I I £NCE* THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID LIBRftHV THE CAMBRIDGE NATURAL HISTORY EDITED BY S. F. HARMER, Sc.D., F.R.S., Fellow of King's College, Cambridge ; Superintendent of the University Museum of Zoology AND A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge ; University Lecturer on the Morphology of Invertebrates VOLUME VIII MACMILLAN AND CO., LIMITED LONDON • BOMBAY • CALCUTTA MELBOURNE THE MACMILLAN COMPANY NEW YORK • BOSTON • CHICAGO ATLANTA • SAN FRANCISCO THE MACMILLAN CO. OF CANADA, LTD. TORONTO AMPHIBIA AND REPTILES By HANS GADOW, M.A. (Cantab.), Ph.D. (Jena), F.R.S., Strick- land Curator and Lecturer on Advanced Morphology of Vertebrata in the University of Cambridge. MACMILLAN AND CO, LIMITED ST. MARTIN'S STREET, LONDON 1909 Gift of C. A. Kofofd First Edition 1901 Reprinted 1909 -.'• SCIE* UBRAtY PREFACE LINNAEUS had but a poor opinion of the Amphibia and their describers, or he would not have called the former " pessima tetraque animalia," nor would he have dismissed the latter with the terse remark : " Amphibiologi omnium paucissimi sunt nullique veri." That was, however, nearly 150 years ago; and at the present time there are fewer difficulties in writing a book on Amphibia and Eeptiles. Those who care for the study of Amphibia and Eeptiles — the Herpetologists, to give them their scientific title — have never been numerous ; but most of them have been serious students. One reason for the fact that this branch of Natural History is not very popular, is a prejudice against creatures some of which are clammy and cold to the touch, and some of which may be poisonous. People who delight in keeping Newts or Frogs, Tortoises or Snakes, are, as a rule, considered eccentric. But in reality these cold-blooded creatures are of fascinating interest provided they are studied properly. The structure of animals is intimately connected with their life-habits ; and this correlation is perhaps more apparent in Amphibia and Reptiles than in any other class. The anatomist who studies internal and external structure is as much struck with the almost endless variety in details as he who takes the trouble to observe the living animal in its native haunts, or at least under conditions not too unnatural. He will agree with V. von Scheffel's Toad " that those above seem to have no VI 1'REFACE notion of the beauties of the swamp" — brilliantly coloured Xewts engaged in amorous play, concert-giving Frogs, and meta- morphosing Tadpoles. The motto assigned to the Eeptiles seems singularly appropriate when we consider that poisonous snakes have been developed from harmless forms, and that many kinds of reptiles have lost limbs, teeth, and eyesight in the process of evolution. The present work is intended to appeal to two kinds of readers — to the field-naturalist, who, while interested in life- histories, habits, and geographical distribution, beauty or strange- ness of forms, is indifferent to the homologies of the metasternum or similar questions ; — and to the morphologist, who in his turn is liable to forget that his specimens were once alive. A great portion of the book is anatomical and systematic. It was necessary to treat anatomy, especially that of the skeleton, somewhat fully, since it has long been recognised that it is impossible to base a scientific classification upon external characters. The reader familiar with Vertebrate anatomy has a right to expect that questions of special morphological interest will be dwelt upon at length. Those who have no anatomical foundation must be referred to one of the now numerous intro- ductory manuals on the subject. The account of the Amphibia is more complete than that of the Reptilia. It was possible to diagnose practically all the recent genera ; and this has been especially done in the Anura, in order to show how in an otherwise very homogeneous group almost any part of the body, internal or external, can be modified in kaleidoscopic variety. The same could not be done with the Keptilia. Their principal groups, — called sub -classes in the present work, in order to emphasise their taxonomic importance in comparison with the main groups of Birds and Mammals,— differ so much from each other that it was decided to refrain PREFACE Vll from attempting a general account of them. Moreover, the number of species of recent lizards and snakes is so bewilder- ing, the genera of many families being but tedious variations of the same theme, that only those forms have been described which are the most important, the most striking, or which the traveller is most likely to come across. The student who wishes to go farther into systematic details must consult the seven volumes of the Catalogue of Reptiles in the British Museum (London, 1889-1896). Mr. G. A. Boulenger, the author of this magnificent series, has rendered the systematic treatment of recent Amphibia and Eeptiles an easy task. During many years of the most friendly intercourse I have profited on count- less occasions by his ever -ready advice. Although he has kindly read the proofs of the part dealing with the Amphibia it would be unfair to associate him with any of its short- comings or with contestable opinions, for which I alone am responsible. Cope's large work on the Crocodilians, Lizards, and Snakes of North America (Rep. U.S. Nat. Mus. for 1898 (1900)) has unfortunately appeared too late to be used in the present work. The drawings on wood were, with few exceptions, made by Miss M. E. Durham, mostly from living specimens — a procedure which has to a great extent determined the selection of the illustrations. Since both the metric and the English systems of measure- ments have been employed, it may be well to state for the convenience of the reader that the length of a line of the text is four inches or approximately ten centimeters. I have frequently and freely quoted accounts of previous authors instead of paraphrasing them. Especial thanks are due to Messrs. Longmans, Green, and Co., and to Messrs. Murray, viii PREFACE for their courteous permission to make several long quotations from Sir J. E. Teunent's Ceylon, and from H. W. Bates' Naturalist on the Eiver Amazons. Lastly, a remark about my Editors. Instead of being a source of annoyance they have rendered me the greatest help. H. GADOW. CAMBRIDGE, December 19, 1900. CONTENTS PAGE PREFACE .............. v SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK . • xi PAKT I. AMPHIBIA CHAPTER I CHARACTERS AND DEFINITION — POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA — HISTORICAL ACCOUNT OF THE CLASSIFICATION OF AMPHIBIA ............ 3 CHAPTER II SKELETON OF URODELA AND ANURA — SKIN — COLOUR-CHANGING MECHANISM— POISON-GLANDS — SPINAL NERVES — RESPIRATORY ORGANS — SUPPRESSION OF LUNGS — URINO-GENITAL ORGANS — FECUNDATION — NURSING HABITS — DEVELOPMENT AND METAMORPHOSIS . .... 11 CHAPTER III NEOTENY — REGENERATION — TEMPERATURE — GEOGRAPHICAL DISTRIBUTION . 63 CHAPTER IV STEGOCEPHALI OR LABYRINTHODONTS— LISSAMPHIBIA — APODA . . . 78 CHAPTER V LISSAMPHIBIA (CONTINUED] — URODELA . 94 CHAPTER VI LISSAMPHIBIA (CONTINUED] — ANURA CONTENTS PAET II. KEPTILIA CHAPTER VII PAGE DEFINITION AND CHARACTERS — POSITION OF THE CLASS REPTILIA IN THE PHYLUM VERTEBRATA — CLASSIFICATION— SKULL AND VERTEBRAE . .277 CHAPTER VIII PROREPTILIA — PROSAURIA--THEROMORPHA 285 CHAPTER IX CHELONIA — ATHECAE — THECOPHORA CHAPTER X DINOSAURIA— CROCODILIA 412 CHAPTER XI PLESIOSAURIA— ICHTHYOSAURIA— PTEROSAURIA— PYTHONOMORPHA . . 473 CHAPTER XII SAUKIA— AUTOSAURI OR LACERTILIA— LIZARDS 491 CHAPTER XIII SAURIA (CONTINUED)— Ormm A— SNAKES 581 INDEX 651 SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK CLASS AMPHIBIA. Sub-Class. Order. Sub-Order. Family. Sub-Family. /•Stegoce- f BRANCHIO- phali Lepo- f SAURI (p. 80). spondyli 1 AISTOPODES (p. 80) 1 (p. 81). Stegoce- STEGOCE- PHALI (p. 78) phali Temno spondyli (p. 81) Stegoce - phali Stereo- spondyli (P- 83) Apoda CoECiLiiDAE(p.89). (p. 84) / AMPHIUMIDAE (p. 97). C Desmognathinae (p. 102). Urodela SALAMANDRIDAE I Plethodontinae (p. 103). (p. 94) (p. 102) 1 Amblystomatinae (p. 109). V. Salamandrinae (p. 115). PROTEIDAE (p. 132). ^ SlRENIDAE (p. 136). AGLOSSA (p. 143). " DlSCOGLOSSIDAE LISSAM- PHIBIA(p.84)" PELOBATIDAE (p. 160). BUFONIDAE (p. 166). Amira (p. 138) ' PHANERO- GLOSSA (p. 152) ( Amphignathodontiiiae HYLIDAE (p. 185)^ (p. 188). ( Hylinae (p. 189). C Hemiphractiuae (p. 210). CYSTIGNATHIDAE 1 Cystignathiuae (p. 211). (p. 209) 1 Dendrophryniscinae I (p- 224). ^ T Engystornatinae (p. 225). ENGYSTOMATIDAE] Dyf Jophinae (p. 12135). I Genyophryninae (p. 236). j Ceratobatrachinae (p. 237). - RANIDAE (p. 237) 1 Raninae (p. 238). ( Dendrobatinae (272). Xll SCHEME OF CLASSIFICATION CLASS REPTILIA (p. 277). PBOREPTILIA (p. 285). Eryops (p. 286). Cricotus (p. 287). Sub-Class. Order. Sub-Order Family. PROSAURIA (p. 288) THERO- MORPHA (p. 300) CHELONIA (P- 312) DINOSAURIA (p. 412) CROCODILIA !'• -131) PLESIO- SAURU (p. 473) (p. 478) (p. 484) PYTHONO (p. 487) Prosauri (p. 290) PROTOROSAUKI (p. 290). RHYNCHOCEPHALI (p. 292). ' Pareiasauri (p. 304). Theriodontia (p. 306). Anomodontia (p. 309). Placodontia (p. 311). Atheca (p. 333) Thecophora (p. 338) Sauropoda (p. 418). Theropoda (p. 420). Orthopoda (p. 424) Ceratopsia (p. 430). Pseudosuchia (p. 432). Parasuchia (p. 433). Eusuchia(p. 434) Nothosauri CRYPTODIRA (p. 338) PLEURODIRA (p. 388) TRIONYCHOIDEA (p. 404) SPHARGIDAE (p. 333). C CHELYDRIDAE (p. 338). DERMATEMYDIDAE (p. 341). J ClNOSTERNIDAE (p. 342). 1 PLATYSTERNIDAE (p. 345). I TESTUDINIDAE (p. 345). \ CHELONIDAE (p. 378). ' PELOMEDUSIDAE (p. 390). CHELYDIDAE (p. 399). CARETTOCHELYDIDAE (p. 404), TRIONYCHIDAE (p. 404). STEGOSAUHI (p. 425). ORNITHOPODA (p. 426) 'TELEOSAURIDAE (p. 450). METRIORHYNCHIDAE (p. 451). MACRORHYNCHIDAE (p. 451). GAVIALIDAE (p. 451). ATOPOSAURIDAE (p. 453). GONIOPHOLIDAE (p. 453). v CROCODILIDAE (p. 454). / MESOSAURIDAE (p. 476). ^ NOTHOSAURIDAE (p. 477). f PLIOSAURIDAE (p. 477). \' PLESIOSAURIDAE (p. 478). ELASMOSAURIDAE (p. 478). 486> ( PTERODACTYLI I (p. 486). "| PTERANODONTES (p. 487). Mosasauri (p. 489). SCHEME OF CLASSIFICATION Xlll Sub-Class. Order. Sub-Order. f GECKONES (p. 502) SAURIA (p. 491) Lacertilia (P- 491) "i LACERTAE (p. 513) CHAMAELEON- TES (p. 567) Ophidia (p. 581) Family. Sub-Family. /' Geckoninae (p. 507). GECKONIDAE I Eublepharinae (p. 507) 1 (p. 512). \ Uroplatinae (p. 512). AGAMIDAE (p. 515). IGUANIDAE (p. 528). XENOSAURIDAE (p. 536). ZONURIDAE (p. 536). ANGUIDAE (p. 537). HELODERMATIDAE (p. 540). LANTHANOTIDAE (p. 541). VARANIDAE (p. 542). XANTUSIIDAE (p. 547). TEJIDAE (p. 547). LACERTIDAE (p. 549). GERRHOSAURIDAE (p. 559). SCINCIDAE (p. 559). ANELYTROPIDAE (p. 564). DIRAMIDAE (p. 564). ANIELLIDAE (p. 564). AMPHISBAENIDAE (p. 565). PYGOPODIDAE (p. 567). -f CHAMAELEONTIDAE (p. 573). TYPHLOPIDAE (p. 593). GLAUCONIIDAE (p. 594). ILYSIIDAE (p. 594). UROPELTIDAE (p. 595). Pythoninae (p. 598). Boinae (p. 601). 3. 605). Acrochordinae (p. 606). Colubrinae (p. 607). Rhachiodontinae (p. 622). Dipsadomorphinae (p. 623). Elachistodontinae (p. 625). Homalopsinae (p. 625). f Elapinae (p. 626). -I Hydrophinae. (p. 635). PHALIDAE (p. 637). VIPERIDAE I Viperinae (p. 638). (p. 637) 1 Crotalinae (p. 644). (n (p. XENOPELTIDAE ( f rAglypha 1 (p. 606) 1 JBRIDAE (p. 6 I Opistho- glypha - (p. 623) 0 O AM I Protero- f glypha - (p. 625) ( BLYCE- PAET I AMPHIBIA VOL. VIII 's scheint, dass die hier oben keine Ahnung haben von dem Sumpf und Seiner Pracht." The "plattgedriickteKrote," SCHEFFEL'S Trompeter von Sdkkingen. CHAPTER I AMPHIBIA CHARACTERS AND DEFINITION POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA HISTORICAL ACCOUNT OF THE CLASSIFICATION OF AMPHIBIA A BIRD is known by its feathers, a Beast by its hairs, a Fish by its fins, but there is no such obvious feature which characterises the Amphibia and the Keptiles. In fact, they are neither fish, flesh, nor fowl. This ill-defined position is indicated by the want of vernacular names for these two classes, a deficiency which applies not only to the English language. All the creatures in question are backboned, creeping animals. Those which are covered with horny scales, and which from their birth breathe by lungs only, as Crocodiles, Tortoises, Lizards, and Snakes,, are the Eeptiles. The rest, for instance, Newts or Efts, Frogs and Toads, are the Amphibia. Their skin is mostly smooth and clammy and devoid of scales ; the young are different from the adult in so far as they breathe by gills and live in the water, before they are transformed into entirely lung-breathing, terres- trial creatures. But there are many exceptions. Proteus and Siren the mud-eel, always retain their gills ; while not a few frogs undergo their metamorphosis within the egg, and never breathe by gills. If we add the tropical limbless, burrowing Coecilians, and last, not least, the Labyrinthodonts and other fossil forms, the proper definition of the class Amphibia, — in other words, the reasons for grouping them together into one class, separated from the other backboned animals, — requires the examination of many other characters. AMPHIBIA CHAP. So far as numbers of living species are concerned, the Amphibia are the least numerous of the Vertebra ta. There are about 40 limbless, burrowing APODA ; 100 UKODELA or tailed two- or four-footed newts, and about 900 ANURA, or tailless, four-footed frogs and toads ; in all some 1000 different species. Few, indeed, in comparison with the 2700 Mammals, 3500 Eeptiles, nearly 8000 Fishes, and almost 10,000 Birds. But we shall see that the Amphibia have not only " had their day," having flourished in bygone ages when they divided the world, so far as Vertebrata were concerned, between themselves and the Fishes, but that they never attained a dominant position. Inter- mediate between the aquatic Fishes and the gradually rising terres- trial Eeptiles they had to fight, so to speak, with a double front during the struggle of evolution, until by now most of them have become extinct. The rest persist literally in nooks and corners of the teeming world, and only the Frogs and Toads, the more recent branch of the Amphibian tree, have spread over the whole globe, exhibiting almost endless variations of the same narrow, much specialised plan. The greatest charm of the Anura lies in their marvellous adaptation to prevailing circumstances ; and the nursing habits of some kinds read almost like fairy-tales. Characters of the Amphibia.1 1. The vertebrae are (a) acentrous, (6) pseudocentrous, or (c) notocentrous. 2. The skull articulates with the atlas by two condyles which are formed by the lateral occipitals. For exceptions see p. 78. 3. There is an auditory columellar apparatus, fitting into the fenestra ovalis. 4. The limbs are of the tetrapodous, pentadactyle type. 5. The red blood -corpuscles are nucleated, biconvex, and oval. 6. The heart is (a) divided into two atria and one ventricle, and (6) it has a conus provided with valves. 7. The aortic arches are strictly symmetrical. 8. Gills are present at least during some early stages of development. 9. The kidneys are provided with persistent nephrostomes. 10. Lateral sense-organs are present at least during the larval stage. 11. The vagus is the last cranial nerve. 12. The median fins, where present, are not supported by spinal skeletal rays. 13. Sternal ribs and a costal or true sternum are absent. 14. There is no paired or unpaired medio- ventral, copulatory apparatus. 15. Development takes place without amnion and allantois. None of these characters is absolutely diagnostic, except 1 (c), and this applies only to the Anura and most of the Stegocephali. 