Hyla.–The pupil is horizontal. The tympanum is distinct or hidden. The tongue is entire or slightly nicked in its hinder margin, which is more or less free behind. The fingers and toes are provided with typical adhesive discs.

This is the largest genus of all Amphibia, containing about 150 species, and its distribution coincides with that of the whole family. Many of the species are very closely allied to each other, differing only in small points, for instance in the extent of the webs to the fingers and toes, the configuration of the vomerine teeth, the size and appearance of the tympanic disc, and the relative length of the hind-limbs. In some of the West Indian, and in one Brazilian species, H. nigromaculata, the upper surface of the head is rough, owing to the cutis being involved in the cranial ossification. Bony or perhaps only calcareous deposits in other parts of the skin are rare, but are notably developed in H. dasynotus of Brazil, in which they extend from the head to the sacrum, rendering the skin immovable.

Many are capable of changing colour to a great extent, and it is a popular error to suppose that all tree-frogs are green, although this colour is perhaps the most common in the arboreal kinds.

H. arborea.–The tongue is rather round, slightly nicked behind, and can be protruded but little. The tympanum is distinct, but small. The upper parts are grass-green, quite smooth and shiny owing to the skin being covered with a film of moisture; the under parts are yellowish-white and granular, flesh-coloured or rosy on the thighs. Total length of large females 2 inches. This, the Tree-frog of Europe, has an enormous range, namely, from Morocco, France, and the south of Sweden, across the whole of Europe and Asia Minor to Japan and Southern China.

Several varieties have been described: the typical or European form is ornamented with a narrow black stripe, which, beginning at the nose, extends backwards along the side of the body to the groin, where it generally forms a hook turned upwards. This black colour forms the ventral boundary of the green, and is itself narrowly seamed with white on its upper border.

In the south of France, the Iberian Peninsula, Morocco, and the Canary Islands the black lateral stripe is often absent; this is the var. meridionalis. In Spain and Portugal both forms are found in the same localities.

In the Asiatic, chiefly in the eastern specimens, the lateral stripes tend to break up into irregular spots, vanishing altogether towards the groins; this var. savignyi s. japonica occurs also on most of the Mediterranean islands.

H. arborea can change colour to a great extent, mostly in adaptation to its immediate surroundings, but ill health and moulting may also influence it. The change is slow. The usual colour is green, brightest on bright, sunny hot days, dull when the sky is overcast, or when it is windy and showery. Day and night have no influence upon the colour-changes. The hue of the green agrees mostly with that of the foliage on which the frog happens to take its rest, for instance a field of Indian corn, birch-trees, or oak-trees. I once received a consignment from Saxony. When the box with moss was unpacked, they were of the dullest greenish-grey; they were put into a wired-off corner of the yard and were given the freshly cut branches of a lime-tree to sit upon. On the following morning I at first looked for most of the frogs in vain. The leaves had withered and all those frogs which sat upon the dark brown branches had put on a light brown garb, mottled with darker patches.

Another specimen, one of several which were at liberty in a greenhouse, took to resting on the frame of the window-pane, in a corner where putty, glass, and discoloured white paint met; in the morning it was always of a mottled leaden colour, but during the nocturnal hunting it was green. In the winter, the window-corner being of course cold, the frog remained stationary for several months, but kept the leaden grey colour, until one day in the early spring it was mottled with green, and soon after it joined its green mates.

Liebe observed a half grown tree-frog which he kept in Gera during the winter in a glass with water-cress. While the temperature was near freezing the frog sat in the water, very lethargic, breathing perhaps once every quarter of an hour. Its colour was light green. When the water-cress was cut and removed, the frog darkened and became at last quite a discoloured grey. When the water-cress was put back, the creature reassumed the light yellowish-green colour, remaining in its lethargic condition until it became lively in the spring sunshine.

