Mitosis in presumptive primordial germ cells in post-blastula embryos of Xenopus laevis.

In X. laevis embryos injected with (3-H) thymidine between early gastrula and late neurula, the presumptive primordial germ cell nuclei were labelled and some were observed in mitosis, confirming that division occurs throughout this developmental period. In all labelled and mitotic cells, the germ plasm adjoined the nucleus, an observation which invalidates the hypothesis that germ plasm inhibits mitosis in presumptive primordial germ cells after gastrula. In embryos which had been irradiated with UV at the vegetal pole at the 2-cell stage, the presumptive primordial germ cells also incorporated (3-H) thymidine and divided during the same developmental period.