ULTRASTRUCTURAL CHARACTERISTICS OF PRIMORDIAL GERM-CELLS AND THEIR AMEBOID MOVEMENT TO THE GONADAL RIDGES IN THE TAMMAR WALLABY

The primordial germ cells (PGCs) of tammar wallaby fetuses are large c ells with large nuclei. The cytoplasm of the PGCs contains characteris tic spherical mitochondria and abundant ribosomes that make the cyopla sm appear dense. No permanent junctional complexes between PGCs and so matic cells were observed, and there were few cytoplasmic inclusions. The majority of migrating PGCs were observed outside the gonad in the dorsal mesentery and in the tissues adjacent to the gonad. The migrati ng PGCs have many finger-like, blunt pseudopodia, within which microfi lament bundles are observed. The numerous dumbell-like PGCs with polar ised cytoplasm suggest that the PGCs of this marsupial move to the gon adal ridges by amoeboid movement, but once the PGCs reach the gonadal ridge, they assume their more characteristic ovoid shape.