1 References to explanations of the terms used below will bo found in the index. i CHARACTERS AND POSITION 5 Numbers 1 (6), 1 (c), 2, 3, 4 and 12 separate the Amphibia from the Fishes. Numbers 1, 6 (6), 7, 8, 9, 11, 13, 15 separate them from the Reptiles, Birds, and Mammals. Number 2 separates them from the Fishes, Reptiles, and Birds. Number 5 separates them from the Mammals. Number 6 (a) separates them from the Fishes (excl. Dipnoi), Birds and Mammals. We can, therefore, very easily define all the Amphibia, both recent and extinct, by a combination of the characters enumerated above. For instance, by the combination of numbers 2, 3 or 4 with either 7, 8, 9, 11, 13 or 15. Amphicondylous Anamnia would be an absolutely correct and all-sufficient diagnosis, but it would be of little use in the deter- mination of adult specimens ; and the tetrapodous character is of no avail for Apoda. Ampliicondylous animals without an intra- cranial hypoglossal nerve is a more practical diagnosis. In the case of living Urodela and Anura the absence of any scales in the skin affords a more popular character ; it is unfor- tunately not applicable to the Apoda, many of which possess dermal scales, although these are hidden in the imbricating transverse rings of the epidermis ; and the frequent occurrence of typical scales of both ecto- and meso-dermal composition in many of the Stegocephali forces us to discard the scales, or rather their absence, as a diagnostic character of the class Amphibia. The same applies to the mostly soft, moist, or clammy, and very glan- dular nature of the skin. The position of the class Amphibia in the Phylum Verte- brata. — There is no doubt that the Amphibia have sprung from fish-like ancestors, and that they in turn have given rise to the Eeptilia. The Amphibia consequently hold a very important intermediate position. It was perhaps not a fortunate innova- tion when Huxley brigaded them with the Fishes as Ichtliyopsida, thereby separating them more from the Sauropsida ( = Reptilia and Aves), than is justifiable, — perhaps more than he himself intended. The connecting-link, in any case, is formed by the Stegocephali ; all the recent Orders, the Apoda, Urodela, and Anura, are far too specialised to have any claims to the direct ancestral connections. The line leading from Stegocephali to fossil Eeptiles, notably to such Proreptilia as Eryops and Cricotus, and even to the Lepospondylous Prosauria, is extremely gradual, and the steps are almost imperceptible. Naturally, 6 AMPHIBIA CHAP. assuming evolution to be true, there must have lived countless creatures which were a " rudis indigestaque moles," neither Amphibia nor Eeptilia, in the present intensified sense of the systematist. The same consideration applies equally to the line which leads downwards to the Fishes. But the great gulf within the Yertebrata lies between Fishes and Amphibia, between absolutely aquatic creatures with internal gills and " fins," and terrestrial, tetrapodous creatures, with lungs and fingers and toes. On the side of the fishes only the Dipnoi and the Crosso- pterygii como into consideration. The piscine descent of the Amphibia is still proclaimed by the following features. — (1) The possession by the heart of a long conus arteriosus, provided with, in many cases, numerous valves, or at least (Anura) one series at the base, another at the beginning of the truncus where the arterial arches branch off; (2) the strictly symmetrical arrangement of these arches; (3) the trilocular heart is still like that of the Lung-fishes or Dipnoi ; (4) the occurrence of as many as four or even five branchial skeletal arches in the larval stage ; (5) the glottis is supported by cartilages which themselves are derivatives of posterior visceral arches; (6) the development of the vertebrae (Stegocephali and Urodela) from four pairs of arcualia, and the formation of the intervertebral joints by a split across the intervertebral ring of cartilage : this feature is unknown in Eeptilia, but it occurs also in Lepidosteus, most probably also in Polypterus ; (7) the hypo- glossal still retains the character of a post-cranial or cervical spinal nerve; (8) the presence of lateral sense-organs; (9) the possession of external gills is of somewhat doubtful phylogenetic value, although such gills occur amongst fishes only in Dipnoi and Crossopterygii. It is not unlikely that in the Amphibia these organs owe their origin to entirely larval requirements, while the suctorial mouth of the larvae of the Anura and many fishes has certainly no ancestral meaning, but is a case of con- vergent development. The usual diagnoses of the Amphibia contain the statement that they, or most of them, undergo a metamorphosis, or pass through a larval stage. The same applies to various fishes ; while, on the other hand, the larval (not ancestral) stage has become permanent in the Proteidae and Sirenidae ; and lastly, we cannot well speak of larvae in the viviparous Salamandra atra. CLASSIFICATION The evolution of an adequate classification of the Amphibia has been a long process. Even their recognition as a class, separate from, and of equal rank with that of, the B-eptilia, was by no means generally accepted until comparatively recent times. A historical sketch of the laborious, often painful, striving for light, in France and Germany, then in England, and lastly in America, is not without interest. The term Amphibia was invented by Linnaeus for the third class of animals in his famous " Systema Naturae." It comprises a very queer assembly, which, even in the 13th edition (1767), stands as follows : — 1. KEPTILES PEDATI, with the four "genera" Testudo, Draco, Laceria,. and Eana. Lacerta includes Crocodiles, Lizards, and Newts ! 2. SERPENTES APODES. 3. NANTES PINNATI. Elasmobranchs, Sturgeons, Lampreys, and various, other fishes. Laurenti, 1768, in a dissertation entitled "Specimen medicum, exhibens Synopsin Reptilium . . .," uses Brisson's term, REPTILES, and divides them into : — REPTILIA SALIENTIA, these are the Anura, GRADIENTIA, namely the Urodela and Lizards. SERPENTIA, the Snakes and the Apoda. Brongniart, 1800, " Essay d'une classification naturelle des Reptiles,"1 dis- tinguishes : — CHELONII, SAURII, OPHIDII, BATRACHII ; the last for the Frogs, Toads, and Newts. Latreille, 1804, "Nouveau Diet. Hist. Nat." xxiv.,2 accepts the four Orders of Brongniart's " Reptiles," but clearly separates the fourth Order, " BATRACHII," from the rest by the following, now time-honoured, diagnosis : Doigts des pattes n'ayant pas $ angles ; des branchies, du moins pendant un temps; des metamorphoses. But there is not one word about " Amphibia " in opposition to " Reptilia." Dumeril, 1806, " Zoologie analytique " (p. 90), and "Clemens de 1'histoire naturelle," 1807, divides the "Reptiles batraciens," or " Batracii," into ECAUDATI and GAUD ATI ; he also introduces the terms " ANOURES " and " URODELES " as their equivalents ; but since these terms appear in the French form purists do not admit their -having any claim to recognition ! Oppel, 1811, "Die Ordnungen, Familien und Gattungen der Reptilien," establishes the term APODA for the Coeciliae, and recognises their affinity to the Ecaudata and Caudata by removing them from the Snakes. De Blainville, 1816, "Prodrome d'une nouvelle distribution du regne animal " 3 — AMPHIBIENS SQUAMIPERES. [The Reptilia.] „ NUDIPELLIFERES s. Ichthyoides. [The Amphibia.] 1 Bull. Soc. Philom. ii. p. 81. 2 Tableaux methodiques, p. 61. 3 Bull. Soc. Philom. p. 113. 8 AMPHIBIA Merrem, 1820, " Tentamen systematis Amphibiorum." PHOLIDOTA. [The Reptilia.] BATBACHIA: APOD A. SALIENTIA. IMutabilia [with metamorphosis, e.g. .INewts.J Ainphipneusta [Perennibranchiate Uro- deles,] F. S. Leuckart, 1821, " Einiges ueber die fischartigen Amphibien." * MONOFNOA. [The Reptilia.] with temporary gills: Ecaudata -f- Caudata DIFNOA. [The Amphibia] permanent gU]s . „ Proteidae;> Meno. ^ poma and Amphiuma. Latreille, 1825, " Families naturelles du regne animal" The Vertebrata are divided into Haematherma and Haemacryma. These terms for warm- and cold-blooded creatures were later on amended by Owen to Haemato- therma and Haematocrya. The latter are divided by Latreille as follows : — REPTILIA. Still including the Coeciliae amongst the Snakes. AMPHIBIA fCaducibranchiata- .A .Mir rHxiJlA » -r\ «i i • , (Perenmbranchiata. PISCES. Wagler, 1830, "Systema Amphibiorum." TESTUDINES, CROCODILI, LACERTAE, SERPENTES, ANGUES, COECILIAE, RANAE, ICHTHYODI. RANAE I. AGLOSSA. II. PHANEROGLOSSA : 1. Cauda nulla. [The Anura.] „ „ 2. Cauda distincta. [The Sala- mandridae.] ICHTHYODI I. ABRANCHIALES. Menopoma [Cryptobranchus] and Amphiama. „ II. BRANCHIALES. [The Peremiibranchiate Urodela.] J. M tiller, 1831, " Beitriige zur Anatomic . . . der Amphibien."2 GYMNOPHIONA, DEROTREMATA, PROTEIDAE, SALAMANDRINA, BAT- RACHIA. J. Bell, 1836, Todd's "Cyclopaedia of Anatomy and Physiology," Art. " Amphibia." AMPHIPNEUSTA, the Perennibranchiate Urodeles ; ANOURA, URODELA ; ABRANCHIA, Menopoma and Amphiuma ; APODA. :Stannius, 1856, " Handbuch der Zootomie : Anatornie der Wirbelthiere." (2nd cd.) AMPHIBIA MONOPNOA. The Reptilia. AMPHIBIA DIPNOA. 1. URODELA. PERENNIBRANCHIATA. DEROTREMATA: Amphiuma and Menopoma. MYCTODERA? 1 Isis, 1821. '-' Treviranus' Zeitschr, f. Physiol. 1831, p. 190. :! Stpr), neck ; /xt5w, close. CLASSIFICATION 9 2. BATRACHIA. AOL OSS A. PHANEROGLOSSA : Systomata = Engystomatidae. Bufoninae. Without manubrium sterni. Raninae. With manubrium. Hyloidea. With adhesive finger- discs, GYMNOPHIONA. Oegenbaur, 1859, " Grundziige der vergleichenden Anatomic." AMPHIBIA as a separate class, equivalent to that of the REPTILIA, are divided into the four Orders: PERENNIBRANCHIATA, SALA- MANDRINA, BATRACHIA, and GYMNOPHIONA. In the second edition of the " Grundziige " (1870) they are divided into URODELA, ANURA, and GYMNOPHIONA. Huxley, 1864, "The Elements of Comparative Anatomy." MAMMALS. SAUROIDS, subsequently changed into SAUROPSIDA = Reptilia + Aves. ICHTHYOIDS, „ „ ICHTHYOPSIDA = Amphibia + Pisces. Haeckel, 1866, " Generelle Morphologic." Amphibia. A. PHRACTAMPHIBIA s. Ganocephala = Labyrinthodonta + Peromela [Apoda]. B. Liss AMPHIBIA s. Sozobranchia =• Sozura [Urodela] + Anura. •Cope, 1869.1 STEGOCEPHALI, GYMNOPHIDIA, URODELA, PROTEIDEA, TRACK YSTOMATA, ANURA. Huxley, 1871, "A Manual of the Anatomy of Vertebrated Animals." Amphibia I. SAUROBATRACHIA [v.d. Hoeven's term] s. URODELA 1. Proteidea. 2. Salamandridae. II. LABYRINTHODONTA. III. GYMNOPHIONA. IV. BATRACHIA s. ANURA. Boulenger, 1882, " Catalogue of the BATRACHIA GRADIENTIA s. CAUDATA and BATRACHIA APODA," divides the Caudata simply into : SALAMAND- RIDAE, AMPHIUMIDAE, PROTEIDAE, and SIRENIDAE. 1882, "Cat. Batrachia Salientia s. Ecaudata," see p. 140. Cope, 1890, " Synopsis of the Families of Vertebrata." 2 CLASS BATRACHIA. Sub-Class I. STEGOCEPHALI. Order 1. Ganocephali : Trimerorhachis, Archegosaurus. 2. Rhachitomi : Eryops 3. Embolomeri : Cricotus. 4. Microsauri : Branchiosaurus, Hylonomus, etc. 1 Proc. Ac. Philad. p. 209. 2 Americ. Natural, xxiii. p. 849. IO AMPHIBIA CHAP, i Sub-Class II. URODELA. Order 1. Proteidae : Proteus. 2. Pseudosauria. [All the rest of the Urodela + Coeciliidae.] 3. Trachystomata : Sirenidae. III. SALIENTIA. P. and F. Sarasin, 1890, " Zur Entwicklungsgeschichte der Ceylonesischeu Blindwiihle, Ichthyophis glutinosa." l Sub-Class I. ARCHAEOBATRACHI s. STEGOCEPHALI. II. NEOBATRACHI. Order 1. URODELA. a. Salamandroidea. [The Urodela.] 6. Coeciloidea = Amphiumidae + Coeciliidae. 2. ANURA. The classification adopted in this volume is as follows : — CLASS AMPHIBIA. Sub-Class I. Phractamphibia. Order I. Stegocephali Lepospondyli. Sub-order 1. Branchiosauri. Sub-order 2. Aistopodes. Order II. Stegocephali Temnospondyli. Order III. Stegocephali Stereospondyli. Sub-Class 1^. Lissamphibia. Order I. Apoda. Order II. Urodela. Order III. Anura. Sub-order 1. Aglossa. Sub-order 2. Phaneroglossa. 1 Sarasins' Ergebnisse . . . Ceylon, 1887-1890. CHAPTER II SKELETON OF URODELA AND ANURA SKIN COLOUR -CHANGING MECHANISM POISON - GLANDS SPINAL NERVES RESPIRA- TORY ORGANS SUPPRESSION OF LUNGS URINO -GENITAL ORGAN S FECUNDATION NURSING HABITS DE VELOPMENT AND METAMORPHOSIS SKELETON OF THE URODELA The vertebral column. — The number of vertebrae is smallest in the terrestrial, greatest in the entirely aquatic forms, and is excep- tionally large in the eel-shaped AmpJiiuma. In the following table the sacral vertebra is included in those of the trunk. Trunk. Tail. Kir en lacertina , . .22 35 + Necturus maculatus . .19 29 Proteus anguinus 30 28 + Cryptobranchus alleghaniensis 20 or 21 24 + G. scheuchzeri . . .21 C. japonicus . .22 22 to 26 Amphiuma means . .63 35 + Amblystoma tigrinum . , 17 or 16 32 + • Salamandra maculosa . .17 27 Triton cristatus ... 17 36 Triton taeniatus . . 14 or 15 36 + Triton palmatus . . . 14 23 to 25 Salamandrina perspicillata . 15 32 to 42 Spelerpes fuscus ... 16 23 The vertebrae of the Urodela and those of the Apoda differ from those of all the other Tetrapoda l by possessing no special centra or bodies. That part which should correspond with the centrum is formed either by the meeting and subsequent complete co-ossification of the two chief dorsal and ventral pairs of arcualia 1 Credner's term for all Vertebrates higher than fishes. I 2 U ROD EL A (tail-vertebrae), or entirely by the pair of chief dorsal arcualia. There is consequently no neuro-central suture. Moreover, the central region of each vertebra is strongly pinched in laterally, widening towards the ends. Another feature of the vertebral column of the Urodela is the possession of a considerable amount of intervertebral cartilage, by which the successive vertebrae are held together. This cartilage does not ossify, and it either remains continuous, serving in its entirety and owing to its flexibility as a joint, or it becomes more or less imperfectly separated into a cup and ball portion, the cup belonging to the posterior end of the vertebra. Such joints are called opisthocoelous, and occur in the Desmognathinae and Salamandrinae. In the adult the cup and ball frequently calcify, and the chorda dorsalis or notochord is completely destroyed. Those vertebrae between which the inter- vertebral cartilage remains unbroken, are called amphicoelous, since in them, most obviously in macerated or dried skeletons, the vertebrae appear hollowed out at either end. In such amphicoelous vertebrae a considerable amount of the chorda always remains, running in an unbroken string through the whole length of the vertebral column. Towards adult life the chorda becomes constricted, and is ultimately squeezed out or destroyed, in the middle of the vertebra, by the invasion of cartilage from the chief arcualia. This intravertebrally situated cartilage has been described erroneously as chordal cartilage. The development of the vertebrae proceeds as follows. First appear a pair of basidorsalia and a pair of basiventralia (Fig. 1,1, B.D, B.V), blocks of cartilage, imbedded in and resting upon the thin sheath of the chorda dorsalis. Next appears a pair of inter- dorsal blocks, immediately behind the basidorsals ; and somewhat later appears a pair of interventral blocks. These four pairs of cartilages or " arcualia " each meet, above or below the chorda, and form semi-rings, which again by extending upwards or downwards fuse into complete rings, in such a way that the interdorsal and interventral elements form the intervertebral mass spoken of above. The basidorsals fuse with the basiventrals, and form the body of the vertebra, the fusion being effected chiefly by the calcification and ossification of the lateral connecting portion of the skeleto- genous layer. The basidorsalia form the neural arches with their unpaired short spinous or neural, and the paired anterior and posterior zygapophysial processes. Concerning the basi- VERTEBRAL COLUMN ventralia we have to distinguish between the trunk and the tail. In the latter they produce a pair of ventral outgrowths or haemapophyses, which ultimately enclose the caudal blood-vessels. In the trunk the basiventral blocks of cartilage are suppressed ; they appear in the early larvae, but disappear during or even before metamorphosis. Towards the end of the tail the vertebrae diminish in size, and their constituent cartilages assume a more and more FIG. 1. — 1-5, Five successive stages of the development of a caudal vertebra of a newt ; 6-7, the second and the first cervical ver- tebra of Cryptobranchus ; 8-9, side view of the constituent cartilaginous blocks of a caudal vertebra (8) and a trunk -ver- tebra (9) of Archegosaurus as typical examples of Temno- spondylous quadripartite and tripartite vertebrae. The cross- hatched parts indicate the artic- ular facets for the ribs. The anterior end of all the vertebrae looks towards the right side. of, In 7, articulating facet for the occipital condyle ; 2?.D,basi- dorsal piece or neural arch ; B. V, basiventral piece or ven- tral arch ; Gh, chorda dorsalis, or notochord ; I.D, interdorsal piece ; /. V, interventral piece ; /. V.L, intervertebral ligament ; N, spinal nerve — these are num- bered I, II, III in 6 and 7 ; E, rib ; T, in 7, rib- like tubercle on the first vertebra. av indifferent shape, until they become confluent into a continuous rod of cartilage, resembling in this respect the Dipnoi and Holocephali. A periodical revival of this rod, at least of its connective tissue, appears in the tail-filament of the male Triton palmatus during the breeding-season. The first vertebra, called the atlas, because it carries the head, is remarkable for the possession of an odontoid process. The latter is formed by a pair of cartilages and represents part of a vertebra, the dorsal portion of which seems to have been added to the occipital part of the cranium. 