The European tree-frog spends most of its time in the summer, after the pairing is over, in trees, often in the very crowns; but the neighbourhood of even a small patch of Indian corn has still greater attractions. There are all sorts of green insects to be caught, there are fair chances of coming across the common Cabbage White, a butterfly which the tree-frog loves, and last not least the large luscious leaves afford a firm foothold, and the axillae between stalk and broad-based leaves are just the places for the frog to slip into, where nobody can find it. During the day they mostly sit still, on the keen look-out for passing insects, which, when they settle within reach, are jumped at; otherwise they have first to be stalked. The jump is quite fearless, regardless of the height above ground; there is the leaf upon which the prey sits, and even if this leaf be missed, there are others, and one of them is sure to be struck by some of the discs of either fingers or toes. If the fall is broken by the toes, and the new leaf or branch is very elastic and bends down, then there are some frantic antics to be gone through until the frog has settled itself again. Then the large blue-bottle, or the butterfly, is devoured at leisure, wings and all being poked in with the assistance of the little hands. But the real hunting-time is the night.

During a shower the frog shifts its position to the under side of the leaf, or into a less slippery position, and during continuous wet it descends into the grass, or it takes to the water. Its greatest enemy is the Grass Snake, which prefers it to anything else, not minding the poisonous secretion of the skin, which is sharp enough to produce sneezing or even temporary blindness when incautiously brought into the human eye.

The male has an internal vocal sac, which, when inflated, bulges out the whole throat into a globe, much larger than the head. The voice is a sharp and rapidly-repeated note, something like "epp-epp-epp," or "creck, creck, creck," with more or less of an a sound. It is uttered at any time of the day, more frequently at dusk, and of course chiefly during the pairing season. This tree-frog suffers from the reputation of being a good weather-prophet, and it is for this reason often kept in confinement, the orthodox abode being a muslin-covered glass jar, with a hole to put flies through, water and plants at the bottom, and a little ladder to sit upon. The prophesying is of the usual popular unreliable nature, although the little creature, provided it is a male, often sounds its voice on the approach of a shower, or when there is a thunderstorm in the air. During continuous fine weather it sits on the top of the ladder, or is glued on near the rim of the glass, while on wet and dull days it is less active, and may keep nearer the ground or in the water. There is a German rhyme which well expresses the prophet's reliability by its ambiguity:–

When the tree-frogs croak, you may wait for rain. Sometimes it does come true.

Tree-frogs are not very intelligent, although they have a keen sense of locality; but they are nice pets, being easily kept, and have a pretty appearance. There is a record of one which lived for twenty-two years in confinement.

The pairing begins soon after the frogs reappear from their hibernation in the ground; in Germany in the month of May. The congregating males make a great noise and take to the water before the females, which join them when ready to spawn. The male grasps his mate near the shoulders, and the pair swim about together, sometimes for days, until the eggs are expelled. These are laid in small clumps of 800 to 1000, which soon swell up and remain at the bottom of the pond. The larvae are hatched in ten days; two days later the adhesive sucker below the throat appears, and after another two days a pair of thread-like external gills are developed. The tadpoles, which reach a length of 2 inches, owing to the long tail, which is nearly three times as long as the body, metamorphose in about twelve weeks, and the baby tree-frogs, scarcely half an inch in length, hide in the grass for the next two years, until they are about half grown, not reaching maturity until the fourth year.

Since many pairs congregate in the same pool, and each produces up to one thousand eggs, most of which are hatched, the neighbouring meadows sometimes literally swarm with tiny tree-frogs. Nevertheless the adults are comparatively rare and are very local.

H. carolinensis s. lateralis of the South-Eastern States of North America greatly resembles H. arborea in general appearance, size, and habits. But the head is more pointed, and the vivid green of the upper parts is separated from the yellowish white under surface by a conspicuous, pure white line, giving the little creature a very smart and neat appearance. According to Holbrook, it ascends trees, but most commonly lies upon broad-leaved water-plants, like Nymphaea, and in fields of Indian corn. Motionless during the daytime, they emerge in the morning and evening from their hiding-places, and become very brisk and noisy, often repeating their single note, which is not unlike that of a small bell. When one begins, hundreds take it up from all parts of the corn-field.

