The larval trematodes of certain fresh-water molluscs

Abstract

1. Observations have been made on the life cycles of Cercaria paracauda, Iles, G. tetraglandis, Iles, and C. Apatemon gracilis minor, Yamaguti. The development of the tetracotyle metacercaria of C. tetraglandis has been followed and also that of the metacercaria and adult of A. g. minor. The pathology and distribution of the metacercariae of the last two species within the leech, Erpobdella testacea (Sav.) has been studied.2. It was noted that development of the metacercariae within the same host and resulting from the same infection was not simultaneous and that it was improbable that a 100 % encystment of the metacercariae would occur. Temperature was found to have a marked effect on the length of time required for encystment.3. Data are given on the infectivity and excystation of the metacercariae of A. g. minor and on the biology and morphology of the adult of this subspecies.4. Stress is placed on the importance, in the systematics of the digenetic trematodes, of considering both the morphological and biological characters of the adult and those of the related larval stages.