The Water Relations and Cuticle of Paradesmus gracilis (Diplopoda, Strongylosomidae)

Water-loss in Paradesmus gracilis depends upon temperature and humidity, and is directly related to saturation deficiency. There is no evidence of any ‘critical point’ to indicate an epicuticular wax layer. Water is readily lost and taken up through the cuticle, the effect of the spiracles and of excretion being negligible. Despite great sensitivity to desiccation, there is nevertheless some degree of impermeability. The cuticle is in many ways similar to that of an insect: it is composed of a ‘cuticulin’ epicuticle, a ‘tanned’ chitinous exocuticle, and a laminated endocuticle of two optically distinguishable layers. The outer endocuticle is strongly calcified. The cuticle is penetrated by pore canals and the ducts of dermal glands. The latter are concerned with the production of exo- and endocuticle, and the secretion of the polyphenols which tan the protein of the exocuticle. The double hardening is probably a specialized condition of millipedes. Transpiration is almost quadrupled by extraction with hot, but not cold chloroform, as the exocuticle is impregnated with lipoids which reduce permeability. These are secreted by epidermal and dermal gland cells, and pass up the pore canals and gland ducts.