. An introduction to zoology : for the use of high schools . ematodes in the formation of chains by budding, each segment in thechain or proglottis, resembling its neighbour, but differing from theoriginal or head-segment, by the absence of organs of lixatiou. The seg-ments have sometimes more, sometimes less capacity for independentlife. The eggs formed witliin them do not at once develop into originalhead-segments, but into larval bladder-like forms (Cysticerci)—which arefound in. some different animal from the host of the adult—and thesemay, by budding, give rise to more than one head-segme
. An introduction to zoology : for the use of high schools . ematodes in the formation of chains by budding, each segment in thechain or proglottis, resembling its neighbour, but differing from theoriginal or head-segment, by the absence of organs of lixatiou. The seg-ments have sometimes more, sometimes less capacity for independentlife. The eggs formed witliin them do not at once develop into originalhead-segments, but into larval bladder-like forms (Cysticerci)—which arefound in. some different animal from the host of the adult—and thesemay, by budding, give rise to more than one head-segment. The adultchains are found in the intestines of all the classes of Vertebrates ; thecystic stages in the flesh, liver or brain of some animal, which serves asfood for the host of the adult chains (Fig. 154). Thus the tape-worms ofthe carnivorous sharks pass through their cystic stages in the Teleosts, HIGH SCHOOL ZOOLOGY. 227 on whichthey feed. Through eating insufficiently-cooked beef, pork orfish, man is liable to several forms of these Fig. 154.—Developmental cycle of Twnia serrata. (A species of tape-wormwhich occurs ia the don). (After Leuckart). 1, A young tape-wonn composed of the head, with hooks (a, b), and suckers, anda chain of immature segments ; 2, a mature segment, the branched uterus of which isfull of ti-hooked shelled embryos, 3 ; these gain access to the liver of the rabbit, loosetheir hooks, become encysted, 4, and iuvaginated at one end which gives rise to the headof the future tape-worm, 5 ; G, a fully formed bladder-worm (Cj/sfrVcrcMS ^jfifyon/iis) ;7, section of the head before its eversion; r, the rostellum which carries the hooks ; s,two of the suckers. MOLLUSCA. 14. From the lowly-organised unsegrnented worms, wliich wehave been considering, to a sub-kingdom like the Mollusca, whichcontains some of the largest and most highly-organised of theInveitebrates, seems a very long step, and yet it is to the Vermes,and not to any of the ot
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
