CHAPTER VI.

_FROGS AND TOADS._

The Amphibian Class, through the Newts and Salamanders more especially, would appear at first sight to have much in common with and to be most closely allied to the Lizards, previously described. As a matter of fact, however, the group is much more nearly related to the Fishes. Quite the most characteristic feature in the Amphibians that is indicative of the above-mentioned affinity is the circumstance that for a more or less longer period of their existence their respiratory organs take the form of external gills, structures not found in any of the preceding vertebrate classes. Another diagnostic character of the Amphibia is afforded by the circumstance that they all pass through a transitional or larval condition before arriving at the adult state. The familiar tadpole phase of the common frog or toad typically illustrates this point. During its earliest larval state the fish-like resemblance is especially conspicuous. In addition to possessing gills, the body is limbless, and produced into a long fish-like tail, having superior and inferior fin-like membranes, with which the little animal propels itself through the water. These locomotive fins, however, are never furnished with supporting fin-rays, as obtains among the Fishes. In contradistinction to the Lizards and Snakes, the skin of Amphibians is never covered with spines or scales, but is soft and naked. In many of the Toads and Salamanders the surface of the skin is, however, warted and highly glandular, and capable of emitting an acrid and sometimes poisonous fluid. More or less pronounced conditions of moisture are essential for the well-being of all Amphibians. The eggs are deposited, and the earlier or larval conditions, with but few exceptions, passed, in the water, while the adults remain in its near proximity, and frequently take up their abode in it. Amphibia do not, however, drink water after the manner of lizards and other reptiles, but absorb all the moisture they require through the surface of their skins. The deeper and more essential skeletal elements of the Amphibia differ conspicuously from those of the preceding groups. The vertebræ in the permanently gill-bearing species more particularly are scarcely to be distinguished from those of fishes. In the Frog and Toad Tribe, on the other hand, they are reduced to a less number, seven or eight only, than is found among any other vertebrates, while ribs do not exist or are rudimentary and functionless throughout the class. Many bones of the skull in the Amphibia, as well as its general construction, are more in accord with those of fishes than of ordinary reptiles. The tongue, not always present, is attached immediately inside the front of the lower jaw, its tip pointing down the animal's throat. It is remarkable that, notwithstanding their aquatic proclivities, no Amphibian has been discovered which frequents salt water.

Amphibians amongst themselves constitute two very easily recognised sub-divisions,--the one including the Frogs and Toads, collectively forming the Tailless group; and the other represented by the Newts and Salamanders, or Tailed Amphibians. The former group has an almost world-wide distribution, numbering some thousand species; it is most abundantly represented in the tropics, ranging thence in diminishing numbers to the limits of the Arctic Circle. In colder climates these Amphibia usually hibernate during the winter months; while in tropical countries, where dry seasons intervene, they often bury themselves in the mud, and remain in a state of torpor till the return of the rains. The majority are more or less essentially nocturnal in their habits. Frogs and toads commence life in an aquatic tadpole phase. While in the adult state they are strictly carnivorous, the tadpoles are vegetarian feeders.

The section to which the COMMON BRITISH FROG belongs includes nearly 150 species, collectively known as Water-frogs, which present considerable differences in both their aspect and habits. While some are perennially aquatic, others only resort to the water during the breeding-season; some are terrestrial and occasionally earth-burrowers, while yet another series is essentially arboreal.

In addition to the familiar British species the much-esteemed EDIBLE FROG of the Continent has become acclimatised in England. A dark-coloured race of this frog, supposed to have been introduced by the monks centuries since on account of its esculent properties, is plentiful in the fens of Cambridgeshire, while a greener race of the same species was imported to and established in Norfolk somewhere about the year 1840. The edible frog may be distinguished from the common species by the more complete webbing of its hind feet, the absence of the dark so-called temporal spot that extends from the eye to the shoulder, and the presence in the males of a globular sac on each side of the head, which confers upon them louder croaking powers than are possessed by the common species.

