Ectoderm Extraembryonic

Ectoderm extraembryonic systems are a special type of cellular structures of some fertilized eggs, located in epiboly, surrounded by several embryonic membranes and intended for the development of embryonic cells of a number of animals. E.v. With. are formed as a result of the epiboly process. After the formation of a special type of partition from the cytoplasm of the developing blastocyst on the side facing the substrate, the cells of the yolk sac approach the body of the fertilized egg. Because these cells have the form of vesicles surrounded by stroma (perigeville), evolutionary morphologists called them follicular cells (foetus - Latin, “future, future tense”).

These cells merge along the entire peripheral edge with the inner surface of the yolk sac, free of yolk cells (periphlebion). The formation of follicular cells, inherent in all eggs of amphibians, birds, prey