The development and morphology of the larva of the South African clawed toad, Xenopus laevis II. The hatching and the first‐ and second‐form tadpoles

I n the following exposition, the development of the larva of Xenopus laevis Daud is described in detail, in an effort to map out the changes leading to the extraordinary morphological organization of the thirdform tadpole, which latter has been fully dealt with in a previous paper (Weisz, '45a). No earlier work on the embryology of the tadpole has come to the writer's attention ; investigators quoted previously were concerned only with larvae equivalent to the third-form stage, in view of their difficulty of obtaining younger forms. No attempt is here made to discuss the embryonic life of Xenopus, between fertilization and hatching. The latter phase, lasting approximately 48 to 60 hours, has been sufficiently described by Bles ( '05) ; the hatching process itself was equally investigated by the same author. A general account of the habits and the life cycle of Xenopus, of methods and materials employed, as well as a definition of the four arbitrary phases of the larval period, has been given in the first paper of this series. The diagnostic characteristics of each phase will however be indicated in the present description.