The spatial pattern and temporal sequence in which feather germs arise in the white Leghorn chick embryo

Feather germs arise in a specific sequence and spatio-temporal pattern within each of 10 feather areas on the White Leghorn chick embryo. The time of feather germ initiation was determined by histological and gross macroscopic analyses. Protruding feather germs are sequentially visualized in the dorsal, thigh, breast, head, humoral, ventral, wing, eye, and external auditory meatus feather areas, respectively, from stage 31- to stage 39+ [V. Hamburger and H.L. Hamilton (1951) J. Morphol. 88, 49-92]. The rate at which successive feather tracts appear was found to differ for different feather areas and was not simply due to the size of a feather area. Feather germ histogenesis was examined in the dorsal, thigh, breast, ventral, wing, and tail feather areas. The stages of feather germ histogenesis, examined on the wing feather area, are similar to those previously described for the dorsal surface. Gross and histological analyses gave different times and temporal sequences of feather germ visualization. Some feather areas were readily visualized at the time of feather germ initiation, while others showed a lag between the histological appearance of feather germs and their macroscopic visualization. Thus, macroscopic observations do not accurately reflect the pattern of histogenesis.