14 URODELA CHAP. All the trunk -vertebrae, with the exception of the atlas, carry ribs, at least vestiges thereof. Owing to the early dis- appearance of the basiventral cartilages the capitular portions of the ribs are much reduced, and are mostly represented by strands of connective tissue only. The ribs develop therefore occasion- ally at some distance from the vertebral column, and that por- tion of the rib which in the metamorphosed young newt looks like the capitulum is to a great extent really its tuberculum. FIG. 2.— Transverse section through a Witness the position of the ver- truuk- vertebra of a larva of Sala- tebral artery, which still indi- nuindra maculosa, enlarged. The right side shows the actually existing state, cates the true foramen trans- The homologies of bable original condition. A, Verte- these parts are Still more ob- !±l^:±^^S£5 s°ired by the fact that a new cartilage ; Ch, chorda dorsalis ; Sp.c, process grows Out from the rib, spinal canal ; *, the false transverse , 1-1-1 i A canai. by which the latter gains a new support upon a knob of the neural arch. Thus an additional foramen is formed, sometimes confounded with the true transverse canal. The meaning which underlies all these modifications is the broadening of the body, the ribs shifting their originally more ventral support towards the dorsal side. The whole process is intensified in the Anura ; it is an initial stage of the notocentrous type of vertebrae. The transverse ossified processes of the adult are often much longer than the vestiges of the ribs themselves, and are somewhat com- plicated structures. They are composed first of the rib-bearing cartilaginous outgrowths of the neural arches ; secondly, of a broad string of connective tissue which extends from the ventro-lateral corner of the perichordal skeletogenous layer to the ribs. The shoulder-girdle is extremely simple. It remains almost entirely cartilaginous, and the three constituent elements are not separated by sutures. Ossification is restricted to the base of the shaft of the scapula, and may extend thence over the glenoid cavity. The coracoids are broad, loosely overlap each other, and are " tenon and mortised " into the triangular or lozenge-shaped LIMB-GIRDLES I 5 cartilaginous sternum, which latter has no connection with the ribs. The precoracoid is a large, flat process, directed forwards, not meeting its fellow ; it is absent in Siren. The humerus articulates with both radius and ulna, and these two bones of the forearm remain separate. The elements which compose the wrist and hand exhibit an almost ideally simple arrangement, slightly varied by the frequent fusion of two or more neighbouring carpalia into one, and by the reduction of the number of fingers. Most frequently the intermedium and the ulnar carpal element fuse together, and there is more often one centrale instead of two. The wrist and hand of the Urodela represent, however, no longer the entirely primitive pentadactyle type, owing to the loss of one finger together with its metacarpal and carpal element. Comparison with the Anura makes it probable that the Urodela have lost the pollex, their four fingers being consequently the 2nd, 3rd, 4th, and 5th. Siren has four or three fingers ; Proteus has only three fingers and three large compound carpal cartilages. In Ampliiuma, with either three or two fingers, the ulnare, intermedium, and carpale are fused together, the radiale with the neighbouring carpale. The number of phalanges in the four-fingered species is generally 2, 3, 3, 2 respectively. The pelvic girdle. — The ilium stands vertically to the vertebral axis, slanting slightly forwards and downwards. It is attached by means of a rib to only one vertebra, and this ilio-sacral connection is acetabular in its position, i.e. it lies in the same transverse plane with the acetabulum, in other words vertically above it. The ventral portion of the pelvis is formed by one large continuous mass, the united pubo-ischia, the anterior or pubic portion of which extends forwards in the shape of a broad triangle (Necturus) or as a slender, stalked, Y-shaped cartilage, the epipubis, which is often movably jointed at its base. The lateral portion of the pubic cartilage is always perforated by the nervus obturatorius. Ossification is restricted to the ischium and to the middle of the shaft of the ilium. The acetabular fossa for the femur is closed. The tibia and fibula remain separate. The foot is still more primitive than the anterior extremity, as the majority of Urodela possess the full complement of five toes, with 2, 2, 3, 3, 2 phalanges respectively. Concrescence of the tarsalia applies most frequently to the fourth arid fifth distal 1 6 URODELA and to the two centralia ; exceptional, for instance, in Crypto - branchus japonicus, are as many as three centralia, but this is an individual, even a one-sided variation, as shown for instance by a specimen in the Cambridge Museum. Loss of the fifth toe occurs sporadically in genera of different groups, namely, in Salamandrella, Batrachyperus, Salamandrina, Necturus, Manculus, Batrachoseps. In Amphiuma the number is reduced to three or two ; in Proteus to two ; and in Siren the hind limbs, with their girdle, are altogether absent. Lastly, in some species of Spelerpes and Batrachoseps both fore and hind limbs have become so small as to be practically without function, parallel cases being found among various Scincidae and other Lizards. The hyoid apparatus is still very primitive in many, especially in larval, Urodela. Besides the hyoid there are as many as four pairs of branchial arches, which, however, decrease in size and completeness, so that the last two have lost their connection with the median copular piece, and become attached in various ways to the second branchial arch. This is the arrangement apparently in all larvae, but four pairs of branchials persist in the adult Siren, AmpJiiuma, and Cryptobranchus alleghaniensis. The whole branchial apparatus is reduced to three pairs of arches in Necturus and Proteus, to two in the adult Crypto- branchus japonicus and in the Salamandridae. Of considerable interest is the vestige of a fifth pair of arches in the larvae of Triton and Salamandra, in the shape of a pair of tiny cartilages, which lie in front and on each side of the opening of the trachea, arid give rise to the formation of the laryngeal cartilages, better developed in the higher Vertebrata. The following are noteworthy characters of the skull of Urodela. The articulation of the skull with the vertebral column is not always effected entirely by the two condyles of the lateral occipital bones, but the median basal cartilage often possesses a pair of facets for the odontoid-like process of the first vertebra ;. such additional facets are perhaps best developed in Crypto- branchus and in the Salamandrinae. The middle portion of the primitive cranium, from the exit of the optic nerve to the ethmoid cartilage, is formed by a pair of separate bones, the orbito- sphenoids. The parietal and frontal bones remain separate. One or more periotic bones exist, besides the prootic, in the aquatic families. SKULL A pair of prefrontal bones is present in most Salamandridae, e.g. Salamandra, Triton, Amblystoma, especially in the larva, and in Cryptobranchus ; these bones are absent in AmpJiiuma, Necturus, Proteus, and Siren. The lacrymalia are still separate in some Amblystomatinae, FIG. 3. — Skulls of various Urodela. 1, Salamandra ma- culosa, ventral view, and 2, dorsal view ; 3, Axolotl stage of Amblystoma ; 4, adult stage of Amblystoma; 5, Salamandrina perspicillata (after Wieders- heim) ; 6, Salamandra ma- culosa, dorsal view of the lower jaw. A, Articulare ; Clt (72, outer and inner occipital con- clyles ; Ch, choana or posterior nasal opening ; d, dentary ; E, ethmoid ; F, frontal ; LO, lateral occipital ; M, maxillary ; N, nasal ; .2V0,nostril ; OS, orbito- sphenoid ; P, parietal ; Pf, pre- frontal ; PI, palatine ; Pm, pre- maxillary ; Po, prootic ; PS, parasphenoid; P£, pterygoid ; Q, quadrate ; S, angulo-splenial ; Sq< squamosal ; St, stapes ; Vo, vomer ; II, VII, X, exits of the optic, facial, and glosso- vagus nerves. e.g. Eanidens and Hynolius. A pair of nasalia are generally present, but are absent in Necturus, Proteus, and Siren. The parasphenoid is furnished with teeth in the Plethodontinae and Desmognathinae. Separate palatine bones exist in Necturus and Proteus, and in the larva of AmUystoma, but in the adult form they fuse with the vomers, producing the vomero-palatines characteristic of the majority of Urodela. VOL. VIII C 1 8 ANURA CHAP. The pterygoid bones are most fully developed, so as to reach the vomero-palatines, in the Aniblystomatinae, in Necturus, and in Proteus; they are reduced, so as to leave a gap, in Crypto- branchus, and still more in the Salamandrinae ; they are absent in Amphiuma and in Siren. The quadrates are directed forwards in Necturus, Proteus, and Siren, while in the other Urodela they extend transversely and almost horizontally. The hyomandibular remnant, the so-called operculum, is small, and forms a plate which fits into the fenestra ovalis, extending as a ligamentous process upon the quadrate. The quadrato-jugal elements are reduced to ligaments. In many Salamandrinae the large orbito-temporal space is divided into an orbital and a temporal fossa by an arch which is formed by the meeting of two corresponding processes from the squamosal and frontal bones respectively. This bridge is rarely bony (Salamandrina, Triton), mostly ligamentous ; — apparently a reminiscence of the Stegocephalous condition. The two pre- maxillary bones are liable to fuse into one, for instance in Cryptolranchus, generally in adult Tritons. They are most reduced, and are toothless, in Siren. The two maxillary bones are absent only in Necturus, Proteus, Typlilomolge, and Siren. Their posterior end is frequently free, loosely connected by ligaments with the pterygoid in Crypto- branchus ; or with the distal portion of the quadrate, and in this case either just touching it (Tylototritori), or forming a broad junction (Pachytritori). Each half of the lower jaw consists of a dentary, articular and angulo - splenial. The splenial remains as a separate element in Siren ; in others only during the larval period. There are no mento-Meckelian elements. SKELETON OF THE ANURA The vertebral column. — The distinctive peculiarities of the vertebrae of the Anura are that they are notocentrous, and that about a dozen of them are modified and fused into an os coccygeum. The whole column is the most specialised found in the Vertebrata ; and various stages are rapidly hurried through and obscured caenogenetically during the embryonic development. Paired cartilages appear on the dorsal side of the thin chordal sheath, and whilst tending to enclose the spinal cord in a II THE DEVELOPING VERTEBRAL COLUMN 19 canal, their bases grow head- and tail- wards into what will ultimately become the intervertebral region. This extension of cartilage leads to a fusion with that of the next following pair of "arches, so that the axial column at this early stage consists of a right and left longitudinal ridge of cartilage which sends off dorsal processes, neural arches, in metameric succession. Next, the intervertebral cartilage increases in such a way as to constrict the chorda either laterally (Rana) or obliquely from above downwards and inwards (Bufo, Hyla). "We recognise in this cartilage the interdorsalia. Ventral arcualia are late and much obscured. There is scarcely any cartilage which could represent the interventralia, the intervertebral cartilage being almost entirely made up of the interdorsalia. These fuse together and form a disc or nodule, which later fuses either with the vertebra in front, and in this case fits into a cup carried by the vertebra next behind (procoelous vertebrae), or the knob is added to the front end of the vertebra, fitting into a cup formed by the tail end of the vertebra next in front (opisthocoelous vertebrae). Much later than the two longitudinal dorsal bands there appears on the ventral side an unpaired band in which appear metamerically repeated swellings of cartilage, likewise unpaired. These swellings become confluent, in a way similar to that which produced the dorsal bands, and form the unpaired ventral band of cartilage, the hypochordal cartilage of some authors. The swellings in this band, equivalent to the basi- ventralia, become semilunar in a transverse view, their horns tending upwards towards the basidorsal cartilages, but there is no actual meeting. Both dorsal and ventral elements are, however, joined together and form the chief portion of the ver- tebrae, owing to the rapidly proceeding calcification and later ossification of the all-surrounding " membrana reuniens " or skeletogenous layer so far as that is not cartilaginous. Procoelous vertebrae exist in the overwhelming majority of Anura ; opisthocoelous are those of the Aglossa, the Discoglossidae, and of some Pelobatidae. The systematic value of this pro- or opistho-coelous character has been much exaggerated. We have seen that the centra of the vertebrae of the Anura are formed entirely by the interdorsal elements, hence the term "notocentrous," and these centra sometimes remain in adult specimens of Pelobates as separately ossified and calcified pieces, 20 ANURA CHAP. not fused withr the rest of the vertebrae. This important dis- covery has been made by Boulenger, but Stannius had previously mentioned a specimen of Pelolates in which the second and fourth vertebrae are biconvex, the third, sixth, and eighth bicon- cave. Moreover, since the sacral vertebra, generally the ninth, in all the Anura is invariably biconvex, the eighth being biconcave in the procoelous families, opisthocoelous like the remaining seven vertebrae in the other families, it is not difficult to imagine that in the Anura the production of pro- or opistho-coelous vertebrae