[Ultrastructure of the gonadal primordia of the viviparous lizard (Lacerta vivipara Jacquin) during the period of colonization by the germ cells].

This ultrastructural study was carried our during colonization of the gonadal primordia by the germ cells which reach the gonads after interstitial migration. During the period of colonization, the germinal epithelia have no basal membrane. The epithelial cells are linked together by desmosomal junctions; they contain many free ribosomes, some lipid droplets, few granular reticula. The Golgi apparatus and the agrangular reticulum are well developed and situated at the distal pole of the cells. The outline of the germinal epithelia is regular in front of the coelomic cavity. At first, the outline of the basal surface is very irregular because the epithelial cells put out many cytoplasmic processes. Then, cytoplasmic processes become more sparse and the outline of the basal surface more regular. The germinal epithelia do not show swellings linked with a merocrine type of excretory process as in the chick (Cuminge and Dubois, 1971). However, this does not rule out a chemotactic type attraction of the germ cells. The first germ cell which arrive in the gonadal areas are incorporated into the epithelia. Later on, the germ cells are immobilized by the mesenchymal cells of the gonadal primordia which prevent them from reaching the epithelia. These germ cells stay in the medullary area of the young gonad which contain a greater number of germ cells than the epithelia.