Cell differentiation in the olfactory pit of the chick embryo
It is well known that the development of the olfactory organ derives from the epithelium lining the surface of the olfactory pit which developed from the ectodermal olfactory placode. The development of the olfactory epithelium has been explored in the chick embryo(Robecchi; 1972, Breipohl and Fernandez;1977) and the mouse embryo(Cuschieri and Bannister;1975, Graziadei and Okano;1978) to a certain extent.In order to investigate the cellular differentiation of chemoreceptor cells in the olfactory organ proimordium, the olfactory placode of the chick embryo(50-53 incubation hours, Hamburger and Hamilton, 1951) and the olfactory pit of the chick embryo(52-69 incubation hours, HH) are utilized in this study with the aid of a scanning and a transmission electron microscope.Olfactory placode; the placode is recognized on the antero-lateral aspect of the head of the chick embryo(50-53 incubation hours, HH), and distingwished from the general surrounding ectoderm as a circular territory of 140 μm in diameter, and the cellular arrangement at the placode surface observed by a scanning electron microscope is characteristic and recognized as a rosette consisted from several oval swollen cellular endings (olfactory. vesicles) which have a single cilium and few microvilli, and the other intercalated cellular elements(supporting cells) (Fig. 1).