Abstract
Metacercarial cysts ofParapronocephalum symmetricum were subjected to an excystment medium containing trypsin and bile salts at 41°C. After approximately 35 min the metacercariae emerged from the cysts, but prior to their release each cyst wall extended outwards at one point, resulting in the cysts becoming pear-shaped. The extensions always occurred adjacent to the anterior regions of the metacercariae, and electron microscopy showed that at these points the structure of the inner cyst layer had changed from a compact to a disaggregated form. This effect was not observed in cysts whose metacercariae were removed before treatment with excystment medium. We concluded that the disaggregation of the inner cyst layer represented a weakening process that was brought about by enzymes released from the anterior regions of the metacercariae. Escape, through the weakened inner layer and the two outer layers, was finally brought about by the physical efforts of activated organisms.
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Irwin, S.W.B., McShane, G. & Saville, D.H. A study of metacercarial excystment inParapronocephalum symmetricum (Trematoda: Notocotylidae). Parasitol Res 76, 45–49 (1989). https://doi.org/10.1007/BF00931071
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DOI: https://doi.org/10.1007/BF00931071