Identification of sex in Schistosoma mansoni cercariae

A simple method for determining the sex of larval stages of Schistosoma mansoni involved cytological demonstration of sex chromatin (heterochromatin) in the interphase and prophase nuclei of cercariae. Cerariae from unimiracidial infections were fixed, and permanent slides were stained with thionin, Giemsa, or fuchsin. On examination, a given cercaria showed either 1 or 2 sex chromatin bodies in the nuclei, the female with 1 and the male with 2 bodies. The results of observation on the sex of cercariae from the slides were matched with those of worms obtained from mice injected with the corresponding batch of cercariae. The accuracy of cytologic sex identification was greater than 80% in these experiments. The sex chromatin in both adult and larval stages was in the form of large, dark purplish bodies usually situated towards the periphery of the nuclei and could be easily distinguished from the other chromatin granules present in the nuclei.