80 ANIMAL PAEASITES. 



IV. The Scoleoc passing into activity. 



In the year 185 1, as lias already been observed, I had come to 

 the notion of testing the opinion formed by Von Siebold upon 

 the identity of the hooks of T. crassicollis and Cyst, fasciolaris, 

 which was previously known to the older writers, and of the ex- 

 ceptional conversion of this cystic worm into a particular tape- 

 worm in the intestinal canal of w a certain predaceous animal, by 

 the intentional administrations of cystic worms to certain mam- 

 malia. By these investigations I arrived at the conviction that 

 all the cystic worms which I could obtain passed into this 

 metamorphosis, and that the cystic worms occurred in those 

 animals ivhich serve as the prey of the predaceous species which arc 

 capable of developing the cystic worm into a tape-worm in their 

 intestine, or, in other words, that the animal infested by cystic 

 worms is usually the source of food, or the prey of that infested by 

 tapeworms. These laws have been confirmed by the most 

 various observers; for example, by Von Siebold, Lewald, Haubner, 

 Gurlt, Roll, Eschricht, Van Beneden, Moller, and especially by 

 Leuckart, and enlarged by the latter as regards Cyst, longicollis, 

 so that this subject may be regarded as set at rest. It is now 

 our task to describe the processes which occur more particularly. 



The host of the cystic worm is devoured by a carnivorous 

 predaceous animal, and by this means the cystic worm arrives, 

 together with his previous host, in the stomach of the carnivorous 

 animal. During the process of digestion, the enveloping cysts in 

 which the cystic worms were enclosed, or, if the worms lived 

 free in cavities, these latter, perhaps both (cysts and cavities), are 

 digested, or even opened previously by the teeth of the pre- 

 daceous animal, when the cystic worm escapes freely into the 

 cavity of the stomach. Here the worm extends itself, its caudal 

 vesicle collapses, from the escape of the fluid through some opening 

 which has been made in it, and perhaps also, in extremely rare 

 exceptional cases, from its escape through the uninjured walls, 

 in accordance with the laws of exosmose. On the caudal vesicle 

 and the middle of the body of the cystic worm, digestion 

 begins to act perceptibly. The body at the same time elongates 

 and extends itself, but the head, together with the short neck, is 

 still inverted, as during the cysticercal period of existence. But 



