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Batrachia

Skeleton.

In the earliest forms of this order, the Stegocephalia, we meet with considerable variety in the constitution of the vertebrae, and these modifications have been used for their classification. All agree, however, in having each vertebra formed of at least two pieces, the suture between which persists throughout life. In this they differ from the three orders which have living representatives. Even the inferior arches or chevrons of the tail of salamanders are continuously ossified with the centra. As a matter of fact, these vertebrae have no centra proper, that part which should correspond with the centrum being formed, as a study of the development has shown (H. Gadow, 14), by the meeting and subsequent complete co-ossification of the two chief dorsal and ventral pairs of elements (tail-vertebrae of Caudata), or entirely by the pair of dorsal elements. In the Ecaudata, the vertebrae of the trunk are formed on two different plans. In some the notochord remains for a long time exposed along the ventral surface, and, owing to the absence of cartilaginous formation around it, disappears without ever becoming invested otherwise than by a thin elastic membrane; it can be easily stripped off below the vertebrae in larval specimens on the point of metamorphosing. This has been termed the epichordal type. In others, which represent the perichordal type, the greater share of the formation of the whole vertebra falls to the (paired) dorsal cartilage, but there is in addition a narrow ventral or hypochordal cartilage which fuses with the dorsal or becomes connected with it by calcified tissue; the notochord is thus completely surrounded by a thick sheath in tadpoles with imperfectly developed limbs. This mode of formation of both the arch and the greater part or whole of the so-called centrum from the same cartilage explains why there is never a neuro-central suture in these batrachians.

During segmentation of the dorsal cartilages mentioned above, which send out the transverse processes of diapophyses, there appears between each two centra an intervertebral cartilage, out of which the articulating condyle of the centrum is formed, and becomes attached B A 6 .?.. 9 ve FIG. 4. - The first two vertebrae of Necturus (Xi). Vt', Atlas; Vt2, second vertebrae; a, intercondyloid process of the atlas; b, the articular surfaces for the occipital condyles. The ribs of the second vertebra are not represented. A, Dorsal; B, ventral; C, lateral view.

either to the vertebra anterior (procoelous type) or posterior (opisthocoelous type) to it, if not remaining as an independent, intervertebral, ossified sphere, as we sometimes find in specimens of Pelobatidae. In the Caudata and Apoda, cartilage often persists between the vertebrae; this cartilage may become imperfectly separated into a cup-and-ball portion, the cup belonging to the posterior end of the vertebra. In such cases the distinction between amphicoelous and opisthocoelous vertebrae rests merely on a question of ossi A S FIG. 5. - Necturus. Posterior (A) FIG. 6. - Vertebral and ventral (B) views of the sacral column of Hymeno- vertebrae (S.V.); S.R.', S.R. 2 , sac- chirus (ventral view). ral ribs; Il, ilium; Is, ischium.

fication, and has occasionally given rise to misunderstandings in the use of these terms.

Amphicoelous (bi-concave) vertebrae are found in the Apoda and in some of the Caudata; opisthocoelous (convexo-concave) vertebrae in the higher Caudata and in the lower Ecaudata; whilst the great majority of the Ecaudata have procoelous (concavo-convex) vertebrae.

All living batrachians, and some of the Stegocephalia, have transverse processes on the vertebrae that succeed the atlas (fig. 4), some of which, in the Cau data, are divided into a dorsal and a ventral portion. Ribs are present in the lower Ecaudata (Discoglos- sidae and larval R.0- but they are never connected with a sternum. It is in fact doubtful whether the so-called sternum of batrachians, in most cases a mere plate of cartilage, has been correctly identified as such. When limbs are present, one vertebra, rarely two a.,.r (fig. 5) or three, are distinguished as sacral, giving attachment to the ilia. In the Ecaudata, the form of the transverse processes of the sacral vertebra varies very considerably, and has afforded important characters to the systematist. In accordance with the saltatorial habits of the members of this order, the vertebrae, which number from 40 to 60 in the Caudata, to upwards of in the Apoda, have become reduced to Io as the normal number, viz., eight praecaudal, one sacral and an elongate coccyx or urostyle, formed by coalescence of at least two vertebrae. In some genera this coccyx is fused with the ninth vertebra, and contributes to the FIG. 7. - Chondrocranium of Rana esculenta - ventral aspect.

rp, The rhinal process.

pnl, The praenasal processes.

an, The alinasal processes, shown by the removal of part of the floor of the left nasal chamber.

AO., The antorbital process.

pd, The pedicle of the suspensorium continued into cv, the ventral crus of the suspensorium.

cd, Its dorsal crus.

tt, The tegmen tympani.

SE, The sphen-ethmoid.

EQ., The exoccipitals.

Qu.J., The quadratojugal.

