Studies on Echinostomatidae (Trematoda) in Malaya IX. The Mehlis' Gland Complex in Echinostomes

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Observations on the functional anatomy of the ducts associated with Mehlis' gland were made in five species of echinostomes: Echinostoma malayanum, E. lindoense, E. audyi, Hypoderaeum dingeri, and a 43-spined, undescribed Echinoparyphium species. In all five species the structure of the Mehlis' gland complex is similar. There is an ovicapt in the form of a chamber which regulates the passage of the ova from the ovary into the oviduct. Ciliated epithelium lines the ovicapt, the oviduct distal to the ovicapt, and the proximal part of Laurer's canal. The movement of the cilia is directed toward Laurer's canal from which excess sperm and vitelline granules are discharged at the dorsal surface. Spermatozoa are stored in the uterine seminal receptacle in the absence of a seminal receptacle. The Mehlis' gland complex of echinostomes is best studied in living worms because the ducts and organs associated with it are not clearly visible in mounted specimens. Moreover, the gland region is often filled with eggs, making a detailed study extremely difficult or impossible. Descriptions are often incomplete and sometimes inaccurate. This paper reports observations on the Mehlis' gland complex in living specimens of five species (three genera) of echinostomes. MATERIALS AND METHODS The following species of echinostomes were studied: Echinostoma nmalayanum Leiper, 1911; E. lindoense Sandground and Bonne, 1940; E. audyi Lie and Umathevy, 1965; Hypoderaeum dingeri Lie, 1964; and an undescribed 43-spined Echinoparyphium species which will be named later when its complete life cycle is described. An unlimited supply of living worms was maintained in the laboratory for life-cycle studies. E. malayanum was obtained from rats, the other four species from pigeons and ducklings. Young adult worms with few eggs in the uterus were preferred. The Echinoparyphium species is the easiest to study since the worm is small and seldom contains many eggs; H. dingeri is the most difficult to examine due to thickness of the worm and density of Mehlis' gland. The living worm is examined dorsal side up in a drop of physiological saline under a cover slip. Received for publication 12 August 1964. * This work was supported by the University of California International Center for Medical Research and Training (The Hooper Foundation, San Francisco School of Medicine) with Research Grant GM-11329 from the Office of International Research, NIH, U. S. Public Health Service. t Present address: Hooper Foundation, University of California Medical Center, San Francisco. When movement of the worm is restricted and the position is suitable, ducts and organs in the Mehlis' gland region can be seen. An oil-immersion lens is required for detailed observation of certain parts.