Among other tree-frogs of the South-Eastern States may be mentioned H. squirella, 1½ inch in length, which is very changeable in colour, generally olive above with darker spots and bars on the limbs, and with a white upper lip. It lives in trees, sheltering in the bark. H. femoralis of the same size, without the white lip, lives high up in the trees of the dense forests of Georgia and Carolina.

H. versicolor is one of the most delicately coloured species of Eastern North America, extending northwards into Canada. It is about 2 inches long. Its colour passes within a short time from dark brown or olive grey to pale delicate grey, almost white, occasionally retaining a few large darker patches on the back, and delicate cross-bars on the limbs. A small portion of the sides and the posterior part of the belly are bright yellow. The skin is granular, owing to the presence of small warts which produce an acrid secretion. It is said to be found in trees, or about old stone fences overgrown with lichens, the colour of which it resembles to perfection. It becomes very noisy towards the evening, in cloudy weather or before rain, the voice consisting of a liquid note, terminating abruptly, like "l-l-l-l-luk." My own captives fully bear out this statement of Holbrook's. Settled motionless during the day upon a piece of bark in a shady corner, but occasionally uttering the quaint and rather faint note, they become very lively in the evening, catching insects by long jumps, or investigating the hollows of decaying mossy stumps. Their general colour is then spotless, almost silvery grey. In the day-time they are sometimes suffused with delicate green.

The propagation has been studied by Miss M. H. Hinckley.^[85] They pair in shallow pools, in Massachusetts, in May. On the 10th of that month eggs were attached singly, and in groups, on the grasses resting upon the surface of the water; first drab-coloured, they became lighter in a few hours. Some larvae escaped from the gelatinous envelopes on the following day, the others on the third day; they clung to the grasses by means of their prominent suckers. The head and body were cream-coloured, with olive dots, and averaged ¼ inch in length. Gills appeared on the fourth day, to disappear again during the four following days, first those of the right, then those of the left, side; the suckers became less conspicuous, and the general colour turned into deep olive-green, with fine golden dots on the upper and lower surfaces. The eyes were of a brilliant flame-colour. On the eleventh day the suckers or "holders" had disappeared, and the hind-limbs were indicated by small white buds. By June 5th, i.e. the twenty-seventh day, the toes developed the terminal discs; the mottling of gold had given way to a uniform olive or pea-green. Movements of the future arms beneath the skin appeared on the 28th of June, at the age of seven weeks. The arms, mostly the right one first, were thrust out on the 2nd of July; the fins of the tail were absorbed rapidly, and towards the end of the seventh week the nearly transformed creatures began to leave the water. The young frogs changed colour rapidly, in adaptation to their surroundings, but the four specimens which survived were never all found to be of the same colour during the next three months. They first lived upon Aphides, later upon flies, and they were alert nocturnally. About the beginning of October they left the fronds of their fernery and nestled away in the damp earth, which they left only when the temperature rose above 60° F.

H. vasta of Hayti is the giant of the tree-frogs, reaching a length of 5 inches. In order to support its great weight the adhesive discs of the fingers and toes are of a surprising size, about as large as a threepenny piece. The skin is covered with small warts, and forms a peculiar fold on the hinder surface of the fore-arm and on the tarsus, and small flaps near the vent. The colour is grey above, blackish on the head, with a brown band between the eyes; the under parts are flesh-coloured, the throat with black spots.

H. maxima, of the forests of British Guiana, is scarcely less gigantic, and is distinguished by a projecting rudiment of the pollex, while the adhesive discs are smaller than the tympanum. The skin forms folds on the arms and tarsus, like those of H. vasta, in addition to a triangular flap at the heel. The general colour is reddish-brown above, sometimes with a dark vertebral line, the under parts are whitish and covered with large granules; the throat of the male, which has an inner vocal sac, is brown.

H. faber of Brazil is closely allied to the last species, but the skin of its upper parts is quite smooth. There is a small tarsal fold, and one extending from the upper eyelid to the shoulder. It is light brown above, with darker marks which form a conspicuous vertebral line, transverse bars on the hind-limbs, and a few irregular, scattered, vermicular or linear marks on the head and body. The adult, when put into a strong light, will rapidly turn pale; at night the longitudinal stripe on the back and the bars on the hind-limbs become very distinct; the under parts are white, and exhibit a beautiful orange tinge. This is the famous "Ferreiro" or "smith." As will be seen from the following graphic account by Dr. Goeldi^[86] of Para, this species doubly deserves its name of faber, not only in virtue of its voice, but also because of the marvellous nest-building habits recently discovered.