H. V. VI. Foramina by which the optic, trigeminal and portio dura, and abducens nerves leave the skull.

sacrum, whilst in a few others the number of segments is still further reduced by the co-ossification of one or two vertebrae preceding that corresponding to the normal sacral and by the fusion of the two first vertebrae, the extreme of reduction being found in FIG. 8. - The skull of Ichthyophis glutinosus. A, Dorsal; B, ventral; C, lateral view. The letters have the same signification as below.

the genus Hymenochirus, the vertebral column of which is figured here (fig. 6.) As stated above in the definition of the order, the Stegocephalia have retained most of the cranial bones which are to be found in the Crossopterygian fishes, and it is worthy of note that the bones termed post-temporals may give attachment to a further bone so prolonged backwards as to suggest the probability of the skull being connected with the shoulder-girdle, as in most teleostome fishes. This supposition is supported by a specimen from the Lower Permian of Autun, determined as Actinodon frossardi, acquired in 1902 by the British Museum, which shows a bone, similar to the so-called "epiotic cornu" of the microsaurians, Ceraterpeton and Scincosaurus, to have the relations of the supra-cleithrum of fishes, thus confirming a suggestion made by C. W. Andrews (28). As in fishes also, the sensory canal system must have been highly developed on the skulls of many labyrinthodonts, and the impressions left by these canals have been utilized by morphologists for homologizing the various elements of the cranial roof with those of Crossopterygians. The pineal foramen, in the parietal bones, is as constantly present as it is absent in the other orders. Although not strictly forming part of the skull, allusion should be made here to the ring of sclerotic plates which has been found in many of the Stegocephalia, and which is only found elsewhere in a few Crossopterygian fishes as well as in many reptiles and birds.

In the orders which are still represented at the present day, the bones of the skull are reduced in number and the "primordial skull," or chondrocranium (fig. 7), remains to a greater or less extent unossified, even in the adult. Huxley's figures of the skull of a caecilian (Ichthyophis glutinosus), fig. 8, of a perennibranchiate urodele (Necturus maculosus = Menobranchus lateralis), fig. 9, and of a frog (Rana esculents), fig. 10, are here given for comparison.

The skull, in the Apoda, is remarkably solid and compact, and it possesses a postorbital or postfrontal bone (marked 1 in the figure) which does not exist in any of the other living batrachians. The squamosal bone is large and either in contact with the frontals and parietals or separated from them by a vacuity; the orbit is sometimes roofed over by bone. The presence, in some genera, of a second row of mandibular teeth seems to indicate the former existence of a splenial element, such as exists in Siren among the Caudata and apparently in the labyrinthodonts.

In the Caudata, the frontals remain likewise distinct from the parietals, whilst in the Ecaudata the two elements are fused into one, and in a few forms (Aglossa, some Pelobatidae) the paired condition of these bones has disappeared in the adult. Prefrontal bones are present in the Salamandridae and Amphiumidae, but absent (or fused with the nasals) in the other Caudata and in the Ecaudata. In most of the former the palatines fuse with the vomers, whilst they remain distinct, unless entirely lost, in the latter. The vomer is single, or absent, in the Aglossa. In the lower jaw of most of the Ecaudata the symphysial cartilages ossify separately from the dentary bones, forming the so-called mento-meckelian bones; but these symphysial bones, so distinct in the frog, are less so in the Hylidae and Bufonidae, almost indistinguishable in the Pelobatidae and Discoglossidae, whilst in the Aglossa they do not exist any more than in the other orders of batrachians.

No batrachian is known to possess an ossified azygous supraoccipital.

Although there are four branchial arches in all the larval forms of the three orders, and throughout life in the Sirenidae, the perenni vZ.3 Pa. YrO, ?, 1Ytrh

Fr LI FIG. 9. - Lateral, dorsal and ventral views of the cranium of Necturus maculosus. In the dorsal view, the bones are removed from the left half of the skull; in the ventral view, the parasphenoid, palato-pterygoid, and vomers are given in outline. The letters have, for the most part, the same signification as before.

VII.p, Posterior division of the seventh nerve.

VII. Chorda tympani. V 1 ,V 2 ,V 3, First, second and third divisions of the trigeminal. s.s.l, Stapedio-suspensorial liga ment.

h.s.l, Hyo-suspensorial ligament. m.h.l, Mandibulo-hyoid ligament. Bb l, Bb l , Ba branchiate Proteidae have only three (see fig. ii). In the adult Apoda these arches and the hyoid fuse into three transverse, curved or angular bones (see fig. 13), the two posterior disconnected from the hyoid. In the Ecaudata, as shown by E. Gaupp (29) and by W. G. Ridewood (30), the whole hyobranchial apparatus forms a cartilaginous continuum, and during metamorphosis the branchialia disappear without a trace. The hyoid of the adult frog (fig. 12) a, Ascending process of the suspensorium.

p, Pterygo-palatine process.

q, Quadrate process.

o, Otic process.

Na, Posterior nares.

Mck, Meckel's cartilage.

Gl. (fig. to), The position of the glottis.

silbranchials.

consists of a plate of cartilage with two slender cornua, three processes on each side, and two long bony rods behind, termed the thyro-hyals, which embrace the larynx. In the Aglossa, which are remarkable for the large size and complexity of the larynx, the thyro-hyal bones are incorporated into the laryngeal apparatus, whilst the recently discovered Hymenochirus is further remarkable for the large size and ossification of the hyoidean cornua (ceratohyals), a feature tt; which, though not un 3 E /L?_ n.s.c s4. z '` common among the salamanders, is unique among the Ecaudata (31).

The pectoral girdle of the Stegocephalia is, of course, only known from the ossified elements, the identification of which has given rise to some diversity of opinion. But C. Gegenbaur's (32) interpretation may be regarded as final. He has shown that, as in the Crossopterygian and Chondrostean ganoid fishes, there co., are two clavicular elements on each side; the lower corresponds to the clavicle of reptiles and higher vertebrates, whilst the upper corresponds to the clavicle of teleostean fishes, and has been named by him "cleithrum." As stated above, there is strong evidence in favour of the view that some forms at least possessed in addition a "supracleithrum," corresponding to the supra-clavicle of bony fishes. The element often termed "coracoid" in these fossils would be the scapula. The clavicles rest on a large discoidal, rhomb o i d a 1, or T-shaped median bone, which clearly corresponds to the interclavicle of reptiles.

