Primordial Germ Cells in the Chordates: Embryogenesis and Phylogenesis

active actually amphibians Anat animal anlage anuran appearance Arch archenteron becomes Biol birds blastoderm blastodisc blastomeres blastula body called capacity characterised chick chordates cleavage complete components concluded contain cytoplasm definitive demonstrated described determination differentiation displacement dorsal early early development ectoderm embryo endoderm entire evidence experimental experiments fishes formation formed further gastrulation genital ridges germinal crescent germinal plasm germinales gonadal anlagen gonadal epithelium groups hypoblast inductive initial invagination lateral lateral plate mesoderm layer leads mammals material mesoderm migration moiety Morphol mouse movements neural Nieuwkoop normal notochord observed occurs organ origin period PGCs phase pole portion posterior present presumptive primary primitive primordial germ cells region represent reptiles seems segregation similar situation somatic somites species stage structures studied subsequent suggests teleosts tissue Tung ultrastructure urodele various vegetal ventral vertebrates Xenopus yolk yolk mass zone Zool