T. viridescens is common throughout the Northern and Eastern parts of the United States. Large females are about 11 cm. long, the males 1 cm. less. The general colour above is brown, with a tinge of green; on each side of the trunk, with a row of bright vermilion spots; the under parts are orange, studded with small black dots. Half-grown specimens are brownish red, with the same lateral red spots as the adult. According to Jordan,^[61] this voracious species lives chiefly on the larvae of insects, on small molluscs such as Cyclas and Planorbis, on earthworms and on small Crustacea. It is eminently aquatic in the adult stage. The eggs are laid from April to June, the period lasting for one individual four to six weeks, or even longer. One female laid 108 eggs in all from 20th April to 30th May. After having selected a suitable plant, for instance an Anacharis or a bunch of Fontinalis leaflets, she bestrides the plant and gathers in the surrounding shoots with her hind-limbs, pressing the leaves closely around the cloaca. She next turns on her side, or occasionally on her back; with fore-limbs outstretched and rigid, with hind-limbs and leaves completely hiding the cloaca, she remains perfectly motionless for six to eight minutes. Then she slowly leaves the "nest," which now holds an egg well protected by a tangle of shoots glued together by the gelatinous secretion poured out of the cloaca. Jordan concludes, from the fact that he never found spermatozoa in the oviducts, that the eggs are fertilised just before they are expelled, when passing the receptaculum seminis.

The metamorphosed young pass their life on land under stones and logs as the so-called red variety, which is merely a stage in the life-history of the species. It seems to take them several years to reach maturity, and to become again typically aquatic. Young, red individuals which I have myself kept, have behaved for more than a year like the young of other newts, spending their time under moss and bark without going into the water.

The change from the red-spotted stage has been exhaustively studied by Gage.^[62] He remarks that this species is very common near Ithaca, in an upland forest and along the head-waters of the Susquehannah. The transformation takes place either in the autumn or in the spring, either while the newt is still on land, or after entering the water.

Of two which were kept in a jar with moist wood, one was especially brilliant, but within two weeks it assumed, in the middle of September, the characteristic coloration of the viridescent form. The two specimens were in the jar until the following July, when they were placed where they could enter the water. This they did with great readiness, and they remained submerged for a considerable time at first. The time under water increased in length, until within two or three days the pharyngeal respiration under water was fully established. On the other hand, viridescent specimens never reassume the red garb when kept out of the water.

Red specimens entering the water in the spring, changed into the greenish form within a few weeks, and established the pharyngeal respiration, losing the ciliated oral epithelium. Branchiate larvae and the adult aquatic forms have non-ciliated epithelium, and the cilia are re-established when a green specimen is forced again to live on land. Ciliation always exists in the red stage, and in the green stage before the newt has taken to the water. The cilia sweep towards the stomach.

The three following South European species belong to the Euproctus group, so called on account of the mostly conical, backward directed, and vividly coloured vent.

T. asper s. pyrenaeus.–The Pyrenean newt has hitherto been found only in the Pyrenees, for instance in Lac Bleu and Lac d'Oncet, which latter lies about 7000 feet above the level of the sea. According to Bedriaga,^[63] it prefers lakes which are supplied during the whole summer with water from glaciers. It is very sluggish, only moving to breathe and when in search of food, which consists of worms and insects. The general colour is greenish brown, dark above; the under side of the head and body are bright orange red in the female, yellow in the male; dark spots separate this bright colour from the flanks. The tail has a narrow ventral stripe of bright red and yellow. The cloaca of the female is bright red, that of the male dull grey. The total length amounts to about 4 inches or 10 cm.

The pairing time is the end of June, or later in cold seasons. The male gets hold of the female by forming a noose with its tail round her; it lies underneath, the cloacae being pressed together so that the spermatozoa can be taken in directly. The larvae have large yellow-green spots on the back and sides, and a bright red ventral tail-fin; when metamorphosed the greenish spots become more confluent on the back, producing a broad spinal band. Larvae which live in deep water are dark, while those in sunny places are light-coloured and spotted with yellow.