The loudest-voiced as well as almost the largest member of this group is the BULL-FROG of Canada and the United States. The length of the body in this species may be as much as from 7 to 7½ inches, exclusive of the legs; and its croakings, or more correctly bellowings, are so loud that it may be heard for a distance of several miles. These croakings are most pronounced during the early spring or breeding-season. In the Southern United States, however, they are maintained more or less persistently throughout the year. While the British frog contents itself with a diet of slugs, worms, beetles, and other insects, the bull-frog aspires to larger quarry, and has an especial penchant for young ducklings. As a compensation the flesh of the bull-frog is said to be very delicately flavoured, and the species is so much esteemed in some localities as to be kept in captivity and fattened for the table. It has been recorded that the bull-frog makes leaps of from 8 to 10 feet in length and 5 feet in height.

In point of size the bull-frog is somewhat eclipsed by a species discovered in the Solomon Islands, and known as GUPPY'S FROG. This huge frog has a body no less than 9 inches in length. It has not been recorded whether its vocal powers are proportionately loud. Another large species allied to the Bull-frogs is found in South and East Africa, whose flesh is attested to by Dr. Livingstone as being excellent eating and resembling chicken when cooked. This frog, known to the natives as the MATLAMITLO, is supposed by them to fall from the clouds, on account of its sudden appearance in even the driest parts of the desert immediately after a thunder-storm. The species, however, is in the habit of making holes at the roots of bushes, into which it retires during the months of drought, rushing out into the hollows filled by the thunder-showers while the rain is still actually falling. Even during the long drought these frogs continue their croakings from their retreats at night, and are very misleading to travellers, who customarily associate their presence with the immediate neighbourhood of water.

There is a remarkable difference in the voice-timbre of the various species of frogs. In England, with its one indigenous variety, comparisons cannot be instituted. In countries, however, like Australia, where numbers of species live in close proximity, the phenomenon is very marked. Some only give voice in the evening or night, while others keep up their clamour throughout the day; with some the note is metallic and almost bell-like, while one diurnal croaking species, which congregates in great numbers in the eastern Tasmanian coast district, emits a loud percussive note closely resembling that of a stone-breaker's hammer. On several occasions, in fact, when driving through the areas these frogs frequented, the impression produced by their croaking was so realistic that the next turn in the road was expected to reveal the presence of a large gang of road-makers engaged in negotiating a wayside stone-heap.

One of the most remarkable species is the FLYING-FROG of Java. The power of flight is simulated in this instance on a different principle to that which obtains in any other group. It is not accomplished through the medium of abnormally produced ribs with connecting membrane, as occurs in the Flying-lizards; nor by means of a flap of skin stretched between the fore and hind limbs, as in the Flying-squirrels and Phalangers. In place of these the toes of all four feet are abnormally prolonged, and their interspaces bridged over to their tips by webbing. The body of this frog is about 4 inches long, while the webs of the feet, when fully expanded, cover collectively an area of fully 12 square inches; they thus constitute aerial floats, which enable their owner to make prodigiously long flying leaps among the trees in which it takes up its abode. The colours of this singular species are striking; the back and limbs are a deep shining green, the under-surface and inner toes yellow, and the webs black rayed with yellow. In common with the typical Tree-frogs, the toes of this Javan flying variety all terminate in a dilated adhesive disk.

Among the oddities of the Frog Tribe prominence may be given to the singular SHORT-HEADED FROGS of East Africa. In these the head is so short, and the body, when puffed out, so nearly globular, that they have been aptly described as more nearly resembling india-rubber balls than frogs. Another notable form, inhabiting Chili, is remarkable for the circumstance that the throat-sac of the male is so enlarged and modified as to form a chamber on the under surface of the body. In this sac the eggs laid by the female are deposited and pass through their tadpole phases.

The HORNED FROGS, or HORNED TOADS, of South America constitute a distinct and interesting group. They are of large size, stout and rotund, gorgeously apparelled, and truculent in bearing. There are nearly a dozen known species, the distinctive feature from which they take their name having reference to the stiff, horn-like development of their upper eyelids. The largest species is a native of Brazil, whose body may be as much as 8 inches long. This species has the horn-like processes of the eyelids most prominently developed. A somewhat smaller but conspicuously handsome species, plentiful in the Argentine Republic, is at the present time represented by several individuals at the Regent's Park Gardens. In this animal the body is relatively more obese and toad-like than in the Brazilian form, but the horn-like angle of the upper eyelid is only slightly produced. The colours vary somewhat, the general ground-tint of the upper-surface is bronze-green or yellow, upon which are distributed large spots and blotches of dark olive or chocolate, having light yellow or golden margins. The spots on the limbs are the widest, and almost take the character of cross-bands. Bright claret-red lines are sometimes developed in and among the body-spots.

