Development in the strobilate phase of Hymenolepis diminuta and many other cyclophyllidean cestodes is extremely rapid. Control of development in these animals will be studied, particularly the roles of neurosecretory function, host bile salts, and carbohydrate metabolism in the worm. Previous work has indicated that each of these major factors is important in worm development, and they well may be physiologically related. Carbohydrate metabolism will be studied by examining control of glycogen synthesis, sugar transport across the worm tegument, and the effects on these processes of worm age, crowding, changes in host diet, and neurosecretory activity. Neurosecretion will be correlated with developmental events in vivo and during in vitro cultivation. It is proposed that development may be at least partially under neurosecretory control, that the control may be exerted by regulation of glycogen synthesis or sugar transport, and that neuroendocrine function may help to account for the manifestations of the "crowding effect" in cestodes. The exclusion of bile salts from cestode tissues will be examined, and whether this exclusion is related to sugar transport, a Na ion-linked pump, and determination of best specificity will be studied.