The skin of primates. XLII. The skin of the silvered sakiwinki (Pithecia monachus).

The following characteristics indicate that the skin of the silvered sakiwinki (Pithecia monachus, E. Geoffroy, 1812) is not only basically similar to other primitive cebids, but also remarkably close to that of callithricids: a thin epidermis with diminished monoamine oxidase activity; a poorly-developed dermis, paucity of elastic fibers, and scant adnexal blood supply; hair follicles arranged in linear perfect sets; grouped hairs present on the cheek; an absence of glycogen and phosphorylase in most sebaceous glands; apocrine glands present throughout most haired body regions, but totally absent from the dorsum; and poorly-differentiated eccrine glands, confined to volar friction surfaces, which are characterized by unusual glycolytic properties. Other noteworthy cutaneous traits include: concomitant epidermal and dermal pigmentation in the face and scalp; Merkel-like disks in the friction surfaces; moderately well-developed Haarscheibe, associated with large, dorsal guard hairs; small, discrete sebaceous glands throughout the dorsum; a 1:1 ratio of apocrine glands to hair follicles in the facial, gular and anogenital areas; and numerous cholinesterase-reactive nerves around eccrine but not apocrine secretory coils. Although previous comparative studies on the skin of New World monkeys suggest that the systematic designation of two familial taxa is warranted, information regarding five of the fifteen genera which comprise the families Callithricidae and Cebidae is totally lacking. Given that three of these genera (Leontopithecus, Chiropotes and Brachyteles) can no longer be obtained from animal dealers because of exportation laws, the authors were fortunate to acquire representatives of the remaining two genera: Callicebus (titi monkeys) and Pithecia (sakiwinkis). Besides defining cutaneous characteristics common to specific taxa, two earlier works by Hanson and Montagna ('62) and Perkins et al, ('68) also suggested that members of the cebid subfamilies Aotinae and Pitheciinae possess cutaneous traits that bridge an interesting gap with the callithricids. Therefore, the acquisition of these two additional aotine and pithecine genera provided the opportunity to test this hypothesis. The following, therefore, is not just another detailed manuscript regarding the skin of primates. Rather, it is an effort to define the integumental characteristics of the last obtainable New World monkey genera, and to assess those cutaneous signatures which are interfamilially common to both the callithricids and more primitive cebids. Primary emphasis is placed on the genus Pithecia; pertinent findings concerning Callicebus will be incorporated into the forthcoming and final summarization of the phylogenetic significance of the skin of New World monkeys (Perkins, '75).