVERTEBRATA. closely-applied commissural cords) to the three ganglia situated in the region of the twelfth to the fourteenth somites of the body. The abdomen contains four ganglia, from the last of which leads two nerves terminating in the extremity of the body. The cerebral ganglion, as in the nsecta, gives off nerves to the eyes and other sense organs; while branches from the sub-cesophageal ganglion are distributed to the maxille and following somites. The visceral nervous system is well developed in these animals. In the Araneina, the nervous system is more concentrated than in the last-mentioned order. It consists of cerebral and sub-cesophageal ganglia with branch-nerves, which proceed to the organs of sense and other parts of the body. In fact it will be observed that in the Avaneina the ganglia are con- centrated round the csophagus. The same arrangement occurs in the Acarina. THE CRUSTACEA. As a representative of the lower Crustacea we describe the nervous system of Cyclestheria hislopi, belonging to the Phyllopoda. The nervous system of this animal has been recently worked out by Dr. G. O. Sars.* The cerebral ganglion or brain (see Fig. 11) is located within the pre-oral part of the head, posterior to the compound eye and im- mediately below the anterior part of the alimentary canal. It is rather large and of a somewhat irregular form, but very difficult to examine minutely on account of its being to a great extent concealed by the scape of the antennae. From the upper part of this ganglion, and somewhat in front, the strong optic nerves originate. These nerves are not united, but quite separate throughout their whole length, each giving rise, at the end, to a ganglion, lying at a short distance posterior to the eye and sending off to this organ numerous * Christiania Videnskabs-Selskabs Forhandlinger, 1887. PHYSIOLOGY OF THE INVERTEBRATA, — 329 fine nerve-fibres. The anterior corner of the cerebral ganglion is exserted to a narrow point, appliedagainst the posterior angle of the ocellus. The antennular nerves, apparently originat- ing from the posterior part of the cerebral ganglion, may be easily traced as a delicate stem running along the axis of the antennule and dividing at their extremity into a number of nerve-fibres, which end with numerous ganglionic cells, filling up the dilated terminal part of these organs at the base of the sensory filaments. The nerves of the antennz do not seem to arise from the cerebral ganglion itself, but from the strong commissures encompassing the cesophagus. The closer structure of these nerves, and the mode by which they innervate the several parts of the antenne, Dr. Sars has not — succeeded in tracing out. The ventral nervous system, and especially its anterior part, is very difficult to examine. By carefully dissecting the trunk, and spreading it out in a ventral aspect after the intestine had been removed, Dr. Sars has succeeded in partly tracing out the double nerve-cord, which seems to agree in structure precisely with that in other known Phyllopoda, exhibiting the peculiar ladder-like appearance characteristic of those animals. In the Cirripedia, “the nervous system consists of a pair of cerebral ganglia situated in front of the cesophagus, and connected by long commissures with the anterior of five pairs of thoracic ganglia, whence nerves are given off to the limbs. In the middle line, the cerebral ganglion gives off two slender nerves, which run parallel with one another in front of the stomach and enlarge into two ganglia, when they are con- tinued to a double mass of pigment, representing the eyes. From the outer angles of the cerebral ganglion arise the large nerves, which proceed into the peduncle and supply the sac. These appear to correspond with the antennary and frontal nerves of other Crustacea; and Mr. Darwin describes an extensive system of splanchnic nerves.” * * Huxley’s Invertebrata, p. 295. 330 | PHYSIOLOGY OF THE INVERTEBRATA. v / | ‘ ae : 8 t ‘ ‘ H a SI : | be \ ns <. Hi) ‘2 ' Fj 4 \ f . » ~ ’ ‘ ’ ‘ rf ' ' ‘ Pie f H ‘ ' / : ae ¢ ‘ \ H ‘ ' H 5 d c ' — fl ' ' Ss) ! ‘ \ { , ' y ! ~ Pod ‘Sy men . s--"T SA USES ; eg 9 Mpa : “A a ae FIG. 65. NERVOUS SYSTEM OF ASTACUS. a=brain. 4=optic nerve. ¢= “collar.” d@ = sub-cesophageal ganglion. e = visceral nerve. 7 = posterio-lateral nerve. & = ‘‘hepatic”’ nerve. The stomach is turned on one side to show its nerves. In some Crustacea, such as the shore-crab (Carcinus mndas), there is a large cere- bral ganglion which gives off nerves to the eyes and antenne ; while the ventral chain of ganglia (of other forms) is fused into one mass (Fig. 64). From this mass radiate the nerve-cords. The nerve-cords connecting the cerebral ganglion with the nervous mass form the cesophageal ring or collar. There isin Carcinus a degree of concentration of the gan- glionic cells, greater, in some respects, than in the Verte- brates themselves. The nervous system of Astacus fluviatilis (Fig. 65, and see also Fig. 13) con- sists of thirteen ganglia joined together by means of commissures. These ganglia are divided as follows: one cerebral, one sub-cesopha- geal, five thoracic, and