In the Urodela both kidneys and testes are much concentrated, the testes

especially have lost all outward appearance of segmentation, 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 suppressed, 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

{51}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_ (6) 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 arrangement 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_ (8) 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 consolidation 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.

Remnants of oviducts, or Müllerian 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 _Discoglossus_ 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 most 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 dilatations. In the Anura they

become greatly elongated during the {52}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

detriment 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 inconspicuous 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 undulating 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

spermatophores, an arrangement which undoubtedly facilitates the internal

{53}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, gelatinous mass,

which is probably produced by the cloacal gland. The shell of jelly is in

fact a cast of the cloacal cavity, reproducing all its ridges, furrows 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 top. Those

of _Amblystoma_ are similar.

The spermatozoa of the Anura show considerable 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_,

_Pelobates_, 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 0.1 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. _Rana temporaria_ and _R. arvalis_, cannot fertilise

each other.

[Illustration: FIG. 8.–A bell-shaped spermatophore of _Triton alpestris_. ×

3. (After Zeller.)[25]]

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 schlegeli_ and the Apoda, approach the

meroblastic type of segmentation. As a rule, the greater the amount of

yolk, the smaller is the number of eggs produced. But the number which is

laid {54}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_ produces up to 1000, _Rana temporaria_

about 3000, _Bufo vulgaris_ averages 5000, _Bufo viridis_ and _Rana

esculenta_ up to 10,000 and more. T. H. Morgan[26] has observed a _Bufo

lentiginosus_ which laid 28,000 eggs within ten hours! The number of eggs

produced by the Apoda and Urodela is comparatively moderate, in the average

a few dozen, _Amblystoma_ alone laying about 1000.

The eggs possess a gelatinous mantle of variable thickness and consistency.

In _Amphiuma_ they are strung together like the beads of a rosary, and the

envelope hardens into a kind of shell. Many Newts and some Anura fasten

their eggs singly on to plants and other objects in the water, with or

without threads of stiffening mucus. In many Anura, _e.g._ Bufonidae, they

pass out as closely-set strings of beads, one string out of each oviduct;

in others, _e.g._ Ranidae, they are disconnected, and form large, lumpy

masses, especially when the gelatinous mantle swells up in the water. The

use of this mantle seems to be chiefly the protection of the growing

embryo, which in many species, when hatched out of the egg proper, drops

into and remains for some time in the softened jelly. Possibly the latter

affords some nutriment to the early larva.

Concerning the mode of FECUNDATION it is to be remarked that copulation

proper takes place only in the Apoda. For the Urodela Boulenger[27] has

given the following summary. In no case does actual copulation take place.

The male deposits the spermatophores which it is the office of the female

to secure:–

I. No amplexus, but a lengthy courtship in the water; the male is more

brilliantly coloured than the female, and ornamented with dorsal and

caudal crests, or other appendages: _Triton_, cf. also systematic part.

II. Amplexus takes place; there are no marked sexual differences in

colour and no ornamental dermal appendages.

A. Amplexus of short duration, partly on land, but deposition of the

sperma in the water. No accessory sexual characters: Terrestrial

Salamanders, namely _Salamandra_, _Chioglossa_, _Salamandrina_.

_Spelerpes_ breeds in damp caves without water.

{55}B. Amplexus of lengthy duration and in the water.

_a._ The male, distinguished by a greater development of the

fore-limbs, which are armed with temporary excrescences, clasps the

female in the axillary region with the fore-limbs: _Triton waltli_.

_b._ The male, distinguished by a greater development of the

hind-limbs and a prehensile tail, clasps the female in the lumbar and

caudal regions: The _Euproctus_-group of newts: _Triton asper_, _T.

rusconii_, and _T. montanus_.

The act of fecundation of most of the other kinds of Urodela, notably

_Cryptobranchus_, _Amphiuma_, _Proteus_, has not yet been observed.

Embracing of the two sexes is the universal rule with the Anura, the male

creeping on to the back of the female and clasping her firmly with the arms

and hands either in the inguinal region, higher up, or under the armpits.

See the numerous statements in the systematic part. This often extremely

forcible, pressing embrace seems to be necessary, although the females can

deposit the eggs without the help of the male, but in such cases the

expulsion takes place at irregular intervals instead of at one time. When

the eggs appear at last, and this happens in many species many hours, or

even some days, after the beginning of the embrace, the male voids the

contents of its seminal vesicles over them. Fertilisation is consequently

external, with the possible exception of _Pipa_, _q.v._ p. 152.

DEPOSITION OF THE EGGS AND NURSING HABITS.–The majority of the Amphibia are

oviparous, but some Apoda and Urodela are viviparous. It is unnecessary to

call the latter condition ovo-viviparous, since this is really a

distinction without a difference.

Viviparous forms:–amongst Urodela; _Salamandra maculosa_, the young burst

the egg-membrane in the act of being born, and are provided with long

gills; _S. atra_, the young undergo their whole development and

metamorphosis within the uterus (see p. 119); _Spelerpes fuscus_, the young

are likewise born in the perfect condition: amongst Apoda; _Typhlonectes

compressicauda_ and _Dermophis thomensis_.

The oviparous Apoda, at least _Ichthyophis_ and _Hypogeophis_, and a few of

the Urodela, as _Desmognathus_ and _Amphiuma_, take care of their eggs by

coiling themselves around them in a hole underground.

Nursing habits are very common amongst the Anura. {56}Boulenger[28] has

summarised the various conditions concerning the deposition and care that

is taken of the eggs, in the following list, in which more recent

discoveries have been interpolated.

I. The ovum is small, and the larva leaves it in a comparatively early

embryonic condition.

A. The eggs are laid in the water:–

_a._ Without further care or preparations: probably the majority of

Anura; all European forms, except _Alytes_.

_b._ The eggs are laid in a specially walled-in part of the pond:

_Hyla faber_.

B. The eggs are deposited out of the water:–

_a._ In holes, or under grass, near the banks of pools. The larvae

are liberated and washed into the water by the next heavy rain:

_Leptodactylus ocellatus_, _L. mystacinus_, _Paludicola gracilis_,

_Pseudophryne australis_ and _P. bibroni_.

_b._ On leaves above the water, the larvae dropping down when leaving

the egg: _Chiromantis rufescens_, _Phyllomedusa iheringi_, _Ph.

hypochondrialis_.

II. The yolk is very large and the young undergoes the whole or part of

the metamorphosis within the egg; at any rate the larva does not assume

an independent existence until after the loss of the gills.

A. The eggs are deposited in damp situations, or on leaves. The young

escape as:–

_a._ Tadpoles: _Arthroleptis seychellensis_, _Rhacophorus schlegeli_,

_Rh. maculatus_.

_b._ Perfect, air-breathing frogs: _Rana opisthodon_, _Hylodes

martinicensis_, _Hyla nebulosa_.

B. The eggs are carried by a parent.

_a._ By the male:–

α. Round the legs; the young leaves the egg in the tadpole stage:

_Alytes_.

β. In the enlarged vocal sacs; the young leave in the perfect

state: _Rhinoderma_.

_b._ By the female:–

α. Attached to the belly: _Rhacophorus reticulatus_.

β. Attached to the back; the young complete their metamorphosis

within the egg: _Pipa_.

γ. In a dorsal pouch which the young leave as tadpoles: _Nototrema

marsupiatum_;–or in the perfect state: _Nototrema testudineum_, _N.

cornutum_, _N. oviferum_, _N. fissipes_, and _Hyla goeldii_.

THE DEVELOPMENT AND METAMORPHOSIS of many species have been described in

the systematic part. The following is a short general account of some of

the more important features. Metamorphosis in the Apoda and Urodela is

restricted chiefly to the reduction of the gills, the closing of the

clefts, and the loss of the {57}gill-chamber and the finny margins of the

tail; but the change from the tadpole to the final Anurous animal implies

an almost entire reorganisation.

[Illustration: FIG. 9.–Four stages of the development of the adhesive

apparatus (_A_) of _Bufo vulgaris_; _M_, Mouth; _Sp.T._ spiracular tube. In

3 the gills are almost completely hidden by the united right and left

opercular folds. The small outlined figures indicate the shape and natural

size of the tadpoles. (After Thiele.)]

In the earliest condition the embryo consists of a large head and body,

while the tail is still absent. Behind the beginnings of the future mouth

appears a transverse crescentic fold, with the convexity looking backwards,

which develops into the paired or unpaired _adhesive apparatus_. This

consists of large complex glands, developed in the Malpighian layer,

originally covered by the cuticula, which soon disappears, whereupon the

sticky secretion enables the larva to attach itself to the gelatinous

mantle of the egg, later on to weeds or other objects in the water. The

name of suckers, often applied to this apparatus, conveys a wrong idea,

there being neither muscles nor any suctorial function. The shape of this

organ undergoes many changes during the early life of the individual, and

differs much in the various genera, affording thereby diagnostic

characters.[29] At first a crescent, it divides into a right and a left

oval or disc, which either remain asunder and behind the mouth (_Rana_,

_Bufo_), or they move forwards to the corners of the mouth (_Hyla_) or

further back, and unite again more or less completely, as in _Discoglossus_

and _Bombinator_. It is mostly of short duration, and disappears by the

time that the larva, by the proper development of the gills and the tail

and the functional mouth, changes into the tadpole. But in a few species

these discs transform themselves into an elaborate ventral disc. Such an

organ persists throughout the greater part of the tadpole-stage in certain

Oriental species of _Rana_, all of which, when adult, possess fully webbed

toes and {58}strongly dilated discs on the fingers and toes, e.g. _Rana

whiteheadi_, _R. natatrix_, and _R. cavitympanum_ of Borneo, _R. jerboa_ of

Java (this larva was originally described and figured as that of

_Rhacophorus reinwardti_), and _R. afghana_ of the Himalayan system. These

tadpoles, at least those of _R. jerboa_, are further remarkable for having

the "spiracular" opening very far back on the left side, nearer to the base

of the tail than to the snout, so as to be well out of the way when the

creature has attached itself by the adhesive disc.

[Illustration: FIG. 10.–1, Front view of the mouth of a tadpole of _Rana

temporaria_, showing the transverse rows of tiny horny teeth; 2, three

successive horny teeth, much magnified. (After Gutzeit.)]

The mouth of the tadpoles of Anura is furnished with horny armaments,

substitutes for teeth. Their development and that of the mouth in general

has been well described by Gutzeit.[30] In the young larvae of _Rana

temporaria_, one or two days after hatching, a shallow groove appears above

the conspicuous pair of adhesive organs. The groove becomes rhombic in

outline, and when the mouth has been formed in its centre, the jaws appear

in the median corners of the rhombus. The epidermis then rises like a

circular wall around the jaws, and divides into an upper and lower lip;

furrows appear on them, and between these various papillae and comb-like

transverse plates of teeth. The papillae are possibly tactile organs, but

although nerves enter them, nerve-endings of a sensory nature have not yet

been discovered. On the fourth day the jaws become black, by the tenth day

horny teeth have appeared upon all the plates of the mouth-armature, and on

the seventeenth day the mouth-apparatus has reached the configuration

typical of the tadpole, which is now about 14 mm. long. The number of horny

teeth in _R. temporaria_ amounts to about 640. These teeth are not

cuticular products, but cornified cells; they are very small, and consist

each of one horny cell, which is shaped like a nightcap, the apex of which

is curved back and serrated. The little teeth are shed continuously,

{59}the renewal taking place by successive cells growing into the bases of

the older series. The shape and size differ much in the various genera and

species. The comb-like plates, composed of those teeth which surround the

lips, seem to be used chiefly for the fixing or hooking of the food, while

those which compose the horny beak proper, the armature of the jaws, are

used like the radulae of snails. These beaks are likewise composed of a

great number of individual teeth, closely packed together in several rows,

but the teeth themselves are simple and not serrated.

In _Hyla arborea_ there are in all about 560 teeth. The development of the

mouth does not begin before the eleventh day; the horny teeth break

through, and the jaws get black edges, on the eighteenth. In _Pelobates

fuscus_ the number of horny teeth is increased to about 1100. In

_Borborocoetes taeniatus_ the horny teeth form series of five bells, which

fit into each other like the joints of a rattlesnake's tail.

