Many-headed Bladder-worm. 251 



ducts. The six spines are to be recognised againj though scattered 

 and dislocated from their position as given here, in the more or less 

 distended, cystic or cysticercoid vesicle, into which the proscolex 

 expands when it reaches its place of lodgment in the tissues. 



See fig. 6 b for Caenurus cerehralis, Van Beneden, I. c, pi. xxvi., 

 fig. 34 ; for the six spines as seen in the cystic stage of Taenia 

 ecUnococcus, Leuckart, I. c, fig. 51, Micrographic Dictionary, 

 pi. 16, fig. 2 ; for the six spines in Taenia solium, Cysticercus 

 cellulosae, see Cohbold, Entozoa, p. 225, fig. 48 ; for those in 

 Cysticercus limacis, and Stein, for similar organisms from the 

 perivisceral cavity of the larvae of Tenehrio molitor, which must 

 be supposed to gain the cestoid form in the digestive tube of 

 some insect-eating bird or mammal, Zeitschrift fiir Wissen- 

 schaftliche Zoologie, Bd. iv., 196, Taf. x., figs. 12, 13, 14, 16, 

 and V. Carus' Icones Zootomicae, Taf vii., fig. 20. 



For a history of the migration of these embryos, see Yan Beneden, 

 I. c, p. 238 ; Leuckart, I. c, p. 198. 



FiGUEE 6. 



Cystic stage in the development of M.any-headed Bladder-worm, Caenurus Cerebralis, 

 after Van Beneden, I. c, pi. xxvi., fig. 31. 



The embryonic hexacanth embryo, figured at 5, has become greatly 

 distended after coming to rest in the organ, ordinarily the brain of 

 a sheep, into which it is carried by the blood after penetrating these 

 vessels. The six hooks are observed to be scattered and dislocated 

 over its surface at 6, and a number of 'scolices/ the potential 

 'heads' or 'nurses' of a future tapeworm, are observed to be 

 developed upon one of the poles of the enlarged vesicle. The way 

 in which these heads are formed in the Taeniadae appears to be as 

 follows. In the innermost submuscular cellular layer of the cyst, 

 a proliferation of cells takes place, and forms a thickened disc. Into 

 this a single depression in the monocephalous Taeniadae, and from 

 3 or 4 up to 300 or 400 in the Caenuri, make their way from the 

 outside of the mother cyst inwards. On and out of the thus 

 inverted external layer, the cuticular layer of the future scolex, with 



