Schistosome parasites have evolved to produce a number of unique features in their life history; one of these is separate sexes. This has, in turn, led to a novel interplay between the male and female parasite that has been recognized for over 50 years: the growth and reproductive development of the female parasite is in some way regulated by the male schistosome. Early classical and later experimental studies established that the presence of the male schistosome is necessary not only for the initiation of female development but also for the maintenance of her mature state. The male parasite regulates the reproductive development of the female, partly by providing a stimulus that is necessary for the development of the vitelline gland. The cells of the vitelline gland provide nutrients and shell precursors for the egg. Also in this review by Philip LoVerde and Li-ly Chen, it is interesting to note that recent molecular studies have confirmed early work by showing that gene expression in the female parasite is developmentally regulated in a tissue-specific manner and that this gene expression is controlled by the presence of a male parasite.