"The Ferreiro is common in the Province Rio de Janeiro, more frequently still in the mountain regions of the Serra dos Orgãos than in the hot lowland. Its voice is one of the most characteristic sounds to be heard in tropical South America. Fancy the noise of a mallet, slowly and regularly beaten upon a copper plate, and you will have a pretty good idea of the concert, given generally by several individuals at the same time and with slight variations in tone and intensity. When you approach the spot where the Tree-frog sits, the sound ceases. But keep quiet, and it will be resumed after a few moments. You will discover the frog on a grass-stem, on a leaf of a low branch, or in the mud. Seize it quickly, for it is a most wonderful jumper, and it will utter a loud and shrill, most startling cry, somewhat similar to that of a wounded cat."

The "Smith" makes very regular pools, in the shallow water of ponds, or nurseries for the tadpoles surrounded by a circular wall of mud. Dr. Goeldi has watched the building process during a moonlit night: "We soon saw a mass of mud rising to the surface carried by a Tree-frog, of which no more than the two hands emerged. Diving again, after a moment's time, the frog brought up a second mass of mud, near the first. This was repeated many times, the result being the gradual erection of a circular wall. From time to time the builder's head and front part of body appeared suddenly with a load of mud on some opposite point. But what astonished us in the highest degree was the manner in which it used its hands for smoothing the inside of the mud wall, as would a mason with his trowel. When the height of the wall reached about 4 inches, the frog was obliged to get out of the water. The parapet of the wall receives the same careful smoothing, but the outside is neglected. The levelling of the bottom is obtained by the action of the lower surface (belly and throat principally) together with that of the hands."

The male takes no active share in the construction of the nest, but will suddenly climb up the wall of his home, and then upon the back of his busy mate. The building operation may take one or two nights, and is performed in the most absolute silence; the croakers around are all males clamouring for a mate.

The eggs are laid during one of the following nights, and are hatched some four or five days later, the parents keeping hidden in the neighbourhood of the nursery. Heavy rains may destroy the walls, and thus prematurely release the tadpoles.

It is only owing to such keen observers and lovers of nature's fascinating ways that the breeding habits of some Brazilian Hylidae have become known.

H. nebulosa s. luteola also living in Brazil, is yellow above, with brown dots; the sides of the belly and thighs have transverse bluish bars, the under parts are whitish. Its size is under 2 inches. Goeldi has often found it in the sheaths of decaying banana-leaves. It glues the lumps of eggs on to the edges and to the inside of the withered leaves, where even during the hot hours of the day sufficient coolness and moisture are preserved. These lumps are enveloped in a frothy substance, in which the nearly metamorphosed tadpoles can be watched wriggling. If these are put into water, all will die in a few hours.

H. polytaenia deposits its eggs in free lumpy masses on water-plants. It is a small creature, little more than 1 inch in length, light olive above, with numerous brown parallel longitudinal bands on the body and limbs. A dark, white-edged band extends from the nose along the side of the body. The heel has a short flap of skin. The male has an internal vocal sac.

H. goeldii is a most interesting form, leading to the allied genus Nototrema. Boulenger^[87] has described a female which was captured by Goeldi in January on the Serra dos Orgãos. It is about 1½ inch long. The whole surface of the back is occupied by a layer of twenty-six pale yellow eggs which are 4 mm. in diameter. The skin of the back is expanded into a feebly reverted fold, which borders and supports the mass of eggs on the sides, thus suggesting an incipient stage of a dorsal brood-pouch. Owing to the great amount of yolk, the young are probably able to remain upon the mother until they are nearly metamorphosed.