T. montanus in Corsica and T. rusconii in Sardinia are allied forms, but the males are distinguished by a spur-like process or dilatation at the end of the fibula.

T. waltli, the Iberian Newt, is olive-brown above, yellowish with blackish markings below. The tail has a yellow or orange ventral line. There is no crest. A remarkable peculiarity of this species (which it shares only with Tylototriton andersoni of the Loo-Choo Islands) is its ribs, which are very long, sharply pointed, and frequently perforate the skin. Before perforation the point of the rib lies in a lymphatic space. This surprising feature has by many authorities been considered as abnormal or pathological. Certainly young, and even many adult, individuals are found in which the skin is not perforated, but when these are handled the wriggling motions of this strong newt force the points of the ribs through the skin, and they remain sticking out to the extent of several millimetres. The wounds heal up, the skin forming a neatly finished-off hole through which the spike projects, not as a formidable, but as a sufficiently awkward, protective weapon.

Large females reach a length of 10 inches. The larvae metamorphose, as a rule, when they are between 2 and 3 inches long, but those which have been bred in tanks often reach double this length. These newts are frequent inhabitants of the rain-water cisterns common in the South of Portugal and Spain, into which they tumble without ever being able to get out again. This species spends most of its time in the water, preferring ponds, among the vegetation of which they can be watched lying motionless, with their limbs hanging down and with the head close to the surface; but they are lively during the night. When their ponds dry up they leave them, crawling into the most unexpected places, to aestivate under rocks, or even in the walls of old buildings, where they are found by accident only. The range extends from Central Spain and Portugal into Morocco.

Tylototriton verrucosus lives in the Eastern Himalayas and in the mountains of Yunnan. The skin is tubercular, with large parotoids; above uniform black-brown, pale below; the tail has a ventral yellow or orange line. Total length about 6 inches. T. andersoni of the Loo-Choo Islands is remarkable for the pointed ribs which perforate the skin.

Pachytriton brevipes, discovered in Kiansi, Southern China, has a smooth skin, olive-brown above, with many black dots; the under parts are yellowish, dotted with black. Total length about 7 inches.

Fam. 3. Proteidae.–The three pairs of fringed external gills persist throughout life. Both fore- and hind-limbs are present. The eyes are devoid of lids. The maxillaries are absent. Teeth are present on the premaxillaries, on the vomers, and on the mandible. The vertebrae are amphicoelous.

This family consists of only three genera, with one species in each.

Necturus maculatus s. Menobranchus lateralis.–The eyes are functional, being covered by the thin transparent skin. The limbs, although short, are well developed, and have four fingers and four toes. The whole animal, which reaches the length of one foot, is quite smooth and slimy, brown with irregular dark, blackish spots and patches, which frequently form a dark lateral band extending from the mouth to the tail. The latter, which measures about one-third of the whole length, is strongly compressed, carries a thick dorsal and ventral fin, and is rounded off at the end. The skin of the throat forms a strongly-marked transverse fold. The thick stalks of the gills are brown, while the numerous and delicate fringes are dark red in life; beneath and behind them are two gill-clefts. N. maculatus is found in the eastern half of the United States, chiefly the eastern part of the basin of the Mississippi and the Canadian lakes.

These creatures are rather dull; they remain mostly at the bottom of the water, more or less concealed in the weeds or between rocks during the daytime. Mine, which are kept in a roomy, light-coloured tank, lie motionless, with their gills spread out transversely. Every now and then the gills contract suddenly and become pale, whereupon they are filled again with blood. Very rarely they rise to the surface, but tiny air-bubbles are let out more frequently, especially when the animals are disturbed. Then the gills collapse, are laid flat against the neck, and the creature darts about with quick, eel-like motions. At night they leave their hiding-places, swim about or creep along the ground with slow, undulating movements, the limbs being scarcely used, in search of food, which in their wild state consists of rather large Crustacea, small fishes, worms, insects and frogs. They are most voracious, and absolutely indifferent to cold. The spawning takes place in the months of April and May.

