[Relations between the structural evolution and visceral endoderm activity of the umbilical vesicle in the guinea pig during pregnancy].

The guinea-pig yolk sac endoderm has been observed through scanning and transmission electron microscopy to correlate ultrastructure and function of the cell surface. Using ferritin, different stages of protein transfer have been traced and a secretory activity of the vitelline endoderm during the last third of pregnancy has been suggested.