Studies on Germinal Development in Rediae of the Trematode Order Fasciolatoidea Szidat, 1936

Abstract

The germinal material was studied in rediae from natural infections of spp. of Paramphistomidae, Notocotylidae, Psilostomidae, and Echinostomidae of the order Fasciolatoidea. In an amphistome, Allassostoma parvum, each immature mother and daughter redia has attached at the posterior end of the body cavity a simple morula-like germinal mass composed of unicellular components which are considered to be germinal cells. Evidence from the study of older rediae indicates that these simple germinal masses are gradually used up by the separation of their components to form embryos. In the daughter rediae of a notocotylid, Notocotylus urbanensis, the germinal masses are similar to those of A. parvum. In this case, also, the number of the components is reduced as the embryos are separated. It can be suggested that this simple type of germinal mass is produced by a limited division of germinal cells early in the development of the rediae, and can result in the production of only a limited number of embryos. In 2 mature mother rediae of N. urbanensis the germinal masses were larger and were composed of both unicellular and multicellular components. This suggests a more extended period of multiplication of the germinal cells associated with a greater production of individuals. Studies were also made of the germinal material in the rediae of a psilo-stome, Psilostomum ondatrae, and 5 echinostome spp., Echinostoma revolutum, Petasiger nitidus, and 3 that were not identified. In mother and daughter rediae of these spp., both the immature and mature, there were found rather large germinal masses composed of both unicellular and multicellular components which were attached at the posterior end of the body cavity. They were still present in the very oldest rediae examined. They resemble in structure the floating germinal masses of the daughter sporocysts of the plagiorchiids. They are interpreted as persistent centers of multiplication of germinal cells, and are considered as a mechanism for the production of rather large numbers of embryos. Evidence was presented on the greater production of individuals in the psilostome and echinostome rediae, as compared with those of amphistomes and notocotylids.