100 ANIMAL PARASITES AND MESSMATES. 



one would think that their tenacity of life is very feeble, 

 and that the sKghtest derangement would be sufficient 

 to kill them. It is not so ; on the contrary, some of 

 them can be entirely dried up, and return to life every 

 time that they are moistened ; and the eggs of some of 

 them resist the most violent reagents. We have known 

 eggs preserved for years in alcohol, in chromic acid, and 

 in other agents which destroy life everywhere else ; and 

 then give birth to embryos directly they are placed in 

 pure water or damp earth. 



Some years ago they had no idea of the migration 

 of animals from one body to another. As we have said 

 elsewhere, Abildgard, half a century ago, made experi- 

 ments on the worms of fishes which he caused ducks 

 to swallow, but these experiments had no result, and 

 formed rather an obstacle to ulterior progress, than an 

 approach to truth. The worms of fishes have been 

 known to live in birds; but these worms were only 

 there as adventitious parasites. Liguli live some days 

 in the goosander, but they do not maintain their position. 



Our great initiator into the world of parasites, Mons. 

 Siebold, arrived also at a conclusion which could not 

 be maintained. Having observed, with his habitual 

 sagacity, that the cysticercus of the mouse is the same 

 worm which lives in the cat, he published his opinion 

 that the eggs of this taenia had lost their way in the 

 mouse, that the young worms had become sick there, 

 and that in the cat alone, they could be healthily and 

 completely developed. It was like a plant lost on a soil 

 where it could not live, and still less flourish. May I 

 be permitted to state by what means we have arrived 

 at the knowledge of the transmigration of worms ? 