depends simply upon the centra or articulating knobs happening to fuse either with the hind or the front end of the vertebrae. This must of course ultimately be determined by a mechanical problem of motion. A second type of the vertebrae amongst the Anura is the epichordal type, an exaggeration in degree of the notocentrous tendencies of the more usual perichordal arrangement. It shows, namely, the almost complete suppression of all the ventral cartilaginous elements, so that the chorda remains for a long time on the ventral surface of the axial column in the shape of a flattened longitudinal band. These two types are not un- connected. The suppression of the ventral elements applies most typically to the trunk region, while hypochordal cartilage exists in the anterior cervical vertebrae, and above all in the coccyx. Typically epichordal are the vertebrae of Pipa, Xeno- pus, BoTribinator , Pelobates, Discoglossus and Alytes. It is significant -that the epichordal often coincide with opisthocoelous vertebrae, and still more suggestive is the fact that Bombinator is eminently aquatic, Pipa and Xenopus entirely so, having lost the tympanum, at least externally. The epichordal feature is not necessarily indicative of relationship. It has probably been developed independently in various groups, in correlation with a resumption of aquatic life. Various genera of Pelobatidae and most likely some Cystignathidae, e.g. Pseudis, will not improbably connect the two types and their several correlated features, for instance, the frequent reduction of the tympanic cavity. The os coccygeum has retained rather primitive features in so far as much dorsal and ventral cartilage is developed ; but this has almost entirely lost its metameric arrangement, and the posterior half of the coccyx is formed chiefly by the ventral mass of cartilage, while the dorsal elements are more or less reduced. H VERTEBRAL COLUMN 21 Only two vertebrae, generally the tenth and eleventh of the whole column, are clearly visible, each being composed of a pair of dorsal and a pair of ventral cartilaginous blocks. The sacral vertebra articulates with the coccyx by one or two convexities, but in the Aglossa, in some Pelobatidae, and a few others, the coccyx is fused with the sacral vertebra. Beyond the first and second component vertebrae of the embryonic coccyx, the cartilage is continued in the shape of two dorsal, and one ventral, bands, which soon fuse with each other. Dorsally this cartilage surrounds the spinal cord; the latter degenerates towards the end of the tadpole-stage, leaving, however, the empty spinal canal. The chorda, completely surrounded by cartilage, persists into the post -larval stage, but is destroyed long before the creature attains maturity. Ultimately the whole coccyx ossifies. The tail proper, namely that portion which is absorbed during the metamorphosis, remains throughout its existence in an apparently primitive condition. The chorda dorsalis and the spinal cord extend through its whole length, surrounded by continuous connective tissue without any cartilage ; in fact it represents a piece of typical vertebral column before the appear- ance of cartilage. The reduction of this swimming organ begins at the hind end. The vertebral column of the adult. — The first vertebra (we will call it the atlas since it carries the skull) is not, as in the Urodela, provided with an odontoid process. It articulates by two cups with the condyles of the occiput. In some Anura it co-ossifies, rather incompletely, with the second vertebra, regularly in the fossil Palaeolatrachus, often in Ceratophrys, Hreviceps, and occasionally in Pelobates, Bufo, Eana, and Xenopus. This is, however, no justification for looking upon the first vertebra as a complex of two vertebrae, although the atlas is frequently very thick and broad, and even carries, in the Aglossa, considerable lateral wings or diapophyses. Those of the trunk-vertebrae are often very long, acting thereby as substitutes for ribs which are absent, except on the second, third, and fourtli vertebrae of the Discoglossidae, and on the second and third of the Aglossa. In. the adult Aglossa these ribs fuse with the processes which carry them. The diapophyses of the sacral vertebra carry no ribs, the ilia being attached to them directly. They are either cylindrical 22 ANURA CHAP. as in the Eanidae and Cystignathidae, or they are more or less dilated as in all the other families, most strongly iii the Pelobatidae and the Aglossa. In some members of the large sub -family of the Cystignathidae the otherwise cylindrical diapophyses are slightly dilated. The sacrum is formed by the ninth vertebra, but there are a few interesting exceptions. Pelobates, Pipa, and Hymenochirus possess two sacral vertebrae ; and, neglecting individual abnor- malities, these three genera form the only exception amongst recent Amphibia. In the three genera the coccyx is fused with the second sacral vertebra, and such a fusion occurs elsewhere normally only in Bombinator with its single sacral vertebra. The morphologically oldest condition is normally represented by Pelobates, the sacral vertebrae being the tenth and ninth. One FIG. 4. — Dorsal view of the sacral or ninth vertebra (9), with the attachment of the ilium, of (1) Rana temporaria, (2) Bufo mdgaris, showing the whole coccyx and pelvis, (8) Pelobates fuscus, as examples of cylindrical and of dilated sacral diapophyses. (About nat. size.) a, Acetabulum ; c, coccyx ; i, ilium ; z, anterior zygapophyses. case has been recorded by Boulenger of Bombinator pachypus " with eleven segments," the last carrying the ilium. Individual lop-sided abnormalities have been described in Bombinator and Alytes, where the right ilium articulated with the tenth, the left ilium with the ninth vertebra. This shifting forwards of the ilium to the extent of one metamere has been continued further in Pipa, in which the sacrum is formed by the ninth and eighth vertebrae, their diapophyses fusing on either side into extra broad wing-like expansions. In old specimens of Palaeobatrachiisfritschi the seventh vertebra is in a transitional condition, the ilium being carried by the ninth and eighth, and slightly also by the diapophyses of the seventh vertebra ; and in P. diluvianus the II VERTEBRAL COLUMN 23 diapophyses of all these vertebrae are united into one broad plate to which the ilia are attached. Lastly, in Hymenocliirus the first sacral is the sixth vertebra, and this creature has thereby reduced the pre-sacral vertebrae to the smallest number known. This shifting forwards of the iliac attachment implies the conversion of original trunk into sacral vertebrae, and the original sacral vertebra itself becomes ultimately added to the urostyle. The second sacral, the tenth of Pelolates, the ninth of Pipa, and the tenth on the right side of the abnormal Bombinator, are still in a transitional stage of conversion. In Discoglossidae the tenth is already a typical post-sacral vertebra, and is added to the coccyx, but it still retains distinct, though short, diapophyses. In the majority of the Anura the tenth vertebra has lost these processes, and its once separate nature is visible in young specimens only. In Bombinator even the eleventh vertebra is free during the larval stage. In fact the whole coccyx is the result of the fusion of about twelve or more vertebrae, which from behind forwards have lost their in- dividuality. We conclude that originally, in the early Anura, there was no coccyx, and that the ilium was attached much farther back ; and this condition, and the gradual shifting for- wards, supply an intelligible cause of the formation of an os coccygeum. The fact that the sacral vertebrae of the Anura possess no traces of ribs as carriers of the ilia, is also very suggestive. The ilia have shifted into a region, the vertebrae of which had already lost their ribs. By reconstructing the vertebral column of the Anura, by dissolving the coccyx into about a dozen vertebrae, so that originally, say the twenty-first vertebra carried the ilia, we bridge over the enormous gap which exists between the Anura and Urodela. That whole portion of the axial continuation behind the coccyx, more or less coinciding with the position of the vent, is the transitional tail. The disappearance of both notochord and spinal cord, and the conversion of the cartilaginous elements into a continuous rod in the case of the os coccygeum, find an analogy in the hinder portion of the tail of Dipnoi and Crossopterygii, and in the tail-end of most Urodela, portions which are not homologous with the os coccygeum. The term urostyle should be restricted to such and similar modifications of the tail-end, and this latter happens to be lost by the Anura during metamorphosis. 24 ANURA CHAP. Strictly speaking, or rather in anatomical parlance, the Vertebrate tail begins with the first post-sacral vertebra. In the Anura that portion of the whole tail has retained most cartilage, and has become the coccygeum, which is required as a "backbone" for the often enormous belly. This require- ment is an outcome of the great shortening of the trunk proper (if the trunk be defined as ending with the pelvic region), and this shortening of the trunk is again intimately connected with the jumping mechanism, enlargement of the hind-limbs, elongation of the ilia, and throwing the fulcral attachment forwards as much as possible. The pre-acetabular ilio-sacral connection is carried to the extreme in the Anura. The shoulder-girdle and " sternum " are more complete than in the Urodela, there being also a pair of clavicles, fused with the precoracoidal bars. The whole apparatus presents two types. In the arciferous type the coracoids and precoracoids retain a great amount of cartilage in their distal portions, and these cartilages (the epicoracoids of some authors) overlap each other movably on one another, the right usually lying ventrally upon the left. The epicoracoidal cartilage of each side, by connecting the distal end of the coracoid with the precoracoid of the same side, forms an arc, hence "arciferous." In the firmisternal type the epicoracoidal cartilages are much reduced, and, instead of overlapping, meet in the middle line and often fuse with each other, forming thereby a firm median bar, which connects the ventral ends of the precoracoids with those of the coracoids. This type is morphologically the higher and more recent, and passes in the larval stage through the arciferous condition. It is restricted to the Eanidae, Engystomatinae, and Aglossa. Although these two types afford an excellent distinctive char- acter for the main divisions of the Anura, they are to a certain extent connected by intermediate forms in such a way, that, for instance, in Bufo and among Cystignathidae in Ceratoplirys, the two opposite epicoracoidal cartilages begin to unite at the anterior end. In many Engystomatinae the precoracoids together with the clavicles are much reduced, sometimes to thin ligaments, being in this case mostly curved back and lying closely against the coracoids ; or they may be lost completely. Very rarely the precoracoidal bars are actually much stronger than the coracoids, SHOULDER-GIRDLE and the median symphysial bar of cartilage is lost ; this is the case in Hemisus. The scapula is always large and curved into transverse, dorsally broadening blades, the dorsal greater portion of which, the so-called supra-scapula, does not ossify but calcifies. It is very doubtful if the Anura possess a true sternum, if by sternum we understand a medio- ventral apparatus which owes its origin to the ventral portions of ribs. The so-called Co. FIG. 5. — Ventral views of the shoulder-girdles of various Anura. (Slightly enlarged.) 1, Bonibinator igneus, and 2, Bufo vulgaris, as examples of the arciferous type ; 3, adult, 4, metamorphosing Rana temporaries, showing change from the arciferous into the firmisternal type ; 5, Hemisus guttatum ; 6, Breviceps gibbosus ; 7, Cacopus systoma. (5, 6, 7, after Boulenger. ) Cartilaginous parts are dotted ; ossitied parts are left white. 01, Clavicle ; Co, coracoid ; E, epicoracoidal cartilage ; H, humerus ; M, metasternum ; 0, omosternum ; P, precoracoid ; Sc, scapula ; &S, supra- scapula. sternal apparatus of the Anura consists of two pieces. One, anterior, variously named episternum, presternum, or omosternum, rests upon the united precoracoids and extends headwards, being either styliform or broadened out. Sometimes it is partly ossified, with a distinct suture at its base ; this is the case especially in the Firmisternia ; in many Arcifera the omosternum remains cartilaginous and is continuous, without a sutural break, with the cartilage of the precoracoids, indicating thereby its genetic relation to the shoulder -girdle. Hence omosternum is the 26 ANURA CHAP. preferable name. It is frequently much reduced, even absent, for instance in most Bufonidae and in the Engystomatinae. The posterior so-called sternal part may be termed metasternum, It forms the posterior counterpart of the omosternum. It is attached behind to the ' epicoracoidal cartilages, or fusing with them forms their posterior continuation. It appears mostly in the shape of a style, which is frequently ossified, and broadens out behind into a cartilaginous, partly calcified blade. In the Discoglossidae only it diverges backwards into two horns, assuming a striking resemblance to the typical xiphisternum of the Amniota. In young Anura the metasternal cartilage is intimately connected with the pericardium, an indication of its being derived not from ribs but from the shoulder-girdle. The glenoid cavity is always formed by the coracoids and by the scapula, but the precoracoid often takes part in its forma- tion, for instance in Bufonidae, Hylidae, and Discoglossidae. In the fore-limb the humerus has a crest, stronger in the males than in the females ; it assumes extraordinary strength in some Cystignathidae, notably in the male Leptodactylus. Eadius and ulna are fused into one bone. The carpalia are originally nine in number : radiale, ulnare, two centralia, and five carpalia distalia, the fifth of which is reduced to a tiny nodule or to a ligamentous vestige. The primitive condition still prevails in the Disco- glossidae. In most of the other Anura the fourth and third distal carpalia, in any case very small, fuse with the enlarged ulnar centrale ; the radial centrale comes, in the Bufonidae and Pelobatidae, into contact with the radius, so that the forearm articulates with three elements as in the Urodela, but with this difference, that the intermedium of the Urodela has been lost by the Anura. There are five metacarpalia and five fingers, but the elements of the first or thumb are nearly vestigial, so that the pollux is reduced to one or two nodules, scarcely visible externally. The normal number of the phalanges of the second to fifth fingers is 2, 2, 3, 3. The distal phalanges are generally straight, either pointed or expanded or with Y or T-shaped ends ; but in the Hylidae, in Hylambates amongst the Ranidae, and in Ceratohyla, one of the Hemiphractinae, the terminal phalanges are produced into curved claws which support the adhesive finger-discs. There are, however, many genera of different families, which possess finger-discs and have no claw-shaped PELVIC GIRDLE 2/ phalanges. The Hylidae, and many of the climbing members of the Kanidae with adhesive discs, possess an extra skeletal piece intercalated between the last and last but one phalanges of the fingers and toes. This piece, a mere interarticular cartilage in Hyla, is in the following Kaninae developed into an additional phalanx, so that their numbers are 3, 3, 4, 4 in the hand and 3, 3, 4, 5, 4 in the foot : Cassina, Hylambates, Rappia, Mega- lixalus, Rliacophorus, Chiromantis, Ixalus, and Nyctixalus. All the other Eanidae are without this additional phalanx, irrespec- tive of the presence or absence or size of digital expansions.1 The pelvic girdle looks like a pair of tongs (see Fig. 4, p. 22). The ilium is enormously elongated and is movably attached to the sacral diapophyses. This connection is always pre-acetabular in position. The ilium and ischium co-ossify com- pletely, and make up nearly the whole of the pelvis ; the pubis is very small, and remains cartilaginous unless it calcines. It rarely possesses a centre of ossification, for instance in Pelolates, where the osseous nodule is excluded from the acetabulum, recalling certain Labyrinth odonta, whose ossa pubis likewise do not reach that cavity. The latter is open or perforated in young Anura and remains so in the Discoglossidae, but in the others it becomes closed up as in the Urodela. The ventral halves of the pelvis, besides forming a symphysis, closely approach each other, just leaving room for the passage of the rectum and the urino-genital ducts. The hind-limbs are in all cases longer than the fore-limbs. The femur is slender, the tibia and fibula are fused into one bone. The tarsus is much modified by the great elongation of the two proximal tarsalia (there being no intermedium) into an astragalus and a calcaneum, both of which fuse together distally and proximally, or completely as in Pelodytes ; in the latter case the limb assumes a unique appearance, since it consists of three successive and apparently single bars of nearly equal length. The other tarsal elements, especially the more lateral ones, are practically reduced to pads. The Anura. have thereby acquired two well - marked joints, one cruro - tarsal, the other tarso- metatarsal ; this shows a high stage of specialisation in com- parison with the Urodelous and Stegocephalous type of still undefined joints. 