Previous studies on the spermatogenesis and oogenesis of digeneans, monogeneans and cestodes are reviewed, including those in which isotopic labelling techniques have been utilized in order to determine the temporal duration of spermatogenic development stages. Similar labelling experiments have also provided information on the development and movement of oocytes in the female reproductive tract as well as indicating patterns of cell division and development in vitelline glands. The literature relating to the inseminative behaviour of parasitic platyhelminths is considered from a number of viewpoints including the patterns of cross- and self-insemination that occur in hermaphroditic digeneans, the mating behaviour of dioecious schistosomes, spermatophore production and insemination among monogeneans and the inseminative behaviour of polyzoic cestodes. The implications of selfing among parasitic platyhelminths are considered with respect to possible genetically deleterious consequences. In addition, consideration is given to the mechanisms underlying the fact that some species require cross-insemination or at least the presence of another worm in order to undergo normal growth and sexual development. Finally, experimental studies are reviewed which shed light on the strength of the barriers against hybridization that exist between well-defined species of parasitic platyhelminths.

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Adults of Echinostoma caproni, F. paraensei, and E. trivolvis were processed for starchgel electrophoresis. Ten enzyme systems representing 12 structural loci were examined using three different buffer systems. E. paraensei and E. caproni were found to be genetically inbred as indicated by the lack of heterozygosity in individual worms. All three taxa showed fixed differences indicating they are distinct species. Fixed differences were found between E. paraensei and E. caproni in six enzyme systems, between E. paraensei and E. trivolvis in five enzyme systems, and betweenE. trivolvis and E. caproni in five enzyme systems. Phenic relationships among the three species showed E. caproni was genetically more similar to E. trivolvis than to E. paraensei.

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