six abdominal ganglia. The cerebral ganglion or brain gives off nerves to the eyes ; to the auditory organs; to the antennz; to the cara- pace in front of the cer- vical suture; to the green glands; to the visceral nervous system; and to the sub- PHYSIOLOGY OF THE INVERTEBRATA, 331 cesophageal ganglion. ‘The latter nerves form the cesophageal collar. The sub-cesophageal ganglion supplies the somites, from the fourth to the ninth, and their appendages, and gives off also delicate nerves to the cesophagus. The five anterior ab- dominal ganglia supply the muscles and the appendages with nerves; while the sixth and last abdominal ganglion sends neryous branches to the telson (tail). The sixth abdominal ganglion also sends out two nerves, which unite into one common trunk, and from which nerve-fibres are given off to the intestine. The genital organs are supplied with nerves from the third, fourth. and fifth thoracic ganglia. “The size of the ganglia is in direct ratio with the development of the segments and their appendages, to which they belong” (Von Siebold). The physiology of the nerves of the Macrowra (under stimulation) have been investigated by Drs. L. Fredericq and G. Vandevelde.* They experimented upon the nerves of the flexor muscles ot the chele of Homarus. The nerves of Homarus when dissected out of the body very rapidly lose their excitability. When a nerve is submitted to section the excitability disappears progressively from the surface of the section to the extremity of the periphery. Concerning Homarus, Fredericq and Vandevelde state: ‘“ Ainsi, sur une pince séparée du corps de l’animal, il arrive un moment ot Yexcitation électrique du nerf prés de la surface de section ne produit plus de contraction musculaire, alors que la méme excitation appliquée sur un point plus rapproché du muscle y provoque de violentes secousses.”’ These experimenters have shown that the nerves of Homarus present the same distribution of electric tensions, and the same negative variation, as those of the frog (Ranz). They have also ascertained the rate of transmission of motor nervous influx in the nerve connected with the flexor muscle of the dactylopodite. In these experiments they had recourse to the graphic method employed by Helmholtz. By * Bulletins de l Académie Roya'e de Belgique, 2 série, t. 47 [1879]. 332 PHYSIOLOGY OF THE INVERTEBRATA. exciting the nerve at a point near the muscle, and noting the moment of excitation and the moment of contraction, one is able to ascertain the time which, elapses between the two phenomena: the same experiment is then repeated on a point of the nerve further from the muscle. The difference in the time observed in these two experiments—that is to say, the Fic. 66.—APPARATUS FOR STUDYING THE TRANSMISSION OF MOTOR EXCITATION IN THE NERVE OF THE CHELA. M = myograph carrying claw of Homarus. s = style attached to the dactyl- opodite. y = elastic spring which holds the dactylopodite. a = pair of electrodes. 4= another pair of electrodes. | C = commutator. P = battery. E = registration cylinder. BB’ = the two coils. A = steel needles for closing the circuit at each revolution of the cylinder. lapse of time between the second contraction and the first— gives the time employed by the motor excitation to run the distance between the two excited points. Knowing this distance, one can calculate the rate of transmission. Fredericq and Vandevelde exposed the nerve (in a living lobster) which leads to the claw by two openings. A style* * The style used was that of Dr. Marey, the distinguished Professor of Experimental Physiology in the College of France. PHYSIOLOGY OF THE INVERTEBRATA. — 333 was attached to the dactylopodite of the chela (Fig. 66), and all firmly fixed, by the aid of bands, upon the horizontal plate of the myograph. The dactylopodite was held by means of a horizontal elastic spring; the object being to keep it away from the other portion of the claw. A pair of platinum electrodes were applied upon each of the two portions of the exposed nerves. The four wires from these electrodes were fastened to the wires of the induction coil by means of a commutator, which allowed the changing of the electric shock into one or other of the pairs of electrodes, and of exciting the nerve in its nearest or furthest point from the muscle. Fig. 66 shows the arrangement of the apparatus used in these experiments. After ascertaining that the muscle reacts sufficiently to the excitation of the nerve, and that the point of the style marks properly on the smoked paper of the registration cylinder, Fredericq and Vandevelde arranged the commutator in such a manner that the induction shock could not act upon the nerve, and then allowed the cylinder to turn until it attained its normal velocity. The point of the style traces upon the paper a horizontal line, an absciss of which the turns are reproduced exactly. The cylinder continuing its revolutions, the commutator was so arranged as to excite the point b of the nerve at the moment when the two points of the needles which close the circuit touch each other. The muscle con- tracted, and the style gave a