. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 246 THE TAPEWORMS plerocercoid type, , they have long wormlike bodies with an invaginated head at one end (Fig. 86C). Fish Tapeworm. — The common fish tapeworm of man, Dibothriocephalus latus, is an important species in the districts in which it occurs. It is found in all countries where fresh-water fish is extensively eaten, and especially in countries where it is commonly eaten raw. In the Baltic countries, Switzerland, Russia, Japan, and about the Central African lakes this parasite is particular
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 246 THE TAPEWORMS plerocercoid type, , they have long wormlike bodies with an invaginated head at one end (Fig. 86C). Fish Tapeworm. — The common fish tapeworm of man, Dibothriocephalus latus, is an important species in the districts in which it occurs. It is found in all countries where fresh-water fish is extensively eaten, and especially in countries where it is commonly eaten raw. In the Baltic countries, Switzerland, Russia, Japan, and about the Central African lakes this parasite is particularly common. Relatively few cases have been re- ported in the United States, though the larvae are said to be found frequently in fish from the Great Lakes.' The fish tapeworm is a large species and commonly reaches a length of from six to 30 feet, or even more, with from 2000 to 4200 short, broad pro- glottids, only the terminal ones of which are as long as broad. The scolex (Fig. 87C) is almond-shaped. Unlike the tapeworms of the family Taeniidae, the genital openings are near the middle of the under surface of the proglottids, instead of at one side. In tha ripe proglottids (Fig. 84E) the uterus is in the form of a rosette near the center of the segment. The proglottids do not usually retain the eggs until they break off from the chain, but void them, as do flukes, Fig. 93. An egg of fish through the genital pore. The empty pro- segm'InS^onlrtiol^rnd glottids, shrunken and twisted, are broken operculum ;B, ciliated em- off in short chains from time to time. 300° °(Afto Loos?.)'''"'"'' The eggs (Fig. 93A), which are large and brown with a lid at one end as in fluke eggs, contain six-hooked embryos which are furnished with a covering of cilia (Fig. 93B). The eggs hatch in water after several weeks and the embryos swim for a time by means of their cilia, though they often slip out of their ciliated envelope and creep on the bottom. It is believed that the embryos fi
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