A Study of some of the Factors Affecting Excystation in vitro of the Metacercarial Stages of Holostephanus lühei Szidat, 1936 and Cyathocotyle bushiensis Khan, 1962 (Strigeida: Trematoda)

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Abstract
In many digenetic trematode life-cycles there occurs a metacercarial stage which is usually the ultimate infective stage for the final host. The metacercarial stage may be free and active as in Diplostomatidae (Strigeida) but in most cases the metacercaria is enclosed within a cyst wall of varying thickness and complexity (Erasmus, 1965). The release of the metacercaria follows the ingestion of the cyst and the digestion of the cyst wall by the appropriate final host. It is apparent that the culmination of the life-cycle in the development of a sexually mature adult will occur only if the release of the metacercaria takes place in the appropriate host. It seems very likely therefore that the factors affecting the excystation of metacercariae play an important role in defining the host specificity of a particular trematode.