The pectoral girdle of the living types of batrachians is distinguishable into a scapular, a coracoidal, and a praecoracoidal region. In most of the Caudata the scapular region alone ossifies, but in the Ecaudata the coracoid is bony and a clavicle is frequently developed over the praecoracoid car tilage. In these batrachians the pectoral arch falls into two distinct types - the arciferous, in which the precoracoid (+clavicle) and coracoid are widely separated from each other distally and connected by an arched cartilage (the epicoracoid), the right usually overlapping the left; and the firmi- sternal, in which both precoracoid and coracoid nearly abut on the median line, and are only narrowly separated by the more or less fused epicoracoids. The former type is exemplified by the toads and the lower Ecaudata, whilst the latter is characteristic of the true frogs (Ranidae), although when quite young these batrachians present a condition similar to that which persists throughout life in their lower relatives. A cartilage in the median line in front of the precoracoids, sometimes supported by a bony style, is the so-called omosternum; a large one behind the coracoids, also sometimes provided with a bony style, has been called the sternum. But these names will probably have to be changed when the homologies of these parts are better understood.

The pelvic arch of some of the Stegocephalia contained a well ossified pubic element, whilst in all other batrachians only the ilium, or the ilium and the ischium are ossified. In the Ecaudata the ilium is greatly elongated and the pubis and ischium are flattened, discoidal, and closely applied to their fellows by their inner surfaces; the pelvic girdle looks like a pair of tongs.

The long bones of the limbs consist of an axis of cartilage; the extremities of the cartilages frequently undergo calcification and are thus converted into epiphyses. In the Ecaudata the radius and ulna coalesce into one bone. The carpus, which remains cartilaginous in many of the Stegocephalia and Caudata, contains six to eight elements when the manus is fully developed, whilst the number is reduced in those forms which have only two or three digits. Except in some of the Stegocephalia, there are only four functional digits in the manus, but the Ecaudata have a more or less distinct rudiment of pollex; in the Caudata it seems to be the outer digit which has been suppresssed, as atavistic reappearance of a fifth digit takes place on the outer side of the manus, as it does on the pes in those forms in which the toes are reduced to four. The usual number of phalanges is 2, 2, 3, 2 in the Stegocephalia and Caudata, 2, 2, 3, 3 in the Ecaudata. In the foot the digits usually number five, and the phalanges 2, 2, 3, 3, 2 in the Caudata, 2, 2, 3, 4, 3 in the Stegocephalia and Ecaudata. There are occasionally intercalary ossifications between the two distal phalanges (33). There are usually nine tarsal elements in the Caudata; this number is reduced in the Ecaudata, in which the two bones of the proximal row (sometimes coalesced) are much elongated and form an additional segment to the greatly lengthened hind-limb, a sort of crus secundarium. In the Ecaudata also, the tibia and fibula coalesce into one bone, and two or three small bones on the inner side of the tarsus form what has been regarded as a rudimentary digit or "prehallux." Integument. - In all recent batrachians, the skin is naked, or if small scales are present, as in many of the Apoda, they are concealed in the skin. The extinct Stegocephalia, on the other hand, were mostly protected, on the ventral surface at least, by an armour of overlapping round, oval, or rhomboidal scales, often very similar to those of Crossopterygian or ganoid fishes, and likewise disposed in transverse oblique lines converging forwards on the middle line of the belly. Sometimes these scales assumed the importance of scutes and formed a carapace, as in the "batrachian armadillo" discovered by E. D. Cope. A few frogs have the skin of the back studded with stellate bony deposits Phyllomedusa, Nototrema), whilst two genera are remarkable for possessing a bony dorsal shield, free from the vertebrae (Ceratorphrys) or ankylosed to them (Brachycephalus). None of the Stegocephalia appears to have been provided with claws, but some living batrachians (Onychodactylus, Xenopus, Hymenochirus) have the tips of some or all of the digits protected by a claw-like horny sheath.

The integument of tailed and tailless batrachians is remarkable for the great abundance of follicular glands, of which there may be two kinds, each having a special secretion, which is always more or less acrid and irritating, and affords a means of defence against the attacks of many carnivorous animals. A great deal has been A A C a..e D FIG. I o. - Dorsal,ventral,lateral and posterior views of the skull of Rana esculenta. The letters have the same signification throughout.

Pmx, Premaxilla. Hy, Hyoidean cornu Mx, Maxilla. P.S, Parasphenoid.

Vo, Vomer. An, Angulare.

Na, Nasal. D, Dentale.

S.e, Sphen-ethmoid. V, Foramen of exit Fr, Frontal. of the trige Pa, Parietal. minal.

E.0, Exoccipital. H, Of the optic. Ep, Epiotic process. X, Of the pneumo Pr.O, Pro-otic. gastric and t.t, Tegmentympani. glosso-pharyn Sq, Squamosal. geal nerves.

Q.J, Quadrato-jugal. V'. Foramen by Pt', Pterygoid, anwhich the or terior process. bito-nasal or Pt e , Internal process. first division of P1 3 , Posterior or exterthe fifth passes nal process. to the nasal Ca, Columella auris. cavity.

St, Stapes.