graphic tracing (a curve) of the contraction. In a similar manner the commutator was arranged so as to excite the point a ; this gave a second curve, situated a little in front of the first. The distance from the beginning of the two curves compared to the length of the nerve enabled the experimenters to determine the rate with which the excitation was transmitted. They then marked on the cylinder the part where the nerve was excited. For this purpose, the commutator was closed in such a manner as to permit excita- tion, when contact was made, between the two needles. At this moment a contraction was produced, which inscribes itself 334 PHYSIOLOGY OF THE INVERTEBRATA. as a simple line raised above the absciss whilst the cylinder was at rest. In these experiments, it had been previously ascertained that the cylinder had a uniform rate of rotation in inscribing by the aid of the “signal Marcel-Despréz ” the interruptions of an electric current produced by a tuning-fork of 100 vibrations per second. It was also ascertained that the contact between the two steel points always took place at the same moment of the rotation of the cylinder. Fig. 67 is an example of a graphic tracing obtained with Homarus. The nerve was excited at A. The curve CD represents the curve inscribed by the muscle when the nerve was excited at the point a (Fig. 66). The curve EF was obtained by exciting the nerve at b (Fig. 66). The distance between the starting points of the two curves represents about 1ooth of a second. Fredericq and Vandevelde measured the distance of the two excited points of the nerve, putting the points of the compass -at each pair of electrodes, with those of the wire which were turned to the side of the muscle. This distance = 56 millimetres. The rate of transmission was consequently 100 x 0°56 = 5°6 metres per second. The following results were obtained in these experiments :— . A lobster (2) weighing 559 grammes (without blood); the right chela being used; and the length of the nerve was 59 mm. Experiments A, interval in hundredths of a second . . 0.9 or 6.49 m. per second. B, ” ” ” Fy Che ” 6.8 ” C, ” ” ” owt gales 5a “ D, ” ” ” 2 OHS ” 6.8 ” A lobster (3) weighing 487 grammes (without blood); the left chela being used; and the length of the nerve was 56 mm. Experiments K, interval in hundredths of asecond . . 1.1 or 5.04 m. per second. F, is 5 * ss Te, a ee a G, 1: 3 $3 ay Pee Spay Resta +. H, ” " és itp 16.06 n PHYSIOLOGY OF THE INVERTEBRATA. 335 The mean of these eight determinations is 5°95 metres, or in round figures 6 metres, per second. The motor nervous excitation is transmitted, then, with infinitely more slowness in the lobster than in the frog or man. In Fig. 67 the distance AC, which separates the beginning of the curve CD from the point A, corresponds to about sooths of a second. ‘This duration represents the sum of the two periods: Ist, the time which is lost from the excita- tion produced at the point @ to run the length of the nerve as far as the termination of it in the muscle ; and 2nd, the time of latent excitation of the muscle. The latter is known and VDVVVV EVI VIVES VE VII YET VV EV VII IVY Fic. 67.—A GRAPHIC TRACING FOR DETERMINING THE RATE OF TRANSMISSION OF MOTOR EXCITATION. A = moment of excitation of nerve. CD = curve of contraction obtained by the excitation of the nerve at a (Fig. 63). EF = curve of contraction ob- tained by the excitation of the nerve at 4 (Fig. 63). (Hundredths of a second.) determined, among other things, upon the same muscle. It suffices to obtain a graphic tracing of the muscular contrac- tions by directly placing the exciting electrodes upon the flexor muscle of the dactylopodite. This time was found to be 1.500ths of a second, and that it did not exceed 2o0oths of a second. There remained, then, at least 5 - 2=300ths of a second, which represented the necessary time for the motor excitation to travel from the point «a along the nerve to the interior of the muscle. The length of this portion of the nerve could not be directly determined ; but it was very probably less than 50oths in these experiments, and did not certainly reach 1000th. That gave a velocity of 1.66 m. per second in the first hypothesis, and 3.33 m. in the second. From these 336 PHYSIOLOGY OF THE INVERTEBRATA, investigations it is evident, that the rate of transmission of the motor nervous influx in its passage from nerve to muscle finds in the last nervous ramifications considerable delay. The following conclusions have been arrived at by Fredericq and Vandevelde :— (1) There appears to be a complete identity in the pro- perties of the muscles of Homarus and those of ana. (2) The motor nerves of Homarus present, from a physio- logical point of view, great points of resemblance to those of Rana. The most characteristic difference consists in the slowness with which the motor excitation travels the length of the motor nerves. In Homarus it is 6 metres, and in Rana 27 metres per second, The slow rate of transmission of the motor excitation proves in Homarus a considerable slackening in the muscular terminations of the motor nerves. The difference in the rate of transmission may be due to the difference in the composition of the nervous matter of the two animals. The following table represents the chemical com- position* of the nerves of Homarus and Rana respectively :— Homarus. Rana, I II i II | Albuminoids . : . 