One of the most extraordinary kinds of tadpoles is that of _Megalophrys

montana_.[31] Mr. Annandale (Skeat Expedition) found it at Bukit Besar,

Malay Peninsula, from 2000 to 3000 feet above the level of the sea. The

tadpoles (Fig. 11) were found in the beginning of the month of May 1899 in

sandy streams and in pools of rain-water; they floated in a vertical

position, the peculiar membranous funnel-shaped expansion of the lips

acting as surface-floats. The inside of the funnel is beset with radiating

series of little horny teeth, and the whole apparatus is possibly used for

scraping the under-surface of the leaves of water-plants in search of food.

Total length of the tadpoles 1 inch.[32]

The gills, the formation of the operculum, and the modifications of the

branchial arterial arches have been described fully on p. 43; those of the

hyo-branchial skeleton on p. 31. Fusion of the opercular fold with the skin

of the neck, across the branchial region, causes the head to become

confluent with the trunk (cf. Fig. 9, 3, p. 57). The body becomes oval,

more or less globular, and the alimentary canal is greatly elongated and

stowed away in the shape of a neat, very regular spiral, shining through

{60}the ventral wall of the body; the anus opens at the end of a somewhat

protruding tube, either in the median line, just in front of the ventral

fin (Discoglossidae, _Pelobates_, _Bufo_), or it assumes an asymmetrical

position by turning to the right side (_Hyla_, _Rana_).

[Illustration: FIG. 11.–Tadpoles of _Megalophrys montana_ from Bukit Besar,

Malay Peninsula. × 3.]

Although both pairs of limbs begin to bud simultaneously, or the fore-limbs

even earlier, the hind-limbs are hurried on, and appear first, long before

the fore-limbs. The latter lie ready beneath the skin of the gill-chamber,

and the right always breaks through the skin, while the left does the same

in the Mediogyrinidae, while in the Laevogyrinidae it is generally pushed

through the left-sided spiracular opening, immediately behind the outer

gills. According to Barfurth the right limb appears, in about 80 per cent.

of _Rana esculenta_, from two to eight hours before the left.

{61}Meanwhile the lungs are being developed, and the tadpole occasionally

rises to the surface to breathe air. The gills, which, as has been

explained elsewhere, are less ancestral than they are larval organs,

degenerate, and all the organs are modified for the coming terrestrial

life. The fins of the tail are absorbed, the horny armature of the mouth

and lips is shed in pieces and makes room for the true teeth, the eyes

receive lids, and the whole cranium, especially the apparatus of the jaws,

undergoes the final modifications–widening and lengthening of the mouth,

arresting of the mento-Meckelian cartilages, elongation of the Meckelian

cartilages or lower jaw proper, shifting backwards of the suspensorium, and

lengthening of its orbital process to form the pterygo-palatine bridge.

The tadpole ceases to feed, the whole intestinal canal is voided of its

contents, and by "histolysis" is thoroughly rebuilt, becoming wider and

shrinking to about one-sixth of its original length,–undoing thereby the

spiral–preparatory for the coarser food, which consists of insects, worms,

and other strictly animal, living matter. Hitherto the tadpoles have lived

on "mud," confervae, Diatoms, rotting vegetable and animal matter. The anal

tube collapses, becomes ultimately absorbed, and a new vent is formed at

and below the root of the tail.

Barfurth[33] has made interesting observations and experiments with regard

to the absorption of the tail and other organs which disappear during the

metamorphosis. This is retarded by low temperature; it is accelerated by

rest and freedom from mechanical disturbances, as, for instance, concussion

of the water. Hunger shortens or hurries on the last stages of

metamorphosis, the absorption of the tail taking place in four instead of

five days. Amputation of the tail has no retarding influence; it is

followed at once by regeneration, although the tadpole may be on the verge

of reducing the tail. Whilst hungering the whole organism draws upon its

available store of material, naturally first upon those parts which sooner

or later are to become superfluous. This applies eminently to the tail,

which represents a considerable amount of "edible" matter, and also to that

portion of the skin which still covers the fore-limbs. The elements of the

cutis are resorbed, thereby thinning the skin; and consequently the limbs

break through earlier in fasting than in well-fed {62}specimens. Nature

herself seems to apply hunger as an accelerator. Mlle. von Chauvin found

that the larvae of Urodela normally fast during the transformation, and

according to Barfurth the larvae of _Rana temporaria_ eat less after their

hind-limbs are fully developed. This is, however, also preparatory for the

reorganisation of the gut, which has to be more or less empty during the

shortening process.

The loss of the tail is not due to a sudden dropping off of this organ–a

crude but by no means uncommon belief–but is brought about by a very

gradual process of resorbtion. When the fore-limbs begin to break through

the skin, the tip of the tail shrinks and becomes black, owing to an

increase, or rather concentration, of the pigment cells. The reduction

proceeds from the tip forwards until on about the fifth day there remains

only a short, conical, black stump. From the beginning of this process of

reduction the tail is scarcely used for locomotion, the tadpole rowing with

its legs, or it crawls and hops about, although the tail may still be 20

mm. long. The cells of the epidermis atrophy, shrink, and peel off, while

those of the cutis, blood-vessels, nerves, muscles, and chorda dorsalis

become disintegrated, often undergoing fatty degeneration. The leucocytes

eat up the débris and other dissolved tissue, and carry it away through the

lymphatic vessels, to be used as new building material in the rest of the

animal.

Barfurth asks very properly, Why do these tissues degenerate and die?

Because the vasomotor nerve-fibres cease to regulate the circulation. And

why does this trophic influence of the central nervous system stop? Because

the function of the tail becomes superfluous through the appearance of the

fore-limbs. The tail is doomed, and degenerates like any other organ

without a function. The whole process is, of course, a recapitulation of

ancestral, phylogenetic evolution.

{63}CHAPTER III

NEOTENY–REGENERATION–TEMPERATURE–GEOGRAPHICAL DISTRIBUTION

NEOTENY.–It has long been known that the larvae of the Spotted Salamander

occasionally attain the size of 80 mm. or about 3 inches, whilst the

majority undergo metamorphosis when they are only 40 mm. long. Again,

larvae of _Triton_ have been found, in the months of April and May, 80 to

90 mm. long, still with functional gills, but with the sexual organs fully

developed. De Filippi[34] found in one locality in Lombardy, besides a few

normal fully metamorphosed specimens of only 30 mm. in length, more than

forty specimens, which, although they had attained full size, about 55 mm.,

and were sexually mature, still retained their gills. According to him such

gill-breathing, otherwise mature specimens, occur constantly in a small

lake in the Val Formazzo, on the Italian slope of the Alps, in the province

of Ossola. Later Duméril[35] astonished the world by his account of the

metamorphosis of the Mexican gill-breathing Axolotl into an entirely

lung-breathing and terrestrial creature, hitherto called _Amblystoma_, and

supposed to be not only a different species, but to belong to a different

family from the Axolotl, which was known as _Siredon axolotl_ s.

_pisciforme_, and naturally classed with the Perennibranchiata.

This discovery led to a series of observations and experiments, chiefly

conducted by Marie von Chauvin, instigated thereto by Koelliker and by

Camerano.[36] It was then found that many, if not most of the European

Amphibia, both Urodela and Anura, {64}occasionally postpone their

metamorphosis, and also that such Urodela sometimes become adult for all

practical purposes, but retain their gills.

This retardation, the retention of larval characters beyond the normal

period, was called _Neotenie_ by Kollmann[37] (νέος, young; τείνω, extend,

stretch). He distinguished further between:–I. Partial Neoteny, namely,

simple retardation of the metamorphosis beyond the normal period, for

instance, the wintering of tadpoles of _Pelobates fuscus_, _Bombinator

pachypus_, _Pelodytes punctatus_, _Alytes obstetricans_, _Hyla arborea_,

_Rana esculenta_, _R. temporaria_, _Bufo vulgaris_, and _B. viridis_: II.

Total Neoteny, where the animal retains its gills, but becomes sexually

mature; hitherto observed in Urodela only, e.g. _Triton vulgaris_, _T.

alpestris_, _T. cristatus_, _T. boscai_, _T. waltli_ and _Amblystoma_.

Intermediate stages between these two categories are not uncommon.

A satisfactory explanation of the meaning of neoteny is beset with

difficulties. Some authorities look upon the phenomenon simply as the

result of adaptation to the surroundings, which make it advantageous for

the creature to retain its larval features. Others think that the

surroundings somehow or other retard or prevent the assumption of the adult

characters. Undoubtedly there are many cases in which larvae have been

reared in water-holes with steep walls, so that they could not change from

aquatic to terrestrial life, and it stands to reason that abnormally forced

and prolonged use of the gills and of the tail may stimulate these organs

into further growth at the expense of the limbs and other organs which are

intended for terrestrial life. But not unfrequently typical neotenic and

overgrown specimens occur side by side with others which have completed

their metamorphosis, and the same is true of larvae of newts which were

reared, for experimental purposes, under exactly the same conditions–for

instance, in a high-walled glass vessel.

Weismann tried to explain neoteny as cases of reversion to atavistic

ancestral conditions, but this idea is based upon an assumption which is

probably wrong. His idea necessitates the supposition that all the Amphibia

were originally gill-breathing, aquatic, and limbless animals, and that

every feature seen in a larva must necessarily indicate an ancestral

phylogenetic stage. It is, on the contrary, much more probable that {65}the

external gills of the Urodela have been developed in adaptation to their

embryonic and larval, essentially aquatic, life. Consequently the

possession of such gills would be a secondary, and not, strictly speaking,

an atavistic feature. Normal loss of these gills, exclusively pulmonary

respiration, and preponderating terrestrial life characterise the final

adult Amphibian. These cases of neoteny are therefore instances of more or

less complete retardation, or of the retention, of partially larval

conditions.

The whole problem is, however, by no means simple. _Salamandra atra_ has

become viviparous, and the whole metamorphosis takes place within the

uterus; in fact, the young have an embryonic, but no larval period, if by

the latter we understand the free swimming and still imperfect stage.

Similarly, various Anura–for instance, _Hylodes martinicensis_–pass rapidly

through their metamorphosis, and have suppressed the stage of free swimming

tadpoles. On the other hand, in many newts, the duration of the larval

period is much prolonged, and moreover is very subject to individual

variation. In the Axolotl this larval period is continued until and after

sexual maturity is reached. The extreme condition would then be represented

by the Perennibranchiate genera. It may seem reasonable to look upon these

as the youngest members of the Urodela, and the loss of the maxillae in the

Sirenidae and Proteidae supports this idea. But it so happens that the

majority of the most neotenic genera are more primitive in the composition

of the skull and the vertebral column than the typically terrestrial and

rapidly metamorphosing genera. Witness the amphicoelous vertebrae, the

completeness of the pterygoids, the separate nature of the palatine bones,

and the separate splenials, as mentioned in detail in the description of

their skull.

We have therefore to conclude, first, that the various Perennibranchiate

genera do not form a natural group, but are a heterogeneous assembly;

secondly, that they have become Perennibranchiate at a phylogenetically old

stage–in fact, that they are the oldest, and not the newest, members of the

present Urodela. At the same time, it would be erroneous to suppose that

the first Urodela were aquatic creatures, provided with a finny tail, with

small, ill-developed lungs, and with epidermal sense organs. All these

features are, on the contrary, directly correlated with aquatic life, and

are larval acquisitions, not ancestral {66}reminiscences. It would be

equally wrong to allude to the absence of lungs in many newts as a piscine

and therefore ancestral feature. The development of the typical

pentadactyloid limb, the connexion of the pelvic girdle with the vertebral

column, the development of the lungs, and absolute suppression of internal

gills point without doubt to terrestrial creatures. What then, may we ask,

were the first Amphibia like? and how about the external gills? They were

undoubtedly akin to the less specialised Lepospondylous Stegocephali, in

particular the gill-less Microsauri, and the various stages may perhaps be

reconstructed as follows:–

(1) Terrestrial, with two pairs of pentadactyloid limbs; breathing by lungs

only; with a fully developed apparatus of five pairs of gill-arches, which

during the embryonic life perhaps still carried internal gills; with or

without several pairs of gill-clefts. Reduction of the dermal armour and of

the cutaneous scutes had taken place.

(2) Additional respiratory organs were developed by the embryo, in the

shape of external gills; these were at first restricted to embryonic life

(as in the existing Apoda), but were gradually used also during the aquatic

life of the larva. These external gills, together with the lungs, have

superseded the internal gills, of which there are now no traces either in

Urodela or in Anura.

