65 



vesicle, when developed into the vesicular stage ; and 

 it also shows that these booklets do not enter into the 

 formation of the scolex. 



When the head begins to form, the caudal vesicle 

 ceases its activity in the Cysticerci : it then becomes 

 only the nutritive receptacle and the protective organ 

 for the head. 



At this point its development ceases, at least in the 

 tissue where it has become a scolex. In order for it 

 to progress to the adult state, it must pass into the 

 intestine of some higher animal. This is usually ac- 

 complished by the bearer of the scolex falling a prey 

 to the larger animal ; and the scolex is thus passively 

 introduced into the intestine of its new host. Should 

 this, however, not happen, the scolex advances no far- 

 ther, but remains a scolex. 



Being introduced into the stomach of the new host, 

 the tissue of the animal in which the scolex is con- 

 tained undergoes digestion and dissolution; and the 

 scolex, with the vesicle, is set free. The enclosing 

 vesicle is either dissolved during the process of diges- 

 tion, or else is opened by mastication ; and then the 

 cystic worm escapes into the cavity of the stomach. 

 The caudal vesicle now collapses, either from exosmo- 

 sis, or by the solvent action of the gastric juice or 

 other digestive fluids ; and, in about five or six hours 

 after the ingestion of the worm, it has found its way 

 into the small intestine. The head and neck then 

 extend themselves by a species of evolution, by which 

 process the margins of the head and neck, which had 

 previously been inverted, now become the free borders 