1 Boulenger, P.Z.S. 1888, p 204. 28 ANURA CHAP. The Anura possesses five well-developed toes with normally 2, 2, 3, 4, and 3 phalanges, and the rudiments of a sixth digit, the so-called prehallux, which consists of from two to four pieces, including the one which represents its metatarsal. This prehallux, as a vestige of a once better developed digit, is exactly like the elements on the radial side of the wrist, which, we are certain, are the remnants of a once complete finger, namely the pollex. The only weighty difficulty against its interpreta- tion as a prehallux lies in the fact that hitherto no six-toed Stegocephali have been found ; but the fact that there are no Stegocephali known with more than four fingers could be used as an argument against there being a pollex -vestige in recent Anura with just as little reason. The skull of the Anura differs from that of the other recent Amphibia in the following features : — The orbital region of the primitive cranium remains carti- laginous, but further forward the cranial cavity is closed by the unpaired sphenethmoid, which forms a ring round the anterior portion of the brain -cavity, hence called " os en ceinture " by some anatomists. The frontals and parietals fuse into one pair of fronto-parietal bones, and these again can fuse together in the middle line ; as in Aglossa and Pelobates. The palatal portion of the palato-quadrate cartilage is complete, reaching forwards to the sides of the ethmoid region. The curved arch, formed by this cartilage, is covered by the following bones: (1) the quadrato- jugal, reduced to a thin splint which connects the quadrate and squamosal with the posterior end of the maxilla ; (2) the ptery- goid, always strong, extending from the distal inner corner of the quadrate to the maxilla, sometimes also to the palatine, and with a broad, median process to the parasphenoid, this process covering ventrally most of the otic region ; (3) the palatines, which vary considerably in shape and size ; they are placed transversely and meet in the middle line ; in Bovibinator and Pelodytes they are absent. The quadrates are directed transversely and backwards, in conformity with the wide gape of the mouth. The squamosal is always well developed, covering the whole of the quadrate on its outer side ; it has a forwardly directed process which ends freely in Rana, meets a corresponding process of the maxilla and forms a bony arch with it in Discoglossus, Pelolates, and others, or SKULL 29 is scarcely developed at all, for instance in Eufo. In Pelolates cultripes the squamosal is very wide and forms a junction with the fronto-parietals, thus producing a broad bridge across the temporal fossa. The nasal bones are large and meet in the middle line. Frequently they leave a space between them and the diverging anterior portion of the fronto-parietals, through which gap appears part of the dorsal surface of the ethmoid cartilage. A fontanelle between the frontals occurs in most Hylidae, many Cystignathidae, some few Bufonidae, in Pelodytes amongst the Pelobatidae, and in the Discoglossidae. The tympanic cavity is bordered in front, above, and below by the squamosal and quadrate, behind by the musculus depressor mandibulae, internally by the otic capsule, and by the cartilage of the cranium between this and the lateral occipital bone. The cavity communicates, however, by the wide and short Eustachian tube with the mouth, the passage being bordered anteriorly by the pterygoid, posteriorly by soft parts. Partly imbedded in these soft tissues is the styloid process or stylohyal, which is attached to the cranium, mostly behind the otic region, and is continued downwards into the anterior horn of the hyoid. The whole partly cartilaginous, ligamentous, and osseous string is, in fact, the entire ventral half of the hyoid arch, while the dorsal half or hyomandibular portion of this, the second visceral arch, is modified into the columellar or auditory chain. The inner end of this chain, the stapes, is inserted into and around the fenestra ovalis of the otic capsule, while the outer end is somewhat T-shaped, and is loosely attached to or near the upper rim of the tympanic ring and to the middle of the tympanic disc. In many Anura this terminal bar can be seen from the outside. The middle portion of the columellar chain is ossified, the rest remains cartilaginous. But the whole chain exhibits various modifications in different genera, especially in the number and the extent of the processes sent out by the outer cartilaginous portion ; these are attached in various ways to the tympanum and its rims. The tympanic disc is carried by a cartilaginous ring, which rests against a special process sent out by the quadrate, and is probably itself a differentiation of this element. In some very aquatic genera, but also in Pelobates, the 30 ANURA tympanic cavity is much reduced, .for instance in Bovibinator, Liopelma. In Batrachophrynus not only the cavity, but also the Eustachian tubes are suppressed. In the Aglossa only the two tubes are united into one short but wide median canal, opening at the level of the pterygoids on the roof of the mouth. The lower jaw is remarkable for the possession of mento- Meckelian cartilages, absent only in the Aglossa and Disco- glossidae. At first they are much longer than the rest of the jaw ; during the larval life they indeed form the functional jaw, and they are now covered with horny sheaths instead of teeth. Owing to the absence of teeth on them, these mento- Meckelian cartilages are later not invested by bone, although in many Anura they ultimately ossify, either retaining their sepa- rate nature or fusing partly with the dentary bones. The bulk of the lower jaw, the Meckelian cartilage, becomes invested by the dentary, a small articulare, and an inner angulare, while a splenial element is absent. The dentary itself is mostly reduced to a small dentigerous splint, while the angulare forms by far the greater part of the bony jaw. Teeth are more restricted in their occurrence than in the Urodela. On the jaws they always stand in one row. With the exception of the Hemiphractinae, Amphignathodontinae, Ceratobatrachinae, and Genyophryninae, no recent Anura carry teeth on the lower jaw, and even in these genera they are mostly much reduced in size and firmness, having all the appearance of vanishing structures. The premaxillae and maxillae are frequently furnished with teeth, except in the Dendrobatinae, Genyophry- ninae, Engystomatinae, Dendrophryniscinae, Bufonidae, Pipa, and Hymenochirus. The vomers mostly carry a series of teeth on their posterior border ; when these teeth are absent, as in many species of Bufo, a kind of substitute sometimes occurs on the palatines in the shape of a row of tuberosities. The palatines carry teeth in Hemiphractinae. The parasphenoids are rarely toothed, e.g. Triprion, Diaglena, Amphodus, and occasionally in Pelobates. A few Anura possess peculiar substitutes for teeth in the anterior portion of the lower jaw, namely, a pair of conical bony processes, sometimes rather long, but always covered by the dense gums, or investment of the jaws ; e.g. Lepidobatraclms, several Rana, e.g. R. adspersa, R. khasiana, R kulili, and Cryptotis brevis. SKIN 3 1 Cranial dermal ossifications are developed in some species of Bvfo, still more in the Hemiphractinae, and above all in Pelo- bates cultripes and in the Cystignathoid genus Calyptoceplialus. The hyoid apparatus of the Anura is complicated. It is originally composed of the hyoidean and four branchial arches, with one median, copular piece. The branchial arches form in the early life of the tadpole the elaborate framework of the filtering apparatus mentioned on p. 44. During metamorphosis the whole filter disappears, owing to resorption of the greater part of the branchial arches ; only their median portions remain, and fuse with the enlarged copular piece and the hyoidean arches into a broad shield -shaped cartilage (corpus linguae), whence several lateral processes sprout out, the posterior pair of which are generally called thyrohyals or thyroid horns. The true hyoid horns give up their larval lean-to articulation with the quadrate, become greatly elongated, and gain a new attach- ment on the otic region of the cranium. The transformation of the whole apparatus has been studied minutely by Kidewood, in Pelodytes punctatus} SKIN The epidermis of the young larvae of Amphibia is furnished with cilia, which later on are suppressed by the development of a thin hyaline layer or cuticula, but clusters of such cilia remain, at least during the larval life and during the periodical aquatic life of the adult, in the epidermal sense-organs. In the frog, currents are set up by the ciliary action at an earlier stage, and are maintained to a later stage than in the newt. In the latter the tail loses its ciliation. whereas in the frog; it remains o active almost up to the time of the metamorphosis. In tadpoles of 3-10 mm. nearly the whole surface is ciliated (Assheton).2 The cilia work from head to tail, causing the little animal, when perfectly quiet, to move forwards slowly in the water. Beneath the cuticula, in the Perennibranchiata and the larvae of the other Urodela, lies a somewhat thicker layer of vertically striated cells, the so-called pseudo-cuticula, which disappears with the transformation of the upper layers of the Malpighian cells into the stratum corneum. The latter is very thin, consists of one or two layers of flattened cells, and is shed periodically by all 1 P.Z.8. 1897, p. 577. 2 Q.J.M.S. xxxviii. 1896, p. 465. 3 2 AMPHIBIA CHAP. Amphibia in one piece. In the Urodela it generally breaks loose around the mouth, and the animal slips out of the delicate, transparent, colourless " shirt," which during this process of ecdysis or moulting becomes inverted. In the Anura it mostly breaks along the middle line of the back, the creature struggles out of it, pokes it into its mouth, and swallows it. Urodela also eat this skin. As a rule the first ecdysis takes place towards the end of the metamorphosis, -preparatory to terrestrial life. So long as the animal grows rapidly, the skin has to be shed frequently, since this corneous layer is practically dead and unyielding. Adult terrestrial Urodela do not seem to moult often, mostly only when they take to the water in the breeding season. Anura, on the other hand, moult often on land, at least every few months. The surface of the new skin is then quite moist and slimy, but it soon dries and hardens. The Malpighian stratum consists of several layers, thickest in the Perennibranchiata ; in them it contains mucous cells throughout life, in others such slime-cells are restricted to larval life. Later, regular slime -glands are developed, which open on the surface. They are very numerous, and more evenly distributed, over most parts of the body, than the specific or poison-glands, which are restricted to certain parts, often form- ing large clusters, especially on the sides of the body. They reach their greatest development in the " parotoid glands " of the Anura. Both kinds of glands are furnished with smooth muscle-fibres, which are said to arise from the basal membrane underlying and forming part of the Malpighian layer ; these muscle-cells extend later downwards into the corium. For the action of the poison, see p. 37. The stratum corneum is mostly thin, but on many parts of the body, especially in Anura, the epidermal cells proliferate and form hard spikes or other rugosities/ generally stained dark brown. With these may be grouped the nuptial excrescences so frequent in the Anura, especially on the rudiment of the thumb, and on the under surface of the joints of the fingers and toes. In many Anura, less frequently in the Urodela, the tips of the fingers and toes are encased in thicker horny sheaths, producing claws or nails. They are best developed among newts in Onycliodactylus, among the Anura in Xenopus and Hymenochirus. The horny covering of the metatarsal tubercles reaches its greatest size in SKIN 33 the digging spur or spade of Pelobates. In most of these cases the cutis is elevated into more or less wart-like papillae, covered, of course, by the proliferated and cornified epidermis. In the female of Eana temper aria nearly the whole surface of the body becomes covered with rosy papillae during the breeding season. Similar nuptial excrescences are common, and are most note- worthy in the male of the Indian Eana liebigi. The epidermis also contains sense-organs. They attain their highest development in the larvae ; later on they undergo a retrogressive change. Each of these sense-organs is a little cup-shaped papilla, visible to the naked eye. It is composed of elongated cells which form a mantle around some central cells, each of which ends in a stiff cilium perforating a thin, hyaline membrane which lines the bottom of the cup, and is perhaps the representation of the cuticula. These ciliated cells are connected with sensory fibres, the nerve entering at the bottom of the whole organ. The cilia are in direct contact with the water, but the outer rim of the whole apparatus is protected by a short tube of hyaline cuticula-like secretion. These sense-organs are, in the larvae, scattered over the head, especially near the mouth and around the eyes, whence they extend backwards on to the tail, mostly in three pairs of longitudinal rows, one near the vertebral column, the others lateral. They are supplied by the lateral branch of the vagus nerve. They disappear during the metamorphosis, at least in the Anura, with the exception of Xenopus, in which they form conspicuous white objects. The white colour is caused by the tubes becoming choked with the debris of cells or coagulating mucous matter, so that it is doubtful if these organs, which moreover have sunk deeper into the skin, are still functional. In the terrestrial