(3_a_) Some Urodeles, retaking to aquatic life, retained and further

enlarged the external gills into more or less permanent organs (cf. also

_Siren_, p. 136).

(3_b_) The majority of Urodela hurried through the larval, aquatic stage,

and some–e.g. _Salamandra atra_–became absolutely terrestrial. The

possession of unusually long external gills by this species and by the

Apoda indicate that these organs are essentially embryonic, not larval,

features.

REGENERATION.–Most Amphibia possess the faculty of regenerating mutilated

or lost limbs. This takes place the more certainly and quickly the younger

the animal. The amputation necessary to study these phenomena need not be

experimental. Axolotls and other Urodelous larvae frequently maim each

other fearfully, by biting off the gills or one or more limbs. The gills do

not even require amputation. If the larvae are kept in stagnant water the

gills often shrivel up or slough off and grow again. {67}The same applies

to the larvae of viviparous species, e.g. _Salamandra atra_, which, when

cut out of the uterus and put into water, soon cast off their long, tender

gills and produce a stronger set. In an Axolotl,[38] two years old, a hand

was cut off. After four weeks there was a conical stump; after the sixth

week this stump had two points; in the eleventh week three or four fingers

were discernible, and a week later the complete hand. Frequently these

creatures reproduce five instead of the normal four fingers. But the more

proximal the cut, the more liable is the new limb to reproduce

supernumerary fingers, or even extra hands and feet. Complete regeneration

of the limb, cut off in the middle of the humerus, took place within five

months.

_Triton taeniatus_, adult, reproduces cut fingers within five or six weeks,

and if the hand be cut above the carpus, new finger-stumps appear in about

one month. Götte has observed that an adult _Proteus_ did not completely

reproduce its whole leg until after eighteen months; and, according to

Spallanzani, more than one year elapses before the limb, bones, and

cartilages of _Triton_ regain their normal strength.

The Anura are likewise capable of regenerating their limbs, the more

readily the younger the specimens. For instance, in a tadpole of _Rana

temporaria_, in which the fore-limbs were still hidden, the hind-limb, cut

at the middle of the thigh, reproduced nineteen days later a knee, followed

by a short two-toed stump. Ultimately the whole limb became completed. The

tail of tadpoles regenerates very quickly and completely, even if it be cut

off shortly before the final metamorphosis, when the tail would in any case

be reduced. Metamorphosed Anura have almost entirely lost this faculty, but

not absolutely. I myself have kept two specimens of _Rana temporaria_,

which, when already adult, had each lost a hand at the wrist. First there

was only the clean-cut stump with a scar, but within a year this changed

into a four-cornered stump, and two of the protuberances developed a little

further, reaching a length of about 4 mm. These specimens lived for four

years without further changes.

TEMPERATURE.–Amphibia, like Fishes and Reptiles, are, as a rule, classed as

cold-blooded animals, in opposition to the warm-blooded Birds and Mammals.

This distinction is one of degree only. The terms poikilothermous and

homothermous (ποίκιλος, {68}variable; ὅμος, equable) are based upon a

sounder principle, but are likewise liable to exceptions. Those creatures

which, like Birds and Mammals, possess a specific temperature of their own

under normal conditions, that of hibernation being excepted, are

homothermous. Cold-blooded creatures have no specific temperature; they

more or less assume that of their surroundings. Frogs and newts, for

instance, when living in the water, naturally assume its temperature, which

is, of course, many degrees lower in a cold spring than in a shallow pond

warmed by the sun on a hot summer's day. The same applies to the changes

from day to night. Dark-coloured tortoises basking in the sun are sometimes

so hot that they are disagreeable to touch, since they possess but little

mechanism for regulating their heat. The same individual cools down during

a chilly night by perhaps 40° C. Anura are, however, very susceptible to

heat; most of them die when their temperature rises to about 40° C. Under

such conditions they die quickly when in the water, but in the air their

moist skin counteracts the heat, lowering it by evaporation; otherwise it

would be impossible for a tree-frog to sit in the glaring sun in a

temperature of 120° F. Toads and others with drier skins seek the shade,

hide under stones, or bury themselves in the coolest spots available, and

many Amphibia and Reptiles aestivate in a torpid condition during the dry

and hot season. Many of them can endure a surprising amount of cold, and

during hibernation their temperature may sink to freezing-point. This power

of endurance does not apply to all alike; tropical species can stand less

than those which live in temperate and cold regions. In spite of many

assertions to the contrary, it may safely be stated that none of our

European frogs, toads, and newts survive being frozen hard. They may be

cooled down to nearly -1° C., and they may be partially frozen into the

ice. Circulation of the blood is suspended in such cooled-down frogs; their

limbs may become so hard that they break like a piece of wood, but the

citadel of life, the heart, must not sink much below freezing-point, and

must itself not be frozen, if the animal is to have a chance of recovering.

The protoplasm resists a long time, and so long as some of it is left

unfrozen the rest will recover. Hibernating frogs are lost if they are

reached by prolonged frost during exceptionally severe winters. Every frog

will be killed in an artificial pond with a clean concrete bottom, {69}but

if there is sufficient mud, with decaying vegetable matter, the creatures

survive, simply because they are not absolutely frozen. A severe winter not

infrequently kills off all the younger creatures, while the older and more

experienced hide themselves more carefully and live to propagate the race.

GEOGRAPHICAL DISTRIBUTION.

There is a very ably written chapter on the geographical distribution of

the Amphibia by Boulenger in the _Catalogue of Batrachia Gradientia_, pp.

104-118. He came to the important conclusion that the geographical

distribution of the Amphibia agrees in general with that of the freshwater

fishes. Günther's division into a Northern, Equatorial, and Southern zone

is modified only in so far as the last two are combined into one, "Tasmania

and Patagonia not differing in any point regarding their Frog Fauna from

Australia and South America respectively."

Boulenger recognises–

I. The Northern zone–(1) Palaearctic, (2) North American, region.

II. The Equatorial Southern zone.

_A._ Firmisternia division = Cyprinoid division of Günther.

1. Indian region.

2. African region.

_B._ Arcifera division = Acyprinoid division of Günther.

1. Tropical American region.

2. Australian region.

In the chapter on geographical distribution in Bronn's _Thierreich, Vögel,

Systematischer Theil_, p. 296 (1893), and in my _Classification of

Vertebrata_ (1898), due attention had been paid to the Amphibia as well as

to the other classes of Vertebrata. It will be seen in the following pages

that my arrangement is well applicable to the Amphibia so far as

fundamental principles are concerned.

It cannot be sufficiently emphasised that any attempt to form the various

faunas of the different classes of animals into one scheme must necessarily

be a _petitio principii_. The time-honoured six zoo-geographical regions

established by Sclater and Wallace represent fairly well the main

continental divisions: North America, South America, Africa, Australia, and

the large northern continental mass of the Old World, with India as a

tropical appendix. There is no correlation and no subordination {70}in this

scheme. Huxley's division (1868) into NOTOGAEA and ARCTOGAEA (see p. 74) is

of fundamental importance. The next improvement was the combination of the

Palaearctic and Nearctic "regions" into one, an advance originally due to

Professor Newton, carried out by Heilprin (1887) as the Holarctic region. I

have, in 1893, substituted for it the more appropriate term _Periarctic_,

meaning the whole mass of land which lies around the indifferent Arctic

zone. The want of further co-ordination and subordination required the

combination of the African and Oriental or Indian countries into a

_Palaeotropical region_ (1893); the Ethiopian or African and the Indian or

Oriental regions of Sclater and Wallace thereby assuming their proper

subordinate rank of subregions.

The two primary divisions NOTOGAEA and ARCTOGAEA are fundamental. The four

secondary divisions, namely the _Australian_ and _Neotropical_,

_Periarctic_ and _Palaeotropical regions_, also stand the test of

application to the various classes and main groups of Vertebrata; but

naturally, under the present configuration of the world, the Palaeotropical

region is nothing but the Southern continuation of the Eastern half of the

Periarctic mass of land. This is especially obvious so far as India is

concerned. There is, however, that broad belt of desert, sand, and

salt-steppes, which extends from North-West Africa to Manchuria, and this

belt is one of the most important physical features of the Old World. It is

complicated by the system of mountain-chains which, broadly speaking,

centre at the Pamirs, and radiate westwards through the Caucasus and Alps

into Spain, eastwards through the Himalayas into China, and north-eastwards

to Kamtschatka; interrupted by Bering's Sea, it is continued as the

backbone of both Americas to Patagonia.

The tertiary divisions, the subregions, have no real existence. They depend

upon the class, or even order, of animals, which we happen to study. The

faunistic distribution of the Urodela is not that of the Anura, and both

follow separate lines of dispersal, different from those of the various

orders of Reptiles, Birds, and Mammals. This must be so. There is no doubt

that the distribution of land and water was totally different in the Coal

Age from what it is now. The face of the globe at the Jurassic Age can

scarcely be compared with the aspect which the world has assumed in the

Miocene period.

This leads to another consideration, often neglected. We {71}know that the

various classes, orders, families, etc., of animals have appeared

successively upon the stage. A group which arose in the Coal Age followed

lines of dispersal different from one which was not evolved until Jurassic

times, and post-cretaceous creatures could not avail themselves of what

assisted their ancestors, and _vice versâ_. The Amphibia are bound

absolutely to the land and to fresh water; transportation across salt water

is not excluded, but must be accidental, and is not a case of regular

"spreading." Speaking generally, the older a group, the more likely is it

to be widely distributed. If it appears scattered, this may be due to

extinction in intermediate countries or to submergence of former

land-connexions.

There is great danger of arguing in a circle. It is one of the most

difficult tasks to decide in cases of great resemblance of groups of

animals between their being due to direct affinity or to heterogeneous

convergence, or parallel development. It is the morphologist who is

ultimately responsible for the establishment of faunistic regions, not the

systematist, least of all he who accepts an elaborate classification, and

then mechanically, mathematically, by lists of genera and species, maps out

the world. Let us take an example. The Neotropical region and Madagascar,

but not Africa, are supposed to be faunistically related to each other. In

both namely occur _Boa_ and _Corallus_ amongst snakes, Dendrobatinae

amongst Ranidae, and of the Insectivora _Solenodon_ in Cuba, _Centetes_ in

Madagascar. More cases can no doubt be found which would strengthen this

resemblance, perhaps in support of the startling view that Madagascar and

South America have received part of their fauna from the famous Antarctica.

But the value of the Insectivores has been disposed of by their recognition

as an extremely ancient group, or as a case of convergence, and the two

genera are no longer put into the same family as Centetidae. The

Dendrobatinae (_Mantella_ in Madagascar, the others in South America) are

decidedly not a natural group, but an instance of very recent convergence

(cf. p. 272). About the members of the ancient Boidae we do not feel quite

so sure.

It is therefore advisable to eliminate for zoogeographical purposes groups

about which there can be any reasonable doubt, otherwise we may argue that

certain genera must constitute a very old family, because they are now

restricted to widely {72}separated countries, or on the strength of their

distribution we may conclude that the genera in question cannot be related

to each other, and do not belong to the same sub-family or family as the

case may be. Such groups are the Engystomatinae and the genus _Spelerpes_;

amongst reptiles the Eublepharidae, Helodermatidae, Anelytropidae,

Ilysiidae, Amblycephalidae.

It is customary to represent the various regions and sub-regions as if they

had boundaries as fixed as political frontiers. Such limitations are quite

arbitrary, and what is of more importance, they differ in reality according

to the class or order of animals with which we happen to deal. Moreover,

there has been, and is probably still going on, an exchange or overlapping

of faunas. Such debatable grounds are Central America and the highlands of

North-western South America. The famous Wallace's line, between Borneo and

Celebes, Java and Lombok, is absolutely inapplicable to the Anura. From

their point of view the Austro-Malayan countries, Papuasia and Polynesia do

not form a sub-region of the Australian, but rather of the Palaeotropical

region. Concerning the Urodela, the division into Palae- and Ne-arctic

sub-regions is unjustifiable since Eastern Asia has emphatically American

affinities (cf. also p. 96). The Sahara and the rest of Northern Africa are

intimately connected with Arabia, Persia, Afghanistan, and Northern India,

just as equatorial Africa and Madagascar possess strong faunistic

relationship with Southern India and the Malay islands.

_Limiting factors of distribution._–Common salt is poison to the Amphibia;

even a solution of 1 per cent prevents the development of their larvae.

