The early development of the daughter sporocysts of the Strigeoidea (Trematoda)

TitleThe early development of the daughter sporocysts of the Strigeoidea (Trematoda)
Publication TypeJournal Article
Year of Publication1953
AuthorsVan der Woude A, Cort WWalter, Ameel DJ
JournalJournal of Parasitology

Our recent studies on the germinal development in the sporocysts of strigeoids have confirmed the earlier work of cort and Olivier (1941). The germinal masses of mother sporocysts belonging to this group are discrete structures consisting of a few germinal cells and embryos in early stages of development. The largest embryos are attached at the ends and may contain as many as 6 to 8 germinal cells. After breaking away from the germinal masses the free daughter sporocyst embryos increase in size and at the same time the number of their germinal cells also increases. As they begin to elongate the germinal cells develop into germinal elements of two to five cells, which resemble those found in the rediae of Clinostomum (Cort, Ameel, and Van der Woude, 1950). In slightly older daughter sporocysts each of these germinal elements develops into a germinal mass and no more free germinal cells can be found. This development of the germinal masses in the daughter sporocysts is like that described earlier for strigeoid mother sporocysts (Cort, Ameel, and Van der Woude, 1951). The development of the germinal masses from the germinal cells in the daughter sporocyst is not synchronous. In stages in which no free embryos are present, the largest germinal masses appear to be fully developed while the smallest have only 4 or 5 components. This lag in the development of a part of the germinal masses is still present in daughter sporocysts containing large numbers of free cercarial embryos. However in mature sporocysts, from which numerous cercariae are escaping, all the germinal masses are fully developed and appear to be producing embryos. In old infections there is usually a reduced number of germinal masses in the daughter sporocysts, and a reduction in the number of germinal cells in them. It is evident, therefore, that the mechanism of germinal development in the germinal sacs of the strigeoids is adapted for the production of large numbers of cercariae over a long period of time. Cercariae are escaping in numbers from the oldest daughter sporocysts before the germinal masses in the mother sporocyst have completed the production of new daughter sporocyst embryos. It appears, therefore, that the number of daughter sporocysts that develop in the snail host is limited by the space and food available in its digestive gland and not by the reproductive potential of the mother sporocyst. Also, the lack of synchronicity in the development of the germinal masses of the daughter sporocysts increases considerably the length of the period during which they can continue to produce cercarial embryos. Therefore, the mechanism of multiplication of germinal cells that has evolved in the STRIGEOIDEA is one of the most effective in producing large numbers of individuals of any found among the digenetic trematodes. The mother sporocyst can continue to produce daughters until the digestive gland of even the largest snail host is filled, and the daughters appear to be able to produce cercariae as long as the snail host lives.