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.

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