Consequently seas, salt lakes, and plains encrusted with saline deposits

act as most efficient boundaries to normal "spreading." But undoubtedly

many individuals have made long and successful voyages across the seas on

floating trees. Solutions of lime are likewise detrimental to many species,

and it is a general fact that limestone-terrain is poor in Amphibian life,

unless, of course, sufficient accumulation of humus counteracts or prevents

the calcareous impregnation of the springs and pools in meadows.

_Salamandra maculosa_ is, for instance, absent in Central Germany on the

Muschelkalk, but it occurs in abundance in neighbouring districts of red

sandstone or granite; nor can the larvae be reared successfully in very

"hard" water. On the other hand, _Proteus_ lives in the {73}subterranean

waters of Carniola, where the whole country is nothing but limestone.

Cold is another powerful limiting factor. The absolute northern limit of

Amphibian life coincides rather closely with the somewhat erratic line of

0° Centigrade of annual mean temperature, a little to the north of which

line the ground remains permanently frozen below the surface. The

surface-crust, which thaws during the summer, engenders an abundance of

insects as food-supply, but its freezing down to the icy bottom makes

hibernation impossible. There are, of course, some exceptions, for instance

the occurrence of Urodela in the Schilka river and in the district of Lake

Baikal.

Ranges of mountains are far less effective barriers than is generally

supposed. In many cases the fauna is the same on either slope, and they act

rather as equalising or dispersing factors, especially when they extend

from north to south. Witness the Andes, owing to which Ecuador and Peru

bear a great resemblance to the Central American fauna, and differ from the

tropical parts of South America. The existence of an _Amblystoma_ in Siam

is another instance.

The more specialised a family the more intimately is it connected with the

physical features of the country. Typically arboreal frogs are dependent on

the presence of trees. Some have undoubtedly spread into treeless countries

and have changed into prairie-frogs, e.g. _Acris_. They come out, so to

speak, as something different at the other end, and it is unlikely that

these modified descendants redevelop exactly the same features as their

ancestors before the migration. Baldwin Spencer[39] met with only six

species of frogs in Central Australia, _Limnodynastes_, _Chiroleptes_,

_Heleioporus_, and _Hyla_. They are in the main identical with certain

forms found in the dry inland parts of New South Wales and Queensland. They

are to be regarded as immigrants from the latter regions, which have been

able in the majority of cases to adapt themselves to unfavourable climatic

conditions by means of a marked development of the burrowing habit, to

which in certain cases has been added a capacity for absorbing and holding

water.

{74}FAUNISTIC DIVISIONS OF THE AMPHIBIA.

NOTOGÆA.–SOUTH WORLD.

* indicates Amphibia which are peculiar to the respective regions or

sub-regions.

Characterised by the Cystignathidae* and by the predominance of Arcifera,

which form nearly 90 per cent of the Anurous population.

I. AUSTRALIAN REGION.–Absence of Apoda and Urodela. All the Anura are

arciferous, with the exception of one species of _Rana_ in the Cape York

peninsula. The fauna of the Australian continent and of Tasmania consists

chiefly of Cystignathidae and Hylidae (_Hyla_ and _Hylella_) and several

small genera of Bufonidae (_Pseudophryne_,* _Notaden_,* and

_Myobatrachus_*).

It is customary, and from the study of other Vertebrata quite justifiable,

to divide the Australian region into several sub-regions, but the Amphibia

lend no support to this. The only Amphibian in the Sandwich Islands is a

_Bufo_, closely related to North American species. The only Amphibian in

New Zealand is _Liopelma_,* one of the Discoglossidae which are otherwise

confined to Europe, North-east Asia, and North-west America, and, to judge

from their low organisation, had formerly a much wider distribution. New

Caledonia possesses no Amphibia. The Fiji Islands are inhabited by one or

two species of _Cornufer_, a genus of Ranidae. The same genus is typical of

the Austro-Malayan and Papuasian islands, the fauna of which consists of

_Rana_ and _Cornufer_, _Ceratobatrachus_, several genera of Engystomatinae,

Hylidae, and Pelobatidae.

II. NEOTROPICAL REGION.–Characterised by Apoda, Aglossa (_Pipa_), abundance

of Cystignathidae (Hemiphractinae,* Cystignathinae, and

Dendrophryniscinae*), Hylidae (Hylinae and Amphignathodontinae*), numerous

Bufonidae and Engystomatinae; Dendrobatinae*; the Raninae are represented

by a few peculiar genera, mostly restricted to the Andesian province; the

genus _Rana_ occurs there in a few species only.

Absence of Discoglossidae, Pelobatidae and Dyscophinae.

Several species of Urodela, of the genus _Spelerpes_, extend from Central

America into the Andesian province, one occurs in Hayti, and _Plethodon

platense_ in Argentina.

This region is by far the richest in the number of families, {75}genera and

species; the total number of the latter being, according to Boulenger,

about four-ninths of the known species. The region comprises South America,

Central America, and the West Indian islands. Central America is naturally

debatable ground; one species of _Hylodes_ and one _Engystoma_, besides

about twenty Hylidae, extend into North America proper, while possibly the

Raninae have entered the Neotropical region from the north. _Bufo_ is too

cosmopolitan to assist our conclusions. The occurrence of four species of

_Hylella_ in South America, one in Australia, and one in New Guinea

indicate that this is not a natural genus.

From the point of the Amphibia the whole region can be divided into two

sub-regions only: (1) The West Indian islands with Central America and the

north-western Andesian province; (2) the rest of South America.

ARCTOGAEA.–NORTH WORLD.

Characterised by the absence of Cystignathidae.

I. PERIARCTIC REGION.–Characterised by the Urodela, these being almost

peculiar to the region (cf. p. 96). Absence of Apoda. Presence of

Discoglossidae, Pelobatidae, Bufonidae, Raninae. Few Hylinae occur.

The whole region can be subdivided into three sub-regions.

1. Western Palaearctic.–Prevalence of Salamandrinae (_Salamandra_,*

_Chioglossa_,* _Salamandrina_,* _Triton_); Proteidae (_Proteus anguinus_*);

_Spelerpes fuscus_.*–_Discoglossus_, _Bombinator_, _Alytes_,* _Bufo_, _Hyla

arborea_, _Pelobates_,* _Pelodytes_,* _Rana_.

2. Eastern Palaearctic.–Amphiumidae (_Cryptobranchus_); Salamandrinae

(_Triton_, _Pachytriton_,* _Tylototriton_*); Amblystomatinae.–_Bombinator_,

_Bufo_, _Hyla arborea_, _Rana_, _Rhacophorus_.

3. Nearctic.–Amphiumidae (_Cryptobranchus_, _Amphiuma_*); Proteidae

(_Typhlomolge_,* _Necturus_*); Sirenidae*; Amblystomatinae; most

Plethodontinae; Desmognathinae.*–Discoglossidae, Pelobatidae

(_Scaphiopus_*); _Bufo_; Hylidae (_Hyla_, _Acris_, _Chorophilus_); _Rana_.

II. PALAEOTROPICAL REGION.–Characterised by the presence of Apoda and by

the great prevalence of Firmisternal Anura, which amount to nearly 90 per

cent of the total population. {76}Absence of Urodela (except _Amblystoma

persimile_*), of Cystignathidae, and practically of the Hylidae, only two

of which occur in the Himalayan district. But this great chain of mountains

should not be included within the region, while the outlying spurs in Upper

Burma (with _Amblystoma_) are debatable ground. The subdivision of this

widely extended region is beset with difficulties, chiefly on account of

Madagascar and Papuasia. The fauna of Madagascar is very remarkable. All

its Amphibia are Firmisternal, a mixture of African and Indian forms. The

island agrees with Africa, in opposition to the Oriental countries, in no

special point; all the Raninae, except _Megalixalus_, _Rappia_, and two

rather common species of _Rana_, belong to different genera. Madagascar

differs from Africa by the absence of Apoda, of Aglossa, and Bufonidae. On

the other hand, it agrees with India or with the Malay islands, in

opposition to Africa, by the possession of Dyscophinae, of the Ranine genus

_Rhacophorus_, and the Engystomatine genus _Calophrynus_.

Africa and India agree with each other, and differ from Madagascar by the

possession of Apoda, the genera _Bufo_ and _Nectophryne_, and by the close

resemblance of several genera of Raninae.

India, the Malay islands, and Papuasia with Melanesia possess Pelobatidae

(_Leptobrachium_,* _Batrachopsis_,* _Asterophrys_*), and thereby differ

considerably from Africa and Madagascar. _Batrachylodes_* of the Solomon

Islands has unmistakable affinities with _Phrynoderma_* of Karen, between

Burma and Siam; _Oreobatrachus_* of Borneo much resembles

_Phrynobatrachus_* of West Africa; and _Cornufer_, typical of the Malay and

Melanesian islands, occurs also in West Africa. All these Raninae indicate

that the Austro-Malayan and Melanesian islands belong to the Palaeotropical

region. _Ceratobatrachus_,* type of a sub-family, is peculiar to Melanesia.

There are consequently several possible modes of subdivision, all with a

different result, according to the group of Amphibia, which we may select

as of leading importance, _e.g._ Apoda or Pelobatidae, or Dyscophinae and

_Rhacophorus_. The Engystomatinae and Raninae are to be eliminated, since

they occur in all the countries in question. We have either to leave the

whole region undivided–and it is a significant fact that the {77}Indian

countries possess not one sub-family of their own–or we must break it up

into four provinces, not sub-regions:–

1. Ethiopian, or continental African, with Aglossa and Apoda, no

Pelobatidae, no Dyscophinae, few Bufonidae, and many Raninae.

2. Indian and Malayan, with Apoda, no Aglossa, but with Pelobatidae,

Dyscophinae, many Bufonidae and Raninae, amongst which _Rhacophorus_.

3. Malagasy, without either Apoda or Aglossa; with Firmisternal Anura

only, chiefly Dyscophinae, and _Rhacophorus_ and other Raninae.

4. Papuasian, without Apoda, Aglossa, Dyscophinae, and Bufonidae, but

with Pelobatidae and Ranidae.

DISTRIBUTION OF FAMILIES AND SUB-FAMILIES OF THE AMPHIBIA.

Aus. = Australian.

N-t. = Neotropical.

N-a. = Ne-arctic.

Pal-arct. = Palae-arctic.

Eth. = Ethiopian.

Mal. = Malagasy.

Ind. = Indian.

Pap. = Papuasian.

N.Z. = New Zealand.

+––––––––––––––––––––+––––+––––+––––+––––+––––+––––+––––+––––+––––+––––+

| |Aus.|N–t.|N–a.|Pal–arct.|Eth.|Mal.|Ind.|Pap.|N.Z.|

| | | | +––––+––––+ | | | | |

| | | | | W. | E. | | | | | |

+––––––––––––––––––––+––––+––––+––––+––––+––––+––––+––––+––––+––––+––––+

|Amphiumidae | | | + | | + | | | | | |

|Salamandridae | | + | + | + | + | | | 1 | | |

|Proteidae | | | + | + | | | | | | |

|Sirenidae | | | + | | | | | | | |

|Apoda | | + | | | | + | | + | | |

|Aglossa | | + | | | | + | | | | |

|Discoglossidae | | | | + | + | | | | | + |

|Pelobatidae | | | + | + | | | | + | + | |

|Bufonidae | + | + | + | + | + | + | | + | + | |

|Hylinae | + | + | + | 1 | 1 | | | | | |

|Amphignathodontinae | | + | | | | | | | | |

|Hemiphractinae | | + | | | | | | | | |

|Cystignathinae | + | + | 1 | | | | | | | |

|Dendrophryniscinae | | + | | | | | | | | |

|Genyophryninae | | | | | | | | | | |

|Engystomatinae | | + | 1 | | | | + | + | + | |

|Dyscophinae | | | | | | + | + | + | | |

|Dendrobatinae | | + | | | | | × | | | |

|Raninae | | + | + | + | + | + | + | + | + | |

|Ceratobatrachinae | | | | | | | | | + | |

+––––––––––––––––––––+––––+––––+––––+––––+––––+––––+––––+––––+––––+––––+

1 signifies the occurrence of only one species of an elsewhere numerous

group.

× _Mantella_, cf. p. 71 and p. 272.