Proteus anguinus.–The fore- and hind-limbs are fully developed, but possess only three fingers and two toes. The eyes are completely hidden beneath the opaque skin. This peculiar creature is restricted to the subterranean waters of Carniola, Carinthia, and Dalmatia. The vast caves of Adelsberg not far from Trieste are especially celebrated for the occurrence of the "Olm," the German name of this animal. The river Poik, a moderate mountain-stream, but a large, fierce torrent during the rainy season, disappears into the limestone-hills, and rushes through enormous stalactite-grottoes, most of which have been only partially explored, until several miles farther on it reappears on the surface. There, deep down below the surface, in absolute darkness, in an almost constant temperature of about 50° F. is the home of Proteus.

Their total length is scarcely one foot. The whole body is white, occasionally suffused with a slight fleshy, rosy tinge, while the three pairs of gill-bunches are carmine-red. They are easily kept in captivity, and live for many years, provided three conditions are strictly adhered to, viz. fresh and clean water, an equable low temperature of about 50° F. = 10° C. and darkness. The question of food is not so very important, since specimens are known to have existed for years, although they refused to take any nourishment. How far darkness is an absolute necessity is not known. Anyhow, the white skin is almost as susceptible to light as is a photographic plate. If light is not absolutely excluded the white skin becomes in time cloudy, with grey patches, and if kept exposed to stronger light, the whole animal turns ultimately jet-black. Mr. Bles has succeeded in producing several totally black specimens, having kept them for several months in a white basin under ordinary conditions of light. No experiments have yet been made to find out if the black pigment deposited is lost again in darkness. Those which are kept in a tank in an absolutely dark cellar of the Cambridge Museum, with permanent water-supply, are doing very well. When approached with a candle they become restless or remain partly hidden in all sorts of seemingly most uncomfortable attitudes, squeezed in between the sharp-edged tiles and drain-pipes with which their lodgings are furnished. But the introduction of a wriggling worm, a little crustacean or other live bait draws them from their hiding-places, and, guided by the motions of the prey in the water, possibly also by the sense of smell, they snap it up and devour it.

If the water is not sufficiently well aerated, they rise to the surface, emit a bubble of air, and take a new supply into their lungs. As a rule they remain motionless under water, but the gills contract spasmodically and become paler, whereupon they fill again with blood and darken; the contrast between the pure white body and the carmine-red feathery gills is very beautiful.

Until recently the mode of propagation was quite unknown. Several Proteus, kept by E. Zeller, laid, in the middle of April, a number of eggs which were then fastened singly on to the under side of projecting stones in the water. The pale yellow yolk measured 4 mm. in diameter and was surrounded by a cover of 1 mm. in thickness, besides an outer gelatinous mantle, so that the whole egg measured about 11 mm. The larvae were hatched after 90 days; they were 22 mm. long, and already much like the adult, except that the fin was not restricted to the tail, but extended over the last quarter of the trunk, and that their eyes were still visible. The fore-limbs were already typical in shape, but the hind-limbs were still toe-less little stumps.^[64]

Typhlomolge rathbuni.–It is of the greatest interest that a subterranean Perennibranchiate newt, in many respects closely resembling Proteus, has recently been discovered in Texas. There can be no doubt that similar conditions of life have produced these two forms from Necturus- and Spelerpes-like ancestors,^[65] one in Europe, the other in North America, absolutely independently of each other. The limbs of Typhlomolge are long and very slender, the four fingers and five toes are thin, free and pointed. The head is large, the mouth square. The eyes are completely hidden and the whole animal is colourless and white. The tail is furnished with a dorsal and a ventral fin. The very deep gular fold is nothing but the pair of united but large opercular flaps. The three pairs of gills are remarkable for their blade-like stalks, while the gill-lamellae proper are short and restricted to the tapering ends. Total length about 75 mm., of which the head measures 15, the tail 32 mm.

