| Abstrakt: |
The terrestrial mollusks Triodopsis caroliniensis (LEA) and Mesodon inflectus (Say) served satisfactorily as the first intermediate hosts for Brachycoelium mesorchiumByrd, 1937. They, along with the other species exposed, served as second intermediate hosts. On losing its ciliated epidermal plates the miacidium became transformed into a syncytium having eight, large nuclei (the primary mass). The primary mass entered a blood vessel where all further development occurred. Within three weeks the mass developed into a multiloculated (compartmentalized) cyst-like organism, the compartments of which were incompletely surrounded by fibers and cells of the blood vessel's wall, strengthened by an accumulation of the host's connective tissue (reactive) cells. The “first generation” embryos developed (in situ) into elongated, sporocyst-like organisms enclosed in a supporting layer of host tissues. After six weeks the parasitic mass comprised many centers of growth, first generation organisms containing second generation embryos and a conglomerate of parasitic cells. By the ninth week the second generation embryos had developed (in situ) into thick-walled, tubular organisms possessing a prominent musculo-glandular, sucking apparatus and had a covering of fibers and cells derived from the host's tissues. As these redia-like forms aged they assumed many different shapes and sizes, although typically they were flask-shaped, with a tubular, neck-like part and a vesicular body: ultimately ranged from flask-shaped forms to individuals having two or more vesicular portions joined by longer or shorter, thick-walled tubular parts. Cercarial embryos filled most of their vesicular portions. The cercaria was tailless, and devoid of a stylus. On escaping from the mollusk it as completely encapsulated in mucous which sustained it for about six days. On being ingested by any of the several species of terrestrial mollusks available, the cercaria reentered the tissues and encysted as a metacercaria. These metacercariae developed into young flukes (some with eggs) within one, two or three weeks after being fed to larval (aquatic) stages of host salamanders, Eurycea bislineata cirrigera (Green) and Desmognathus fusca fuscaRafnesque. |
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