H. coerulea s. cyanea is one of the largest Australian green tree-frogs, ranging from the South to the very North of Australia. The discs are as large as the fully-exposed tympanum. There is no projecting rudiment of the pollex, but a slight cutaneous fold borders the inner side of the tarsus. The skin is smooth and shiny, always a little moist, and studded with numerous rather large pores on the nape and shoulders; this somewhat thickened region forms a prominent fold which begins behind the eyes. The belly and the under parts of the thighs are granular as in most Hylidae. The male has an internal vocal sac; and during the breeding season, which seems to occur during our autumn and winter, develops brown rugosities on the inner side of the first finger. The tongue is round, slightly notched behind and free enough to be protruded a little.

The alternative specific names are most unfortunately chosen, as they apply only to spirit-specimens. During life this tree-frog exhibits a considerable amount of colour-changes. The normal colour is bright green above, white below. A conspicuous feature of this species is the frequent occurrence of white specks or spots, which are probably due to the deposition of guanine, a peculiar white colouring matter. The spots appear in any part of the green skin, and are quite irregular in their distribution. Sometimes they remain for weeks in the same place, or they disappear after a few days and others appear. They are in no way connected with the shedding of the skin, nor do they indicate ill-health. H. coerulea lives well in confinement, and becomes tame enough to take food from one's fingers, even when sitting upon the hand. Some of mine took to living during the daytime in a small box, preferring a crowded condition in companionship with Natterjacks. Others squeeze themselves into the most uncomfortable cracks, while others again prefer the broad leaves of Philodendron. A favourite place for two or three at a time is the funnel-shaped spaces formed by Bromelia-plants. Those specimens which are hidden in the box or in the hollows of rotten stumps are, almost without exception, dull, very dark brownish olive, while those on the Bromelias assume exactly the sombre dull green of its leaves. Lastly, those which sit in the light, exposed places, no matter if upon a leaf, on a white stone, or upon a board, are emerald-green, especially beautiful on hot, sunny days;–and they are not always averse to the full glare of the sun. When squatting upon a flat surface, such as a broad leaf, they tuck the fore-paws under the head like a cat, and with half open eyelids, the pupil contracted to a tiny slit, so that the golden iris is exposed, they remain motionless during the day. They take food when offered, but at night they roam about, either hopping on the ground, or making enormous leaps from leaf to leaf, sometimes deliberately stalking some choice insect, and patiently climbing up a stem, hand over hand. At night their whole aspect is changed. The colour is saturated green, the eyes are transformed into round, projecting shiny black beads, and the head is erect. The ludicrously dreamy, complacent look has given way to wide-awake alertness. They take all kinds of living food. When they find an earthworm, they first look at it, bending the head sharply down, lift themselves upon the fore-limbs and then pounce upon it, nipping the prey with the jaws, and then poking it down deliberately with the hands. Cockroaches are simply lapped up, and disappear in the twinkle of an eye. Mealworms, wood-lice, butterflies and moths, flies and spiders are taken. The stomach of a specimen in the Dresden Museum, from the Aru Islands, contained some four or five young freshwater Crustaceans of the genus Sesarma. They fortunately do not molest smaller frogs of their own kind and of other species. Like many Amphibia they like a change of diet, and ultimately refuse their food if it is unvaried. To my surprise my largest specimen, which measures a little more than 4 inches, takes snails, Helix virgata, half-a-dozen at a time, and on the following day, not during the night, vomits the sucked-out shells in a lump, like the pellets of birds of prey. During this rather painful-looking procedure the whole tongue and about half an inch of the everted gullet are protruded out of the mouth, and are then slowly withdrawn. After having roamed about all night, they return to their respective resting-places, where each individual is sure to be found in exactly the same spot, day after day. They do not mind being looked at, but if taken up and put back they avoid that place for perhaps a week, taking shelter somewhere else.

Both sexes have a voice, but that of the female is only a grunting noise, while the male inflates its gular sac and sends forth a sharp cracking sound, which can turn into a regular bellowing like the gruff barking of an angry dog. They bellow at any time of the year, frequently on the approach of a shower or during a thunderstorm. Certain noises will also induce them to bark. The rattling produced by the syringing of the greenhouse, sawing of wood, hammering, the raking of the gravel, or even the scraping of boots on the gravel-path is liable to start one of the males, and the others are sure to chime in.