This peculiar creature inhabits subterranean caves in Texas, to judge from the fact that all the specimens hitherto known have come up with the water of an artesian well 188 feet deep, near San Marcos. According to Blackford,^[66] "the legs are used for locomotion and the animals creep along the bottom of the aquarium with a peculiar movement, swinging the legs in irregular circles at each step. They climb easily over the rocks piled in the aquarium, and hide in the crevices between them. All efforts to induce them to eat have been futile, as has also been the case with blind cave-fish in captivity, and they are either capable of long fasts or live on infusoria in the water." It seems more reasonable to suppose that these newts live upon Crustacea, four kinds of which, all new to science, also came up with the water.

Fam. 4. Sirenidae.–The three pairs of fringed external gills persist throughout life. The body is eel-like. Hind-limbs are altogether absent, while the fore-limbs are short and have three or four fingers. The maxillary bones are absent. With the exception of small teeth on the vomer the mouth is toothless, but the jaws are furnished with horny sheaths. The eyes are devoid of lids, but shine through the skin.

The Sirenidae are the most degraded members of the Urodela and are represented by two closely-allied genera, each with one species, in the south-eastern parts of the United States. Their most interesting feature, which bears upon the question of neoteny, is their retrograde metamorphosis as described by Cope.^[67] The gills atrophy in the young and are subsequently redeveloped. Cope therefrom concludes rightly that the ultimate or persistent gills of Siren are signs of maturity and not a larval character. In young specimens of Siren of 5 to 6 inches in length the gills are functionless; in one of 3 inches they were found to be entirely vestigial and "subepidermal," i.e. covered by a common dermal investment. Unfortunately really young larvae are still unknown. Old Sirens can live without gills, as has been shown by aquarium-specimens. In the adult Pseudobranchus all the gills are normally covered up by an investment of the skin so as to be quite without function and movability.

Siren lacertina, the "mud-eel," is distinguished by the possession of three pairs of gill-clefts and by its four fingers. It reaches a length of 70 cm., or about 2½ feet, of which about one-third is taken up by the tail, which is strongly compressed and finned. The skin is smooth, mostly blackish, lighter below, sometimes with whitish specks all over the body. This creature is frequently found in ditches and ponds, where it burrows in the mud. When swimming the limbs are folded back. They are said sometimes to leave the water and to crawl about on the moist ground.

Pseudobranchus striatus has only one pair of gill-clefts and only three fingers. The slightly granular skin is dusky brown above, with a broad yellow band on either side and with a paler, narrower stripe below. Total length about 7 inches.

CHAPTER VI

LISSAMPHIBIA (CONTINUED)–ANURA

Order III. ANURA or TAILLESS AMPHIBIA.

The recent tailless Amphibia, or Frogs and Toads in the widest sense, contain such a great number of species (about 900), with such a diversity of characters, that it is necessary, if only for the sake of mere convenience, to group them into a considerable number of families and sub-families. The characters available for this purpose are few.

By means of these characters we can arrange the Anura in the following key:–

Concerning the evolution of the classification of the Anura, it is interesting to follow the changes of the value attached to the various anatomical characters by systematists. At first the presence or absence of teeth and of adhesive discs on the fingers and toes were considered to be of prime importance for the division of the Phaneroglossa.

Stannius, 1856 (see p. 8), separated the Engystomatidae as "Systomata," and used the presence or absence of the "manubrium sterni" (omosternum) as a character of distinction between his Bufoninae and Raninae.

Günther, 1858, "Catalogue of the Batrachia Salientia." No progress was made by his scheme, which relied upon the tongue and digits.

Cope, 1864. "On the limits and relations of the Raniformes."^[68] He introduces the shoulder-girdle and the sacral diapophyses, and drops the discs as too adaptive and misleading. He distinguishes between Raniformes and Arciferi.

Cope, 1865. "Sketch of the primary groups of the Batrachia Salientia."^[69]

In 1867 Cope separates the genus Hemisus as Gastrechmia on account of its peculiar pectoral arch.^[70]

In 1875, "Check-list of North American Batrachia and Reptilia," Cope elaborates his system:

Boulenger, 1882, "Catalogue of the Batrachia Gradientia s. Ecaudata," recognises that the pectoral arch is of greater systematic value than the dentition. The latter is used, together with the shape of the sacral diapophyses, for the separation into families.

