Although there have been a great many studies on the morphogenesis of hydroids, the emphasis has been largely with regeneration and with grafting experiments, and mostly using the hydras, Cordylophora and Tubularia as material. Some of these investigations have made reference to cell movements and cell division, but none have considered both these fundamental morphogenetic processes and their interrelationships in a single hydroid. In this paper the occurrence of cell movements and cell division in normal growth and in the regeneration of Clytia johnstoni is considered.
The investigation has revealed extensive cell movements, not only in the coenosarc but also passively by the hydroplasm. Cell division is almost exclusively confined to the ectoderm and rarely occurs in the endoderm.
Material and Methods The animal was cultured in the laboratory on glass plates in running sea-water (Hale, 1957, 1960). All the observations (except those on cell division) were made on the living material kept at 18°C. (± 1).
Planar cell movements and oriented cell division during early primitive streak formation in the mammalian embryo
