By a variety of microscopical techniques, an initial survey has been made of the functional organization of ovarian balls from mature, inseminated female Moniliformis dubius and Polymorphus minutus. On the basis of evidence from observations made with the transmission electron microscope, we have concluded that the ovarian ball consists of three components; these are two separate, multinucleate syncytia and a cellular zone. The inner region is considered to be an oogonial syncytium from which the germ-line cells arise to form the cellular zone. The oogonial syncytium and the cellular elements are embedded in a supporting syncytium which also forms the boundary of the ovarian ball. Details of the ultrastructure of these components, observations on fertilization and a hypothesis to account for the main events occurring in an acanthocephalan ovarian ball are also presented.
Acanthocephalans are dioecious parasites which become sexually mature in the alimentary tract of vertebrates. After insemination, individual female worms begin to release embryonated eggs at rates which have been estimated to vary, on average, from 2000 per day in the case of Polymorphus minutus (Crompton & Whitfield, 1968) to 260000 per day in the case of Macracanthorhynchus hirudinaceus (Kates, 1944). Irrespective, however, of the species of acanthocephalan and the number of eggs produced, a most interesting mode of ovarian development and multiplication is believed to exist (see Bullock, 1969). Within the female worm, the primordial ovarian tissue gives rise to separate ovaries which are often termed ovarian balls. These in turn give rise to more ovarian balls and the process continues until large numbers have been formed. The ovarian balls of a mature female have no permanent attachment to the tissues of the worm. They are contained in the fluid of the body cavity either freely, or loosely constrained in large membranous chambers known as ligament sacs.
Few investigations have been made into the structure and cytology of the ovarian balls of the Acanthocephala. Early observations on the histology of the germ-line constituents of ovarian balls were made by Hamann (1891), Kaiser (1893) and Meyer (1928), each of whom suggested that some of the developing oogonial stages were arranged in a syncytial manner. In a study of the embryology of P. minutus. Nicholas & Hynes (1963) interpreted preparations of ovarian balls, which had been subjected to the Feulgen reaction, as indicative of syncytial tissue in the central region of the ball. They also recorded their uncertainty about whether an ovarian ball has a bounding membrane or not. More recently, Robinson (1964, 1965) described mitotic and meiotic divisions in oogonia and oocytes from ovarian balls of Mac. hirudinaceus and Moniliformis dubius and Stranack (1972) included an electron micrograph of part of an ovarian ball of Pomphorhynchus laevis in a description of the nature of the egg envelopes of that species. In this paper, we present a general survey, based largely on evidence obtained with the electron microscope, of the functional organization of the ovarian balls of mature M. dubius and P. minutus.
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