A very interesting account of the habits of this frog appears in Mr. W. H. Hudson's "The Naturalist in La Plata." Mr. Hudson reports it as being common on the pampas as far south as the Rio Colorado, in Patagonia. In the breeding-season it congregates in pools, and displays extraordinary vocal powers, which are exercised at night. The notes uttered are long, resembling those of a wind instrument, and are so powerful that on still evenings they may be heard distinctly a mile off. After the pairing-season the frogs disperse, and, retiring to moist places, bury themselves just deep enough to leave their broad green backs on a level with the surface. The eyes, under these conditions, look out as from a couple of watch-towers, and are on the _qui vive_ for any approaching prey. This consists of any moving creature which they can capture, such as other frogs and toads, birds, and small mammals. In very wet seasons they will frequent the neighbourhood of houses, and lie in wait for chickens and ducklings, often capturing and attempting to swallow objects much too large for them. In disposition they are exceedingly pugnacious, savagely biting at anything that comes near them. When teased, the creature swells itself out to such an extent that one expects to see it burst. It follows its tormentors about with slow, awkward leaps, its vast mouth wide open, and uttering an incessant harsh croaking sound. When they bite, these frogs hold on with the tenacity of a bull-dog, poisoning the blood of the creature seized with their glandular secretion. Mr. Hudson records two instances in which to his knowledge horses were killed through being bitten by a horned frog. One of them, while lying down, had been seized by a fold in the skin near the belly; the other had been grasped by the nose while cropping grass. In both instances the vicious frog was found dead, with jaws tightly closed, still hanging to the dead horse. "It would seem," Mr. Hudson remarks, "that they are sometimes incapable of letting go at will, and, like honey-bees, destroy themselves in these savage attacks."

The TREE-FROGS represent one of the most distinct groups of the tribe. All its members are more or less arboreal in their habits, repairing to the water only during the breeding-season, or leaving the trees to seek shelter in the earth or underneath stones or timber for the purposes of hibernation. As an adaptation for their special habits, the toes of the tree-frogs are provided at their tips with suctorial disks, so that they can walk on perpendicular or smoothly glazed surfaces after the manner of the Geckos among the Lizards. Another characteristic feature is the development on the under surface of their bodies of peculiar granular glands pierced by numerous pores, through the medium of which they rapidly absorb the moisture deposited by dew or rain on the surfaces of the leaves among which they live. The colours of the tree-frogs harmonise, as a rule, so completely with those of their leafy environments that their presence very readily escapes detection. Many of the species, moreover, rival the chamæleon in their capacity of quickly adapting their tints to that of a newly occupied surrounding. Green is naturally the dominant ground-tint of these frogs. Often, however, it is intermixed with stripes and bands of other colours, while sometimes the green hue is entirely replaced, as in the BLUE or BICOLOURED TREE-FROG of South America, which is brilliant azure above and pure white beneath. A very beautiful Australian species, abundant in Tasmania and Victoria, and appropriately named the GOLDEN TREE-FROG, has its grass-green overcoat thickly overlaid and embroidered with, as it were, the purest beaten gold.

One small species of tree-frog is common on the European Continent, its distribution extending to North Africa and eastward throughout Asia north of the Himalaya to Japan. The species is imported into England in considerable numbers, and readily becomes acclimatised in a conservatory. Green above and whitish beneath constitute the prevailing tints of this species, such uniformity being, however, varied by the presence of a darker, often nearly black, light-edged streak, that extends from the snout through the eye and ear along each side of the body, and sends a branch upwards and forwards on the loins. The male of this European species shares with many others of its tribe the possession of a large external vocal sac, which when inflated bulges out from the throat in a spherical form to dimensions little inferior to those of the creature's body. It may be observed of examples of these frogs acclimatised in a conservatory that the falling of heavy rain on the roof is an almost certain incentive to their croakings. By pouring water resonantly from a little height into another vessel, the writer also found that he could produce a frog chorus at command.

