[Migration of the primordial germ cells in urodele amphibianPleurodeles waltlii Michah].

Unilateral removal of ectoderm and subjacent mesoderm practised onPleurodeles waltlii, at different stages of the neurula and tailbud embryo, causes a more or less important reduction of larval gonocytes on the operated side. It has thus been possible to locate the germ cells at the stage of the young neurula (st. 15) in the neighbourhood of the blastopore. Between stages 21 and 22, these cells begin a dorsal migration along the pronephric duct. The absence or reduction of the number of gonocytes, as a consequence of the extirpation of an ecto-mesodermal area, leads us to think that the germ cells are located in the mesoderm and that their removal cannot be compensated by presumptive somatic cells.