{78}CHAPTER IV

STEGOCEPHALI OR LABYRINTHODONTS–LISSAMPHIBIA–APODA

_SUB-CLASS I. STEGOCEPHALI OR PHRACTAMPHIBIA_

_With a considerable amount of dermal armour, especially on the head._

The earliest known terrestrial four-footed creatures occur in the

Carboniferous strata of Europe and North America. They and their immediate

allies, which extend through the Permian into the Upper Trias, are now

comprised under the name of STEGOCEPHALI, so called because the whole of

the dorsal side of the cranium is covered, or roofed over, by dermal bones

(στέγος, roof; κεφαλή, head). That these creatures, of which naturally only

the skeletal parts are known, were not fishes, is shown by the typically

pentadactyloid limbs; but to recognise them as Amphibia, and as distinct

from Reptiles, is difficult, especially if the incipient Reptilia, which

have sprung from some members of this Stegocephalous stock, are taken into

account. However, they possess either two occipital condyles, or none, and

their vertebrae are either pseudocentrous or notocentrous, but not

gastrocentrous. Moreover, the whole skeletal organisation is still so

ideally generalised, that it is easy to derive directly from it the

arrangement prevailing in the Apoda and Urodela.

The vertebral column always comprises a well-developed, sometimes a very

long tail. The vertebrae exhibit three types, two of which are

fundamentally distinct, while the third is a further development of the

second.

1. _Lepospondylous and pseudocentrous._–The vertebra consists of a thin

shell of bone surrounding the chorda dorsalis, and is composed of two pairs

of arcualia, which meet each other, {79}forming a suture, along the lateral

side of the vertebra, both partaking in the formation of a transverse

process which carries the rib.

2_a_. _Temnospondylous._–The vertebra is composed of three pairs of units,

which remain in a separate, unfused state. Two of them are dorsal arcualia,

one of which tends to form the centrum of the vertebra, which then carries

the neural arch.

2_b_. _Stereospondylous._–The three component units fuse by co-ossification

into a solid, amphicoelous vertebra.

The ribs are one- or two-headed, rather strong, but short, rarely reaching

half-way round the body. They occur on all the vertebrae of the trunk and

on most of those of the tail. One pair of ribs connects one vertebra, the

sacral, with the pelvis, of which the ilium and ischium are generally

ossified, rarely also a portion of the pubic region.

The shoulder-girdle is very primitive, greatly resembling that of the

Crossopterygian fishes. It consists of the following bones:–a median,

rhombic, or T-shaped interclavicle, a pair of clavicles, of cleithra, of

coracoids, and of scapulae. The limbs show the typical pentadactyle plan,

but even in these earliest Tetrapoda the hand possesses only four fingers,

with 2, 2, 3, 2 phalanges respectively. The foot has five toes, with 2, 3,

4, 4, 3, or 2, 2, 3, 4, 3 phalanges.

Many Stegocephali were possessed of a dermal armour, covering either the

whole body or only the under parts. Hence the term Phractamphibia (φρακτός,

armoured). The armour consists of a great number of small cutaneous scales,

partly calcified, or perhaps ossified, and arranged in many more or less

transverse rows. We can only surmise that these scales were covered by

corresponding epidermal sheaths. The skull is ideally complete in the

number of separate bones which appear on its surface. Besides the outer

nares and the orbits there is always an unpaired, small, interparietal

foramen. The whole temporal region is completely roofed over. The following

bones are present:–nasals, frontals, parietals, supra- and

latero-occipitals; lacrymals (unless fused with the jugals?), prefrontals,

postfrontals, postorbitals, squamosals, and epi-(or opisth-)otics;

premaxillaries, maxillaries, jugals, quadrato-jugals, and supra-temporals;

quadrates, pterygoids, palatines, vomers, and an unpaired parasphenoid.–The

lower jaw is composed of a pair of dentaries, {80}articulars, angulars, and

splenials. The dentaries and apparently sometimes the splenials, the

palatines, maxillae, and vomers carry teeth. The eyes possess a ring of

sclerotic bones.

ORDER I. STEGOCEPHALI LEPOSPONDYLI.

Vertebrae pseudocentrous.

SUB-ORDER 1. BRANCHIOSAURI.–The young had several pairs of gill-arches,

which, to judge from their size and from the fact that they are beset with

numerous nodules, denticles, or irregular little processes like

gill-rakers–seem to have been exposed to the surface and to have carried

gills. In the adult the arches and gills seem to be absent.

[Illustration: FIG. 12.–A, Dorsal and B, ventral views of the cranium of

_Branchiosaurus salamandroides_, × about 4. (After Fritsch.) C, Posterior

view of the cranium of _Trematosaurus_, × about ½. (After Fraas.) _Br_,

Branchial arches; _C_, condyle; _Ep_, epiotic; _F_, frontal; _J_, jugal;

_L.O_, lateral occipital; _M_, maxillary; _N_, nasal; _No_, nostril; _Pa_,

parietal; _Pl_, palatine; _Pm_, premaxillary; _P.o_, postorbital; _Pr.f_,

prefrontal; _Ps_, parasphenoid; _Pt_, pterygoid; _Ptf_, postfrontal; _Q_,

quadrate; _Qj_, quadrato-jugal; _S.o_, supraoccipital; _Sq_, squamosal;

_St_, supratemporal; _V_, vomer.]

One of the commonest genera is _Branchiosaurus_, including _Protriton_. _B.

salamandroides_ of the Lower Red Sandstone of Europe is known in every

stage, from larvae of 16 mm. to the full grown animal of 64 mm. in length.

The whole body was {81}covered with little cutaneous scales. _Pelosaurus_

and perhaps _Melanerpeton_ are allied genera.

The following genera are small newt-like creatures of the Carboniferous age

of Europe and North America. In _Keraterpeton_ of Bohemia, Ireland, and

Ohio, the dermal scales were restricted to the under parts; and the ribs

were rather long, reaching half way round the body. Gills have not been

observed. _K. crassum_, a European species, reached more than one foot in

length, two-thirds of which fall to the tail. The ventral side is covered

with a most elaborate armour, which consists of about eighty chevron-shaped

rows of little scale-shaped nodules. The epiotic bones end in strange

processes, carrying a pair of spikes, giving the skull a "horned"

appearance, hence the generic name. _Urocordylus_ is an allied genus.

SUB-ORDER 2. AISTOPODES.–Body snake-like and without any limbs, hence the

name ἄιστος, unseen; ribs long, and reaching half way round the body; from

Carboniferous strata in Ireland and Bohemia, with allied, or perhaps

identical forms in Ohio. _Dolichosoma longissimum_ possessed more than 150

vertebrae, and was about a yard long. The epiotics end in obtuse

projections, recalling those of _Keraterpeton_. These marvellous creatures

had strange appendages, extending from behind the sides of the head, which

were possibly the supports of external gills; since the upper end of one of

the visceral arches, probably the hyoidean arch, is attached to the

labyrinthic region, and from this arch starts a bony rod which carries long

skeletal filaments. The body seems to have been naked.

_Ophiderpeton_ had a compound ventral shield, while the skin of the back

contained granular scutes. Although the Aistopodes have, not without

reason, been looked upon as greatly resembling the Coeciliae or Apoda in

organisation, especially in that of the vertebral column, the total absence

of any other fossils which might bridge over the enormous gulf between the

Coal Age and recent times, makes the attempt to derive the Apoda from these

creatures very hazardous.

ORDER II. STEGOCEPHALI TEMNOSPONDYLI.

Mostly with rather long ribs and with chiefly ventral armour.

{82}_Chelydosaurus_ from the Lower Red Sandstone of Bohemia was 3 feet

long, and possessed a beautiful, complicated, ventral armour, consisting of

about sixty chevron-shaped rows, about three times as numerous as the

vertebrae in the corresponding region. _Sphenosaurus_ from the same strata

and localities must have been 2 yards long. The trunk-vertebrae of both

these genera were composed of four pairs of arcualia. _Trimerorhachis_ from

the Permian of Texas is very imperfectly known, but its trunk-vertebrae, as

the name implies, consist of three pairs of separate arcualia, one of

which, the interdorsal pair, tends to form a kind of centrum.

_Dissorophus multicinctus_, also from the Permian of Texas, has been

described by Cope[40] as a "Batrachian Armadillo," and considered allied to

_Trimerorhachis_. Ten vertebrae are known, of an aggregate length of 93

mm.; the length of the creature was perhaps one yard. The neural spines are

elevated, and the apex of each extends in an arch on each side to the ribs.

These spinous branches touch each other, forming a carapace. Above, and

corresponding to each of them, is a similar dermal and osseous element,

which extends from side to side without interruption in the median line,

forming a dermal layer of transverse bands which correspond to the skeletal

carapace beneath it. This creature remotely approaches the genus

_Zatachys_, Cope, where a dermosteous scute is co-ossified with the apex of

the neural spine. The systematic position of this genus is at least

doubtful.

_Archegosaurus decheni_ from the Lower Red of Germany, known by many

well-preserved specimens, reached a length of 4 or 5 feet. The trunk

vertebrae are tri-partite, those of the tail quadri-partite, like those of

the trunk of _Chelydosaurus_. Young specimens show traces of gill-arches.

The thoroughly terrestrial walking limbs have four fingers and four toes;

the arrangement of the tarsalia, most of which are ossified, lend support

to the view that the morphological axis went through femur, fibula,

intermedium, the centralia, the second distal tarsale, and the second toe.

The dentine and enamel of the teeth are much folded, and this feature,

which applies to most members of this Order, to a lesser degree also to

others, has caused them to be comprised under the name of LABYRINTHODONTA.

The upper {83}surface of the head shows very characteristically arranged

grooves, which probably contained slime-canals and possibly sensory organs.

_Actinodon_ and _Euchirosaurus_ are closely allied forms, chiefly from the

Lower Red Sandstone of France; _Gondwanosaurus_ occurs in the Permian of

India.

ORDER III. STEGOCEPHALI STEREOSPONDYLI.

These are the most highly developed members of the typical Labyrinthodonta,

characterised by their much-folded teeth, and by their solid, bi-concave

vertebrae. _Loxomma_ occurs in the Upper Carboniferous of England and in

the Lower Red of Bohemia: _Trematosaurus_, _Capitosaurus_, and _Metopias_

from the New Red or Lower Trias to the Keuper of Germany. _Mastodonsaurus_

from the Trias of England and Germany is the most gigantic Amphibian known,

with a skull of nearly 1 yard in length.

_Labyrinthodon_ from the Keuper of Warwickshire is one of the latest

members of the group. Labyrinthodont creatures have also been described

from the Trias of South Africa, _e.g._ _Rhytidosteus_; those from North

America are insufficiently preserved.

Many of these and allied genera have left their footprints in slabs of

Sandstone, both Lower and New Red, in Europe, Africa, and America. But

although their spoors are common enough, only a few can with certainty be

referred to Stegocephali, _e.g._ _Saurichnites salamandroides_ of the Lower

Red of Germany. The spoors of _Chirotherium_, common in the New Red of

Germany and England, for instance in Cheshire, belong to unknown owners;

both the large hind feet (which measure nearly half a foot in length) and

the much smaller fore feet, had five digits, the first of which stood off

like a thumb. Five-fingered Stegocephali are unknown.

There is an almost complete absence of fossil Amphibia from the Upper Trias

to the Oligocene. The Stegocephali as such seem to have died out with the

Trias. The recent Amphibia, of course, must have had ancestors in the

Mesozoic age. There is one little skeleton, from the Wealden of Belgium,

which belonged to a newt-like creature, called _Hylaeobatrachus croyi_.

Scarce fragments, described as _Megalotriton_, are known from the Oligocene

of France, and _Triton_ itself seems to be indicated by {84}remnants in the

Lower Miocene of France and Germany. But fairly complete specimens of large

creatures, much resembling _Cryptobranchus_, have been found in the Upper

Miocene of Oeningen, Canton Solothurn, Switzerland. The first known

specimen, now at Haarlem, indicating a total length of 3 feet or more, was

described and figured in the year 1726 by Scheuchzer, in a learned

dissertation entitled "_Homo diluvii testis_."

Betrübtes Beingerüst von einem alten Sünder

Erweiche Herz und Sinn der neuen Bosheitskinder.

Which may be rendered as follows:–

Oh, sad remains of bone, frame of poor Man of sin

Soften the heart and mind of sinful recent kin.

This was the motto attached to the illustration, and it remained a warning

to mankind until Cuvier declared the skeleton to be that of some large

newt. Tschudi named it _Andrias scheuchzeri_, but it is scarcely

generically distinct from _Cryptobranchus_, being almost intermediate

between _C. alleghaniensis_ and _C. japonicus_, see p. 97.