FIG. i I. - Hyoid and branchial apparatus of Necturus maculosus. Hh, Hypo-hyal. Ep.b1,Ep.b2,Ep.b3, Ch, Cerato-hyal. First, second Bb l , First basiand third epi branchial. branchials. Bb l , Ossified second Gl, Glottis. basibranchial.

FIG. 12. - Ventral view of the hyoid of Rana esculenta. a, Anterior; b, lateral; c, posterior processes; d, thyrohyals.

published on the poisonous secretion of batrachians (34), which is utilized by the Indians of South America for poisoning their arrows. Some of the poison-secreting glands attain a greater complication of structure and are remarkable for their large size, such as the so called "parotoid" glands on the back of the head in toads and salamanders.

m In all larval forms, in the Caudata, and in a few of the Ecaudata (Xenopus, for instance), the epidermis becomes modified in relation with the termination of sensory nerves, and gives rise to organs of the same nature as those of the lateral line of fishes. In addition to diffuse pigment (mostly in the epidermis), the skin contains granular pigment stored up r' in cells, the chromatophores, restricted to the cutis, which are highly mobile and send out r2 branches which, by contraction and expansion, may rapidly alter the coloration, most batrachians being in this respect quite comparable to the famous chameleons. Besides white (guanine) cells, the pigment includes black, brown, yellow and red. The green and blue, so frequent in frogs and newts, are merely subjective colours, due to interference. On the mechanism of the change of colour, cf. W. Biedermann (35).

One of the interesting recent discoveries is that of the "hairy" frog (Trichobatrachus), in which the sides of the body and limbs are covered with long villosities, the function of which is still unknown (36).

The nuptial horny asperities with which the males of many batrachians are provided, R$4 for the purpose of clinging to the females, will be noticed below, under the heading Pairing and Oviposition. Dentition. - In the Microsauria and Branchiosauria among the Stegocephalia, as in the other orders, the hollow, conical or slightly curved teeth exhibit simple or only slightly folded walls. But in the Labyrinthodonta, grooves are more or less marked along the teeth and give rise to folds of the wall which, extending inwards and ramifying, produce the complicated structure, exhibited by transverse sections, whence these batrachians derive their name; a somewhat similar complexity of structure is known in some holoptychian (dendrodont) Crossopterygian fishes. In the remarkable salamander Autodax, the teeth in the jaws are compressed, sharp-edged, lancet shaped. The teeth are not implanted in sockets, but become ankylosed with the .ttr c bones that bear them, and are replaced by FIG. Vent others developed at their bases. Teeth are 3. - Ventral present in the jaws of all known Stegocephalia view of the head and Apoda and of nearly all Caudata, Siren and trunk of Ichthy- alone presenting plates of horn upon the ophis glutinosus. gingival surfaces of the premaxillae and of Mn, Mandible. the dentary elements of the mandible. But Hy, Hyoid. they are nearly always absent in the lower Br', Br 2, Br a , Branjaw of the Ecaudata (exceptions in Hemi- chial arches. phractus, Amphignathodon, Amphodus, Cerato- Gl, Glottis. batrachus, the male of Dimorphognathus), many Tr, Trachea. of which (toads, for instance) are entirely Ivc, Inferior vena edentulous.

cava. There is great variety in the distribution V, Ventricle. of the teeth on the palate. They may occur Au, Auricles. simultaneously on the vomers, the palatines, Rsvc, Lsvc, right the pterygoids and the parasphenoid in and left supesome of the Stegocephalia (Dawsonia, Seeleya, rior cavae. Acanthostoma), on the vomers, palatines and Ta, Truncus arparasphenoid in many salamandrids (Pletho- teriosus. dontinae and Desmognathinae), on the vomers, Ao, Left aortic Pterygoids and parasphenoid (some Pelobates), arch. on the vomers and parasphenoid (Triprion, P.A. Right pulmon- Amphodus), whilst in the majority of other ary artery. The batrachians they are confined to the vomers pericardium and palatines or to the vomers alone (37).

(lightly shaded) As regards the alimentary organs, it will extends as far suffice to state, in this very brief sketch, that as the bifurcaall batrachians being carnivorous in their tion of the perfect condition, the intestine is never very synangium. long and its convolutions are few and simple.

But the larvae of the Ecaudata are mainly herbivorous and the digestive tract is accordingly extremely elongate and coiled up like the spring of a watch. The gullet is short, except in the Apoda. The tongue is rudimentary in the perennibranchiate Caudata, well developed, and often protrusile, in the Salamandridae and most of the Ecaudata, totally absent in the Aglossa.

527 The organs of circulation cannot be dealt with here; the most important addition made to our knowledge in recent years being found in the contributions of F. Hochstetter (38) and of G. B. Howes (39), dealing with the azygous (posterior) cardinal veins in salamanders and some of the Ecaudata. The heart is situated quite forward, in the gular or pectoral region, even in those tailed batrachians which have a serpentiform body, whilst in the Apoda (fig. 13) it is moved back to a distance which is comparable to that it occupies in most of the snakes.

The Respiratory Organs

The larynx, which is rudimentary in most of the Caudata and in the Apoda, is highly developed in the Ecaudata, and becomes the instrument of the powerful voice with which many of the frogs and toads are provided. The lungs are long simple tubes in some of the perennibranchiate Caudata; they generally shorten or become cellular in the salamandrids, and attain their highest development in the Ecaudata, especially in such forms as the burrowing Pelobates. Although the lungs are present in such forms as preserve the gills throughout life, it is highly remarkable that quite a number of abranchiate salamanders, belonging mostly to the subfamilies Desmognathinae and Plethodontinae, are devoid of lungs and breathe entirely by the skin and by the bucco-pharyngeal mucose membrane (20). Some of the Salamandrinae show the intermediate conditions which have led to the suppression of the trachea and lungs. In the Apoda, as in many serpentiform reptiles, one of the lungs, either the right or the left, is much less developed than the other, often very short.

