DIMENSIONS OF CYSTICERCUS TENUICOLLIS. 577 



a kind of neck, and drawn out into a hollow cylinder, which some- 

 times projects externally (Fig. 310, A), and is at other times retracted 

 (Fig. 313), so that the head-process is deeply sunk within the bladder. 

 Although the presence of this process has given rise to the specific 

 name of this bladder- worm, it is by no means a characteristic mark, 

 since it varies very much in development, and is sometimes altogether 

 wanting. I have, for example, seen bladder-worms 70 mm. long, 

 with a neck of the same length, and others in which the neck only 

 measured 5 mm. As a rule, the bladder- worms have long necks 

 (in the two specimens mentioned the neck measured 60 mm. in one 

 case, and 14 in the other) ; but, on the other hand, the contrary is 

 sometimes observed. 



As the bladder- worm grows older, not only do the bladder and the 

 receptacle alter, but the whole head-process undergoes change. For 

 when the head-process has attained a certain size (as in Cysticercus 

 fasciolaris), it is protruded from the bladder by evagination, and ulti- 

 mately assumes the form of a wrinkled and somewhat solid cylinder 

 1 to 2 cm. in length, and situated at the end of the neck of the 

 bladder. Only the head-proper remains, as a rule, drawn in. 



This appendage is, however, visible generally only in those cases 

 in which the neck of the bladder hangs freely outwards. If the 

 latter be invaginated into the interior of the bladder of the worm, 

 the body lies hidden in the interior of this neck as in a sheath. 

 At the posterior end, where it is connected with the base of the 

 sheath, one sees the floating gelatinous band issu- 

 ing from it, looking as if it were a direct con- 

 tinuation of the body of the worm. The 

 receptacle as such is no longer present. It has 

 apparently been invaginated along with the head, 

 and has probably been used in the progressive 

 solidification of what we have seen to be origi- 

 nally a tubular body. 



It is not known to what age Cysticercus tenui- 

 collis may live, but it appears almost as though FIG. 313. Anterior 

 it might exist uninjured for many years. At least end . of Cysticercus tenui- 

 this may be supposed from the colossal size which nec k,' and ribbon-like 

 the bladder -worm sometimes attains. The appendage. 

 Giessen zoological collection possesses a specimen, procured from an 

 ox with retracted neck, which is 160 cm. long and from 6 to 7 cm. 

 thick ; and Diesing has reported a specimen taken from a pig, which 

 was almost a foot long, 1 and had a diameter of 4 inches. The true 



1 Could that have been the specimen of "five" feet mentioned by Kuchenmeister 

 ( " Parasiten," p. 517.) ? 



2 



