382 



THE DEVELOPMENT OF CESTODES. 



work I myself expressed this opinion, but have been convinced 

 by repeated experiment that this structure disappears as completely 

 as the caudal bladder. This indeed occurs some hours later, when the 

 worm has reached the small intestine, but this is readily explained by 

 the greater resistance offered by the more parenchymatous structures 

 to the action of the digestive juice. 



Thus, of the original worm only the head with its long narrow 

 neck remains, 1 and produces by its metamorphosis the jointed tape- 

 worm. And this is not the case only in the ordinary bladder-worms, 



FIG. 224. Metamorphosis of the bladder-worm of the rabbit into the young tape- 

 worm. ( x 4.) 



but also, according to my observations, in Cysticcrcus fasciolaris, 

 although in this case the appendage has even in the bladder-worm 

 stage grown out into a long, jointed, tape-worm body (Fig. 202). 



Posteriorly, where the neck passed into the appendage, there 

 may at first persist a few traces of the former body of the worm, but 

 these vanish within twenty-four hours after the transference of the 

 bladders, and then only a small, almost scar-like, notch is left to recall 

 the former state. The scar can be detected on the terminal joint of 

 the chain till the latter is liberated. It leads into a small bladder- 

 like cavity (Fig. 228), the porus terminalis, which receives the four 

 longitudinal vessels. The cavity which formerly penetrated the 

 head and neck has disappeared through the coalescence of the opposite 

 surfaces, and thus sections already show the subsequent condition 

 of the parenchymatous sheath. The musculature of the receptacle has 

 not the slightest share in filling up the head. 



In the Cysticercoids, whose anterior portion consists entirely of 

 head and neck, the caudal bladder alone is lost. It is doubtful whether 

 the same may be said of those forms whose caudal bladder is destitute 

 of any histological differentiation. Judging from the analogy of the 

 Echinococcw-he&ds, it is possible that the bladders may persist, as 

 has been hinted at above, and pass directly by segmentation into the 

 adult tape-worm. 



1 With this agree the results of Moniez, as stated in his essay on the history of the 

 bladder-worm, which has just appeared. 