This emendation of the Arcifera and Firmisternia was accepted by Cope in his synopsis of the families of Vertebrata (Amer. Natural. xxiii., 1890), except that he still retained his suborder Gastrechmia.

Since the publication of Boulenger's great work a number of forms have been discovered which, from the characters of their dentition, have necessitated the establishment of certain new families, namely, Ceratobatrachidae and Genyophrynidae; and Boulenger was the first to recognise that the taxonomic value of the mere presence or absence of teeth in the jaws had been overestimated. I therefore propose using it as a character distinctive of the sub-families only, thereby reducing the number of families, relying first (leaving the Aglossa aside) upon the firmisternal or arciferous condition of the pectoral arch, secondly upon the dilated or cylindrical shape of the sacral diapophyses, thirdly upon the dentition. Blindly consistent application of these principles would reduce the Phaneroglossa to four families only, namely Ranidae, Engystomatidae, Cystignathidae and a fourth family comprising all the Arcifera with dilated sacral diapophyses. This would obviously be wrong. We have therefore to resort to other additional characters or rather peculiarities. The opisthocoelous character of the vertebrae and the possession of distinct ribs, together with the disc-shaped tongue, separate the Discoglossidae and justify their retention as a family. The Hylidae are marked off by the claw-shaped terminal phalanges, but the remaining forms, comprising the Bufonidae and Pelobatidae, cannot be separated except by their dentition, and I plead guilty of inconsistency in retaining them as separate families.

After all, our classification may not represent the natural system, and it may be nothing but a convenient key.

When we have eliminated the characters of the vertebrae, the dentition, the claw-shaped phalanges and the adhesive discs, it may well be asked what characters remain. The firmisternal is a further, higher modification of the older, more primitive arciferous condition. The difference between the dilated and cylindrical shape of the sacral diapophyses is in not a few cases very slight, and there are various, most suggestive exceptions. The presence or absence, size and shape of the omosternum and metasternum are of very limited taxonomic value, not always applicable to all the members of the same family. The fact is, that the Anura are a very recent and a most adaptive, plastic group. The earliest known fossils are scarcely older than the Middle Eocene.

Almost every one of the greater families has produced terrestrial, arboreal, aquatic, and burrowing forms. Their habits have modified, and are still shaping their various organs, first of course those by which the animals come first and most directly into contact with their surroundings (e.g. adhesive discs, dentition, general shape of the body, length of limbs, wartiness of the skin, tympanic disc). These are the so-called adaptive characters, sometimes decried as merely physiological; as if habits, use, and requirements did not likewise influence and ultimately model every other organ (e.g. tympanic cavity, Eustachian tubes, vertebrae, ribs, coccyx, pectoral arch, etc.). There are true Toads, Bufonidae, which are as smooth, wartless, slender-bodied and long-legged as the most typical of "Frogs"; true Ranidae, like Rhacophorus, which by their green colour, large adhesive discs and arboreal habits may well put many of the Hylidæ to shame. Ceratohyla has developed the claw-shaped terminal phalanges which are otherwise typical of, and peculiar to, the Hylidae, but this genus reveals itself by various details as a close relation of the other Hemiphractinae; and these fall in with the Cystignathidae on the strength of their cylindrical, not dilated, sacral diapophyses.

In sketching the phylogenetic tree of the families of the Anura we have to proceed with great caution.

There is not much doubt about the Aglossa. They have retained some of the most primitive characters, but have by now been so much modified and specialised that they are to be looked upon as an early side-branch.

