by j. p. hill. ,65 



General Considerations. 



Diesing* divides tlie cystic forms into four genera : — (I) Echi- 

 nococcKS, (2) Ccenurus, (3) Cynticercus, (4) Piestocystis. With the 

 two latter we are for the present alone concerned. 



According to Diesing the presence or absence of hooks serves to 

 distinguish the genus Cysticercus from the genus Piestocystis ; the 

 Cysticerci are armed forms, the Piestocystes unarmed, and it is 

 clearly among the unarmed Piestocystes that we must look for the 

 relationships of the two forms described in the foregoing ; they 

 are both the cystic forms of bookless Tsenise. 



Villot,t basing his classification on the mode of formation of 

 the caudal bladder, has divided the cystic forms into two groups. 

 His first group includes cystic forms whose caudal vesicle arises 

 from the proscolex by simple growth and modification of structure, 

 without, strictly speaking, the production of any new part. His 

 second group includes cystic forms in which the caudal vesicle 

 arises from the proscolex by a process of budding, i.e., by the 

 addition of a new part. In the first group he includes tlie three 

 genera, Cysticercus, Echinococcus, and Ccenurus, and it is with the 

 first of these genera, with the Cysticerci properly so-called, that he 

 classes the forms included in Diesing's genus Piestocystis. He 

 says| : — " L'etat inerme, pas plus que I'etat arme, ne peut carac- 

 teriser une coupe generique parmi les Cystiques ; et il est bien 

 evident que le groupe des Piestocystis doit di.sparaitre de la 

 nomenclature." In support of this view he instances the case of 

 Tcenia saginata, a form which in the adult has no hooks and only 

 a rudimentary (persistently embryonic) rostellum, but whose 

 affinities structurally are with the armed Tsenite. 



Leuckart,§ however, has shown that the Cysticerci of this tbrm, 

 '* although the descendants and young forms of a bookless tape- 



* Systema Helminth um, Vol. i. p. 478. 



+ Loc. cit. " Cystiques des Tt^nias." 



X Loc. cit. p. 5. 



§ Loc. cit. p. 463. 



.-a K 



