ANNULOIDA : SCOLECIDA. I 87 



these cases the " neck " of the scolex becomes partially seg- 

 mented, so that it comes to resemble an imperfectly developed 

 Tcenia, and is called a " strobila-embryo." The series of 

 changes, however, whereby the scolex is converted into the 

 " strobila," or adult tape-worm, cannot be carried out unless 

 the scolex gain access to the alimentary canal of a warm- 

 blooded vertebrate. In this case, the scolex attaches itself to 

 the mucous membrane of the intestinal tube by means of its 

 cephalic booklets (when these are present) and suckers. The 

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



Fig. 68. Morphology of Taeniada. i. Ovum containing the embryo in its leathery 

 case. 2. Cysticercus longicollis. 3. "Head" of adult Teenia solium enlarged, 

 showing the hooklets and cephalic suckers. 4. A single generative joint, or pro- 

 glottis, magnified, showing the dendritic ovary (o), the generative pore (a), and the 

 water-vascular canals (b). 5. A portion of a tape-worm (strobila), snowing the 

 alternate arrangement of the generative pores. 



into the " head " of the tape-worm. Gemmation then com- 

 mences 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 " proglottides " 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 " stro- 

 bila" is now applied. 



In the development, therefore, of the tape-worm we have 

 to remember the following stages : 



