ON PARASITES. 37 



face. All the steps of their formation are the same as in the cysti- 

 cerci. The scolices may be everted by pressure in the same manner. 

 They also have sucking discs and a corona of booklets, like the pre- 

 ceding. The term caudal vesicle is not appropriate in this condition. 



THE ECHINOCCI. 



The embryonic globular vesicle is still more active among these 

 worms than in the preceding two. It is a true maternal vesicle. 

 The prolification is from the internal surface of the mother vesicle. 

 Upon this internal surface there are formed conical nodulations which 

 develope into daughter vesicles, and these united to the mother vesi- 

 cle by a footstalk, prolificate vesicles after the manner of csenuri. 

 The maternal vesicle varies in size with the growth of the daughter 

 vesicles. The stem remains permanent in E. scolieiparena. In E. 

 afctriciparens it separates from the mother vesicle. 



When the mother vesicle is cut, the daughter vesicle, upon being 

 squeezed, exhibits the scolices in the usual way i. e. by eversion. 



The formation of the suckers and hooks is similar to what holds 

 among the cysticerci and csenuri.* In addition to the three forms 

 of scolex generating cystic worms, there are what may be called 

 scolices without caudal appendage, and those with a band-like appen- 

 dage. The scolices develope from the six-hooked embryos with all 

 the usual appendages, — suckers and hooks, but the caudal appendage 

 atrophies into the band-like process or disappears. 



THE ACTIVE SCOLEX. 



The scolices of all the forms of the third stage, having entered, by 

 whatever means, into the intestines of a suitable animal, pass into a 

 state of activity. The head becomes everted, the suckers and hooks 

 change their position, — the hooks projecting forward and outwards. 

 The scolex now fastens by the suckers and hooks upon the intestinal 

 mucous membrane, and casting off his caudal appendage, commences 

 the process of gemmation from the posterior surface. After a time 

 the buds become transversely striated, marking the future divisions 

 into joints, the oldest and most developed being necessarily furthest 

 from the scolex. This process of gemmation comprizes the last stage 

 in the developement. 



*A11 three of these forms of cystic worms, if by any means they become sterile the vesicle 

 is called an Acephalocyst, a structure that has so much puzzled the ingenuity of medical men. 



