Electron Microscopy of Postembryonic Stages of the Tapeworm, Hymenolepis citelli

Abstract

The morphology of precysticercoids of the tapeworm, Hymenolepis citelli, was studied at the ultrastructural level and has provided baseline data which may be applicable to other species of the family Hymenolepididae. Differences in cellular morphology between the developmental stages and those of the hatched oncosphere are described. Histogenesis of some major tissue types is discussed. Microvilli, structurally unlike those of the adult, are found on the periphery of the organism. The host response to the postembryonic stages is indicated by beetle hemocyte attachment to the cestode microvilli. Degeneration of these hemocytes occurs with time and may be related to contact with the microvilli. The structural characteristics of cestode postembryonic stages have received little current attention, particularly with more advanced technology. Studies by Voge (1956, 1960a, 1961) have helped to elucidate the development of the postembryonic stages of Hymenolepis diminuta and H. citelli, and have provided data on which the present study is based. Due to the limitations of the light microscope and the cellular density of these small organisms, a considerable amount of structural detail remains unresolved. Braten (1968a, b) has described the fine structure of the larval stages of the pseudophyllid, Diphyllobothrium latum. Race et al. (1965) studied developing stages of the taenioid cestode, Multiceps serialis, and Morseth (1967) investigated the morphology of the hydatid cyst and protoscoleces of Echinococcus granulosus. However, little has been done to describe the cytomorphogenesis of tissues which lead to the formation of adult structures of a cyclophyllidean cestode. The adult stages of the hymenolepids have been used extensively for biochemical and ultrastructural studies but the general morphology of developmental stages has not been investigated at the utrastructural level. This study describes the cell types present in 3and 5-day developmental stages of Hymenolepis citelli with the hope of establishing a pattern of morphogenesis applicable to other cestodes of the group. Incorporated are also observations of the cellular interaction between Received for publication 12 March 1970. * This investigation was supported by the NIH Fellowship 7 F02 AI40-01A1 from NIAID. the host, Tribolium confusum, and the para-