_SUB-CLASS II. LISSAMPHIBIA._

_Amphibia without dermal armour._

ORDER I. APODA OR LIMBLESS AMPHIBIA.

The Amphibia Apoda, Coeciliae or Gymnophiona, are a small group of

worm-shaped, burrowing creatures, restricted to the Neotropical and

Palaeotropical regions, excluding Madagascar. They have no limbs and no

girdles. The tail is extremely short; the vertebrae are pseudo-centrous,

and most of them carry rather long ribs, none of which, however, meet to

form a sternum. The whole snake-like body is covered with a smooth and

slimy skin which forms numerous transverse folds or rings.

The most remarkable feature of the SKULL is its solid compactness, which

stands in direct correlation with the burrowing habits of these creatures.

The whole dorsal surface of the cranium is practically roofed in by bone,

so that, in this respect, it greatly resembles that of the Stegocephali;

but this resemblance is produced chiefly by a broadening of those bones

which exist also in the other Lissamphibia, while supratemporals and

supra-occipitals are absent.

{85}[Illustration: FIG. 13.–Skull of _Ichthyophis glutinosa_. × 3. (After

Sarasin.) A, Lateral, B, ventral, C, dorsal view. _A_, Posterior process of

the os articulare; _Ca_, carotid foramen; _Ch_, choana or posterior nasal

opening; _F_, frontal; _J_, jugal; _Lo_, lateral occipital; _Mx_,

maxillary; _N_, nasal; _No_, nostril; _O_, orbit; _P_, parietal; _Pa_,

palatine; _Pm_, premaxillary; _Pof_, postfrontal; _Prf_, prefrontal; _Pt_,

pterygoid; _Q_, quadrate; _S_, squamosal; _St_, stapes; _T_, tentacular

groove; _Vo_, vomer; _X_, exit of vagus nerve.]

There is, however, a pair of bones which represent either the postorbitals

or the postfrontals, perhaps both, of the Stegocephali. The quadrato-jugal

arch is enormously developed, and by reaching the parietal, frontal, and

postorbito-frontal bones (which latter occur only in _Ichthyophis_ and

_Uraeotyphlus_) and the maxilla, extends over the whole of the

orbito-temporal fossa. The squamosal is completely fused with the

quadrato-jugal. The stapes has the typical stirrup-shape, is even

perforated by an artery, and articulates distally with the shaft of the

quadrate (as in the snakes). The maxilla is very large and broad. Owing to

its broad junction with the quadrato-jugal arch, the prefrontal and

frontal, the orbital fossa is reduced to a very small hole, or the maxilla

completely covers the eye. Somewhere between the latter and the nares the

maxilla is perforated by the tentacular groove. The periotic bones are

represented by the prootics and epiotics; they fuse with the lateral

occipitals and with the parasphenoid. The whole {86}orbito-ethmoidal region

of the primordial skull is also turned into one mass of bone.

The angular element of the lower jaw forms a thick and large process which

projects upwards and backwards from the mandibular joint. The former

possession of a splenial bone is indicated by the occurrence of a second

series of teeth in the mandibles of _Ichthyophis_ and _Uraeotyphlus_. Other

genera have vestiges of this second row, or it may be completely lost.

The hyoid and branchial apparatus is more primitive than in any other

recent Amphibia. In the larva the hyoid and the first and second branchial

arches are connected with each other by a median copular piece. The third

branchial arches are free from the rest, but are fused in the middle line,

the fourth are loosely attached to the previous pair. In the adult both

fuse into one transverse, curved bar, and the second pair of branchials

lose their connexion with the basal longitudinal piece and likewise form a

transverse bar.

The vertebrae are built upon the pseudocentrous type, are amphicoelous, and

the chorda is intravertebrally destroyed by cartilage, as in the majority

of the Urodela. The number of vertebrae is great, amounting in some species

to between 200 and 300, of which a few belong to the tail. The first

vertebra is devoid of an odontoid process. The ribs are proximally

bifurcated as in the Urodela.

The eyes are practically useless, being either more or less concealed under

the skin, or they are covered by the maxillary bones. All Coecilians

possess a peculiar tentacular sensory apparatus, which consists of a

conical flap-shaped or globular soft tentacle, which is lodged in a special

groove or canal of the maxilla, between the eye and the nose, whence it is

frequently protruded while the animal is crawling about. These tentacles in

the young _Siphonops_ lie, according to the Sarasins, quite close to the

eyes, but are later transferred nearer to the nose. The organ consists of a

peculiarly rolled up and pointed fold which arises from the bottom of the

sac or pit, where it receives a nerve. It is protruded by becoming turgid

with blood, and is retracted by a strong muscle. Into the lumen of the sac

are poured secretions from the large orbital (Harderian) gland, to keep the

apparatus clean. Hence arose the mistaken {87}notion of its being a

poison-organ. The whole structure is possibly an offshoot of the

naso-lacrymal duct.

The skin is most remarkable. In the ripe embryo the epidermis passes

smoothly over the surface. Beneath follow two layers of soft cutaneous

connective tissue, bound together by transverse or vertical lamellae, so

that ring-shaped compartments are formed, and in these are embedded

slime-glands. In the adult each compartment is modified into an anterior

glandular belt and a posterior space, from the bottom of which grow several

scales. The number of cutaneous rings agrees originally with that of the

vertebrae; but later, and especially in the hinder portion of the trunk,

each ring breaks up into two or more secondary segments, and these no

longer agree with those of the skeleton. Each scale is beset with numerous

smaller scales which consist of hardened cell-secretions infiltrated with

calcareous matter. The whole scale is consequently an entirely mesodermal

product of the deeper layers of the cutis. The usual statement that the

skin forms imbricating lamellae, on the inner side of which appear the

scales, is wrong. The "lamellae" can be lifted up only after the general

epidermal sheath has been broken artificially in the constrictions between

the rings. No scales exist in the Indian genus _Gegenophis_ and in the

American _Siphonops_, _Typhlonectes_, and _Chthonerpeton_, a secondary loss

which does not indicate relationship. The scales develop late in embryonic

life, and they are reasonably looked upon as inheritances from the

Stegocephali. The glands either produce slime, whose function seems to be

the keeping clean of the surface of the body, or they are squirt-glands.

The latter kind are also numerous and are filled with a fluid which is

squeezed out by muscular contraction, and seems to be poisonous, as it

causes sneezing to those who handle or dissect fresh specimens.

The Coecilians live in moist ground and lead a burrowing life. Their

developmental history has only recently been studied, and in but a few

species, see _Ichthyophis_, p. 91, and _Hypogeophis_, p. 92. The female is

fertilised internally, copulation taking place by means of eversion of the

cloacal walls in the shape of a tube. The spermatozoa possess an undulating

membrane; the eggs undergo meroblastic division and the embryos have three

pairs of long external gills. Some are viviparous.

The snake-like, limbless shape of the body (Fig. 15) is, as in {88}snakes,

correlated with an asymmetrical development of the lungs; the left is

reduced, while the right is drawn out into a long cylindrical sac. The

liver is likewise very long, and partly constricted into a great number of

lobes. Owing to the great reduction of the ribs progression is effected in

an almost earthworm-like fashion by the peristaltic motion of the skin,

assisted by its numerous ring-shaped constrictions.

The systematic position of the Coeciliae has been, and is still, a

controversial matter. The Sarasins took up Cope's suggestion, that their

nearest allies are the Urodela, especially _Amphiuma_, and they went so far

as to look upon _Amphiuma_ as a neotenic form of the "Coecilioidea," which

they divided into Amphiumidae and Coeciliidae; the Coecilioidea and

Salamandroidea forming the two sub-orders of the Urodela. They based this

startling conclusion chiefly upon remarkable resemblances between

_Amphiuma_ and _Ichthyophis_, namely, (1) the mode of laying the eggs on

land and coiling themselves around them; (2) the existence of remnants of a

tentacular apparatus in _Amphiuma_; (3) Cope's statement that _Amphiuma_

alone among the Urodela possesses an ethmoid like the Coeciliae. This

latter point is, however, erroneous; it has since been shown by Davison[41]

that _Amphiuma_ possesses no ethmoid bone, but that, instead of it,

descending plates of the frontals join below the premaxilla and function as

a nasal septum, with a canal for the olfactory nerves.

We look upon the Apoda with more reason as creatures which of all the

Lissamphibia have retained most Stegocephalous characters and at the same

time form a highly specialised group equivalent to the Urodela and the

Anura. The following are Stegocephalous inheritances peculiar to the Apoda

in opposition to the other recent Amphibia: retention of cutaneous scales

with calcareous incrustations, greatly resembling the scales of the

Carboniferous Microsauri; occasional retention of post-frontal and lateral

nasal or lacrymal bones, and of a second row of teeth in the mandible. To

these may be added the presence of epiotic bones, and the primitive

character of the branchial arches. The loss of all these characters would

turn the present Apoda into limbless Urodela, but this assumption does not

justify their inclusion in this Order. The possible homology of the

tentacular apparatus has been discussed elsewhere, p. 45.

{89}Fossil Apoda are not known; their subterranean life does not favour

preservation.

[Illustration: FIG. 14.–Map showing the distribution of the Coeciliae or

Amphibia Apoda.]

Only family, COECILIIDAE. About forty species are known. These have been

placed in seventeen genera, mostly on comparatively slight grounds, and

several of these genera are probably unnatural, the distinctive characters

having undoubtedly been developed independently in various countries. We

have to remember that the recent species are the remainder of a formerly

much more numerous group; it is also likely that more will be discovered in

the tropical forests of South America and Sumatra.

Boulenger[42] has distinguished them as follows:–

I. Cycloid scales embedded in the skin.

_A_. Eyes distinct, or concealed under the skin.

_a_. Two series of teeth in the lower jaw.

α. Quadrato-jugal (squamosal) and parietal bones in contact.

Tentacle between eye and nostril.

_Ichthyophis_, 2 species, India and Malay islands, p. 90.

" below and behind nostril.

_Hypogeophis_, 3 species, East Africa and Seychelles, p. 92.

" below and in front of eye.

_Dermophis_, 5 species, America and Africa, p. 93.

" below the nostril. _Coecilia_, 6 species, America.

β. Quadrato-jugal separated from parietal.

Tentacle close to the eye. _Rhinatrema_, 2 species, America.

" below and behind nostril.

_Geotrypetes_, 1 species, West Africa.

" below nostril.

_Uraeotyphlus_, 3 species, West Africa and India.

_b_. One series of teeth in the lower jaw.

Tentacle in front of the eye.

_Cryptopsophis_, 1 species, Seychelles.

_B_. Eyes below the cranial bones. Quadrato-jugal in contact with{90}

parietal.

Tentacle near the nostril.

_Gymnophis_, 4 species, South America.

_Herpele_, 2 species, Panama and Gaboon.

II. Without scales.

_A_. Eyes distinct, or concealed under the skin.

_a_. Two series of teeth in the lower jaw.

α. Quadrato-jugal in contact with parietal.

Tentacle behind nostril; end of body laterally compressed.

_Typhlonectes_, 3 species, America, p. 93.

β. Quadrato-jugal separated from parietal.

Tentacle between eye and nostril.

_Chthonerpeton_, 2 species, America.

_b_. One series of teeth.

α. Quadrato-jugal and parietal in contact; tentacle in front of

the eye.

_Siphonops_, 4 species, America.

β. Quadrato-jugal separated from parietal.

_Bdellophis_, 1 species, East Africa.

_B_. Eyes below the cranial bones.

_a_. Two series of teeth. Quadrato-jugal and parietal in contact;

tentacle behind and below nostril.

_Gegenophis_, 1 species, India.

_b_. One series of teeth. Quadrato-jugal separated from parietal.

_Scolecomorphus_, 1 species, East Africa.

_Boulengerula_, 1 species, East Africa.

_Ichthyophis glutinosa_ extends from the slopes of the Himalayas to Ceylon,

the Malay islands, and into Siam. A second species, _I. monochrous_, occurs

in Malabar, Malacca, Borneo, and Java. _I. glutinosa_ reaches about one

foot in length, with a greatest thickness of a little more than half an

inch. The general colour is dark brown or bluish black, with a yellow band

along each side of the body.

