SPONTANEOUS GENERATION. 141 



their prey. The eggs, being thus introduced into the stom- 

 ach of the fish, find conditions favorable to their develop- 

 ment ; and thus the species is propagated, and at the same 

 time transmitted from one generation of the fish to another. 

 The eggs which are not swallowed are probably lost. 



363. All animals swallow, in the same manner, with 

 their food, and in the water they drink, numerous eggs of 

 such parasites, any one of which, finding in the intestine of 

 the animal favorable conditions, is hatched. It is probable 

 that each animal affords the proper conditions for some par- 

 ticular species of worm ; and thus we may explain how it is 

 that most animals have parasites peculiar to themselves. 



364. As respects the Infusoria, we also know that most 

 of them lay eggs. These eggs which are extremely minute, 

 (some of them are only T^-^IJ f an inch in diameter), are 

 scattered everywhere in great profusion, in water, in the air, 

 in mist, and even in snow. Assiduous observers have not 

 only seen the eggs laid, but moreover, have followed their 

 development, and have seen the young animal forming in 

 the egg, then escaping from it, increasing in size, and, in its 

 turn, laying eggs. They have been able, in some instances, 

 to follow them even to the fifth and sixth generation. 



365. This being the case, it is much more natural to sup- 

 pose that all the Infusoria are products of like germs, than 

 to assign to them a spontaneous origin altogether incompati- 

 ble with what we know of organic development. Their 

 rapid appearance is not at all astonishing, when we reflect 

 that some mushrooms attain a considerable size in a few 

 hours, but yet pass through all the phases of regular growth ; 

 and, indeed, since the knowledge of the different modes of 

 generation among the lower animals, no substantial difficul- 

 ties to the axiom " omne vivum ex ovo " (275), any longer 

 exist. 



