ANNULOIDA: SCOLECIDA. 163 



develops itself, when received into the alimentary canal of a 

 warm-blooded vertebrate. The strobila is constituted by the 

 ''head," and by a number of immature and mature generative 

 segments or joints, termed the "proglottides." 



The subject will, perhaps, be more clearly understood by 

 following the development of one of the common Tape-worms 

 of man viz., the Tcenia solium. Commencing with an indivi- 

 dual who is already suffering from the presence of this para- 

 site, one of the most distressing symptoms of the case is found 

 to be the escape of the joints of the animal from the bowel. 

 These joints are the ripe " proglottides," containing the fecun- 

 dated ova. When the ova which are microscopic in size 

 are liberated by the decomposition of the proglottis, they may 

 gain access to water, or be blown about by the wind. In 

 many ways, it is easy to understand how one of them may be 

 swallowed by a pig. When this occurs a "proscolex" is libe- 

 rated from the ovum, and bores its way through the walls of 

 the stomach, to become a " scolex." It now takes up its abode, 

 generally in the muscles, in which position it was originally 

 described as a cystic worm under the name of Cysticercus cellu- 

 loses, constituting what is commonly known as the " measles " 

 of the pig. In this state the scolex will continue for an in- 

 definite period ; but if a portion of " measly " pork be eaten by 

 a man, then the scolex will develop itself into a tape-worm. 

 The scolex fixes itself to the mucous membrane of the intes- 

 tine, throws off its caudal vesicle, and commences to produce 

 " proglottides " instead, becoming, thus, the " strobila " of the 

 Tcenia solium, with which we originally started. The other 

 common tape-worm of man viz., the Tcenia mediocamllata is 

 derived 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 fa sciolaris) ; the tape-worm of the fox (Tcenia 

 pisiformis) is derived from the cystic worms of hares and 

 rabbits ( Cysticercus pisiformis) ; and the tape-worm of the dog 

 ( Tcenia serrata) is the developed form of the Ccenurus cerebralis 

 of the sheep, the cystic worm which causes the " staggers " in 

 the latter animal. 



Besides tape-worms, however, man is liable to be affected 

 with " scolices," which are the larvae of the tape-worms of other 

 animals. Thus, what are professionaly called "hydatids"in 

 the human subject, are really the scolices of the tape-worm of 

 the dog. The disease is indicated by the presence of the so- 

 called " hydatid-tumour," which consists of a strong membran- 

 ous cyst the "hydatid" proper situated in some solid organ, 