This species has been studied extensively by the Sarasins.[43] It breeds in

Ceylon after the spring monsoon. The ovarian egg is oval, measuring 9 by 6

mm. The yolk is yellow; the blastoderm lies towards one of the poles. The

strong vitelline membrane becomes surrounded in the oviduct by a dense

albuminous membrane, which forms twisted chalazae, just like those of

birds' eggs, and by these two cords the eggs are strung together. Around

all this lies another mantle of albumen. The female digs a hole close to

the surface in moist ground near {91}running water, and there lays about

two dozen eggs. The egg-strings become glued together, entangled into a

bunch, and the female coils herself round the bunch and remains in that

position, probably to protect the eggs against other burrowing creatures,

as blind snakes (_Typhlops_ and _Rhinophis_) and certain limbless lizards,

with which the ground literally swarms. During this kind of incubation the

eggs assume a round shape, and grow to twice their original size, and the

mature embryo weighs four times as much as the newly laid egg.

[Illustration: FIG. 15.–_Ichthyophis glutinosa_ × 1. (After P. and F.

Sarasin.) 1, A nearly ripe embryo, with gills, tail-fin, and still with a

considerable amount of yolk; 2, female guarding her eggs, coiled up in a

hole underground; 3, a bunch of newly laid eggs; 4, a single egg, enlarged,

schematised to show the twisted albuminous strings or chalazae within the

outer membrane, which surrounds the white of the egg.]

The external gills are delicately fringed and red, and they move up and

down in the fluid of the egg. The body of the embryo is at first white, but

becomes pigmented with dark grey. A strong line of lateral sense-organs is

formed, and a ring of them lies around the eye and others on other parts of

the head. The short tail develops a fin. Of the three pairs of gills the

third is the shortest, and is generally turned dorsalwards. In embryos of 4

cm. in length the longest gill measures as much as 2 cm. Yolk is still

present in embryos which have reached the surprising length of 7 cm. Then

the gills begin to shrink a little, and at this time one pair of

gill-clefts breaks through at the base of the third external gill.

When the larvae are hatched the gills are lost. The young larva takes to

the water in a gill-less state, and moves about like an eel. At the bottom

of the gill-hole on each side two arches are visible, and there are at this

stage neither inner nor {92}outer gills. The larvae frequently come up to

the surface to breathe. The eyes are large and clearly visible, but the

tentacles are still undeveloped. The epidermal sense-organs are numerous,

and appear as white spots in the grey skin; about fifty extend from the

gill-opening to the tip of the tail.

_Ichthyophis_ seems to live a long time in the larval state. At last the

gill-clefts close, the tail-fin disappears, and the tentacles come to the

surface. The whole skin assumes a totally new structure, and the fish-like

larva turns into a burrowing, subterranean creature so terrestrial that it

gets drowned when made to remain in the water.

_Hypogeophis._–According to A. Brauer[44] three species of Coecilians are

found in the Seychelles: _Cryptopsophis multiplicatus_, which is rare,

_Hypogeophis rostratus_ and _H. alternans_. They live in moist ground, near

the coast in swamps, higher up in humus, under rotten trees and rocks, down

to the depth of one foot. In the island of Silhouette, Brauer found them in

brooks, at least during the dry season, from May to September. The natives

call them "vers de terre." They seem to propagate during the greater part

of the year, provided there is sufficient moisture. The female coils round

the eggs, which vary from half a dozen to thirty in number, those of _H.

rostratus_ measuring 7-8 mm., those of _H. alternans_ only 4-5 mm.

The embryos undergo their whole development in the egg. Four pairs of

gill-clefts break through, the first between the hyoid and the first

branchial arch, the fourth between the third and fourth branchial arches.

There appears also a spiracular cleft between the quadrate and the hyoid

arch; this cleft is, however, only developed dorsally, and persists for a

shorter time. The external gills appear at the same time as the clefts,

upon the first three branchial arches; the third gill is the latest, and

remains in a vestigial condition covered up by the two others. The gills,

of which the second is the longest, are not (as stated by the Sarasins)

direct prolongations of the gill-arches, but they begin as button-like

growths upon the arches. They begin to disappear with the absorption of the

yolk, getting actually smaller. In embryos of 6 cm. they are 6 mm. long,

while in embryos of 6.5 cm. they are reduced to 4.5 mm. in length. The

{93}first to disappear is the third gill, of course by being resorbed; and

the clefts are closed before the creature leaves the egg. _Hypogeophis_ not

leading an aquatic larval life possesses no tail-fin in the embryonic

state, the gill-holes are closed, and the epidermal sensory organs

disappear long before the time of hatching.

Vestiges of gills appear also on the hyoid and on the mandibular arch, but

on the latter they are of very short duration. Those of the hyoid gradually

fuse with the first of the branchial gills, and these also concentrate with

their bases so that they ultimately seem to spring from one common stem.

Brauer remarks that the distinction between internal and external gills

seems to be one of degree only; the hyoidean and mandibular gills namely

start from the hinder margin of the arches, just like the internal gills of

_Torpedo_ according to Ziegler, while the other gills start from the sides

of the branchial arches. He also found a pair of little swellings behind

the last gill-cleft, and an unpaired swelling (corresponding with a double

one in _Ichthyophis_) in front of the vent. Not unreasonably he sees in

these swellings the last, very transitional vestiges of the paired limbs.

_Typhlonectes compressicauda_ of Guiana and Venezuela is one of the largest

Coecilians, reaching a length of 18 inches, with a body-diameter of ¾ inch.

The general colour, as in most of these creatures, is olive brown to black.

A sort of adhesive disc surrounding the vent occurs in this genus. Peters,

who described this species, found in one female six embryos of

comparatively enormous size, one of them being 157 mm. (more than 6 inches)

long, and 12 mm. thick, and devoid of a tail-fin. Instead of lateral

gill-openings there is a "bag" on each side 55 mm. long, upon which is

distributed a blood-vessel. The Sarasins have examined the same specimen:

The gills are not a bag, but consist of two flat, unbroken membranes which

are closely connected with each other. In fact the outer gills of all

Amphibia may be said to begin in the shape of small bags, whence sprout

secondarily the gill-fringes; but in _Typhlonectes_ they form these flaps

instead of growing into the usual three gills. The embryos have no

epidermal sense-organs, but plenty of skin-glands. Probably when born they

take at once to terrestrial life, the flaps are possibly shed at birth, and

there remains a little cicatrix.

_Dermophis thomensis_ of West Africa (its other relations live in East

Africa, South and Central America) is also viviparous.

{94}CHAPTER V

LISSAMPHIBIA (_CONTINUED_)–URODELA

ORDER II. URODELA OR TAILED AMPHIBIA.

The recent tailed Amphibia, Salamanders and Newts in the wider sense, have

been grouped into four families which can be conveniently diagnosed by the

following characters:–

Both the upper and lower jaws are furnished with teeth. Fore- and

hind-limbs are always present.

Maxillary bones present.

Eyes free and devoid of lids .......... AMPHIUMIDAE, p. 97.

Eyes with movable lids[45] .......... SALAMANDRIDAE, p. 102.

Maxillary bones absent.

Eyes without lids. Perennibranchiate .......... PROTEIDAE, p. 132.

Both jaws are toothless. The hind-limbs, the maxillary bones and eyelids

are absent. Perennibranchiate .......... SIRENIDAE, p. 136.

These four families are closely allied to each other, especially the

Amphiumidae and the Salamandridae.

The geographical distribution of the Urodela is essentially Periarctic,

except that about one dozen species each of _Amblystoma_ and of _Spelerpes_

extend southwards into Central America, and in the case of the latter genus

even into the Andesian parts of South America. _Plethodon platense_

inhabits Argentina.

The Urodela afford good reasons for dividing the Periarctic region into

three co-ordinate sub-regions, namely, Nearctic, Eastern and Western

Palaearctic. The difference between the European and the Eastern Asiatic

fauna is well marked; the two are–at least with our present

knowledge–separated by a wide stretch of country very poor in Urodele

forms; while, lastly {95}there are not a few resemblances between this

Eastern Asiatic and the American fauna. The Urodela thus lend no support to

the usual division of the Periarctic into a Palaearctic and a Nearctic

sub-region. Nor is it possible to divide the Palaearctic into a Eurasian

and a Mediterranean province. We have in this case to distinguish between

an American, an Asiatic, and a European fauna. The Asiatic or Eastern

Palaearctic sub-region assumes the central position, at least from a merely

geographical point of view. It would be unjustifiable to assume a spreading

from this centre into Europe, and, on the other hand, into America. The

centre existed more probably in the Arctic circle, now devoid of Urodela.

[Illustration: FIG. 16.–Map showing the distribution of the Urodela.

"Ichthyodea" = Amphiumidae + Proteidae + Sirenidae.]

So far as mere numbers of species are concerned the huge Asiatic or Eastern

Palaearctic region is the poorest, but it is also the least explored, and

China will probably yield a good many new forms. We know at present only 15

species, nearly all from the eastern half. These 15 species represent no

less than 11 genera, 8 of which (= 73 per cent) are peculiar to the

sub-region. Next comes the Western Palaearctic or European sub-region with

about 21 recent species of 5 genera, 4 of which are peculiar. America is by

far the richest, with no less than 66 species (36 eastern, about 16

western, and the rest Central American, etc.), belonging to 19 genera, 17

of which (= 90 per cent) are peculiar to the New World. But this richness

in species is due mainly to the abundance of the two genera _Amblystoma_

and _Spelerpes_, just as Europe is characterised by its many Tritons.

One of the most striking features of the Asiatic sub-region is {96}its

difference from the European. They have very little in common.

_Pachytriton_, _Tylototriton_, and two species of _Triton_ (_T.

pyrrhogaster_ and _T. sinensis_) are the only Salamandrinae, while all the

rest are Lechriodont (see p. 102), like the American Urodela, excepting the

two American Tritons, _T. torosus_ and _T. viridescens_.

GEOGRAPHICAL DISTRIBUTION OF THE URODELA

+–––––––––––––––+–––––––––––––––––+––––––––––––––––––+––––––––––––––––––+

| | Western | Eastern | American. |

| | Palaearctic. | Palaearctic. | |

+–––––––––––––––+–––––––––––––––––+––––––––––––––––––+––––––––––––––––––+

| Sirenidae | ... | | 1 Siren |

| | ... | | 1 Pseudobranchus |

| | | | |

| Proteidae | 1 Proteus | | 1 Necturus |

| | | | |

| Amphiumidae | (1 _Andrias_, | ... | 1 Amphiuma |

| | Miocene) | 1 Cryptobranchus | 1 Cryptobranchus |

| | | | |

| Salamandridae | Desmognathinae |

| | –––––––––––––– |

| | ... | | 1 Thorius |

| | ... | | 1 Haptoglossa |

| | ... | | 3 Desmognathus |

| | ... | | 1 Typhlotriton |

| | | | |

| | Pleithodontinae |

| | ––––––––––––––– |

| | 1 Spelerpes | | 21 Spelerpes |

| | ... | | 2 Manculus |

| | ... | | 7 Plethodon |

| | ... | | 3 Batrachoseps |

| | ... | | 1 Typhlomolge |

| | ... | | 2 Autodax |

| | | | |

| | Amblystomatinae |

| | ––––––––––––––– |

| | | 1 Amblystoma | 16 Amblystoma |

| | | ... | 1 Dicamptodon |

| | | 1 Batrachyperus | |

| | | 1 Ranidens | |

| | | 1 Geomolge | |

| | | 1 Onychodactylus | |

| | | 2 Salamandrella | |

| | | 3 Hynobius | |

| | | | |

| | Salamandrinae |

| | ––––––––––––– |

| | ... | 1 Pachytriton | |

| | ... | 1 Tylototriton | |

| | 14 Triton | 2 Triton | 2 Triton |

| | 1 Salamandrina | | |

| | 1 Chioglossa | | |

| | 3 Salamandra | | |

| +–––––––––––––––––+––––––––––––––––––+––––––––––––––––––+

| | 21 species, | 15 species, | 66 species, |

| | 6 genera | 11 genera | 18 genera |

+–––––––––––––––+–––––––––––––––––+––––––––––––––––––+––––––––––––––––––+

The occurrence of an _Amblystoma_, _A. persimile_, in the mountains of Siam

and Burmah, is most suggestive, and others will in all probability be

found. It must also be borne in {97}mind that the differences between the

genera of Amblystomatinae are in reality very slight; and the same applies

to the sub-families themselves. The presence or absence of teeth on the

parasphenoid, the possession of amphi- or opistho-coelous vertebrae, do not

mean much, and certainly do not forbid the notion that all the recent

Urodela are the offspring of one common generalised stock which inhabited

the northern portion of the globe. Nothing is gained by hiding the solitary

European species of the essentially American genus _Spelerpes_ under the

name of _Geotriton_. It is a _Spelerpes_ in all characteristic points.