20.61 21.00 29.20 30.00 Lecithine ‘ : = 7.79 8.11 9.92 9.90 Cholestrine and fats : 58.34 57-67 47-13 40.44 Cerebrine : : : 8.26 | 8.03 9.78 9.75 Insoluble substances (in 4.10 | 4.26 3.50 3.46 ether) . Salts ; : : 2 0.90 | 0.92 0.47 0.45 | 100.00 | 99-99 | 100.00 100,00 * Dr, A. B. Griffiths’ analyses, PHYSIOLOGY OF THE INVERTEBRATA. 337 The composition of the ashes of the nervous matter in each case is represented in the following table :— —— eS Homarus. Rana. Potash . , : é ; : . : 33.00 36.24 | Boda” ©. 2 , . : : : : 11.98 10.87 | Magnesia ; : : P : : : 1.87 1.30 | Lime. 2 : : : : : ; 0.99 | 0.81 | | Iron oxide. : : : : : ; 0.16 0.21 Phosphoric acid (combined) . i ; ; 41.51 | 40.32 Phosphoric acid (free) . : P é z| 6.81 | 7.92 Sulphuric acid. : F : : : 0.90 | 0.72 | Chlorine MPL c : f : 2 | 1.96 | 1.21 Silica. : : ¢ : ‘ é : 0.82 | 0.40 | | | 100.00 | 100.00 The first table gives the chemical composition of the ner- vous matter in a dry state; the following table gives the composition of the nervous matter with its accompanying water :— | | Homarus. Rana. | Water | 70.21 66.42 | Solids. ; : ; : : : : | 29.79 33-58 | accra Ya 100.00 100.00 The last two tables represent the averages of six analyses in each case. Ys 338 PHYSIOLOGY OF THE INVERTEBRATA. J The difference in the composition of the nervous matter of the two animals, may possibly account for the difference in the rates of transmission as observed by Fredericq and Vandevelde. THE POLYZOA. The nervous system of these animals is very simple, and consists of a ganglion, situated between the mouth and the anus (see Fig. 17), which gives off many nerve-fibres to the tentacula and the alimentary canal. THE BRACHIOPODA. The nervous system of the Clistenterata consists of a ganglion on the ventral side of the oral aperture. From this ganglion proceeds a commissure, which surrounds the cesophagus, and bears two small ganglia. ‘The latter probably answer to the cerebral, the former to the pedal, ganglia of the Lamellibran- chiata. Immediately behind the pedal mass, from which two large nerves to the dorsal or anterior lobe of the mantle are given off, are two elongated ganglia, connected by a commis- sure of their own, which possibly correspond with the parieto- splanchnic ganglia of the higher Molluscs. The nerves to the ventral lobe of the mantle, and those to the peduncle arise from these ganglia.” The nervous system of the Zvetenterata has not been so thoroughly worked out as that of the Clistenterata ; but in Lingula, Sir Richard Owen, F.R.S., has shown that the visceral nerves are more developed than those of Zerebratula, which belongs to the latter order. ‘ Filaments to the muscles are also more distinct: a pair, which come off from the sub- cesophageal ganglion, diverge as they pass backwards along the visceral chamber, then converge to their insertion in the anterior muscles ; a second pair, also from the sub-cesophageal ganglia, run more parallel as they pass along the ventral aspect of the anterior muscles to go to the posterior muscles. PHYSIOLOGY OF TRE INVERTEBRATA. 339 Lingula has also the pallial and brachial systems of nerves as well developed as in Zerebratula.”* THE Mo.uusca. In the Mollusca there are usually at least three ganglia with radiating nerves—one in the head, one in the foot, and one posterior and above the alimentary canal. A Fic. 68.—NERVOUS SYSTEMS OF THE MOLLUSCA. A = diagram of nervous system of 4 xodontza. a = cerebral ganglia. 6 = pedal ganglia. c¢ = parieto-splanchnic ganglia. B = nervous system of Zimax. a-=cerebral ganglia. dc = pedal parieto-splanchnic ganglia. «@ = nerves to foot. C = nervous system of Sepia. @ = posterior buccai ganglion. 6 = anterior buccal ganglion. c¢ = pedal ganglion. ad = parieto- splanchnic ganglion. e = cerebral ganglion. = optic nerve and ganglion. = splanchnic ganglion. = ganglion stellatum. As an example of the Lamellibranchiata, we describe the nervous system of Anodonta. There are three pairs of ganglia.(«@) The cerebral ganglia, which are united by a com- missure, are situated at the sides of the mouth. They send * Owen’s Comparative Anatomy and Physiology of the Invertebrate Animals, p- 492 (2nd ed.). 340 PHYSIOLOGY .OF .THEgINVERTEBRATA. off nerves to the anterior portion of the pallium; to the anterior adductor muscle ; to the labial palps, &c.; and tothe branchiz. (b) The pedal ganglia are situated in the foot, or in the corresponding part of the body when the foot is absent, as is the case in some of the Lamellibranchiata. These ganglia are fused together on the median line of the body, and are connected by commissures with the cerebral ganglia. The pedal ganglia send off nerves to the foot.