Identifier: introductiontozo00dave Title: Introduction to zoology; a guide to the study of animals, for the use of secondary schools; Year: 1900 (1900s) Authors: Davenport, Charles Benedict, 1866-1944 Davenport, Gertrude Anna Crotty, 1866- Subjects: Zoology Publisher: New York, Macmillan company London, Macmillian and co., ltd. Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image: B FIG. 146. — Development of Distomum. A, ciliated larva ; /?. sporocyst con-taining developing rediae ; C, redia, containing a daughter redia and embryoliver-flukes; D, free-swimming, tailed larva of liver-fluke;- b. op, birthopening; etit, food canal of redia; eye, eyespots; gast, young redia; r/erni,mor, early stages in formation of the embryo liver-fluke; int, intestine oflarval liver-fluke; o?s, oesophagus; or. SK, oral sucker; pap, head papilla ofciliated larva, A: ph, pharynx; proc, processes of redia; vent, su, ventralsucker. After Thomas. animal, the embryos attach themselves to the food canal of •> their host and form, by rapid growth, a long chain of seg-ments, each of which is full of germs. The chain, or NEREIS AND ITS ALLIES 157

Text Appearing After Image: FIG. 147.— Tsenia solium, the human tapeworm. Entire specimen, aboutnatural size. Cap, head. After Leuckart. 158 ZOOLOGY tape, absorbs fluid food, which soaks through its bodywall. As the segments at the older end of the animalmature, they are set free and pass out of the alimentarytract, to be picked up, perchance, in the food of an herb-ivorous animal or else to perish. The economic importance of parasitic worms is verygreat. Thus, although no great epidemics of the flukes have occurred in this coun-try, a million sheep areannually lost by this para-site in Great Britain; andin 1879 and 1880 it wasestimated that three millionsheep died annually inEngland alone of thisparasite. In Buenos Ayres,during 1882, a millionsheep died of fluke disease.By great care in prevent-ing infection, especiallyduring damp seasons, wemay be able to prevent Fi<i. 148.—Cerebratulus, a cream-colored any such disaster ill thisnemertean. Head end at upper part of figure ; mouth turned toward observer,

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