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Show 70 ON T H E HABITS O F X E N O P U S L_EVIS. [Feb. 4, Elizabeth ; and I have now the honour to lay before the Society results of my observations. Xenopus Icevis is called by the colonists the Plathanda. It is commonly found in the Sunday, Zwartkop, Baakens, and Sharks Rivers and the adjacent vleys. Its habits are essentially aquatic, the animal never leaving the water except in search of places where tood or shelter are better supplied. Unlike other frogs, it feeds in the water, on insects, small fishes, or even young and larvae of its own kind, and is apparently unable to feed out of that element. The mode of eating is by forcing the prey into the mouth by means of the hands, which act as a pair of claspers ; the deglutition always takes place under water. Locomotion on land is by difficult and awkward crawling and leaping. But Xenopus is a most admirable swimmer, and remarkable for the manner in which it remains poised for a long time immediately under the surface of the water, with the nostrils only exposed. The whole structure of the animal denotes its thoroughly aquatic habits-the broadly webbed toes, the smooth slimy skin with its symmetrically disposed muciferous tubules; there are no eyelids proper, but merely the transparent nictitating membrane, moving up and down ; and the nostrils have a disk-like internal valve. When at rest, Xenopus never assumes a sitting posture like other frogs and toads, and the back never appears humped. Pairing takes place in early spring (August), when the male, of which the palmar surface and inner side of the forearm acquire a black horny layer, clasps the female with his arms round the waist, the fingers interlocking on the pubic region. The ova are extruded singly and appear to be held for a short time between the cloacal labial folds which are so much developed in, and characteristic of, the female. I separated a pair during copulation, and placed the female in a small clean aquarium, and witnessed the oviposition. After about 90 ova had been deposited, I killed her for dissection and observed a small lot more of ova in the oviduct. These did not hatch, thus proving that the cloacal folds are not seminal receptacles. The eggs immediately after being laid measured j-^inch in diameter ; 24 hours after, through swelling of the mucilaginous envelope, they measured g inch. They are found attached singly to aquatic plants or stones. After leaving them to be a type affined to the lowest Ecaudata, viz. the Biscoglossidce and Pelobatidce, though in many respects more specialized, i. e. diverging more from the Urodele type. The larva of Xenopus, however, was known to approach more nearly to the Urodele than to the Anurous type, as is exemplified by the structure of the mouth without horny armature, by the two spiracula, and especially by the presence of a pair of barbels which are the homologues of the well-known 'balancers' of the Newt-larvae. From Mr. Leslie's investigations we learn that Xenopus agrees with the lower Ecaudata (Biscoglossidce, Pelobatidce, some Bufonidce and Cyst ig nat hid being inguinamplex, to use the term proposed by de l'lsle, i. e. the male holding the female round the waist during oviposition; and with the Discoglossoid genera Biscoglossus and Bombinator, as well as with the Newts, in the mode in which the eggs are deposited.-G-. A. BOULENGER.] |