According to Fletcher, H. coerulea and H. aurea lay their eggs in round white frothy patches, which float in the water, chiefly during the months of August and September; but when the spring months are very dry, the pairing is delayed until the following January. Several other Australian species of Hyla, e.g. H. ewingi, spawn at any time of the year if the conditions are favourable. They attach their eggs to submerged blades of grass or to twigs.

H. aurea is one of the commonest and most beautiful species, occurring throughout Australia and Tasmania, excepting of course in the large deserts. It has the appearance and restlessness of a water-frog, is not unlike Rana esculenta, and grows to about three inches in length. The tympanum is very distinct, but rather small. The fingers are without a pollex-rudiment, the tarsus has a fold along its inner edge. The adhesive discs are decidedly small. The male has two internal vocal sacs, which bulge out sideways. The skin is smooth and shiny. The under parts are white; the upper parts are, speaking generally, a mixture of blue and olive, with blue or brown spots, but spirit-specimens give no idea of the beauty which this changeable species can assume. Sometimes the same individual is saturated blue and green, with several longitudinal stripes of burnished copper along the back; a few minutes later the stripes glitter like gold, and in other moods the whole upper surface is mottled blue, green, and brown. My specimens often went into the water and did not climb. The food is said to consist chiefly of other small frogs in preference to insects.

Nototrema differs from Hyla in so far as the female has a pouch on the back for the reception of the eggs. This bag is formed by an infolding of the skin; it opens backwards in front of the vent, it has a sphincter and is permanent, although it distends to larger dimensions when in use. An initial stage of such a pouch is possessed by Hyla goeldii (Fig. 38). The pupil is horizontal, the tongue can be protruded but little; the tympanum is free, and the adhesive discs of the fingers and toes are well developed. These "marsupial frogs," of which about half-a-dozen species are known, live chiefly in the tropical forest-region of South America, notably from Peru to Venezuela.

N. marsupiatum is green with darker blue-green spots, or with longitudinal patches which are each surrounded by a whitish or yellow seam of little dots. The limbs have cross-bars. Total length about 2½ to 3 inches. The eggs of this species are comparatively small and numerous. The very small tadpoles have no external gills, and escape from the pouch to finish their metamorphosis in the water.

N. testudineum, about 3 inches in length, is of a uniform lead-colour, but is lighter beneath. The skin of the back is studded with stellate calcareous deposits, a peculiarity which is alluded to in the specific name.

N. oviferum is brown above, with darker patches on the sides of the body and with cross-bars on the limbs. The last two species and N. fissipes of Brazil, near Pernambuco, carry their young in the pouch until the metamorphosis is completed. This long nursing-period necessitates a great amount of food-yolk in the eggs, and this enlargement in turn implies a considerable reduction in their number. The female's load consists of about fifteen eggs only, but these are of a great size, namely one-eighth of the length of the mother's body.

N. pygmaeum, in Venezuela, is a tiny creature. The female, just one inch in length, carries only from four to seven eggs. It looks then "as if it carried a sac filled with a few gigantic balls." This species is further worthy of note on account of the opening of the brood-pouch, which is a longitudinal slit, whence a kind of thin and slightly elevated ridge or fold of the skin extends on to the neck. The suggestion, that this seam is burst open, in order to set the full-grown young free, instead of their passing through the existing opening, is scarcely credible.

These Neotropical tree-frogs seem to be rare, and females with embryos are of course still more uncommon, so that the best account of their structure is still that given by Weinland^[88] of N. oviferum. How the eggs get into the pouch has not yet been observed, but it is most likely with the help of the male, immediately after fertilisation. The pouch forms two blind sacs which extend forwards over the sides of the back. The eggs are large, 1 cm. in diameter, and the enclosed embryos, or rather tadpoles, had a length of 15 mm., with a large amount of yolk still contained in the spirally wound intestine. The first two gill-arches carried each a double thread, which expanded into a funnel-shaped membrane, not unlike the flower of a Convolvulus, and furnished with a capillary network; the stalk contained muscular fibres. These most peculiar structures are of course the much modified external gills. Those of N. testudineum and N. cornutum are likewise bell-shaped.

