234 MANUAL OF ZOOLOGY. 



intercalation of fresh articulations, they become sexually mature, 

 thus constituting the " proglottides " of the adult tape-worm 

 with which the cycle began. To the entire organism, with its 

 "head" and its mature and immature joints (" proglottides"), 

 the term "strobila" is now applied. 



In the development, therefore, of the tape-worm, we have to 

 remember the following stages : 



1. The ovum, set free from a generative joint or proglottis. 



2. The proscolex, 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 scolex 

 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 Tcenta solium. Commencing with an indivi- 

 dual who is already suffering from the presence of this parasite, 

 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 fecundated 

 ova. When the ova which are microscopic in size are lib- 

 erated 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 liberated 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 cellulose (fig. 113,^), 

 constituting what is commonly known as the "measles" of the 

 pig. In this state the scolex will continue for an indefinite 

 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 intestine, 

 throws off its caudal vesicle, and commences to produce " pro- 

 glottides " instead, becoming thus the " strobila " of the Tcenia 

 solium, with which we originally started. The other common 

 tape-worm of man viz., the Tania mediocanellata is derived 