Urodela these organs undergo a periodical process of retrogression and rejuven- escence. During the life on land they shrink and withdraw from the surface, and their nerves likewise diminish, but in the breeding season, when the newts take again to aquatic life, they revive, are rebuilt and become prominent on the 'surface. They are an inheritance from the fishes, in which such lateral line organs are universally present. The cutis of most Amphibia is very rich in lymph -spaces, which, especially in the Anura, assume enormous proportions, since the so-called subcutaneous connective tissue forms com- VOL. VIII D 34 AMPHIBIA CHAP. paratively few vertical septa by which the upper and denser layers, the corium proper, are connected with the underlying muscles. The spaces are filled with lymph, and into some of them the abnormally expanded vocal sacs extend, notably in Paludicola, Leptodactylus, and other Cystignathidae, and in Rhinoderma. The cutis frequently forms papillae and prominent folds, sometimes regular longitudinal keels on the sides of the back ; but dermal, more or less calcified or ossified, scales are restricted to the Stegocephali and to the Apoda, q.v., pp. 79, 87. We con- clude that the Urodela and Anura have entirely lost these organs. Dermal ossifications, besides those which now form an integral part of the skeleton, like many of the cranial membrane-bones, are rare, and are restricted to the Anura. They are least infrequent on the head, where the skin is more or less involved in the ossification of the underlying membrane-bones, for instance in Triprion, Calyptocephalus, Hemipliractus and Pelobates. The thick ossifications in the skin of the back of several species of Ceratophrys are very exceptional. In Brachycephalus ephippium these dermal bones enter into connection with the vertebrae ; small plates fuse with the dorsal processes of the first to third vertebrae, while one large and thick plate fuses with the rest of the dorsal vertebrae. Simple calcareous deposits in the cutis are less uncommon, for instance, in old specimens of Bufo vulgaris. We are scarcely justified in looking upon these various calcifications and even ossifications as reminiscences of Stego- cephalous conditions. The skin contains pigment. This is either diffuse or granular. Diffuse pigment, mostly dark brown or yellow, occurs frequently in the epidermis, even in the stratum corneum. The granular pigment is stored up in cells, the chromatophores, which send out amoeboid processes, and are restricted to the cutis, mostly to its upper stratum, where they make their first appearance. Contraction of the chromatophores withdraws the pigment from the surface, expansion distributes it more or less equally. The usual colours of the pigment are black, brown, yellow, and red. Green and blue are merely subjective colours, due to interference. A peculiar kind of colouring matter is the white pigment, which probably consists of guanine, and is likewise deposited within cells ; cf. the description of the white spots in the skin of Hyla coerulea. ii CHANGES OF COLOUR 35 Most Amphibia are capable of changing colour, the Urodela, however, far less than the Anura, some of which exhibit an extraordinary range and adaptability in their changes. The mechanism by which the change of colour is produced in frogs has been recently studied by Biedermann.1 If we examine the green skin of the common Tree-frog, Hyla arborea, under a low power and direct light, we see a mosaic of green, polygonal areas, separated by dark lines and interrupted by the openings of the skin - glands. Seen from below the skin appears black. Under a stronger power the black layer is seen to be composed of anastomosing and ramified black pigment-cells. Where the light shines through, the skin appears yellow. The epidermis itself is quite colourless. The mosaic layer is composed of polygonal interference-cells, each of which consists of a basal half which is granular and colourless, while the upper half is made up of yellow drops. Sometimes the tree-frog appears blackish, and if then the black pigment-cells are induced to contract, for instance, by warming the frog, it appears silver-grey ; in this case the pig- ment in the yellow drops is no longer diffuse, but is concentrated into a round lump lodged between the interstices of the granular portions; the black pigment -cells are likewise balled together. These black chromatophores send out numerous fine branches, which occasionally stretch between and round the polygonal cells. When each of these is quite surrounded and covered by the black processes, the frog appears black. On the other hand, when the black pigment-cells withdraw their processes, shrink up, and, so to speak, retire, then the light which passes through the yellow drops is, by interference, broken into green. Stoppage of the circulation of the blood in the skin causes the black chromatophores to contract. Carbon dioxide paralyses them and causes them to dilate. This is direct influence without the action of nerves. But stimulation of the central nerve - centres makes the skin turn pale. Low temperature causes expansion, high temperature contraction, of the chrom- atophores. Hence hibernating frogs are much darker than they are in the summer. Frogs kept in dry moss, or such as have escaped into the room and dry up, turn pale, regardless of light or darkness, probably owing to a central, reflex, nerve-stimulus. Tree-frogs turn green as the result of the contact with leaves. 1 Arch. ges. Physiol. li. 1892, p. 455. 36 AMPHIBIA CHAP. Dark frogs will turn green when put into an absolutely dark vessel in which there are leaves. This is reflex action, and blinded specimens do the same. The principal centres of the nerves which control the chromatophores, lie in the corpora bigemina and in the optic thalami of the brain. When these centres are destroyed, the frog no longer changes colour when put upon leaves, but if a nerve, for instance the sciatic, be stimulated, the corresponding portion of the body, in this case the leg, turns green. Eough surfaces cause a sensation which makes the frog turn dark. Eana seems to depend chiefly upon temperature and the amount of moisture in the air, so far as its changes of colour are concerned. Biedermann concludes that the " chromatic function of frogs in general depends chiefly upon the sensory impressions received by the skin, while that of fishes depends upon the eye." All this sounds very well, but the observations and experi- ments are such as are usual in physiological laboratories, and the frogs, when observed in their native haunts, or even when kept under proper conditions, do not always behave as the physiologist thinks they should. There is no doubt that in many cases the changes of colour are not voluntary, but reflex actions. It is quite conceivable that the sensation of sitting on a rough surface starts a whole train of processes : roughness means bark, bark is brown, change into brown ; but one and the same tree- frog does not always assume the colour of the bark when it rests, or even sleeps upon, such a piece. He will, if it suits him, remain grass -green upon a yellow stone, or on a white window - frame. I purposely describe such conditions, changes, coincidences, and discrepancies in various species, notably in Hylci arborea, If. coerulea, Rana temporaries, Bufo mridis, to show that in many cases the creature knows what it is about, and that the eye plays a very important part in the decision of what colour is to be produced. The sensory impression received through the skin of the belly is the same, no matter if the board be painted white, black, or green, and how does it then come to pass that the frog adjusts its colour to a nicety to the general hue or tone of its surroundings ? Boulenger * has given us a summary of the action of the poison of Amphibia : 1 Nat. 8d. i. 1892, p. 185. POISON 37 It is well known to all who have handled freshly-caught newts, and certain toads, especially Bombinator, that their secre- tion acts as a sternutatory, and causes irritation of the nose and eyes, the effects produced on us by Bomlinator being comparable to the early stages of a cold in the head. Many collectors of Batrachians have learned, to their discomfiture, how the intro- duction of examples of certain species into the bag containing the sport of their excursion may cause the death of the other prisoners ; for although the poison has no effect on the skin of individuals of the same species, different species, however closely allied, may poison each other by mere contact. But when inoculated the poison acts even on the same individual. Miss Ormerod, to personally test the effect, pressed part of the back and tail of a live Crested Newt between the teeth. " The first effect was a bitter astringent feeling in the mouth, with irritation of the upper part of the throat, numbing of the teeth more immediately holding the animal, and in about a minute from the first touch of the newt a strong flow of saliva. This was accompanied by much foam and violent spasmodic action, approaching convulsions, but entirely confined to the mouth itself. The experiment was immediately followed by headache lasting for some hours, general discomfort of the system, and half an hour after by slight shivering fits." Numerous experiments have shown that the poison of toads, salamanders, and newts is capable, when injected, of killing mammals, birds, reptiles, and even fishes, provided, of course, that the dose be proportionate to the size of the animal. Small birds and lizards succumb as a rule in a few minutes ; guinea- pigs, rabbits, and dogs in less than an hour. This poison of Amphibia is not septic, but acts upon the heart and the central nervous system. That of the common toad has been compared, in its effects, to that of Digitalis and Eryfhrophlaeum. Some authorities hold that the poison is an acid, others regard it as an alkaloid. Phisalix1 has come to the conclusion that toads and sala- manders are possessed of two kinds of glands, different both anatomically and physiologically. These are, first the mucous glands, spread over the greater part of the body, with an alkaloid secretion, which acts as a narcotic ; secondly, specific glands, as 1 0. £. Ac. Sci. cix. 1889, pp. 405, 482. 38 AMPHIBIA CHAP. the parotoids and larger dorsal glands, the secretion of which is acid, and acts as a convulsive. The Indians of Colombia are said to employ the secretion of Dendrobates tinctorius for poisoning their arrows. The poison is obtained by exposing the frog to a fire, and after being scraped off the back is sufficient for poisoning fifty arrows. It acts on the central nervous system, and is used especially for shooting monkeys. Concerning the use of this poison for " dyeing " parrots, see p. 272. The milky secretion of toads protects them against many enemies, although not always against the grass-snake. A dog which has once been induced to bite a toad, suffers so severely that it will not easily repeat the experiment. The handling of tree-frogs also irritates both nose and eyes. The hind limbs of the Water-frog, Eana esculenta, have a very bitter, acrid taste. In short, most, if not all, Amphibia are more or less poisonous, and it is significant that many of the most poisonous, e.g. Salamandra maculosa, Bombinator, Dendrobates, exhibit that very conspicuous combination of yellow or orange upon a dark ground, which is so widespread a sign of poison. Other instances of such warning colours, protective in a defensive sense, are the Wasps and Heloderma, the only poisonous lizard. NERVES Spinal nerves. — Each spinal nerve issues originally immedi- ately behind the neural arch of the vertebral segment to which it belongs. This iutra-vertebral position is ultimately modified into a more inter-vertebral one, owing to the predominant share of the neural arches, basidorsalia, in the composition of the whole vertebra. Consequently the nerves issue behind their corresponding vertebrae. The first spinal nerve, or N. suboccipitalis, is exceptional in several respects. It develops a dorsal and a ventral root like a typical spinal nerve, but the dorsal root soon degenerates in all Amphibia, while in the Phaneroglossal Anura the whole nerve disappears. The first spinal nerve reduced to its ventral half persists therefore only in the Apoda, Urodela, and the Aglossal Anura. It issues originally between the occiput and the atlas, but in the adult it is partly imbedded in the anterior portion of the atlas. Its own vertebra is lost, having probably been added to the cranium. NERVES 39 In the Urodela the first spinal nerve either remains separate, or it joins the second spinal, forming with it and with a branch from the third nerve the cervical plexus, which supplies the muscles of the cervical region. The third, fourth, and fifth nerves, and sometimes also the sixth, form the brachial plexus. In the Aglossal Anura N. spinalis I. mostly sends a fine thread to the second spinal nerve, the rest supplies chiefly the M. levator scapulae, in Pipa the abdominal muscles also. In all the other Anura this N. spinalis I. is lost ; occasional vestiges have been reported in Bufo vulgaris and Eana catesbiana, and remnants of it may possibly be found in Pelobatidae and Discoglos- sidae. The first actually persisting nerve of the Phaneroglossa is consequently N. spinalis II. The brachial plexus is composed as follows : — Pipa, N". spinalis II. and III. ; Xenopus and Phaneroglossa, N. spinalis III. and IV., with a small branch from the second ; the next following three nerves, numbers V., VI., and VII., behave like ordinary trunk nerves. The pelvic plexus of the Phaneroglossa is formed in Eana by the VIII. + IX. + X. + XIth nerves, the tenth issuing between the sacral vertebra and the coccyx. In Bufo and Hyla the plexus is composed of five nerves, the seventh spinal sending a branch to it. Occasionally the twelfth nerve contributes a small branch to the posterior portion of the 'plexus. This and the eleventh nerve leave the coccyx by separate holes, thereby indicating its composition. The rest of the spinal cord gives off no more recognisable nerves, owing to its reduction during the later stages of metamorphosis ; its terminal filament passes out of the posterior end of the coccygeal canal. Concerning the cranial nerves it is necessary to draw atten- tion to one point only. The last nerve which leaves the cranium of the Amphibia is the vagus or tenth cranial nerve. There is consequently no eleventh, and no twelfth or hypoglossal, pair of cranial nerves. Their homologues would be the first and second spinal nerves, but the whole tongue of the Amphibia, with its muscles, is supplied by the glossopharyngeal/or ninth cranial pair, and is morphologically not homologous with the tongue of the Amniota. 