Speaking broadly, each of the three principal sub-families of Salamandridae

is characteristic of a sub-region; the Salamandrinae of the Western

Palaearctic, the Plethodontinae of the American, while the Amblystomatinae

are chiefly Asiatic, at least so far as diversity of genera is concerned.

FAM. 1. AMPHIUMIDAE.–Without gills in the perfect state. The gill-clefts

are in a vanishing stage, being either reduced to one pair of small holes

or being altogether absent. The maxillary bones are present. Teeth occur in

both jaws; those of the vomers form transverse rows. The vertebrae are

amphicoelous. The fore-limbs and hind-limbs are present, but small. The

small eyes are devoid of lids.

This family is now represented by two genera, with only three species,

found in the United States and in Eastern Asia.

_Cryptobranchus._–The limbs are functional, with four fingers and five

toes. The outer digits and the sides of the limbs are bordered with folds

of skin. The head and body are stout and depressed; the tail is short,

laterally compressed, and provided with a fin. The skin is very glandular

and slimy, and forms a thick, irregularly-shaped fold along the side of the

body.

_C. (Menopoma) alleghaniensis._–The gill-clefts are normally reduced to one

pair, individually to the left cleft, the right closing up. There are,

however, four branchial arches and vessels. The general colour is brown or

grey above, sometimes with darker patches, lighter below. The "Hellbender"

reaches a length of nearly 18 inches (about 46 cm.), is entirely aquatic,

and is apparently restricted to the rivers and streams of the mountainous

districts of the Eastern United States. It is very voracious, living on

worms and on fish, being much disliked by the fishermen, as it takes the

angler's bait, and destroys great quantities of the valuable food-fish

_Coregonus albus_. Although rather common and easily kept, its larvae still

remain unknown.

{98}[Illustration: FIG. 17.–_Cryptobranchus japonicus._ Japanese Giant

Salamander. × ⅙.]

{99}_C. japonicus_ s. _maximus_.–The Giant Salamander of Japan differs from

its American relation in one essential point only, namely, by the absence

of gill-openings and of the modifications of the branchial apparatus

connected therewith. It has but three branchial vessels, and the skeletal

arches are reduced to two. It lives in Japan and in China, from 600 to 4500

feet above the level of the sea, in small streams of mountain-meadows. It

feeds upon fishes, Amphibia, worms, and insects. It is easily fished with

the hook and is eaten by the Japanese.

The first living specimen was brought to Europe in 1829 by Th. von Siebold,

its discoverer. It grew within a few years from 1 foot to 3 feet in length,

and died in 1881, at least fifty-two years old. Another specimen lived in

the Hamburg aquarium for fourteen years, during which time it is said to

have grown 36 cm. (more than 14 inches), having attained a length of nearly

4½ feet, or 134 cm. The largest specimen known measures 159 cm = 5 feet 3

inches.

The life-history of this species is still imperfectly known. Japanese

picture-books contain drawings of the adult and of larvae, the latter

showing three pairs of fringed external gills. Young specimens of 16 cm.

length have already lost the gills, but still retain a cleft on either side

of the neck, in the shape of a horizontal slit, and this is soon after

closed up by the skin.

The best account has recently been given by Sasaki.[46] According to him

the Giant Salamander leads a solitary life, concealed in dark places, under

rocks in swift-flowing, thickly shaded small brooks of clear and cold

water.

The animal may be easily captured with a fish-hook, baited with a fish,

frog, or several earth-worms, and tied to a string a few feet in length.

This is thrust by the aid of a small bamboo-stick into the salamander's

retreat. The string is not tied to the stick, but the point of the loaded

hook is forced into one end of it, far enough to keep it in place while

this end of the rod is pushed under the rock. When the bait has been thus

brought near the salamander, any bite will be instantly felt through the

{100}rod. The latter is then withdrawn as quietly as possible, the hook and

bait being left. As soon as a jerk of the string is noticed, a pull is

made, which generally ends in the capture of the unfortunate animal. If the

first pull should fail, the bait is replaced as before, and a second

opportunity is offered, which the unwary creature accepts as readily as the

first. The fisherman, having obtained one bite, is sure of ultimate

success, as the salamander does not learn by experience to refuse the

proffered morsel. When captured, it emits a peculiar slimy secretion,

having an odour much like that of the leaves of the Japan pepper

(_Xanthoxylon peperitum_). This secretion hardens into a gelatinous mass

after a short exposure to the air.

Temminck and Schlegel state that the act of inspiration is ordinarily

performed once every 6-10 minutes. This is true for specimens kept in tubs;

but Sasaki is inclined to think that they perform this act less frequently

in their native brooks. The eyes are so small that they are obviously of

little importance; the salamanders capture their prey not by pursuing, but

by waiting for its near approach, whereupon they seize it with their teeth

by a swift lateral movement of the head. The eggs are said to be laid in

August and September, and they form a string resembling a rosary. Each egg

floats in a clear fluid, inclosed in a bead-shaped gelatinous envelope, and

this is connected with the next by means of a comparatively small string.

The egg measures about 6 mm. by 4 mm., and is yellow everywhere except at

the upper pole, where it is whitish. All attempts to make _Cryptobranchus_

breed in captivity have failed hitherto, owing no doubt to the difficulty

of obtaining the cool temperature of its mountain streams. Sasaki's

smallest specimens measured 19 to 20 cm. These had three pairs of very

short branchial processes, from 3 to 5 mm. in length, attached just inside

the branchial orifice. Each process was somewhat flattened and tapering,

most of them still with branchlets. In another specimen, 20.5 cm. in

length, the gills had almost wholly disappeared, but the branchial slits

were still visible. One of 24.5 cm. length showed no trace of gills, and

the branchial orifice was completely closed, but still marked by a light

streak.

{101}[Illustration: FIG. 18.–_Amphiuma means._ × ⅕.]

_Amphiuma means_ s. _tridactyla_.–The limbs are very much reduced, and end

in two or three little fingers or toes. Just in front of the fore-limbs

lies the pair of small gill-clefts, each guarded by two flaps of the skin.

There are four branchial arches. The general colour of this eel-shaped

creature is black, lighter below. The head is covered with numerous pores,

arranged in several rows, which unite in the region of the neck, so that

only two rows extend along the sides of the body. It reaches a length of

three feet, and lives in swamps or muddy waters, for instance in the

ditches of rice-fields, burrowing occasionally in the mud, feeding on

crayfishes, molluscs, small fishes, etc. It is confined to the

south-eastern States of North America, from Carolina to Mississippi.

According to Davison,[47] copulation takes place in May. The rather

hard-shelled eggs are deposited in the following August or September, and

are connected by a twisted cord. The female lies about them in a coil. The

embryos, which are hatched in the month of November or December, have

well-developed external gills. By the following February they have

{102}reached a length of from 68 to 90 mm. (about 3 inches), living in damp

localities under rocks or rooted stumps, and have already lost their gills.

The legs are said to be relatively longer than they are in the adult.

FAM. 2. SALAMANDRIDAE (Salamanders and Newts).–Without gills in the perfect

state. Maxillaries are present. Both jaws are furnished with teeth. The

eyes are protected by movable lids, except in _Typhlotriton_. Fore- and

hind-limbs present, although sometimes very much reduced.

To this family belong by far the greater number of tailed Amphibia. They

have been, for the sake of convenience, grouped into four sub-families, the

determining characters of which are all internal and of comparatively

slight importance. Little better is the division into _Mecodonta_, with the

teeth of the palate in two longitudinal rows diverging behind and inserted

upon the inner margins of the two palatine processes, which are much

prolonged posteriorly, and _Lechriodonta_, in which the series of palatal

teeth are restricted to the posterior portion of the vomers and form either

transverse or posteriorly converging rows.

I. Series of palatal teeth transverse, restricted to the posterior

portion of the vomers. Parasphenoid beset with dentigerous plates.

Vertebrae opisthocoelous: _Desmognathinae_, p. 102.

" amphicoelous: _Plethodontinae_, p. 103.

II. Series of palatal teeth transverse or posteriorly converging,

restricted to the posterior portion of the vomers. Parasphenoid

toothless. Vertebrae amphicoelous: _Amblystomatinae_, p. 109.

III. Series of palatal teeth in two longitudinal series, diverging

behind, inserted on the inner margin of the long palatine processes.

Parasphenoid toothless. Vertebrae amphicoelous: _Salamandrinae_, p. 115.

SUB-FAM. 1. DESMOGNATHINAE.–Comprising only three genera, with five

species, in North America. Five toes.

_Desmognathus._–The tongue is attached along the median line, free behind,

oval in shape. Three species in the eastern half of the United States. _D.

fuscus_ is one of the lungless Urodela, for which condition see p. 46. The

skin is nearly smooth; parotoids prominent, gular fold strongly marked.

General colour above, brown suffused with pink and grey, sometimes with a

dark lateral band; under parts mottled brown. The vomerine teeth are

frequently absent. Total length, about 4 to 5 inches. They live, carefully

concealed in the daytime, under {103}stones in or on the edge of the banks

of little mountain streams. The eggs are laid in two long strings, and are

wrapped round the body of the female like a rosary, the female having

resorted to a hollow in the mud, below a stone or other suitable place. The

outer envelope of each egg tapers out into a short stalk, and the several

stalks all converge, or are glued together into one common knot, "much like

a bunch of toy balloons held in the hand of a street vendor." The egg is

said to be meroblastic. The larvae seem to remain in the egg until they are

nearly adult, and they emerge at midsummer, with the gills already much

reduced. The complete metamorphosis takes place in the autumn of the same

year. These little newts can, according to Wilder,[48] be collected all the

year round, in Massachusetts from March to December, except during the time

of deep snow. They are nocturnal and are easily kept.

[Illustration: FIG. 19.–_Desmognathus fuscus_; female with eggs in a hole

underground. × 1. (After Wilder.)]

_Thorius pennatulus_, from Orizaba, Mexico, the only species, is noteworthy

for its extremely large nostrils, and for the tongue, which is supported by

a central pedicle, free all round, and ending in a thick knob, which can

probably be protruded. The limbs are weak, and the digits are also much

reduced. Total length, under 2 inches, or 50 mm.

_Typhlotriton spelaeus_, of the Rock House Cave in Missouri, is blind, the

eyes becoming concealed by the skin during metamorphosis, when the gills

are lost.

SUB-FAM. 2. PLETHODONTINAE.–The five genera of this almost entirely

American sub-family (only one species of which, _Spelerpes fuscus_, occurs

in Europe) can be distinguished as follows:–

I. The tongue is attached by its central pedicle only, is free all round,

ends in a soft knob and can be shot out to a considerable distance.

With 5 toes: _Spelerpes_, p. 104.

With 4 toes: _Manculus_, p. 106.

{104}II. The tongue is attached along the middle line and cannot be

protruded out of the mouth.

Jaws with numerous small teeth.

With 5 toes: _Plethodon_, p. 106.

With 4 toes: _Batrachoseps_.

Maxillary and mandibular teeth few in number but very large.

With 5 toes: _Autodax_, p. 107.

_Spelerpes._–Except in a few species the limbs are well developed and

possess 4 fingers and 5 toes, which are either free or webbed. But in the

Colombian _S. parvipes_, still more in _S. lineolus_ of Orizaba and _S.

uniformis_ of Costa Rica the limbs and digits are reduced to mere vestiges,

and are practically without function, the body, with the extremely long

tail, having assumed a wormlike shape. The young of many, if not all,

species have a pair of short balancers below each nostril; in the adult

these organs are reduced to little swellings or lost completely. Several

species are lungless, see p. 46.

The geographical distribution of this genus, of which some twenty species

are known, is very remarkable. The majority live in Mexico and in the

United States, a few are found in Colombia and Northern Peru (_S.

altamazonicus_ and _Plethodon platense_ being the only Urodeles hitherto

recorded from south of the equator), one in Hayti (_S. infuscatus_), two

(_S. subpalmatus_ and _S. uniformis_) in Costa Rica, and _S. fuscus_ in

Europe.