抄録
The skin of the extremities of Xenopus laevis shows various surface differentiations, which were studied with several microscopical methods.
The normal stratum corneum consists of flattened cells with irregular outlines. A pattern of numerous, finger- and pleat-like protuberances constitutes a rough surface profile, which seems to assist the adhesion of the epidermal mucin. This pattern is already preformed at the surface of the replacement layer as intercellular bridges and free cell-processes.
The lateral finger skin and, to a lesser extent, the ventral toe skin are covered by so-called cupola cells, which have the shape of a spherial cap with a regular, mostly hexagonal outline. The external surface of these cells possesses a typical surface profile constisting of fungiform protuberances which gradually develop from progressive and regressive transformations of cellular surface and contact structures in the upper epidermal layers. The cupola cells cover vertical cell piles which arise from a single basal regenerative cell. From the histological findings it may be concluded that the regenerative cells divide once per moulting cycle and that their frequency of division is on the average 15 times greater than in the stratum germinativum cells at epidermal regions with normal stratum corneum.
A further local protrusion of the epidermis leads to the formation of conical epidermal claws. These exist as two types: 1. unicellular claws scattered on the dorsal skin of the extremities; their stratum corneum consists of a single hollow coneshaped cell. 2. as multicellular claws densely covering the ventral skin of the fore-legs; their conical stratum corneum is multicellular. The unicellular claws are sets of superimposed cone-shaped cells. The tip of the multicellular claws and their tip-producing cell sets reveal the same construction, but in most cases their cones consists of two cells. Multicellular claws with piles of unicellular cones and such with piles of mixed unicellular and bicellular cones can be regarded as transitional forms. The multicellular claws of the fore-legs apparently have a mechanical function assisting feeding and copulation.
Furthermore, there are scattered skin warts which, in contrast to the cupola cells and epidermal claws, result from local protrusions of the epidermis including the corium. The morphological similarities of these different surface structures indicate that they are, in principle, differentiation of the same kind produced by locally varying growth pessure.
