A tadpole is the larva of a tailless Batrachian after the loss of the external gills and before the egress of the fore limbs (except in the aberrant Xenopus) and the resorption of the tail.
In the Aglossal Xenopus, the tadpoles are likewise devoid of circular lip, horny teeth, and beak, and they are further remarkable in the following respects: There is a long tentacle or barbel on each side of the mouth, which appears to represent the "balancer" of Urodele larvae; the spiraculum is paired, one on each side; the fore limbs develop externally, like the hind limbs.
Beddard, "Notes upon the Tadpole of Xenopus laevis," P.Z.S., 1894, p. tot; S.
The recent addition of a third genus of Aglossa, Hymenochirus (24) from tropical Africa, combining characters of Pipa and Xenopus, has removed every doubt as to the real affinity which connects these genera.
None of the Stegocephalia appears to have been provided with claws, but some living batrachians (Onychodactylus, Xenopus, Hymenochirus) have the tips of some or all of the digits protected by a claw-like horny sheath.
M In all larval forms, in the Caudata, and in a few of the Ecaudata (Xenopus, for instance), the epidermis becomes modified in relation with the termination of sensory nerves, and gives rise to organs of the same nature as those of the lateral line of fishes.
It may be said that, on the whole, the distribution of the batrachians agrees to some extent with that of fresh-water fishes, except for the much less marked affinity between South America and Africa, although even among the former we have the striking example of the distribution of the very natural group of the aglossal batrachians, represented by Pipa in South America and by Xenopus and Hymenochirus in Africa.
(23) "On the Development of the Vertebral Column in Pipa and Xenopus," Anat.