Hylella differs from Hyla chiefly by the absence of vomerine teeth, and consists of about half-a-dozen small species, about one inch in length. The fact that two species live in Queensland and New Guinea, while the others are natives of tropical America, suggests that this genus is not a natural but an artificial assembly, an instance of convergent evolution.

Phyllomedusa, composed of about one dozen species of tree-frogs, is characterised by the vertically contracted pupil, large adhesive discs, and the opposable nature of the inner finger and of the hallux, the last joints of which are like thumbs. The sacral diapophyses are strongly dilated. The range of the genus extends from tropical Central America to Buenos Aires. Most of the species are about 2 inches in length, blue-green to violet above, with white purple-edged patches on the sides of the body; the under parts uniform white, or with purple or brown patches. The male has a subgular vocal sac. Some have more or less distinct parotoid glands. Ph. dacnicolor of Mexico is uniform green above, whitish below, and attains a size of more than 3 inches. In Ph. bicolor of Brazil, the skin of the upper parts is studded with calcareous deposits, and the parotoids are large. It is blue-green above, purplish white below, the sides of the body and limbs with white purple-edged spots.

Ph. hypochondrialis has been found breeding freely in the Paraguayan Chaco by Budgett,^[89] from whose account the following notes have been extracted. This brilliantly coloured frog is green above, which colour may become brown-grey or bluish at will; below, white and granular. The flanks are scarlet, with black transverse bars, and the plantar surfaces are deep purplish black. Total length about 1½ inch.

The "Wollunnkukk," as it is called by the Indians, from the call of both male and female at pairing time, is extremely slow in its movements, and is active only at night. At this time, if it is seen by the aid of a lantern as it slowly climbs over the low bushes and grass, it is very conspicuous. In the daytime, however, nothing is seen but the upper surface of the body as it lies on the green leaf of a plant. It has a remarkable power of changing its colour to harmonise with its surroundings, and can effect a change from the brightest green to light chocolate in a few minutes. The skin is also directly sensitive to light; for if the frog is exposed to the sun while in a tuft of grass in such a way that shadows of blades of grass fall across it, on removal it will be found that dark shadows of the grasses remain on the skin, while the general colour has been raised to a lighter shade. Its food consists largely of young locusts. The ovaries on each side are divided into five distinct clusters. The rectum has a large saccular diverticulum, which is very heavily pigmented.

In the breeding season–December to February–this beautiful frog collects in considerable numbers in the neighbourhood of pools. During the night-time they call incessantly to one another, and produce a sound as of a dozen men breaking stones, well imitated by the native name.

The eggs are enclosed in batches in leaves near the margin of the water. Budgett has been able to watch the whole process of oviposition and fertilisation. He found, at 11 P.M., a female carrying a male upon her back, wandering about in search of a suitable leaf. At last the female, climbing up the stem of a plant near the water's edge, reached out and caught hold of the tip of an overhanging leaf, and climbed into it. Both male and female held the edges of the leaf together, near the tip, with their hind-legs, while the female poured her eggs into the funnel thus formed, the male fertilising them as they passed. The jelly in which the eggs were laid was of sufficient firmness to hold the edges of the leaf together. Then moving up a little further, more eggs were laid in the same manner, the edges of the leaf being fastened together by the hind-legs, and so on up the leaf until it was full. As a rule, two briar-leaves were filled in this way, each containing about 100 eggs. The time occupied in filling one leaf was three-quarters of an hour.

Development proceeds rapidly. Within six days the embryo increases from the 2 mm. of the egg-diameter to 9 or 10 mm. When it leaves the leaf it is a transparent glass-like tadpole, whose only conspicuous parts are the eyes. These are very large and of a bright metallic green colour, so that when swimming in the water all that is seen is a pair of jewel-like eyes. The newly-hatched tadpole has also a bright metallic spot between the nostrils somewhat in front of the pineal spot. This is the point which touches the surface of the water when the tadpole is in its favourite position. Whether it is a protective coloration, or some mechanical arrangement for holding the surface, Budgett could not make out.

