Studies on the morphology, biology and development of a strigeid cercaria (Cercaria XBaylis 1930)

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Abstract
1. Cercaria X (Baylis & Taylor, 1930) and its sporocyst have been redescribed with some additions to the original descriptions.2. The details of the development of the cercaria into a metacercaria of the diplostomulum type have been obtained and the anatomy of the mature metacercaria is described in detail for the first time. It is proposed to name the metacercaria Diplostomulum X. Development of the cercaria into a metacercaria takes from 40 to 90 days and the metacercariae have been shown to survive for a period of 544 days after the time of infection. This development has been obtained in the lenses of rats, frogs and a wide variety of fish. Development is not completed in any other region of the host's body.3.The effect of the sporocyst, migration of the cercariae, and the metacercaria on the appropriate host tissues has been considered. All these stages produce extensive changes in the host tissues.4. Histochemical tests have shown the presence of alkaline phosphatase activity in the cuticle of the sporocyst. The glycogen storage regions of the cercaria are described and it has been demonstrated that the caudal bodies in the tail-stem contain large amounts of glycogen which are utilized during the free-swimming period.5. Attempts at the completion of the life cycle were unsuccessful.
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