Urino-genital Organs

The genital glands, ovaries and testes, are attached to the dorsal wall of the body-cavity, in the immediate vicinity of the kidneys, with which the male glands are intimately connected. The oviducts are long, usually more or less convoluted tubes which open posteriorly into the cloaca, while their anterior aperture is situated far forward, sometimes close to the root of the lung; their walls secrete a gelatinous substance which invests the ova as they descend. In most male batrachians the testes are drained by transverse canals which open into a longitudinal duct, which also receives the canals of the kidneys, so that this common duct conveys both sperma and urine. In some of the discoglossid frogs, however, the seminal duct is quite independent of the kidney, which has its own canal, or true ureter. Many of the Ecaudata have remnants of oviducts, or Miillerian ducts, most developed in Bufo, which genus is also remarkable as possessing a problematic organ, Bidder's organ, situated between the testis and the adipose or fat-bodies that surmount it. This has been regarded by some anatomists as a rudimentary ovary. Female salamandrids are provided with a receptaculum seminis. Copulatory organs are absent, except in the Apoda, in which a portion of the cloaca can be everted and acts as a penis. The urinary bladder is always large.

The spermatozoa have received a great share of attention, on the part not only of anatomists and physiologists, but even of systematic workers (40). This is due to the great amount of difference in structure and size between these elements in the various genera, and also to the fact that otherwise closely allied species may differ very considerably in this respect. The failure to obtain hybrids between certain species of Rana has been attributed principally to these differences. The spermatozoa of Discoglossus are remarkable for their great size, measuring three millimetres in length.

Pairing and Oviposition. - Batrachians may be divided into four categories under this head: - (t) no amplexation; (2) amplexation without internal fecundation; (3) amplexation with internal fecundation; (4) copulation proper. The first category embraces many aquatic newts, the second nearly all the Ecaudata, the third the rest of the Caudata, and the fourth the Apoda.

In the typical newts (Molge) of Europe, the males are adorned during the breeding season with bright colours and crests or other ornamental dermal appendages, and, resorting to the water, they engage in a lengthy courtship accompanied by lively evolutions around the females, near which they deposit their spermatozoa in bundles on a gelatinous mass, the spermatophore, probably secreted by the cloacal gland. This arrangement facilitates the internal fecundation of the female without copulation, the female absorbs the spermatozoa by squeezing them out of the spermatophore between the cloacal lips. Other newts, and many salamanders, whether terrestrial or aquatic, pair, the male embracing the female about the fore limbs or in the pelvic region, and the males of such forms are invariably devoid of ornamental secondary sexual characters; but in spite of this amplexation the same mode of fecundation by means of a spermatophore is resorted to, although it may happen that the contents of the spermatophore are absorbed direct from the cloaca of the male. The spermatozoa thus reach the eggs in the oviducts, where they may develop entirely, some of the salamanders being viviparous.

In all the tailless batrachians (with the exception of a single known viviparous toad),the male clings to the female round the breast, at the arm-pits, or round the waist, and awaits, often for hours or days, the deposition of the ova, which are immediately fecundated by several seminal emissions.

The fourth category is represented by the Apoda or Caecilians in which, as we have stated above, the male is provided with an intromittent organ. Some of these batrachians are viviparous.

In those species in which the embrace is of long duration the limbs of the male, usually the fore limbs (pleurodele newt, Ecaudata), rarely the hind limbs (a few American and European newts), according to the mode of amplexation, acquire a greater development, and are of ten armed with temporary horny excrescences which drop off after the pairing season. These asperities usually form brush-like patches on the inner side of one or more of the digits, but may extend over the inner surface of the limbs and on the breast and chin; the use of them on these parts is sufficiently obvious, but they are sometimes also present, without apparent function, on various parts of the foot, as in Discoglossus, Bombinator, and Pelodytes. In some species of the South American frogs of the genus Leptodactylus the breast and hands are armed with very large spines, which inflict deep wounds on the female held in embrace.

In most of the Caudata, the eggs are deposited singly in the axils of water plants or on leaves which the female folds over the egg with her hind limbs. The eggs are also deposited singly in some of the lower Ecaudata. In many of the Ecaudata, and in a few of the Caudata and Apoda, the eggs are laid in strings or bands which are twined round aquatic plants or carried by the parent; whilst in other Ecaudata they form large masses which either float on the surface of the water or sink to the bottom.

A few batrachians retain the ova within the oviducts until the young have undergone part or the whole of the metamorphosis. Viviparous parturition is known among the Caudata (Salamandra, Spelerpes fuscus), and the Apoda (Dermophis thomensis, Typhlonectes cornpressicauda); also in a little toad (Pseudophryne vivipara) recently discovered in German East Africa (41).

Development and Metamorphosis.-In a great number of batrachians, including most of the European species, the egg is small and the food-yolk is in insufficient quantity to form an external appendage of the embryo. But in a few European and North American species, and in a great many inhabitants of the tropics, the egg is large and a considerable portion of it persists for a long time as a yolk-sac. Although the segmentation is always complete, it is very irregular in these types, some of which make a distinct approach to the meroblastic egg.

