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FETAL EPIDERMIS 127 Figure 3. Ultrastructure of fetal guinea pig epidermis at 53rd day of gestation. D, desmo- somes DB, "Dark Bodies of Odland" K, keratohyalin granule cytoplasm contains well defined Golgi zones, numerous mitochondria, and rough endoplasmic reticulum. Ribosomes were found intracellu- larly and also between cells. Their presence in the latter may be asso- ciated with pinocytosis which is readily observed in the electron micro- graph. On the 53rd day of gestation (Fig. 3) the first evidence of development of a functional barrier is indicated by the appearance of small keratohya- lin granules and the presence of a thin, undifferentiated horny layer. Epidermal desmosomes are now well developed and provide greater inter- cellular adherence. The 56th day of gestation is a near midpoint in the genesis of a func- tional barrier. This phase of development is characterized ultrastruc-