186 ANIMAL PABASITES AND MESSMATES. 



latter it moves freely, and has, in addition to sexual 

 organs, those which are proper to this condition which 

 we have called Proglottis. Thus these parasites undergo 

 metamorphoses. 



For a long time, metamorphoses seemed to be the 

 attributes of frogs and insects exclusively. In the class 

 of worms, in which they are complicated with the change 

 of hosts, they much surpass in reality the most bril- 

 liant and extravagant fictions of the poets. The 

 phenomena of these transmigrations were completely 

 unknown before our researches were made. If some 

 naturalists, like Abildgaard or Pallas, suspected their 

 existence, it was rather by accident, and the experiments 

 to which they devoted themselves were all unfavourable 

 to their suppositions. 



The knowledge of these transmigrations has at the 

 same time dispersed the latest illusions of the partisans 

 of spontaneous generation ; it was the more difficult to 

 explain the presence of worms in enclosed organs, since 

 these worms were always without sex. By the same 

 means, we have ascertained the true prophylactic treat- 

 ment, and thus discountenanced the numerous anthel- 

 mintic remedies which had often caused more serious 

 accidents than the parasites themselves. 



When it was considered that parasites were the result 

 of an especial degeneration of some of the intestinal 

 papillae, the physician would at once consider that there 

 was some morbid condition, and we can understand 

 that all his efforts would be employed against the 

 enemy which had arisen. Now it is known that every 

 healthy animal living in freedom contains parasites 

 almost as invariably as the organs which support its 