With the exception of a number of forms in which the whole development takes place within the egg or in the body of the mother, batrachians undergo metamorphoses, the young passing through a free-swimming, gill-breathing period of considerable duration, during which their appearance, structure, and often their regime, are essentially different from those of the mature form. Even the fossil Stegocephalia underwent metamorphosis, as we know from various larval remains first described as Branchiosaurus. They are less marked or more gradual in the Apoda and Caudata than in Ecaudata, in which the stage known as tadpole is very unlike the frog or toad into which it rather suddenly passes (see Tadpole). In the Caudata, external gills (three on each side) persist until the close of the metamorphosis, whilst in the Apoda and Ecaudata they exist only during the earlier periods, being afterwards replaced by internal gills.

Many cases are known in which the young batrachian enters the world in the perfect condition, as in the black salamander of the Alps (Salamandra atra), the cave salamander (Spelerpes fuscus), the caecilian Typhlonectes, and a number of frogs, such as Pipa, Rhinoderma, Hylodes, some Nototrema, Rana opisthodon, &c. A fairly complete bibliographical index to these cases and the most remarkable instances of parental care in tailless batrachians will be found in the interesting articles by Lilian V. Sampson (42), and by G. Brandes and W. Schoenichen (43). It will suffice to indicate here in a synoptic form, as was done by the present writer many years ago, when our knowledge of these wonders of batrachian life was far less advanced than it is now, the principal modes of protection which are resorted to: I. Protection by means of nests or nurseries.

A. In enclosures in the water.-Hylafaber. B. In nests in holes near the water.-Rhacophorus, Leptodactylus. C. In nests overhanging the water.-Rhacophorus, Chiromantis, Phyllomedusa. D. On trees or in moss away from the water.-Rana opisthodon, Hylodes, Hylella platycephala. E. In a gelatinous bag in the water.-Phrynixalus, Salamandrella. 2. Direct nursing by the parents.

A. Tadpoles transported from one place to another.- Dendrobates, Phyllobates, Sooglossus. B. Eggs protected by the parents who coil themselves round or "sit" on them.-Mantophryne, Desmognathus, Autodax, Plethodon, Cryptobranchus, Amphiuma, Ichthyophis, Hypogeophis, Siphonops. C. Eggs carried by the parents.

(a) Round the legs, by the male.-Alytes. (b) On the back, by the female.

(I) Exposed.-Hyla goeldii, H. evansii, Ceratohyla. (2) In cell-like pouches.-Pipa.

(3) In a common pouch.-Nototrema, Amphignathodon. (c) On the belly.

(I) Exposed, by the female.-Rhacophorus ticulatus. (2) In a pouch (the produced vocal sac), by the male.-Rhinoderma. (d) In the mouth, by the female.-Hylambates brevirdstris. Geographical Distribution.-If a division of the world according to its batrachian faunae were to be attempted, it would differ very considerably from that which would answer for the principal groups of reptiles, the lizards especially. We should have four great realms:-(1) Europe and Northern and Temperate Asia, Africa north of the Sahara (palaearctic region) and North and Central America (nearctic region); (2) Africa and South-Eastern Asia (Ethiopian and Indian region); (3) South America (neotropical region); and (4) Australia (Australian region). The first would be characterized by the Caudata, which are almost confined to it (although a few species penetrate into the Indian and neotropical regions), the Discoglossidae, mostly Europaeo-Asiatic, but one genus in California, and the numerous Pelobatidae; the second by the presence of Apoda, the prevalence of firmisternal Ecaudata and the absence of Hylidae; the third by the presence of Apoda, the prevalence of arciferous Ecaudata and the scarcity of Ranidae, the fourth by the prevalence of arciferous Ecaudata and the absence of Ranidae, as well as b y the absence of either Caudata or Apoda. Madagascar might almost stand as a fifth division of the world, characterized by the total absence of Caudata, Apoda, and arciferous Ecaudata. But the close relation of its very rich frog-fauna to that of the Ethiopian and Indian regions speaks against attaching too great importance to these negative features. It may be noted here that no two parts of the world differ so considerably in their Ecaudata as do Madagascar and Australia, the former having only Firmisternia, the latter only Arcifera. Although there is much similarity between the Apoda of Africa and of South America, one genus being even common to both parts of the world, the frogs are extremely different, apart from the numerous representatives of the widely distributed genus Bufo. It may be said that, on the whole, the distribution of the batrachians agrees to some extent with that of fresh-water fishes, except for the much less marked affinity between South America and Africa, although even among the former we have the striking example of the distribution of the very natural group of the aglossal batrachians, represented by Pipa in South America and by Xenopus and Hymenochirus in Africa.

