| Abstract: | Samples of dorsal skin were obtained from 18-, 19- and 20-day rat fetuses. Comparative developmental studies were carried out from a portion of the samples, while the remaining samples were cultured for four days in a medium containing tritiated thymidine and studied autoradiographically. At 18 days the epidermis contained a periderm, a stratum intermedium and a stratum basale. By 19 days the strata granulosum and spinosum had developed. At 20 days, a stratum corneum was present. Cultured samples of 18-day fetal rat skin resembled those that developed in utero with respect to time, whereas, the samples of 19- and 20-day fetal rat skin developed a more extensive stratum corneum, fewer keratohyalin granules, and a more condensed stratum Malpighii. Autoradiographic studies were made to determine the time taken for cells to migrate from the stratum basale to the outermost layer of the stratum granulosum (transit time). A similar “transit time” was noted for the three fetal ages studied. The rates of cell migration varied. The results of this study suggest that the extent of cornification impedes cell migration by providing a physical resistance or barrier against the outward forces presumably exerted by the division of basal cells. |
