Cell movement, proliferation and death in the formation of the embryonic axis of the rabbit

Rabbit blastocysts of ages six to eight days, post coitum were used to study the roles of cell proliferation, cell movement and cell death in the formation of the primary embryonic axis. Neutral red staining of local spots on the surface of cultured embryos provided information on the direction and speed of cell movement. Nile blue sulphate was used to detect necrotic cells in the embryonic areas. Mitotic indices were determined from counts made of the cells of serially sectioned embryos. It is concluded that the formation of the embryonic shield and primitive streak from the disc in the rabbit embryo is primarily achieved by migrations of cells that are being rapidly proliferated over the entire surface of the embryonic area. Cell death occurs but is an insignificant factor in this phase of embryonic growth.