Blastoderm structure, cell migration and formation of the embryonic shield during gastrulation in the carp (Cyprinus...

This paper describes an ultrastructural study of the cell movements during the gastrulation of the common carp, Cyprinus carpio, using scanning electron microscopy. The morphology of the deep cells was studied in several consecutive stages ranging from 0-100% epiboly. Furthermore, the formation of the embryonic shield was followed from its earliest appearance at 50% epiboly onwards. This paper gives morphological evidence for the existence of two different pathways for involving and convergent movements. Firstly, cells may move along the inner surface of the not (yet) involuted cells. Secondly, a much smaller group may use the YSL as their substrate. These results are discussed in the light of the hypothesis that the two migrating cell populations may be differently induced, subsequently leading to the formation of mesoderm and endoderm.