Introduction

Abstract

In his introductory remarks at the first Symposium on the Comparative Biology of Skin held in London in 1975, Alistair Graham described the skin as “the end of me and the beginning of the rest of the universe”. Such a statement may be construed to imply that the structure of the skin of an organism might be expected to reflect the immediate environment in which it lives. This holds, by and large, for vertebrates, with the fishes and amphibians having “moist”, mucus-secreting integuments, and the terrestrial classes having “dry” skins. It is, however, patently untrue for many invertebrates. For example, the soil is the habitat for animals with integuments as different as the collagenous cuticles of nematodes and oligochaetes, the ciliated surface of the mucus-cushioned foot of pulmonate molluscs, and the sclerotized, chitinous cuticle of insects. The vertebrate gut harbours a number of parasites including both tapeworms and nematodes. The latter protect themselves against potentially destructive attack from enzymes and antibodies by a structural device — the inert cuticle, which moults to bring about a renewal of the surface. Tapeworms, in contrast, are anenteric and must necessarily possess an absorptive/digestive tegument which, at the same time, needs to serve a protective role. Here, the true interface is the surface plasma membrane and its associated glycocalyx which, due to its fast turnover rate, provides a frequently changing contact point with the environment.