(¢) The parieto- splanchnic or visceral ganglia lie on the ventral side of the posterior adductor muscle. They are united with the cerebral ganglia by commissures (Fig. 68 A), which traverse the organ of Bojanus (kidney). These ganglia send off nerves to the branchiz ; to the posterior and middle parts of the pallium ; to the posterior adductor muscle ; to the heart ; to the siphons —as in Mya; and to the viscera generally. In the Gasteropoda, represented by Helix, the nervous system consists of the following parts: (a) The cerebral or supra-cesophageal ganglia, lie on the dorsal side of the ceso- phagus, and are joined close together by a transverse nervous band (Fig. 68 B). Hach ganglion sends off a commissure to the pedal ganglia, which are situated close together on the ventral side of the cesophagus. Commissures also join the cerebral ganglia with the so-called parieto-splanchnic ganglia (a group of paired ganglia), which come into close relationship with the pedal ganglia; in fact, they are fused together with the latter ganglia. The cerebral ganglia supply nerves to the eyes, tentacula, &c., and also give off a pair of nerves— one on either side of the cesophagus—to the buccal ganglia. (0) The pedal ganglia are closely united. (¢) As already stated, the parieto-splanchnic ganglia are fused with the pedal ganglia. They send off nerves to the nephridia, heart “lung,” sexual and olfactory organs, and pallium.(d@) The small paired buccal ganglia are situated above and below the buccal mass. These regulate the movements, &c., of the mouth; and they have been regarded by some investigators as sympathetic in function. PHYSIOLOGY OF THE INVERTEBRATA. 341 In the Cephalopoda, the nervous system consists of a cerebral or supra-cesophageal, pedal and parieto-splanchnic ganglia situated around the cesophagus, and connected by commis- sures. ‘In addition to these, buccal, visceral, branchial, and pallial ganglia may be developed on the nerves which supply the buccal mass, the alimentary canal, heart, branchiz, and mantle.” In the Dibranchiata (Fig. 68 C), the cerebral ganglia send off nerves to the eyes, &c., and to the buccal ganglia; in the Letrabranchiata, the same ganglia supply nerves to the eyes, &ec., and to the buccal mass. The pedal ganglia, in the Dibranchiata, supply the arms, funnel, and they are-connected with the auditory nerves. In the Zetrabranchiata, the pedal ganglia supply the branchie and the funnel. In both sub- orders of the Cephalopoda, the parieto-splanchnic ganglia supply the branchiz, but in the Dibranchiata they also send nerves to the pallium and sexual organs. In the last-men- tioned sub-order, “each parieto-splanchnic ganglion gives off a nerve, which runs along the shell-muscles to the anterior wall of the mantle, and there enters a large ganglion—the ganglion stellatum.” The anterior and posterior buccal ganglia give off nerves to the cesophagus and stomach. The nervous system of the Cephalopoda is characterised by its great concentration and high development. Notwithstanding the apparent irregularity of its general arrangements, the nervous system of the Mollusca is modelled upon the same plan as that of the Arthropoda. In the Mollusca, we still find the cesophageal ring, giving off from its central portion a ganglionic peripheral nervous system, distributing itself to the various organs, but without sym- metry, as, however, the general conformation of the body demands. The cerebral or super-cesophageal ganglia are very small in the Lamellibranchiata ; but are not exceptionally so, as these animals have no head provided with sense-organs. The cerebral ganglion is, however, very large in the Cephalopoda, due to the highly developed sense-organs. 342 PHYSIOLOGY OF THE INVERTEBRATA. The cerebral or supra-cesophageal ganglion of'the Mollusca appears to have special functions. According to M. Vulpian,* if this ganglion in Helix is removed, the animal survives the operation four or five weeks, but remains completely motion- less, On the other hand, the removal of the sub-cesophageal ganglion kills the animal in twenty-four hours. Mechanical or electrical stimulation of the supra-cesophageal ganglion of the Mollusca produces little or no effect; but with the sub- oesophageal ganglion, both kinds of stimulation cause vigorous muscular agitation. Hlectrical stimulation often causes the heart to stop, in the state of diastole. Hxactly the same phenomenon occurs when electrical stimulation is applied to the pneumogastric nerves in the Vertebrata.t These facts would seem to confirm the theory of the German school of evolutionists, who connect the genealogy of the Vertebrata with the Mollusca; but this theory has had its day, and the latest embryological researches explain the origin of the Vertebrate brain and spinal cord as the outcome of the nervous system of the Arthropoda. 