Scanning electron microscopic observation of the dermal side of the epidermis in developing chick embryos.

The dermal side of the chick embryonic skin was observed by scanning electron microscopy (SEM) after the removal of dermal components. Epidermis free of dermis was prepared as follows: Tissues were fixed, hydrolyzed with hydrochloric acid (HC1), digested with collagenase or trypsin, and processed for SEM observation. The epidermis from the anterior tarsometatarsus and the foot pad was examined. The base of the tarsometatarsal epidermis of a 13-day-old embryo was smooth except for the ridge demarcating each large overlapping scale. The base of each basal cell of 18to 20-day-old embryos, bulged in hemispherical fashion on the dermal side. The undulation of the base of the epidermis (i.e. the formation of the dermal papillae) was not prominent in the tarsometatarsal epidermis. In the foot pad, small round depressions, each corresponding to a reticulate scale, were observed on the dermal side of the epidermis. The bottom of a depression was smooth in a 13-day-old embryo. After 18-20 days of incubation, the downgrowth of the epidermis occurred. Many pits corresponding to the dermal papillae were clearly seen. These observations show the morphological diversity of the epidermis in its dermal side during the development. In addition, HC1 treatment followed by protease digestion is useful in the study of morphogenesis of the epidermis.