Abstract
The chitinous procuticle of pentastomids is permeated by small pores which communicate with specialized epidermal cells previously termed cuticular cells. Ultrastructural evidence is presented which suggests that these cells are concerned with the regulation of the hydromineral balance of the haemolymph. Probably all pentastomids regulate hypo-osmotically: that is they maintain a blood concentration which is lower than that of their host. Since pentastomids feed on host blood or lymph which is rich in sodium and chloride, it suggested that chloride cells secrete excess ions. The extent to which chloride cells must concentrate ions depends upon the nature of the food, the rate of exosmosis and the rate of salt gain by diffusion.