[Cytological characteristics of the gonocytes in the course of their migration in early rat embryos].

The work was carried out in 23 rat embryos from 9,5 to the 11th day of development. In 9,5-day embryos the primary sex cells are localized in the mesenchyma of the allantois and in the intestinal entoderm. Later they migrate either with the blood flow or on the surface of cellular layers towards gonad germs which are reached by the 11th day of the intrauterine development. In the course of this process there occur structural and cytochemical changes in gonocyte nuclei. The nucleolus is replaced to the periphery of the nucleus, around it there appears a rim intensively stained with methylene green. Chromatin has a shape of thin threads. These changes of the nuclei seem to be associated with an increased synthesis of r-DNA and hence with the synthesis of substances having the role to prevent the somatic differentiation of primary sex cells in the course of migration.