ABSTRACT
The amphistomes have a dixenous type of developmental cycle, and, accordingly, they develop in a single intermediate host. Cercariae encyst on vegetation or other objects in their vicinity. Five larval stages - miracidium, sporocyst, redia, cercaria, and adolescaria - are involved in their ontogenetic cycle. The chapter reviews these are under: preparasitic stage, intramolluscan stage, and development in definitive host. The eggs of amphistomes belong to the ones which are larger in size. They are oval or spherical in shape and enveloped with transparent thin or thick eggshell. Sporocyst developmental stage is included in all the examined amphistomes except for Stichorchis subtriquetrus, Basidiodiscus ectorchis, and Sandonis sudanensis. In the species, miracidia contain fully formed rediae and after penetrations of the miracidia into the snails the rediae are liberated and continue their development. The amphistomes are parasitic either in the lower part or in the upper one of the digestive tube of the definitive hosts.