Bibliography.-(1) On the use of the names Batrachia and Amphibia, cf. E. D. Cope, Geol. Mag. (3) ii., 1885, p. 575; G. Baur, Science (2), vi., 1897, pp. 170, 372; B. G. Wilder, t.c. p. 295; T, Gill, t.c. p. 446; O. P. Hay, t.c. p. 773; T. Gill, Science (2), xx., 1900, p. 730; L. Steineger, op. cit. xx., 1904, p. 924. (2) E. Fraas, "Die Labyrinthodonten der schwabischen Trias," Palaeontogr. xxxvi., 1889, p. 1. (3) Proc. Zool. Soc., 1904, ii. p. 170. (4) E. D. Cope, "Synopsis of the Extinct Batrachia of North America," Proc. Ac. Philad., 1868, p. 208. (5) "Researches on the Structure, Organization and Classification of the Fossil Reptilia, vii" Phil. Trans. clxxxiii. (B), 1892, p. 311. (6) Cambridge Natural History, viii. (1901). (7) "Die Urvierfiissler (Eotetrapoda) des sachsischen Rotliegenden," Allgem. verstdndl. naturh. Abh., Berlin, 1891, No. 15; "Die Entwicklungsgeschichte von Branchiosaurus amblystomus," Zeitschr. deutsch. geol. Ges., 1886, p. 576. (8) C. Emery, "Ober die Beziehungen des Chiropterygium zum Ichthyopterygium," Zool. Anz. x., 1887, p. 185; E. D. Cope, "On the Phylogeny of the Vertebrata," Proc. Amer. Philos. Soc. xxx., 1892, p. 280; H. B. Pollard, "On the Anatomy and Phylogenetic Position of Polypterus," Zool. Jahrb. Anat. v., 1892, p. 414; G. Baur, "The Stegocephali: a Phylogenetic Study," Anat. Anz. xi., 1896, p. 657; L. Dollo, "Sur le phylogenie des dipneustes," Mem. soc. beige geol. ix., 1895, p. 79; T. Gill, "On the Derivation of the Pectoral Member in Terrestrial Vertebrates," Rep. Brit. Ass., 1897, p. 697. (9) E. D. Cope, "The Origin of the Mammalia," Proc. Amer. Philos. Soc. xxii., 1884, p. 43; cf. Discussion on Origin of Mammals, Proc. Intern. Congr. Zool., Cambridge, 1898; also H. Gadow, "The Origin of the Mammalia," Z. f. Morphol. iv., 1902, p. 345; and R. Broom, Rep. Brit. Ass., 1905, p. 437. (10) A. Fritsch, Fauna der Gaskohle and der Kalksteine der Permformation Bohmens, vols. i. and ii (Prague, 1879-1885, 4to); H. Credner, "Die Stegocephalen aus dem Rotliegenden des Plauenschen Grundes bei Dresden," Zeitschr. deutsch. geol. Ges., 1881-1894; J. W. Dawson, "On the Results of Recent Explorations of Erect Trees containing Animal Remains in the Coal Formation of Nova Scotia," Phil. Trans. clxxiii., 1882, p. 621; H. B. Geinitz and J. V. Deichmiiller, "Die Saurier der unteren Dyas von Sachsen," Palaeontogr. xxix., 1882, p. I; A. Gaudry, Les Enchainements du monde animal dans les temps geologiques, fossiles primaires (Paris, 1883, 8vo), p. 251; E. D. Cope, "The Batrachia of the Permian Period of North America," Amer. Nat. xviii., 1884, p. 26: E. Fraas, "Die Labyrinthodonten der schwabischen Trias," Palaeontogr. xxxvi., 1889, p. I; L. v. Ammon, Die permischen Amphibien der Rheinpfalz (Munich, 1889-1891, 4to); R. Lydekker, Catalogue of the Fossil Reptilia and Amphibia in the British Museum, part iv. (London, 1890, 8vo); E. Fraas, Die schwdbischen TriasSaurier nach dem Material der k. Naturalien-Sammlung in Stuttgart zusammengestellt (Stuttgart,1896, 4to); O. Jaekel, "Die Organization von Archegosaurus," Zeitschr. deutsch. geol. Ges. xxviii., 1896, p. 505; F. Broili, "Ein Beitrag zur Kenntnis von Eryops megacephalus," Palaeontogr. xlvi., 1899, p. 61. (11) " Amphibian Footprints from the Devonian," Amer. Journ. Sci. ii., 1896, P. 374(12) "Decouverte du plus ancien amphibien connu ... dans le famennien superieur de Modave," Bull. soc. beige geol. xv., 1888, p. cxx. (13) "A Batrachian Armadillo," Amer. Nat. xxix., 1895, p. 99 8. (14) C. Gegenbaur, Untersuchungen zur vergleichenden Anatomie der Wirbels¢ule bei Amphibien and Reptilien (Leipzig, 1862, 4to); H. Gadow, "On the Evolution of the Vertebral Column of Amphibia and Amniota," Phil. Trans. clxxxvii. (B), 1896, p. I. (15) R. Wiedersheim, Die Anatomie der Gymnophionen (Jena, 1879, 4to); W. Peters, "Ober die Einteilung der Caecilien," Mon. Berl. Ac., 18 79, p. 924; G. A. Boulenger, Catalogue of Batrachia Gradientia s. Caudata and Batrachia Apoda in the Collection of the British Museum (London, 1882, 8vo), and "A Synopsis of the Genera and Species of Apodal Batrachians," P.Z.S., 18 95, p. 401. (16) "On the Structure and Affinities of the Amphiumidae," Proc. Amer. Philos. Soc. xxiii., 1886, p. 442. (17) Ergebnisse naturwissenschaftlichen