170 MANUAL OF ZOOLOGY. 



2. The proscokx, or the minute embryo which is liberated 

 from the ovum, when this latter has been swallowed by any 

 warm-blooded vertebrate. 



3. The scolex, or the more advanced, but still sexually im- 

 perfect, embryo, into which the proscolex develops, when it has 

 encysted itself within the tissues of its host. (Under this head 

 come the so-called " Cystic Worms.") 



4. The strobila, or adult Tape-worm, into which the uolex 

 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 Tmnia 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 b)' a pig. When this occurs, a " proscolex " is hbe- 

 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- 

 losm, 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 

 Tmnia solium, with which we originally started. The other 

 common tape-worm of man — viz^ the Tmnia mediocanellata — is 

 derived in an exactly similar manner from the " measles " of 

 the ox. The young, however, of another of the Tape-worais of 

 man (viz., the Bothriocephalus latus) is said not to be " cystic." 

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

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

 fasciolaris) ; the tape-worm of the fox {Tmnia pisiformis) is 

 derived from the cystic worms of hares and rabbits {Cysticercus 

 pisiformis) ; and the tape-worm of the dog {Tmnia serratd) is 



