ANNULOSA: TVENIADA. 235 



in an exactly similar manner from the " measles " of the ox. 

 In like manner, the tape-worm of the cat (Tcenia crassicollis) is 

 the mature form of the cystic worm of the mouse {Cysticercus 

 fasciolaris) ; the Tcenia crassiceps of the fox is derived from the 

 Cysticercus longicollis of the vole (Arvicola terrestris] ; one of 

 the tape-worms of the dog (T. serrata) is the fully developed 

 form of the Cysticercus pisif or mis of hares and rabbits ; another 

 of the tape-worms of the dog (T. ccznurus) is the adult of the 

 Ccenurus cerebralis, which gives rise to the " staggers " of the 

 latter animal; and another (T. echinococcus) spends its larval 

 stage in the tissues of man ; while T. marginata of the dog 

 and wolf is the mature stage of the Cysticercus tenuicollis of the 

 ruminants and of the pig. On the other hand, the embryo of 

 the "Russian tape-worm" (Bothriocephalus latus] is not "cystic," 

 but is ciliated and furnished with hooklets, whilst the scolex 

 apparently leads an independent life in water, and its inter- 

 mediary bearer (supposed by some to be a fish of the salmon 

 tribe, or by others to be a fresh-water Annelide) is at present 

 unknown. 



Besides being liable to the attacks of various species of adult 

 tape-worms, man is not uncommonly attacked by " scolices," or 

 the larval forms of the tape-worms of other animals. Thus, 

 what are professionally termed " hydatids " are really the 

 scolices of one of the tape-worms of the dog (the Tcenia echino- 

 coccus). The "strobila" or adult worm (fig. 115, A) is only 

 about a quarter of an inch in length, and is singular in con- 

 sisting of only four segments, including the " head." The 

 last segment is sexually mature, and the head is furnished with 

 hooklets and suckers. The egg gives rise, when swallowed by 

 man, to a "proscolex," which bores its way through the walls 

 of the stomach, and finds a lodgment in some solid organ 

 very commonly the liver. The primitive scolex now consists 

 of a spherical vesicle (fig. 115, C) with a thick laminated ex- 

 ternal covering enclosing a central granular mass. This mass 

 ultimately forms a cellular membrane lining the outer lamin- 

 ated envelope, and from it are developed numerous secondary 

 " scolices," each of which is attached to the parent cyst by a 

 pedicle, and is furnished with a crown of hooklets and four 

 suckers, but is destitute of a caudal vesicle (fig. 115, D). In 

 fact the parent cyst may be regarded as morphologically com- 

 posed of the coalescent caudal vesicles of the contained 

 "heads" or " Echinococci" The parent cyst may grow to a 

 great size, and is filled with a clear fluid, whilst instead of 

 producing simple " Echinococci," it may bud off numerous 

 " brood - capsules," each of which develops in its interior a 