Among the Phaneroglossa the Discoglossidae are with certainty the oldest, but are now scarce in genera and species, and much specialised. The Pelobatidae connect them with the Bufonidae. The Cystignathidae form a rather ill-defined assembly which points downwards to the Pelobatidae, upwards to the Hylidae. There is no divergence of opinion about the Ranidae being the highest of all the Anura, and amongst them the Raninae the most typical, the Dendrobatinae the most specialised. If we assume that moderately dilated sacral diapophyses represent a more primitive stage than cylindrical processes, we shall naturally look to the Engystomatidae as the connecting link between the Ranidae and the Arcifera, through Bufonoid creatures still with teeth in both jaws. If, on the other hand, we take the dilatation to be a further development from more or less cylindrical processes, then the Ranidae can be considered as having sprung from Cystignathoid creatures, which have consolidated their pectoral arch into the firmisternal condition; and in this case the Firmisternia would not be a natural group, the Engystomatidae pointing, to the Bufonoid stock. This would, to a great extent, mean a reversion to Cope's idea.

Sub-Order 1. Aglossa.–The two diagnostic peculiarities of the few members of this group are: first, the absence of a tongue; secondly, the union of the Eustachian tubes into one median pharyngeal opening in the posterior portion of the palate.

The pharyngeal opening and the tubes themselves are wide, the tympanic cavities are present, but the tympanic discs are not distinct from the rest of the skin. The fronto-parietal bones are fused into one mass, a rare feature in the Anura. The nasals are large. Pipa and Hymenochirus have no teeth, Xenopus has teeth on the upper jaw. The vertebrae are opisthocoelous and typically epichordal in their development; the second, third, and fourth carry long ribs, which in old specimens fuse with the supporting diapophyses. The sacral diapophyses are enormously dilated, and the sacrum is fused with the os coccygeum. The serial number of the sacral vertebrae exhibits a most interesting gradation. In Xenopus the ilium is carried by the diapophyses of the 9th, in Pipa the 9th and 8th, in Hymenochirus the 7th and 6th. In these cases the two diapophyses of each side are fused together into a single broad blade, and their original duplicity is indicated only by the holes for the spinal nerves. Hymenochirus has consequently only 5 presacral vertebrae, the vertebral column being shortened to the greatest extent known amongst Vertebrata. For further information see p. 22. The ilia are much broadened vertically, and are firmly attached to the sacrum. The shoulder-girdle is sometimes described as of the arciferous type, but this is quite unjustifiable. The epicoracoid cartilages do not overlap each other, but meet, and partly fuse in the middle line. The three genera exhibit some differences. In Pipa and Hymenochirus the bony portions of the coracoids are much expanded dorsally, and there is a considerable amount of epicoracoid cartilage, that of the precoracoid bars extending backwards as a broad-based and blunt omosternum. Xenopus is devoid of an omosternum, and the configuration of the whole apparatus is more slender. The metasternum of Xenopus and Hymenochirus broadens out laterally. Hymenochirus greatly resembles Breviceps, a genus of Engystomatinae, in the relative position and size of the various parts of the shoulder-girdle and sternum.

The tibio-fibula of Hymenochirus has a wing-like expansion of thin bone on each side, forming a deep groove on the outer aspect. The astragalus and calcaneum are united by a similar bony expansion with wing-like projections.

The lungs are remarkable for the prominent development of trabecular projections and niches, so that their free lumen is much restricted; they have thereby reached a much higher stage than in any other Amphibia or even many Autosauri. The persistence of an arteria sacralis s. caudalis, a vessel absolutely absent in the adult Rana, is a primitive feature, and the same applies to the presence of a true first spinal or suboccipital nerve.

