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MANUAL OF ZOOLOGY. 



membrane of the intestinal tube by means of its cephalic 

 hooklets (when these are present) and suckers. The caudal 

 vesicle now drops off, and the scolex is thus converted into the 

 " head " of the tape-worm. Gemmation then commences from 

 its posterior extremity, the first segments being immature. 

 As the first-formed joints, however, are pushed further from 

 the head by the constant intercalation of fresh articulations, 

 they become sexually mature, thus constituting the "pro- 

 glottides " of the adult Tape-worm with which the cycle began. 

 To the entire organism, with its " head " and its mature and 

 immature joints (" proglottides "), the term " strobila " is now 

 applied. 



In the development, therefore, of the Tape-worm we have to 

 remember the following stages : 



1. The ovum, set free from a generative joint, or proglottis. 



2. The proscolex, or the minute embryo which is liberated 

 from the ovum, when this latter has been swallowed by any 

 warm-blooded vertebrate. 



Fig. 46. Morphology of Tseniada. i. Ovum containing the embryo in its leathery 

 case. 2. Cysticercus longicollis. 3. " Head "of adult Tcenia soliutn enlarged, showing 

 the hooklets and cephalic suckers. 4. A single generative joint, or proglottis, 

 magnified, showing the dendritic ovary (<?), the generative pore (a), and the water- 

 vascular canals (b). 5. A portion of a Tape-worm (strobila), showing the alternate 

 arrangement of the generative pores. 



3. The scolex, or the more advanced, but still sexually im- 

 perfect, embryo, into which the proscolex develops, when it 

 has encysted itself within the tissues of its host. (Under this 

 head come the so-called " Cystic Worms.") 



4. The strobila, or adult Tape-worm, into which the scolex 



