The skin and hair of the Southern Elephant Seal Mirounga leonina (L.) III. morphology of the adult integument

Abstract

The histological structure and certain histochemical features of the skin, hair follicles, and associated glands have been studied in 57 male and 49 female elephant seals. The epidermis comprises only three layers, stratum germinativum, stratum spinosum, and stratum corneum. The absence of granular and clear layers leads to a parakeratotic condition of the horny layer which is made up of large cornified sheets joined to lateral strands of the pelage hairs. Although pigment abounds in the interfollicular epidermis, it does not extend into the external root sheath cells of the hair follicles. There are no arrector pili muscles attached to the pelage hair follicles which are simple, unbranched, and contain only one fully developed lanceolate hair. Hairs are firmly anchored in their follicles by means of lateral filaments insinuated between external root sheath cells. A single, small, apocrine-type sweat gland opens into the hair canal below the common duct of the large, bilobed, sebaceous gland on the ental side of the follicle. The lipid-rich sebum is secreted within the lamellae of the stratum corneum and its function appears to be the maintenance of the outer horny layers in a pliable and perhaps water-resistant condition. The walls of the sebaceous duct are replete with glycogen. The dermis comprises a network of collagenous fibres and a decreasing number of elastic fibres in aging seals, as well as histiocytes and dermal fat cells. Problems of thermoregulation arising from loss of hair in seals exemplified by M. leonina and compensatory features apparent in the morphology of the skin and hair are discussed.