Latterly these creatures have frequently been brought over to England. They stand confinement very well, even in a little aquarium with sufficient water-weeds to keep the water fresh; and they do not require special heat. They greedily snap up worms, strips of liver, or meat, and poke the food in with their hands. A few kept by Boulenger in a glass jar have lived for the last eleven years in the ordinary temperature of a room in London. Curiously enough they are often in amorous embrace, regardless of the season, but they have never shown any signs of spawning.
Some of those in the Zoological Gardens in London laid eggs on Saturday the 27th of May, and on the morning of the following Monday the larvae were already hatched. They have been described by Beddard.[[74]] The larvae are provided with an unpaired circular, ventral sucker. The tentacles begin to sprout out on the sixth day after hatching, at first not in connexion with the cranial cartilage, but soon a cartilaginous rod runs into the tentacle from the ethmoid "just above the joint with the under jaw.". Boulenger has most reasonably compared these organs with the "balancers" of Triton and Amitystoma (cf. p. [46] for the possible homologies of the balancers). The tentacles soon reach a great length and give the tadpole a curious appearance. In tadpoles of X. calcaratus, 65 mm. long, the tentacles are 30 mm. long, and are inserted just at the angle of the mouth. By the time that these tadpoles show their fore-limbs, the feelers are reduced to 4 mm. in length, and their relative position has been shifted to a little above the angle of the gape, and whilst the latter gradually extends further and further back, the feelers come to lie, or rather remain, below and a little in front of the eyes.
The tadpoles have no traces of horny teeth. External gills project as low conical or lamellar processes from the first three branchial arches, but so-called internal gills are not developed.
Amongst a number of Clawed Toads imported in the spring one female became swollen with eggs, but as they did not show signs of wanting to breed, a pair was put into the tropical tank in the Cambridge Botanic Gardens, a transfer which had the desired effect. Eggs were laid, and more during the following nights; they hatched out within thirty hours. The whole brood was lost, before any of them were older than a few days, since they were attacked, beyond the possibility of a cure, by a Saprolegnia or some similar pest.
Hymenochirus, represented by one species, H. boettgeri, has been discovered in the Ituri, German East Africa, and in the French Congo, and has no doubt a much wider distribution. It is scarcely 1½ inch long, and is easily recognised by the toothless mouth, the half-webbed fingers (hence the generic name), the incompletely webbed toes, the third of which is longer than the fourth, and the absence of sensory muciferous canals in the skin. The three inner toes are, as in Xenopus, furnished with small black claws. The skin is rough, beset with small granular tubercles. The general colour above and below is olive-brown. The vent is, as in Xenopus, produced into a spout or semi-canal, but is devoid of dorsal flaps of skin.
Pipa.–This Neotropical member of the Aglossa is quite toothless, but the jaws of the adult have horny substitutes. The only species is P. americana, the famous Surinam Toad, chiefly known from the Guianas, but undoubtedly extending much further, having recently been reported from the neighbourhood of Pará.
The general shape of this creature is very peculiar. The head is much depressed and triangular; the eyes are very small; the skin forms several short, irregularly-shaped flaps and tentacles on the upper lips and in front of the eye, and at the angle of the mouth. The tympanum is invisible. The pupil is round. The fingers are very slender and free, ending in star-shaped tips; the toes are broadly webbed. The whole skin is covered with small tubercles and is dark brown above, while the under parts of the very flat and depressed body are whitish, sometimes with a dark brown stripe along the middle line. In the female the skin of the back forms growths for the reception of the eggs, and in these the young undergo their whole metamorphosis.
Fig. 30.–Pipa americana. Surinam Toad. × ⅔.
The most characteristic feature of the skin,[[75]] which has exactly the same structure in both sexes, is the papillae, which are spread over the whole surface, except on the webs of the toes, on the cornea and on the star-shaped points of the fingers. Each papilla carries a little horny spike, and a poison-gland frequently opens near its base. Larger poison-glands exist on the dorsal and ventral side in four rows, and smaller glands open upon the sides of the body, but there are no parotoid complexes. Slime-glands occur all over the surface. The epidermis consists of the usual layers, namely the Malpighian, the stratum corneum, and the part which is shed periodically. The latter is completely horny, appearing to be structureless like a cuticle, but it is in reality composed of polygonal cells with flattened nuclei; each little spike is one modified horny cell. The whole outermost layer contains black-brown pigment. The upper portion of the cutis is devoid of pigment, then follows a layer of clusters of ramified dark pigment-cells, and lastly the rest of the cutis.