Text-book of comparative anatomy . a tapeAvorm head with suckers, rostellum,etc. (Fig. 120). While most investigators regard this process as 172 COMPARATIVE ANATOMY CHAP. one of gemmation, we hold it to be simply one of growth anddifferentiation. The head with the vesicle is, according to our opinion,a young sexless Cestode answering to the scolex of Tcenia cucumerina inthe body cavity of the louse, only in this case the trunk or proscolexbecomes extended into a large vesicle by the accumulation of fluidbefore the head of the tapeworm with its suckers, etc., forms. The development of this vesi

Text-book of comparative anatomy . a tapeAvorm head with suckers, rostellum,etc. (Fig. 120). While most investigators regard this process as 172 COMPARATIVE ANATOMY CHAP. one of gemmation, we hold it to be simply one of growth anddifferentiation. The head with the vesicle is, according to our opinion,a young sexless Cestode answering to the scolex of Tcenia cucumerina inthe body cavity of the louse, only in this case the trunk or proscolexbecomes extended into a large vesicle by the accumulation of fluidbefore the head of the tapeworm with its suckers, etc., forms. The development of this vesi Stock Photo
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Text-book of comparative anatomy . a tapeAvorm head with suckers, rostellum, etc. (Fig. 120). While most investigators regard this process as 172 COMPARATIVE ANATOMY CHAP. one of gemmation, we hold it to be simply one of growth anddifferentiation. The head with the vesicle is, according to our opinion, a young sexless Cestode answering to the scolex of Tcenia cucumerina inthe body cavity of the louse, only in this case the trunk or proscolexbecomes extended into a large vesicle by the accumulation of fluidbefore the head of the tapeworm with its suckers, etc., forms. The development of this vesicle ought to beregarded as a special adaptation for the pro-tection of the head. If such a Cysticercusreaches, with the tissue of its host, theintestine of a new host, not only the cyst, but the whole vesicle dissolves, while thehead and rudimentary neck which areevaginated resist digestion because of thecalcareous bodies they contain. In otherwords, the young, sexless, unsegmented tape-worm loses its vesicular trunk. The scolex of. FIG. 120.—Cysticercus cellu-losae. Finn of Tsenia solium, cut in half. The scolex, which is invaginated into the vesicle, is , , , , , , /• •, seen with its suckers and rostei- fastens itself, by means of its organs adhesion, to the intestinal wall, and at onceregenerates the lost portion of the body inthe first proglottis, which in the developed tapewormbecomes the last and oldest, and new segments lum. After Leuckart. length the form ofchain atfollow this one. The vesicle of the Cysticercus of different tapeworms varies in sizeaccording to the amount of fluid contained. It is sometimes a largesphere, sometimes merely a small swelling at the posterior end ofthe worm-like Cysticercus. In a few tapeworms development is complicated by the occurrenceof an alternation of generations, the young unsegmented form in theintermediate host, the finn, multiplying asexually by gemmation. Onthe wall of the finn there thus arise, not only one rudimentary head, b