'The nervous system of the acranial Vertebrates can be considered as a coalescent ganglionic nervous system. The central nervous system of Amphioxus (one of the acranial Vertebrates) is a spinal cord with a series of ganglionic enlargements, each of which corresponds with the origin of a pair of nerves. An enlargement, which is comparable to the central ganglion of the Arthropoda, terminates (anteriorly) the spinal cord of the acranial Vertebrata. It does not perceptibly differ from the others, but gives off five pairs of nerves, among which are the optic and auditory nerves. The great difference between the Arthropoda and the Vertebrata is the complete absence in the latter of an cesophageal nervous ring; and that the nerve-cord has a dorsal aspect in the Vertebrata, * Tecons sur la Physiologie Générale et Comparée du Systeme Nerveux, pp. 757-761. + From these investigations it is difficult to decide whether the supra- or the sub-cesophageal ganglion represents the brain in the J/ollusca. PHYSIOLOGY OF THE INVERTEBRATA 343 whereas it is situated ventrally in the Arthropoda. Never- theless there is a certain amount of homology between the spinal cord of the cranial and acranial Vertebrata on the one hand, and the ganglionic chain of the Arthropoda on the other. In both the Vertebrata and the higher Invertebrata, there is a special nervous network, which supplies the alimentary canal, the respiratory and urino-genital organs, and the circulatory system. In both of these sub-kingdoms this system has its origin, or at least its roots, in the great nervous centres. In concluding these remarks, it may be stated that on the whole, every nervous system, whether Invertebrate or Verte- brate, resolves itself into a number of cells, and into a number of fibres, which connect the cells or terminate therein. The parts of the system where the cells accumulate in great number are the nervous centres. The parts are almost wholly composed of fibres from the nervous cords, and if we look at the animal kingdom as a whole, we see that where the cellular centres are the more voluminous and tbe less numerous, the higher the animal is in the zoological scale. In fact, the mammal has been said to be “a sort of summary of the entire kingdom. In him are combined all the tissues, all the apparatus scattered through the entire series: he has a special nervous system, but he possesses, nevertheless, a portion of the ganglionic system of the Invertebrates, and in him, as in them, this ganglionic system is constituted essentially of fibres,” derived in the first instance from a protoplasmic basis. THE TUNICATA. The nervous system of these animals consists of an elongated cerebral ganglion situated on the dorsal side of the pharynx. Nerves are given off from this ganglion to the entrance of the pharyngeal sac, &c.; nerves are also sent out laterally and posteriorly. In the Ascidian larva the nervous 344 PHYSIOLOGY OF THE INVERTEBRATA. system is composed of a cerebral ganglion, which has at first the form of a cord containing a cavity. This ganglion is constricted into three parts, and is connected with ganglia in the tail. The first or anterior part of this ganglion gives off nerves to the margin of the pharyngeal aperture. The middle portion of this ganglion has on it the auditory vesicle, the optic organ, and a stalked ciliated olfactory organ. The optic and auditory organs degenerate just before the adult condition is reached. The third or posterior portion of the ganglion is continued into a long nerve, which at the base of the tail forms a ganglionic enlargement. This ganglion gives rise to a nervous cord, which passes into the tail, where it forms a number of small ganglia. Just before the animal reaches maturity, the tail aborts, the muscles and notochordal sheath degenerate, and the notochordal axis contracts. The nervous system and sense-organs also degenerate, and the cavity in the nerve-cord and cerebral ganglion disappears. In concluding the chapter it may be stated that Prof. E. Ray Lankester* states that “the structure and life-history of the Ascidians may be best explained on the hypothesis that they are instances of degeneration; that they are the modified descendents of animals of higher, that is, more elaborate structure, and, in fact, are degenerate Vertebrata, standing in the same relation to fishes, frogs, and men, as do the barnacles to shrimps, crabs and lobsters.” f * Degeneration, p. 41. t For further information relative to the above'subject see the papers of Dr. A. Giard in the Archives de Zoologie Expérimentale, t. i (1872); Associa- tion Frangaise pour V Avancement des Sciences, t. 3 (1874): Revue Scientifique du 11 juillet 1874; Revue des Sciences Naturelles, septembre 1874’; et Comptes Rendus, 1874-5; and also Dr. W. A. Herdman’s papers in the Challenger Reports. CHAPTER XI. THE ORGANS OF SPECIAL SENSE, ETC., IN THE INVERTEBRATA. As we have already seen, all nerves have not the power of transmitting sensations to the brain or its equivalent ; some, on the contrary, are clearly nerves of motion, whether acted on by will or excited by other means. Some nerves, as the optic, transmit only the impressions received from colours—- z.e., due to the action of light; to other stimulants this nerve is insensible. The olfactory nerve is sensible to various odours, but it is insensible to the action of light or sound. To these modifications of the sensibility of nervous elements are due the phenomena of special senses. ‘The senses of touch, taste, smell, hearing, and seeing, are so many distinct faculties putting the animal kingdom in