The growth difference depending upon the sex of Oncomelania nosophora and O.hupensis,the vector snails of Schistosoma japonicum.

The growth of Oncomelania nosophora in its natural habitat has been studied by McMullen (1951), Kawamoto (1954) and Iijima (1959). In these studies, however, the growth rate was calculated on the basis of measurements of different specimens collected periodically from the field. Recently, Hosoka et al.(1959), with numerous young snails liberated in a confined natural habitat, carried out periodically measurements of their shell length, the data of which has been published elsewhere. Chi et al.(1957) published the results of laboratory experiments on the growth of O. nosophora, O, quadrasi and O. formosana. In fact, Chi et al. have been the only ones to pursue the growth curves of male and female O. nosophora. They thus reported without full data that the growth curvess of both sexes paralleled each other until snails had increased in size up to 6.2mm. On the other hand, our experience led us to suppose that the growth curve would be different between both sexes when snails had grown to at least 3 or 4mm. The presentt study was carried out to gain the data concerning this problem.