From cleavage to primitive streak formation: A complementary normal table and a new look at the first stages of the development of the chick: II. Microscopic anatomy and cell population dynamics

• Published in: Developmental biology Vol. 79; no. 2; pp. 296 - 308
• Main Authors: Kochav, Shimshon, Ginsburg, Malka, Eyal-Giladi, Hefzibah
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 1980
• Subjects: Animals; Cell Division; Chick Embryo - anatomy & histology; Chick Embryo - physiology; Egg Yolk; Female; Kinetics; Uterus - physiology; Zona Pellucida - physiology
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/0012-1606(80)90117-7

The microscopic anatomy of uterine and freshly laid unincubated and briefly incubated chick germs is described. Special attention is paid to the difference between the three developmental periods involved: cleavage, area pellucida formation, and primary hypoblast formation. During cleavage the cytoplasm of the germinal disc divides into blastomeres, which become constantly smaller, and the subgerminal cavity is formed. The germ is accumulating extensive glycogen reserves for utilization during the next period. The most fascinating period is the formation of the area pellucida, which arises as a result of a polarized cell-shedding process. During this process all the subepithelial cells round up and fall into the subblastodermic cavity, where they assemble beneath the future anterior side of the blastoderm. The cell-shedding process is presumably energy consuming and the glycogen reserves are utilized as cell shedding progresses, starting at the posterior and terminating at the anterior side of the germ. The germ loses about one-fifth of its initial cytoplasmic mass during this process. The formation of the primary hypoblast is again polarized, posterioanteriorly. The onset of the process of polyinvagination takes place concomitantly with the shedding of the last subepithelial cells.