relation with the various qualities of the external world. The apparatus or mechanism of the sensibility is not com- posed only of the different parts of the nervous system, whose use we have already alluded to; for the sense-nerves do not terminate freely in the exterior, so as to receive directly the contact of the producing agents of sensations, but terminate in various mechanisms destined to collect the excitation, and to prepare it in such a way as to assure its action. ‘These mechanisms are the sense-organs, and it is essentially by the intermedium of these organs that the sensations reach the brain or its equivalent ; but it may be remarked that they are not indispensable for the exercise of all the special senses ; the tactile sensibility may be called into play everywhere, where nerves exist adapted to conduct the ordinary sensa- 346 PHYSIOLOGY OF THE INVERTEBRATA. tions, and it is only by the senses of taste, smell, hearing, and sight, that this intermediate organ between the nerve and the external world is a necessary condition. We now proceed to describe the sense-organs in the principal divisions of the Jnvertebrata. THE PROTOZOA. As these organisms are destitute of any true nervous system, it would be consistent, on & priovt grounds, to assume that they have no special sense-organs. But would it be consistent to assume that these lowly organisms do not digest, respire, and excrete, because there are present no special organs set apart for the functions of digestion, respiration, and excretion ? Certainly not, and there is every reason to believe that one or more of the special senses are represented in the Protozoa. Tactile sensibility is generally distributed over the whole surface of the body; frequently, however, it is concentrated on processes and appendages of it. ‘This is more or less true in the whole animal kingdom. In the Protozoa, the whole surface of the body is exceedingly sensitive; but it may be stated that the protoplasmic expansions called pseudopodia have been regarded as fulfilling the function of organs of touch as well as of locomotion. In other forms (¢.g., Para- mecium, see Fig. 3) the vibrating cilia are considered by Dr. Stein to be organs of touch; and the long rigid bristle in Cryptochilum, according to M. Maupas, has a similar function, its principal use being “to advise the animal of the approach of other Jnfusoria.” In touch, sensibility is brought into play by simple shock, or contact of bodies: it is spoken of as the least perfect of the senses, and is also the one, which offers the least variety in the different animal classes, compared among themselves. Of all the sense-organs, the eye is the one which is first PHYSIOLOGY OF THE INVERTEBRATA. 347 differentiated ; and a large number of the lowest organisms possess an ocular spot, which is a differentiated organ having the function of sight. In the Protozoa, this organ is chiefly found in the group of Monads or /lagellata, and is generally coloured red. Klebs has studied the structure of these ocular spots in the Euglena. When one of these organisms is treated with a solution of sodium chloride (1 to 1co), the contractile vesicle, which is in close proximity to the ocular spot, dilates enormously, and consequently causes the same thing to occur in the ocular spot itself. By this means Klebs observed that the spot “is a small discoid or triangular mass, of jagged and irregular outline (see Fig. 1); it is formed of two parts: for a base it has a small mass of reticulated protoplasm, and in the meshes of the protoplasm there are small drops of an oily substance coloured red.” ‘‘ What is the physiological significance of these spots? Ehrenberg considered them as eyes; hence the name Luglena (word for word, pretty eye), which he had given to a species of the Flagellata provided with ocular spots. This interpre- tation had been questioned by all the authors of his time, and especially by Dujardin.” At the present day, however, many distinguished French naturalists hold the same opinion as Ehrenberg—viz., that the so-called ocular spots of the Protozoa are true visual organs. According to M. Pouchet, the ocular spot of Glenodinium polyphemus (one of the Peri- dinew) has without doubt the function of an eye. It always occupies a fixed and definite position in the cell, and it is composed of two parts—a crystalline humour and a choroid. “The crystalline humour is a strongly: refractive, hyalin, club-shaped body, rounded at its free end, which is always directed forwards, while the other end is immersed in the mass of pigment which represents the choroid. The latter is clearly determined; it forms a sort of hemispherical cap, enveloping the posterior extremity of the crystalline humour. In fact, the visual organ of this organism is composed of 348 PHYSIOLOGY OF THE INVERTEBRATA. exactly the same parts as the eye of a Metazoon, with one exception, the absence of the nerve-element.” The ocular spots of other Flagellata had been previously investigated by Kiinstler, Claparéde, and Lachman, and they found crystalline humours and pigmented capsules (a choroid); but what their true function