FETAL EPIDERMIS 125 Table II (Continued) Histological Observations at Various Stages of Development of Fetal and Neonatal Guinea Pigs Postnatal Age Dermis Appendages Epidermis 1 hour Typical skin picture Typical skin picture 12 hours Typical skin picture Typical skin picture 4 days Typical skin picture Typical skin picture Prominent granulosum is out- standing feature Same Granulosum still prominent, but beginning to take on normal proportion with respect to other layers 10.0. 40 ' s% 6'0 [erin Days Figure 1. $Vater permeability of skin of guinca pig fetus during second half of gestation (semilogarithmic plot) The period of most rapid development of the water barrier extended from shortly after the 50th day of fetal life to parturition (ca. 63 days). During this interval, the efficiency of the water barrier increased logarith- mically with time (Fig. 1). Barrier Structure Using light microscopy, we have followed the morphological changes taking place in guinea pig skin during fetal life and into the postnatal period. These observations are summarized in Table II.

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