The Epidermis of the Gopher Tortoise <em>Testudo Polyphemus</em>(Daudin).

1. Light microscopical histological and histochemical methods were used to examine the epidermis of the Gopher tortoise Testudo polyphemus. 2. The living germinative epidermis did not develop a granular layer and it was only a few cells in depth but the overlying stratum corneum was about twenty cells deep. The mature keratinized cells were extremely flattened and solid in structure but all nuclear basophilic staining was lost. The small horny scales in the neck skin were intermediate in appearance between the loose hinge horny layer and the larger compact scales of the legs. In the narrow hinge regions between the leg scales and also in the wider hinge zones in the neck epidermis, the stratum corneum was made up of layer upon layer of loosely arranged, separate keratinized lamellae. These were formed of horny cells joined at their lateral edges but free on their upper and lower surfaces. 3, The loose hinge horny layer contained some cystine but there was a much stronger reaction in the leg horny scales. Cysteine showed a reversed distribution with a greater concentration in the lunge horny layer and little in tile leg scales. 4. Protein-bound phospholipids were found in the epidermis and were also strongly present in the hinge horny layer and in the neck scales, but the compact leg scales showed only a very weak reaction. There was a similar distribution of protein-bound calcium in the stratum corneum. Nucleic acids were not found in the keratinized cells. 5. Growth rings showed sites of retention in the stratum corneum of old horny cells of previous years. These occurred on the leg scales as well as on the carapace. 6. The stratum corneum of the tortoise appears similar in structure throughout its depth in contrast to the Squamata where differences occur through the thickness of the horny layer. These differences are discussed in relation to keratinization and sloughing. It is suggested that the tortoise horny layer is more homogeneous than in snakes and lizards because keratinization is probably a continuous process in contrast to the cycles of the Squarnata. [ABSTRACT FROM AUTHOR]