was, they did not know, as no nerve-apparatus fitted to perceive the impressions received was, in the least, demonstrable in these organisms. On the other hand, certain French savants state that ‘the co- existence of a pigment and of a crystalline humour amply suffices to characterize a visual organ. As to the nerve- apparatus susceptible of perceiving impressions, it is re- placed by the protoplasm, which, as is well known, is sensi- tive to light.” It has also been stated, by some observers, that the red pigment in the ocular spots of the Pvotozoa exhibits similar reactions to the pigment, which is present in the rods of the retina of the Vertebrata. But it should be borne in mind that pigment is not indispensable for the sensation of light, because there are many eyes of complicated structure from which pigment may be altogether absent. Therefore the only reasons which those observers, who state that a visual organ is present in certain Protozoa, have for such an assertion is, that the ocular spot has a definite position, and it possesses a crystalline humour. Are these facts sufficient to speak of it as an eye? The Rev. W. H. Dallinger, F.R.S., and Dr. J. Drysdale,* who examined the ocular spots in various Monads, failed to discover the function of these bodies after a most searching inquiry. In concluding this account of the sense-organs in the Protozoa, it may be stated that the vesicles of Miiller in Loxvodes rostrum (one of the Ciliata) have been considered as possessing an auditory function. * The Monthly Microscopical Journal, vol, 11, p. 8 PHYSIOLOGY OF THE INVERTEBRATA. 349 THE PORIFERA OR SPONGIDA. In these animals the sense-organs are not further differen- tiated than those of the Protozoa. THE Ca:LENTERATA. The sense of touch in these animals is believed to be chiefly located in the tentacula, which surround the mouth, but in Hydra, as well as in other forms, every cell is sensitive to touch. The small pits in connection with nerves, and provided with an epithelial lining of hair-bearing sense cells, in the Meduse, are regarded as the simplest olfactory organ. They are situated round the margin of the bell; in fact in all the Meduse the sense-organs are marginal. The small pigmented spots are undoubtedly eyes ; and according to some writers, otolithic sacs or simple auditory organs are also situated on _the edge of the bell. The rudimentary eyes of the Medusw are much better developed than those which are supposed to exist in the Protozoa ; for in certain species, nerves penetrate manifestly into the capsule (Gegenbaur). But the exact function of the ocular spots in these animals was not understood . until Dr. G. J. Romanes, F.R.S.,* investigated their nature from a physiological standpoint. His mode of investigating this subject was to put two or three hundred Sarsie into a large bell-jar, and then to completely shut out the daylight from the room in which the jar was placed. By means of a dark lantern and a concentrating lens, he cast a beam of light through the water in which the Sarsi@ were swimming. ‘“‘ From all parts of the bell-jar they crowded into the path of the beam, and were most numerous at that side of the jar which was nearest to the light. Indeed, close against the glass they formed an almost solid mass, which followed the light wherever it was moved. The individuals composing * Philosophical Transactions, 1875, p. 295; ibid., 1879, p. 189. 350 PHYSIOLOGY OF THE INVERTEBRATA. this mass dashed themselves against the glass nearest the light with a vigour and determination closely resembling the behaviour of moths under similar circumstances. ‘There can thus be no doubt about Sarsia possessing a visual sense.” To prove that the ocular spots of these animals are really eyes, Dr. Romanes experimented in a like manner with a dozen vigorous specimens; nine of which had previously had their ocular spots removed, while three specimens were left intact. The difference in the behaviour of the mutilated and the unmutilated individuals was very marked. The three unmutilated individuals sought the light as before, while the nine blind or mutilated individuals swam hither and thither without paying it any regard. It was suggested by Professor L. Agassiz, that it was the heat, or ultra-red rays of the spectrum, which was the real cause of the above phenomenon, but Dr. Romanes has shown that when a heated piece of iron (“just ceasing to be red”) was placed against the bell-jar containing the specimens of Sarsia, not one of the organisms approached the heated metal. These investigations prove that in Sarsia the faculty of appreciating luminous (but not heat) rays is present, and that this faculty is lodged exclusively in the ocular spots. Dr. Romanes has also shown that the lithocysts of the covered-eyed Medusw resemble, in function, the marginal bodies of the naked-eyed Medusw—that is, they are rudi- mentary or incipient organs of vision. The lithocysts are stimulated by the approach of a candle or the access of day- light, but if the lithocysts are removed, the approach of a luminous object produces no stimulating effect. The ocular spots in the