40 AMPHIBIA CHAP. RESPIRATORY ORGANS A very important and characteristic feature of the Amphibia is the development of two sets of respiratory organs : Gills and Lungs. It is as well to give definitions of these organs. LH/II/X are hollow evaginations from the ventral wall of the pharynx, and their thin, vascularised walls enable the blood to exchange, by osmosis, carbon dioxide for oxygen from the air which enters the lungs by the mouth or the nostrils, and the windpipe. The latter is unpaired, the lungs themselves are paired. Gills are highly vascularised, more or less ramified excrescences, covered by a thin epithelium of ecto- or endo-dermal origin, which permits of the exchange of carbon dioxide for oxygen from the air which is suspended in the surrounding water. It is obvious that this definition applies to all sorts of well-vascularised organs whose thin surface comes into contact with the water. Various recesses of the pharyngeal cavity, the dorsal and ventral folds of the tail-fin, nay, even any part of the skin of the body can, and does occasionally, assume additional respiratory functions. The proper definition of gills, in Vertebrates, requires, therefore, the restric- tion that they must be developed upon and carried by visceral arches. The general statement that the Amphibia breathe by lungs, and, at least during some stage of their life, also by gills, requires various restrictions. As a rule the majority of Amphibia first develop gills, later on also lungs, whereupon, during the meta- morphosis, the gills are gradually suppressed, so that the perfect animal breathes by lungs only (see p. 61). But a number of Urodela retain their gills throughout life, although the lungs are also functional. These are the Perennibranchiata, not a natural group, but a heterogenous assembly, Proteidae and Sirenidae. Some species of Amblystoma remain individually Perenni- branchiate (cf. Axolotl, p. 112). On the other hand, in some Anura the gills are almost or entirely suppressed, or restricted to the embryonic period only. Lastly, a considerable number of Salamandridae have lost their lungs ; they breathe by gills until their metamorphosis, but have in the adult state to resort to respiration by the skin (cf. p. 46). The general plan of the development of the branchial re- spiratory apparatus is as follows : — The six visceral arches, GILLS 4 1 namely, the mandibular, the hyoidean, and the four branchial arches, correspond, long before they are cartilaginous, with four main arterial arches of the truncus arteriosus. The first, the arteria hyo-mandibularis, belongs to the hyoidean and mandibular segments, the second to the first branchial, the third to the second branchial, while the fourth soon splits in two for the third and fourth or last branchial arch. On the dorsal side these branchial arterial arches combine to form the radix of the dorsal aorta. These arches, especially the three branchials, appear in newts, less clearly in frogs, as transverse ridges on the sides of the future neck. Between the arches the pharynx gradually bulges out in the shape of five lateral gill-pouches ; the first between the mandibular and the hyoidean arch, the second between the hyoidean and the first branchial arch, etc. These pouches soon break through to the outside and become gill-clefts, except the first pouch in Urodela. Before the breaking through of the clefts there appears upon the outside of the middle of the rim of each arch a little knob, which soon ramifies and forms an external gill. The knob owes its origin to the development of a blood- vessel which buds from the arterial arch, ramifies and breaks up into capillaries, and returns a little further dorsalwards into the arch. A secondary loop to the outside of the primary arterial arch is thus formed ; and whilst this outer loop sprouts out further, driving before it the likewise proliferating skin, and thus producing the gill, the middle portion of the primary arch remains in the Urodela as a short cut, but in the Anura it partly obliterates, and henceforth acts as the internal efferent vessel of the gill. When, during metamorphosis, the gills dis- appear, their intrinsic afferent and efferent vessels vanish likewise, and the short cut completes the circuit. In order to do this they have, in the Anura, to form new connections with the trunks of the afferent vessels. The arterial arches themselves are modified as follows : — The first pair become the carotids, the second form the right and left aortic arches, while the third and fourth unite and are trans- formed into the pulmonary arteries and " ductus Botalli," the last arterial arch having previously sent a branch into the developing lungs. In the Anura the third arch obliterates. The gills and clefts present various modifications. The Urodela possess three pairs of gills, one each upon the dorsal 42 AMPHIBIA CHAP. half of* the three branchial arches, just near the upper corners of the clefts ; and the skin of the body is continued upon the stem of each gill, pigmented like the rest of the surface of the body. Such a gill is more or less like a blade, standing vertically, and is composed of a stem of connective tissue, thick at the base, and, as a rule, carrying two series of fine lamellae, which, however, do not form two opposite series, but hang downwards, being, so to speak, folded down, so that the upper surface of the stem is bare, and carries the lamellae on its under side. In the Axolotl some of these lamellae are further subdivided. In Necturus they are enormously increased in numbers, but are rather short, and they stand no longer in two rows, but are crowded into one. Those of Proteus form two rows of dendritic filaments ; those of Siren are likewise much ramified. The larvae of the Urodela have four clefts. In the adult Siren these are reduced to three, the first, namely, that between the hyoid and the first branchial arch, being closed up. In Necturus, Proteus, and Typhlomolge the clefts are further reduced to two, owing to the closing up of the first and last, only those between the first, second, and third arches remaining. Amphiuma, and usually Cryptobranchus alleghaniensis, possess only one pair of clefts, while in C. japonicus and in the Salamandridae all the clefts are abolished. The gills of the Urodela are always uncovered, although a short operculum is formed from the posterior margin of the hyoidean arch; the halves of this fold meet below the throat, and persist in various terrestrial and aquatic species as the " gular fold." It reaches its greatest size just before metamorphosis, but scarcely ever produces a proper outer gill-chamber, and it does not cover the gills owing to their rather pronounced dorsal position. It is perhaps best developed in Typhlomolge, and even there its dorsal portion is continued upon the first of the three broad vertical and short-fringed blades which form the gills. A description of the gills of the Apoda will be found in the systematic part. In the Anura the gills are complicated, owing to the develop- ment of the so-called internal gills. First appear, exactly in the same way as in the Urodela, the external gills, one upon each of the first three branchial arches. In the larva of Rana esculenta, 5 mm. in length, a little protuberance appears upon the first, GILLS 43 and then upon the second arch. In the 6 mm. larva the first gill shows four knobs, the second two, the third one knob. They are always delicate and thin, although sometimes pigmented, long, and much -ramified structures. The first pair is always the largest ; well developed and persisting a long time in Eana temporaria ; smaller in E. esculenta and Bufo vulgaris ; very short, scarcely forked, in B. viridis and Hyla arborea. They are relatively largest in Alytes, while still in the egg. Numerous descriptions of these gills will be found in the systematic part. Great changes take place about the time when the fourth or last branchial arch and the pulmonary arteries are developed. This occurs in R. esculenta when the larva is about 9 mm. long. The sprouting of the gills extends gradually downwards along the arches upon their ventral halves, and these new gill- filaments or loops transform themselves into numerous dendritic bundles, resting in several thickset rows upon the hinder margin of the first to the third arch, one row only on the fourth arch, which carries no external gill. These " internal gills " look like red bolsters or thick and short -tasselled bunches. Whilst they are developing the dorsal, older gills become arrested in their growth and disappear, and at the same time a right and left opercular fold grows out from the head and covers these new gills, shutting them up in an outer branchial chamber, just like that of Teleostei and other Tectobranch fishes. This is the reason why these new gills have been called internal, and the mistaken notion has sprung up that they are comparable with the true internal gills of fishes. In reality Amphibia have only external gills. They are always covered by ectoderm, are restricted to the outside of the branchial arches, and are developed before the formation of the clefts. These gills are in many cases directly continuous with the more dorsally and more superficially placed earlier external gills ; but although nearly every one who has studied their development has observed this agreement, the old error still prevails. They are morphologically as little internal as the true internal gills of Elasmobranch embryos are external gills, because these have become so elongated that they protrude out of the gill-clefts. The fact that the Amphibia possess only external gills throws important light upon their phylogeny. Not only do the Apoda, Urodela, and Anura agree much more with each other than 44 AMPHIBIA CHAP. would be the case if the Anura possessed both internal and external gills, but the Amphibia reveal themselves also in this point as connected with the Crossopterygii and the Dipnoi, some of which fishes also possess external gills. It is of course quite possible that the Amphibia have developed these organs in- dependently, but we understand now that the latter are accessory, and not the primitive respiratory organs ; they are developed in adaptation to embryonic conditions and to prolonged larval, occasionally perennibranchiate, aquatic life (cf. the chapter 011 Neoteny, p. 63). There is no valid reason for supposing that the Stegocephali had true internal gills. We know their branchial skeleton, and we can discern even gill-rakers on the arches. Such gill-rakers occur also, although but feebly developed, in Urodela. The whole branchial framework of the Urodela and Apoda undergoes simple reductions during metamorphosis (see p. 86), but in the Anura these arches are in early tadpole life transformed into a most complicated basket-work which acts as a straining apparatus or filter, to prevent any particle of food or other foreign matter from finding its way into the delicate gills, the current of water passing from the mouth through the filter, past the gills and out of the clefts. During metamorphosis this whole elaborate apparatus is again transformed, almost beyond recognition, into the hyoidean apparatus for the support of the generally very movable and much-specialised tongue. The fact that the hyoid apparatus of the Aglossa, especially that of Xenopus, is con- structed upon the same lines, is a strong indication that these creatures have arrived at their tongueless condition through the loss of this organ, and this is intelligible in correlation with their absolutely aquatic life. The opercular folds assume great dimensions in all tadpoles. They cover the whole gill-region, thereby producing on either side an outer gill-chamber. The posterior margins of the folds gradually become continuous with the rest of the surface of the body. Each gill -chamber opens at first by one lateral canal, usually called the spiracle. This condition prevails in the tadpoles of the Aglossa. In the Discoglossidae the two canals gradually converge and combine into one median opening on the middle of the belly. In all the other Anura the right opening becomes closed, or rather its canal passes over to and joins that of the ii GILLS 45 left side, both opening by one short tube laterally on the left side, at a variable distance between the eye and the vent. Hence the elegant terms of Amphi-, Medio-, and Laevo-gyrinidae (yvplvos being the Greek for tadpole). The external gills lead to a further consideration. Protopterus possesses a vestigial external gill on the shoulder-girdle. Lepi- dosiren has them on the gill-arches, resembling piscine internal gills, and Polypterus has a large biserially fringed external gill (in some cases not disappearing until the fish is adult), which starts from the mandibular arch, at the level of the spiracle or first visceral cleft, and overlaps the operculum externally. The axis of this peculiar organ is possibly based upon the homologues of the spiracular cartilages, which themselves are the branchiostegal rays of the dorsal half of the quadrato-mandibular arch. The branchiostegal rays of the hyoidean arch, at least their material, have given rise to the elaborate opercular apparatus ; and, in con- formity herewith, the hyomandibular itself is not known to carry a gill. Quite possibly the large external gill of Polypterus is not serially homologous with other external gills — it may not be a true gill at all, it has perhaps quite a different function- — but it seems to throw light upon a mysterious pair of organs which are common in larval and young Urodela, in the larval Aglossa and in the Apoda. These are the " balancers." In Triton taeniatus, before hatching, there appears a little protuberance behind and below the eye ; it rests upon the angle of the mandibular arch, and is separated from the first trans- verse, externally visible ridge of the first branchial arch by the beginnings of the hyoidean arch. A few days later the arteria hyomandibularis sends a vessel into this knob, forms a vascular coil, and leaves it as a vein which, instead of returning into the arterial arch, passes into the veins of the body. Its epithelium is not covered with flat, but with cubical cells ; and sensory cells have not been found in it. These organs attain some size, and are shaped like rods, with thickened ends ; they are movable, and are used by the larvae as " balancers," keeping the head from sinking into the slime at the bottom. But they may have other functions besides, and it is not unlikely that they develop into sensory organs like feelers. They occur in many Salamandridae, and are not reduced until, or even after, the metamorphosis, and during this time they shift their place with relation to the eye and the mouth. 46 AMPHIBIA CHAP. The same kind of organs occur in Amblystoma.1 They appear, previous to the breaking open of the gill-clefts, as protrusions of epiblast, long before any of the external gills on the branchial arches. When the clefts have broken open, the quadrate sends out laterally a tiny crescent-shaped process a little above the jaw- joint, and this process extends to the base of the balancer, but not into it, and a bundle of muscle-cells grows into the balancer. It is easy to recognise the same organ in the extremely long thread-like structures of the larva of Xenopus. In the Apoda they are likewise present, but are retained permanently as highly specialised, probably tentacular organs (cf. p. 86, Apoda). One of the most unexpected features is the suppression of the lungs in various kinds of Salamandridae. The lungs are either reduced to useless vestiges or they are quite absent. This occurs in aquatic and terrestrial, American and European forms, and it is noteworthy that the reduction of the lungs does not apply to all the species of the various genera, nor is it restricted to one sub-family. The following list is due to the researches of H. H. Wilder,2 L. Camerano,3 E. Lonnberg,4 and G. S. Hopkins 5 : — All the Desmognathinae and Plethodontinae ; Amblystomatinae, Ambly- stoma opacum ; Salamandrinae, Salamandrina perspicillata. In Triton and other Salamandrinae the length of the lungs varies ; in some they extend more, in others less, than half way down the distance between head and pelvis. Hopkins remarks : " Two questions are naturally suggested by this apparently aberrant condition of the respiratory organs. First, what structures or organs have taken on the function of the lungs and branchiae ; and secondly, is there any modification in the form or structure of the heart which in any way may be .correlated \vith the above- mentioned peculiarities of the lungless forms ? " Wilder con- cluded that respiration was probably carried on by the skin, and perhaps, to some extent, by the mucosa of the intestine. Camerano thinks that, at least in the European forms, respiration is effected by the bucco-pharyngeal cavity, and that the skin affords no efficient aid. The left auricle in the lungless forms is much 1 Orr, Quart. J. Micr. Sci. xxix. 1889, p. 316. 