Forschungen auf Ceylon, ii. (Wiesbaden, 1887-1890, 4to). (18) "The Chondrocranium of the Ichthyopsida," Stud. Biol. Lab. Tufts Coll. No. 5, 1898, p. 147. (19) G. A. Boulenger, Catalogue, &c., 1882. (20) H. H. Wilder, "Lungenlose Salamandriden," Anat. Anz. ix., 1894, p. 216; L. Camerano, "Ricerche anatomofisiologiche intorno ai Salamandridi normalmente apneumoni," Atti Acc. Toxin. xxix., 18 94, p. 705, and xxxi., 1896, p. 512; H. H. Wilder, "Lungless Salamanders," Anat. Anz. xii., 1896, p. 182; E. Loennberg, "Notes on Tailed Batrachians without Lungs," Zool. Anz. xix., 1896, p. 33. (21) "Note sur le batracien de Bernissart," Bull. mus. belg. iii., 1884, p. 85. (22) G. A. Boulenger, Catalogue of Batrachia Salientia s. Ecaudata in the Collection of the British Museum (London, 1882, 8vo). (23) "On the Development of the Vertebral Column in Pipa and Xenopus," Anat. Anz. xiii., 18 9 8, p. 359. (24) G. A. Boulenger, "On Hymenochirus, a New Type of Aglossal Batrachians," Ann. and Mag. N.H. (7), iv., 1899, p. 122. (25) L. M. Vidal, Mem. Ac. Barcelona (3), iv., 1902, No. 18, pl. iv. (26) W. Wolterstorff, "Ober fossile FrOsche, insbesondere Palaeobatrachus," Jahresb. Nat. Ver. Magdeb., 1885 and 1886. (27) W. Peters, "Ober die Entwickelung eines Batrachiers, Hylodes martinicensis, ohne Metamorphose," Mon. Berl. Ac., 1876, p. 709; A. Kappler, "Die Tierwelt im hollandischen Guiana," Das Ausland, 1885, p. 358 G. A. Boulenger, "Reptiles and Batrachians of the Solomon Islands," Trans. Zool. Soc. xii., 1886, p. 51; H. v. Ihering, "On the Oviposition of Phyllomedusa iheringii," Ann. and Mag. N.H. (5), xvii., 1886, p. 461; H. H. Smith, "On Oviposition and Nursing in the Batrachian genus Dendrobates," Amer. Nat. xxi., 1887, p. 307; G. B. Howes, "Notes on the Gular Brood-pouch of Rhinoderma darwini," P.Z.S., 1888, p. 231; W. J. Holland, "Arboreal Tadpoles," Amer. Nat. xxiii., 1889, p. 383; E. A. Goeldi, "Contribution to the Knowledge of the Breeding Habits of some Tree-frogs of the Serra dos Orgaos, Rio de Janeiro, Brazil," P.Z.S., 18 95. p. 89; G. A. Boulenger, "On the Nursing Habits of two South American Frogs," P.Z.S., 1895, p. 209; A. Brauer, "Ein neuer Fall von Brutpflege bei Froschen," Zool. Jahrb. Syst. xi., 1898, p. 89; S. Ikeda, "Notes on the Breeding Habit and Development of Rhacophorus schlegelii," Annot. Zool. Japan. i., 1898, p. I 13; G. Brandes, "Larven zweier Nototrema-Arten," Verh. deutsch. zool. Ges., 18 99, p. 288; L. v. Mehely, "Beitrage zur Kenntnis der Engystomatiden von Neu-Guinea," Termes. Fuzetek, Budapest, xxiv., 1901, p. 216; G. A. Boulenger, "Ceratohyla bubalus carrying eggs on its back," P.Z.S., 1903, ii. p. 115; Idem. " Description of a new Tree-frog of the genus Hyla, from British Guiana, carrying eggs on the back," op. cit., 1904, ii. p. 106; H. S. Ferguson, "Travancore Batrachians," J. Bombay N.H. Soc. xv., 1904, p. 499. (28) Geol. Mag. iv., ii., 18 95, p. 83. (29) "Das Hyobranchial-Skelett der Anura," Morph. Arb. iii., 18 94, P. 399. (30) "On the Structure and Development of the Hyobranchial Skeleton of the Parsley Frog," P.Z.S., 1897, p. 577. (31) W. G. Ridewood, "On the Hyobranchial Skeleton and Larynx of H y menochirus," J. Linn. Soc. xxviii., 1899, P. 454(32) Morphol. Jahrb. xxiii., 1895, p. I. (33) G. B. Howes and A. M. Davies, P.Z.S., 1888, p. 495. (34) G. A. Boulenger, "The Poisonous Secretion of Batrachians," Nat. Science, i., 1892, p. 185; F. Gidon, Venins multiples et toxicite humorale chez les batraciens (Paris, 1897, 8vo). (35) Arch. Ges. Physiol. li., 1892, P. 455. (36) G. A. Boulenger, P.Z.S., 1900, P. 433, and 1901, ii. p. 709; H. Gadow, Anat. Anz. xviii., 1900, p. 588. (37) G. A. Boulenger, "On the Presence of Pterygoid Teeth in a Tailless Batrachian, with remarks on the Localization of Teeth on the Palate," P.Z.S., 1890, p. 664. (38) Morphol. Jahrb. xiii., 1887, p. 119. (39) P.Z.S., 1888, p. 122.

(40) G. A. Boulenger, Tailless Batrachians of Europe (1897), p. 75.

(41) G. Tornier, "Pseudophryne vivipara, ein lebendig gebarender Frosch," Sitzb. Ak. Ben. xxxix., 1905, p. 8 55. (42) "Unusual Modes of Breeding and Development among Anura," Amer. Nat. xxxiv., 1900, p. 405. (43) "Brutpflege der schwanzlosen Batrachier," Abh. Nat. Ges., Halle, xxii., 1901, p. 395. (G. A. B.)