Germinal Development in the Sporocysts of a Bird Schistosome Trichobilharzia physellae (Talbot, 1936)

Publisher Website
Google Scholar
Abstract
Development of the germinal material in mother and daughter sporocysts is described in juveniles of Physa parkeri experimentally infected with Trichobilharzia physellae. This development and growth of mother and daughter sporocysts is similar to that of spirorchiids and other schistosome species. The germinal cells multiply rapidly in the early stages of development of the sporocysts and are attached to the wall along the whole length; no germinal masses that serve as centers of multiplication of germinal cells are present. The first daughter sporocysts escape from the mother at about 10 days after infection, and in 5 or 6 days more the migration is practically completed; after this the mother sporocyst soon dies. The daughter sporocysts grow rapidly in the digestive gland of the snail and by about 21 to 24 days after infection, when the first cercariae begin to escape, all appear to have reached full size. In infections in large juveniles from which cercariae have been escaping for from 9 to 15 days, numbers of partially collapsed almost empty daughter sporocysts are present, which appear to be alive and normal. They contain a reserve of germinal material but few if any large embryos. It is suggested that a new crop of cercariae will develop from this germinal material the next spring. In small laboratory-raised juveniles the infections are greatly modified in the later stages of their development. Most of the smallest snails died before or just after their infections reached maturity. Death appeared to be produced by injury to the digestive gland by the rapid increase in size of the daughter sporocysts during the final stages of growth. It takes about a week longer for the infections to mature in the smaller snails than in the larger ones. Only a small proportion of the daughter sporocysts that migrate into the digestive gland grow to full size and produce cercariae, while the others die soon after migration. These findings suggest that very small juveniles infected under natural conditions are usually killed by the parasite, and if they survive produce only small numbers of cercariae. Examination of natural infections of T. physellae in adults of P. parkeri suggest that the larger the snails are at the time of infection, the larger will be the number of daughter sporocysts that develop and escape from the mother, and the larger the number of cercariae produced.
Keywords

This publication has 2 references indexed in Scilit: