BY J, P, HILL. 67 



and the head of the Cysticercus. In the forms under considera- 

 tion, these two layers enclosing an interparietal cavity do not 

 appear to be represented, and further, as Leuckart states,* the 

 sheath or so-called receptacle is in these forms "not only connected 

 with the mass of the head, but, like the ordinary body muscles, 

 bound up with the tissue of the bladder." Hence, if this sheath 

 be taken as representing the body of the Cysticerci properly so 

 called, we may take it as characteristic of the genus Piestocystis 

 that the body, unlike that of the Cysticerci properly so-called, is 

 not represented by a part distinct from the caudal vesicle. 



The absence of a well-marked bladder cavity containing fluid is 

 also a noteworthy feature and one which has given rise to the 

 name j)arenchymatous bladder worms for these forms. The 

 cavity may be entirely absent or it may be represented by an 

 irregular sjjace bounded by thick walls. With reference to this 

 feature Leuckart say sf :—" With the loss of the bladder cavity 

 most of the characteristic peculiarities of the bladder worms have 

 been also lost, so that it is hardly possible to distinguish these 

 forms from developed bladder worms with evaginated heads. In 

 fact, even in spite of the attached caudal bladder, such a form as 

 that represented on Fig. 185c looks exactly like a young still 

 unsegmented tapeworm." 



The Cysticercus which most closely approaches the.se parenchy- 

 matous forms in the absence of a distinct bladder cavity is that of 

 Tcenia elliptica (cucwnerina), but it is at once distinguished from 

 them by the possession of hooks, and further, as Grassi and Rovelli 

 have shown, I the fully formed Cysticercus represents only the 

 anterior part of the six-hooked embryo, the posterior part which 

 forms the tail being lost on the Cysticercus reaching maturity. 



As one of -the characters of the genus Piestocystis, Diesing 

 gives the absence of a rostellum, but its homologue, the frontal 



* Loc. cit. p. 347. 

 t Loc. cit. p. 343. 

 J " Embryologische Forschungen an Cestoden," Centralb. f. Bakt. u. 

 Parasit., Band v. 1889. 



