OBSERVATIONS OF PRIMORDIAL GERM CELLS IN THE TURTLE EMBRYO (CARETTA CARETTA): LIGHT AND ELECTRON MICROSCOPIC STUDIES

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Abstract
Primordial germ cells (PGC) in the turtle embryo (C. caretta) were observed with light and transmission electron microscopes. Identification of the PGC for light microscopy was made by the periodic acid-Schiff (PAS) technique. PGC were first found in the yolk-sac endoderm through the 5th-6th day of development. PGC freed from the endoderm then migrated to the root area of the dorsal mesentery and the coelomic angle from the 7th-11th day of development, and finally settled down in the gonadal anlage by the 14th day. Turtle PGC were characterized by a large size (16 .mu.m in diameter) and large nuclei with distinct nucleoli, and by the presence of large numbers of lipid droplets, yolk platelets and glycogen particles in the cytoplasm. Cell organelles were well-developed in PGC at later stages. Ameboid features of the PGC were observed in the mesenchyme, indicating active locomotion. PGC were usually surrounded or encircled by neighboring somatic cells. No intravascular PGC were detected at any stage of development examined.