The egg contains a great amount of yolk; the rest of the jelly-like contents of the egg becomes fluid, so that towards the end of embryonic life the larva comes to lie quite freely within a membranous capsule. The external gills appear on the third day, and reach their greatest size on the fifth, when these bright red filamentous organs extend beyond the vent. By the time the tadpoles are ready to be hatched these gills have quite disappeared, there is a median spiracle, and the lungs are shining through the transparent body-wall. Five weeks later, i.e. six weeks after the eggs were laid, the tadpole is 8 cm. long, glossy green above, rosy and silvery below, and the hind-limbs protrude. The young frog at the close of its metamorphosis is two-thirds the length of the adult, and at this time acquires the red flanks barred with black.

The first account of the breeding of Phyllomedusa was given by v. Ihering^[90] concerning Ph. iheringi of Southern Brazil.

"Phyllomedusa does not lay its eggs in the water, although the larva develops in that element, but in the open air in masses 50 millim. long by 15-20 broad, between leaves hanging over the water. Willows are frequently used for that purpose. The egg-mass contains rather large white ova, wrapped up between two or three leaves in such a way as to be completely enveloped save an inferior opening. My attempts at rearing the eggs failed owing to the leaves drying up; but I am assured that the tailed larvae may be seen wriggling in the gelatinous mass. As at a later period the latter is found empty, we must infer that the larvae drop into the water below. The eggs are found only on plants hanging over stagnant water."

"The adult animal is a stupid creature, and will let itself be taken without attempting to escape. Their moderately loud voice resembles somewhat the sound produced by running the finger nail over the teeth of a comb. Only during the breeding season, in the month of January in Rio Grande do Sul, do these frogs make their appearance; at other times not one is to be seen, probably because they establish themselves high up in the trees."

Agalychnis, with two species in Central America, is practically like Hyla; but the pupil is vertical, and the tongue is extensively free behind.

Nyctimantis differs from either by its round tongue, which is not nicked behind, and is almost completely adherent, much resembling that of the Discoglossidae. The sacral diapophyses are but slightly dilated. The only species, N. rugiceps, lives in Ecuador, and grows to nearly three inches in length. The head is large and rough owing to the skin being involved in the cranial ossification. It is further peculiar in its coloration, the under parts being chestnut-brown instead of whitish. The upper parts are olive-grey or brown.

The following four genera, each represented by one or two species only, much resemble each other in the curious shape of the head, which forms a flat projecting snout, used probably for digging in rotten wood in search of insects. There is a peculiar degradation in the extent of dentition of the palatal region. Diaglena and Triprion are the only Hylidae which possess a longitudinal row of parasphenoid teeth. Diaglena petasata of Mexico and D. jordani of Ecuador have, moreover, a transverse row of teeth on the palatine bones in addition to those on the vomer.

Triprion petasatus of Yucatan has parasphenoid and vomerine teeth. The head is a bony casque, with strong superciliary ridges, the skin being extensively ossified. The mouth forms a flat snout, owing to the long projection of the upper over the lower jaw. The skin of the back is smooth brown with darker spots; the under parts are uniform whitish. The male has a subgular vocal sac. Like Diaglena and Corythomantis they possess adhesive discs on the fingers and toes, and climb trees. The total length of this curious creature is 2 inches.

Corythomantis greeningi of Brazil has a similar head. The vomers alone carry teeth, besides of course the maxillae. The pupil is rhomboid. The tongue, as in the two previous genera, is roundish, scarcely free. General colour above olive, with darker freckles; the sides are studded with whitish tubercles; the under parts are whitish. The male is devoid of vocal sacs. Total length 3 inches.

Pternohyla fodiens of Mexico approaches the previous three genera by the curious shape of the head and prominent upper jaw, although these features are not so exaggerated. The dentition agrees with that of Corythomantis and other normal tree-frogs. The fingers and toes are not provided with discs, in conformity with the burrowing, not climbing, habits of this creature. The next following three genera connect the Hylidae with the Cystignathidae. The sacral vertebrae are but slightly dilated.