The skin of the back and belly is supplied by two great branches from the arteria anonyma, one arising proximally, the other distally from the subclavian; herewith is correlated the almost complete absence of the arteria cutanea magna, which as a branch of the ductus pulmo-cutaneus plays such a prominent rôle in the other Anura. Only in Pipa, but not in Xenopus, is the great cutaneous vein represented by a very small branch. Both these genera possess a much more complicated "diaphragm" than the other Anura, chiefly owing to a special muscle which arises from the anterior end of the ilia and spreads out fan-like to the oesophagus and to the bases of the lungs.^[71] This diaphragmatic arrangement is correlated with the great development of the lungs, and is not a primitive but an advanced feature. It is reasonable to suppose that this has caused the reduction of the usual arteria pulmo-cutanea, and that the other two cutaneous arteries have been developed secondarily. The Aglossa are generally considered as the lowest Anura, and only Cope looked upon Pipa and Xenopus as two convergent terminal branches. Beddard came to the conclusion that both are closely related to each other, chiefly on account of their peculiar diaphragmatic arrangement. The whole question has entered upon a new stage since the recent discovery of Hymenochirus, which is in many ways intermediate between the two other genera. Moreover, the mid-Tertiary Palaeobatrachus of Europe is undoubtedly related to them, and we conclude now that all these four genera belong to one group with a distribution formerly much wider than Africa and part of South America. But this does not necessarily mean that the Aglossa are in all respects the most primitive group of living Anura. On the contrary, they possess few decidedly primitive characters, namely, the long typical ribs, the presence of the first spinal nerve, the unimportant persistence of the arteria sacralis, and lastly, the possession in the tadpoles of a right and left opercular "spiracle." The absence of the tongue cannot possibly be an archaic feature, considering its universal presence in all the other Amphibia, including the Apoda, and the suggestive circumstance that this organ is least developed in the entirely aquatic members of the Urodela. In fact, thoroughly aquatic creatures, which seize and swallow their prey under water, require no elaborate tongue; and since we know that the Anura must owe their typical formation to terrestrial life, it follows that those which have again taken to the water and are tongueless, have lost this organ. As I have shown elsewhere,^[72] the epichordal development of the vertebrae is likewise a secondary feature, far from primitive; and the tendency of the shortening of the vertebral column, which has reached its extreme in Hymenochirus, points to the same conclusion. The apparatus of the shoulder-girdle and sternum is in the last transitional stage from the former arciferous to the typically consolidated firmisternal type. In fact there is little left which is primitive, but much that is very specialised and highly developed in the Aglossa, mostly in adaptation to their absolutely aquatic life, to which they must however have taken very early. They are in a position somewhat analogous to the Ratitae among Birds, which are likewise an old group, although many of their most striking features have been acquired secondarily.

Xenopus s. Dactylethra. The upper jaw is furnished with teeth. The ilia are attached to the ninth vertebra. The pupil is round. The terminal phalanges are pointed. The fingers are free, the toes broadly webbed, and the first three are covered with sharply pointed, horny, black-brown nails, a feature which is alluded to by the alternative generic names. A cutaneous tentacle projects from below the eye and naturally invites comparison with the tentacle of the Apoda and of Urodela. The skin is smooth, rich in mucous glands, besides certain tube-like apparatuses, possibly sensory, which are scattered over the body, especially on the head, and form a conspicuous series of white dots along the dorso-lateral line, from the eye to the vent. The general colour of the upper parts is olive brown, mottled darker, while the under parts are whitish. The female has three cutaneous flaps closing the vent. The male develops black nuptial brushes along the inner side of the fingers. There are several species, all African (Ethiopian).

X. laevis, ranging from the Cape to Abyssinia, is distinguished by the absence of a metatarsal spur. The tentacle is very short. Size about 3 inches. X. muelleri of Zanzibar and Benguella, is smaller. The tentacle is conspicuous, as long as the diameter of the eye. The inner metatarsal tubercle carries a sharp claw. X. calcaratus of tropical West Africa is only 2 inches long, and has strong metatarsal claws, short tentacles and very minute eyes.

The habits and oviposition of the "Clawed Toad" have been described by Leslie.^[73] The Boers call it "Plathander," i.e. flat hand. Entirely aquatic, it rests floating in the water, with the nostrils exposed, and leaves the water only if it has to change the locality on account of drought or scarcity of food. The pairing takes place, at least at Port Elizabeth, in the early spring, i.e. in the month of August. The only sound which is emitted is heard during this time, a very slight and dull tick-tick, audible at only a few feet distance. The male grasps the female by the loins; the eggs are extruded singly, measuring only 1.5 mm. in diameter, but swell to double that size. They are attached singly to stones or water-plants.