2 "Lungenlose Salamandriden," Anat. Anz. 1894, p. 676 ; 1896, p. 182. 3 " Nuove ricerche anatomo-fisiologiche intorno ai Salarnandridi iiormalmente apneumoni." Torino, 1894. 4 Zool. Anz. 1896, p. 33 ; 1899, p. 545. 5 Amcr. Natural, xxx. 1886, p. 829. LUNGS VOICE 47 smaller in comparison than the right, and there is no pulmonary- vein. The auricular septum has a large aperture, the communi- cation between the auricles being larger than even in Necturus (which breathes essentially by gills). The sinus venosus, instead of opening into the right auricle only, opens more freely into the left than into the right, and the latter communicates more directly with the ventricle than the left, instead of about equally. In short, the heart of these creatures appears almost bilocular, instead of being trilocular, at least functionally. The lungs of the Urodela are always simple, extremely thin- walled bags. They are highly developed in the Anura, the walls being modified into numerous air-cells, whereby the respiratory surface is considerably increased. The lungs are filled with air by the pumping motion of the throat while the mouth is closed, the nostrils being provided with muscular valves. A muscular apparatus assists the filling of the lungs in the Anura.1 Most, if not all, Anura and some Urodela have a voice pro- duced by the larynx, which, especially in the Anura, is provided with a complicated cartilaginous and muscular apparatus and with vocal cords. The voice of the Urodela is at the best a feeble squeak. The females of the Anura are either mute or they produce a mere grunt, but that of many males is very loud, and, moreover, in many species it is intensified by vocal sacs which act as resonators. These sacs are diverticula of the lining of the mouth-Cavity, and bulge Rana esculenta, B, Bufo calamita (cf. Fig. 52, ,, , . -, p. 269). Ch, Choana, or inner nasal opening ; OUt the OUter Skin and the ^ opening of the Eustachian tube ; S, slit muscles, chiefly the mylo- leading into the vocal sac ; T, tongue ; Vo, JL. patches of teeth on the vomers. hyoid, of the throat. The nostrils and the mouth are firmly closed during the croaking. " The sacs are called internal when they are covered by the unmodified gular integument, however much this may be dis- tended ; external when their membrane projects through slits at B FIG. 6. — Internal view of the mouth of A, 1 For the mechanism of the frog's respiration, see Gaupp, Arch. Anat. 1896, p. 239. 48 AMPHIBIA CHAP. the sides of the throat, 'as in Rana esculenta (Fig. 52, p. 269), or when the skin is thinned and converted into a bladder-like pouch, as in Hyla arborea" l These sacs exhibit many modifica- tions. They may be unpaired and median, and open by two slits into the mouth, on either side below the tongue ; in Bufo one of the slits or openings, either the right or the left, is obliterated. They may be paired and symmetrical, and open one on each side of the head, below and near the posterior angle of the jaws. These modifications differ in closely allied species. They reach their greatest complication in Rhinoderma and in some of the Cystignathidae by extending far back beneath the skin into the wide lymphatic spaces. In Rhinoderma they are put to the unique use of nurseries for the young (see p. 228). Leptodactylus typhonius has a very distinct pair of outer vocal sacs and a well-marked unpaired sac which extends into the belly and com- municates with each outer sac. Several species of Paludicola, e.g. P.fuscomaculata and P. signifera, have a similar arrangement, in addition to an unpaired gular sac which can be inflated independently of the rest (see Fig. 45, p. 220). URINO-GENITAL ORGANS The kidneys and the male generative glands are still inti- mately connected with each other. The general plan is as follows : — The kidneys consist of a large number of glomeruli, produced by the coiled segmental tubes, each of which is composed of a nephrostome or funnel opening into the body-cavity, a Mal- pighian body and an efferent canal. The latter combine to form the segmental duct which opens into the cloaca. The testes, composed of a large number of sperm-producing glands, are drained by transverse canals which combine into a longitudinal canal, and this again sends off numerous efferent canals which open into the efferent canals of the kidney, so that the segmental duct (Leydig's duct of many authors) conveys both sperma and urine. In the female the network of transverse and longitudinal canals, which originally connect the generative glands with the kidney's efferent canals, is reduced in so far as the connection is 1 Boulenger, The Tailless Batrachians of Europe, Ray Soc. 1896. URINO-GENITAL ORGANS 49 Ov. '4-s.d. V.s FIG. 7. — Diagrammatic representation of modifications of the urino - genital ducts. 1, 2, Male and female Newt; 3, a tubule of the kidney; 4, male Rana ; 5, male Bufo ; 6, male Bombinator ; 7, male Discoglossus ; 8, male Alytes. a, Artery entering, and producing a coil in, the Malpighian body, M ; B, Bidder's organ ; ef.s.c, efferent segmeutal canal ; F.B, fat-body ; gl, glomerulus ; K, kidney ; l.c.c, longitudinal collecting canal ; M, Malpighian body ; Md, Miillerian duct ; N, nephrostome ; 0, ovary ; Ov, oviduct ; s.d, segmeutal duct ; T, testis ; Ur, ureter ; V.d, vas deferens ; V.s, vesicula seminalis. VOL. VIII E 50 AMPHIBIA CHAP. interrupted and the vestiges of the transverse canals are no lonuvr functional. The eggs fall into the body-cavity and are caught up by the ostium or inner abdominal opening of a special duct, the oviduct (Miillerian duct of many authors). Vestiges, more or less complete, of these oviducts persist in the males of most Amphibia. This general scheme presents some modifications in the various groups of Amphibia. The Apoda retain the most primitive conditions. The kidneys are still long and narrow, and the glomeruli are, at least in the anterior part of the organ, still strictly segmental, agreeing in number and position, each with a vertebral segment ; later, the number of the glomeruli is greatly increased, and the former agreement becomes quite disturbed. The generative glands still retain their segmental arrangement, but they are restricted to a much shorter region than the kidneys. In the male Apoda a considerable portion of the cloaca can be everted by special muscles, and acts as an intromittent organ. Both sexes possess a ventral urinary bladder. In the Urodela both kidneys and testes are much concentrated, the testes especially have lost all outward appearance of seg- mentation, and their efferent canals, connecting them with the longitudinal collecting canal, are much reduced in numbers. The greater portion of the kidneys, at least their anterior half, has all the appearance of a degenerating organ and is on the way to losing its urinary function, although it still possesses Malpighian bodies and complete ducts ; the main function of the latter is now the conveyance of the sperma. In the Perennibranchiata, 'and in some others, e.g. Spelerpes variegatus, the longitudinal collecting canal, between testis and kidney, is sometimes sup- pressed, a very simple, but pseudo- primitive arrangement. A urinary bladder is present. The cloaca is not eversible. In most Anura, e.g. Rana and Bufo (Fig. 7 ; 4, 5), the same scheme is adhered to. The efferent canals of the testis form a network, with a longitudinal canal, and open into the efferent canals of the kidney, in the substance of which they are more or less deeply imbedded. The ducts which lead out of the kidney to compose Leydig's duct, are frequently dilated, or the latter duct is much elongated, convoluted or varicated, and this whole portion is enclosed in a sheath of connective tissue, giving an ii URINO-GENITAL ORGANS 5 I appearance as if the single duct itself were dilated in the greater part of its length ; hence the occasional name of vesicula seminalis. Such means of storing the sperma enable the latter to be ejected suddenly in great quantities. In Bombinator (e) some of the most anterior seminal canals do not perforate the kidney, but run over it superficially and open directly into a branch of Leydig's duct. This branch, no doubt equivalent to a number of segmental canals which have lost their uriniferous function, is curved round the upper end of the permanent kidney, while its forward continuation, ending blindly, is the remnant of its former headward extension. This arrange- ment of Bombinator is carried further in Discoglossus (7). The testis conveys its sperma through a wide duct directly into Leydig's canal, without interfering with the kidney, and all the testicular efferent network is lost. The anterior end of Leydig's duct still extends headwards ; its middle portion acts solely as a vas deferens, while the lower portion still behaves like a typical segmental duct, conveying both sperma and urine. Lastly, in Alytes (s) the functional division of the old segmental duct has been carried to an extreme. The kidney is drained by one canal only, now a true ureter, and this is of course produced by a consolida- tion of the multiple exclusively uriniferous canals of the lower half of the kidney. The whole of the segmental duct is now in the service of the testis, and near its junction with the ureter it forms a large diverticulum or true vesicula seminalis. Eemnants of oviducts, or Miillerian ducts, are common in the male Anura ; they are best developed in Bufo, much reduced, and individually absent, in Rana. In Bombinator each duct is restricted to its upper or abdominal portion, and is attached to the vestigial headward extension of Leydig's duct. Lastly in Dis- coglossus and in Alytes all traces of oviducts seem to have vanished, at least in the adult males. It is interesting to note that in the arrangement of the urino- genital ducts the Discoglossidae are the most advanced of all Amphibia, instead of showing the mos;b primitive conditions. This is rather unexpected, but is paralleled by the epichordal type of the vertebral column. The oviducts of the Apoda and Urodela remain more or less straight ; in the viviparous species they form uterus-like dilata- tions. In the Anura they become greatly elongated during the 52 AMPHIBIA CHAP. breeding season and form many convolutions. As a rule each oviduct opens separately into the cloaca, but in Hyla they have one unpaired opening, while in Bufo and Alytes the lower parts of both oviducts are themselves confluent. All Amphibia possess Fat-bodies. They consist of richly vascularised lymphatic tissue, the meshes of which are filled with lymph-cells, globules of fat and oil. In the Apoda these bodies lie laterally to the generative glands, and along the posterior half of the kidneys. In the Urodela they accompany the anterior half of the kidney. In the Anura they are lobate, and are placed upon the anterior, end of the testes or ovaries. Their exact function is still doubtful, but it is intimately connected with that of the generative glands. The old notion, that they are simply stores of fat for the nourishment of the animal during hibernation, is quite untenable. The fat-bodies do not decrease during this period, on the contrary they attain their fullest size in the spring at the time of the rapidly awaking activity of the reproductive organs, and they enable considerable quantities of sperma and of eggs to be produced and ripened without detri- ment to, or utter exhaustion of, the animals, which often spawn before they have had time or opportunity to feed. After the spawning season the fat-bodies have dwindled down to incon- spicuous dimensions. Lastly, there is in some Anura, hitherto observed in Bufo only, a mysterious organ, intercalated between the fat-body and the testis or ovary. This is " Bidder's organ " and it seems to be a rudimentary ovary, or rather that upper, anterior portion of the whole organ which undergoes retrogressive metamorphosis. It disappears in old female toads, but in the males it sometimes assumes a size equal to, or surpassing that of the testes. The males are in this respect hermaphrodite, and cases are known in which parts of the generative glands have developed testes and egg-bearing ovaries. The spermatozoa of the Apoda and Urodela have an undulat- ing membrane along the tail, while the head-end is either pointed or truncated. Those of Spelerpes fuscus and of Ichthyophis glutinosa measure about 0'7 mm. in total length, those of the other Urodela being much smaller. A peculiarity of the Urodela is that their spermatozoa are massed together in or upon spermato- phores, an arrangement which undoubtedly facilitates the internal SPERMA-EGGS 5 3 fecundation of the female without actual copulation. The female takes up such a deposited spermatophore with the cloacal lips, squeezes the sperma out of the capsule which remains behind, and either conveys the former into a special receptaculum seminis, e.g. in Salamandra atra and in Triton, or the spermatozoa wriggle their way, thanks to the undulating tail, directly up the oviducts to the ova. The spermatophores are composed of a colourless, soft, gela- tinous mass, wThich is probably produced by the cloacal gland. The shell of jelly is in fact a cast of the cloacal cavity, reproducing all its ridges, furr6ws and folds, while a toad -stool -shaped papilla of the cloaca makes the inside lumen of the cast, e.g. in Triton. Those of Salamandra maculosa are much simpler, consisting, in conformity with the absence of a cloacal papilla, merely of a cone with a globular mass of sperma on the „„ „ 6 . T1 " ., FIG. 8.-A bell-shaped top. Inose oi Amolystoma are similar. spermatophore of The spermatozoa of the Anura show con- Triton aipestris x3. r . . (After Zeller.) 1 siderable differences in the various genera, of which, however, only the European forms have been properly examined. The " head " is wound like a corkscrew in Discoglossus, Pelolates, and Pelodytes ; spindle-shaped, more or less curved, in Rana temporaria and R. agilis, Hyla, Bufo and Bombinator, in the latter with an irregular membrane on one side ; cylindrical in Rana esculenta and R. arvalis. The tail is mostly long and filiform, but in Bufo vulgaris and Discoglossus it is provided with an undulating membrane. Their size is generally very small, only about O'l mm., excepting those of Discoglossus which reach the astonishing length of 3 mm. These differences in shape, especially that of the head, explain why species of the same genus, e.g. liana temporaria and R. arvalis, cannot fertilise each other. The eggs differ much in size, colour, and numbers. They are holoblastic, with unequal cleavage, but those species which possess an unusual amount of food-yolk, for instance Rhacophorus scklegeli and the Apoda, approach the meroblastic type of segmen- tation. As a rule, the greater the amount of yolk, the smaller is the number of eggs produced. But the number which is laid 1 Zeitschr. wiss. Zool. xlix. 1889, p. 583. 54 AMPHIBIA CHAP. during one season is not only difficult to calculate, but it varies individually, old females laying more than young specimens. Moreover, some kinds, e.g. the Discoglossidae, spawn several times in one year. Alytes, Rhinoderma, Hylodes, Rhacophorus, Pipa, in fact those kinds which are remarkable for special nursing habits, lay only a few dozen eggs at a time. Hyla arborea pro- duces up to 1000, Rana temper aria about 3000, Bvfo vulgaris averages 5000, Bufo viridis and Rana esculenta up to 10,000 and more. T. H. Morgan * has observed a £i