The European and other tree-frogs deposit their eggs in the water, some species constructing a symmetrical crater-like nest of mud for the reception of the eggs and tadpoles. Certain kinds, however, never leave the trees, having adapted their requirements to the naturally provided environments. Thus one Brazilian species deposits its eggs in the water almost invariably contained in the central cup of a tree, while another allied frog chooses for the same purpose the moist interstices at the bases of decaying banana leaves. A step further, resulting in complete independence of external water, is arrived at by the MARSUPIAL or POUCHED TREE-FROG of Central America. In this species the female develops a capacious pouch on her back, which opens backward, and wherein both the eggs--primarily assisted to their position by the male--and tadpoles undergo their characteristic transformations.

As a contrast to the foregoing exclusively tree-dwelling forms, one very fine species common in Queensland has pronounced social proclivities. He is a fine fellow, with a bright pea-green coat and large, lustrous black eyes, and either with or without your leave invades your bedroom from the adjoining verandah, and makes the lip of your water-jug his headquarters. Here he will "lie low" the livelong day. With the approach of night, however, this lethargy is thrown aside, and he hops forth, making excursions through every room in search of black-beetles, spiders, moths, or other acceptable quarry. In this vermin-destroying capacity he is a welcome guest to all except perhaps the ultra-squeamish housekeeper, his occasional offence of an upset glass or cup during his excited chase of the wily cockroach being readily condoned. He has a playful habit too, during his midnight wanderings, of climbing up walls and ceilings, to which he readily clings with his adhesive toes, and mayhap drops down on the recumbent form of some peaceful sleeper, who, if a stranger, possibly wakes with an alarming apprehension of snakes or other uncanny intruders. When once this QUEENSLAND GREEN FROG has determined upon his camping-ground, he clings to it with remarkable pertinacity. You may deport him time after time, and even carry him half a day's journey into the wilderness, but he turns up again the next morning or the following one.

Toads are distinguished from frogs by their sluggish creeping movements and by their non-possession of teeth. There are over eighty species, having collectively an almost cosmopolitan range, though they are not found in Australia, New Guinea, Madagascar, or the Pacific Islands. The common British species enjoys a wide distribution, being found throughout Europe, Asia excepting India, and North-west Africa. Its somewhat clumsy, brown, wrinkled, and warted body, with darker spots and markings on the upper-surface and white-speckled under-surface, will be familiar to every reader. With many it is an unwarranted object of aversion, and in country districts is not infrequently accredited with venomous properties. Toad-spawn is plentiful in ponds and ditches in the early spring, and may be distinguished from that of the frog by the fact of its being deposited in chain-like strings, the eggs being arranged in a double alternating row, instead of in irregular masses, as obtains with the last-named species. The individual eggs are, moreover, smaller, and deposited two or three weeks later in the season than those of the frog. A second and somewhat rarer British toad is known as the NATTERJACK. It may be distinguished from the ordinary species by the shorter hind limbs, the more prominent eyes, and the conspicuous yellow line down the middle of its back. It is also somewhat more active than the common species.

The last member of the group which demands brief notice is the singular WATER-TOAD of Surinam. This animal, also known as the PIPA, is an inhabitant of the moist forest regions of the Guianas and Central America, and remarkable on account of the singular phenomena connected with its breeding habits. The eggs, from 60 to over 100 in number, are deposited by the female in the water in the ordinary manner, but at this stage they are taken in hand by the male and literally planted in the back of the female, whose skin in this region becomes abnormally soft and thickened at this season. The young toads undergo their complete development in the parental integument, each egg and its resulting embryo occupying a separate primarily cylindrical chamber, which by lateral pressure becomes hexagonal, resembling a honeycomb-cell. Eighty-two days are occupied from the time of the deposition of the eggs until the young toads emerge into the outer world, their appearance as they make their _début_, with here a head and there one or it may be two limbs thrust out from the surface of the parent's back, being highly grotesque.

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