290 Account of a Filaria in a Horse's Eye. 



feeding in a particular manner. But if such transitions occur in 

 worms, we should sometimes observe them while undergoing the 

 process, for it would be contrary to all analogy to suppose that the 

 change would be sudden. But we see no such transitions ; we 

 never find these animals " half way between what they were and 

 what they are." No zoologist, not even Bremser, who devoted ' 

 twelve years of his life to the study of Entozoa, ever witnessed 

 any such change; indeed, he states expressly, "that after having 

 diligently examined 15,000 specimens of worms in the Cabinet 

 of Vienna, he never was for one moment at a loss to say which 

 were intestinal worms and which were not." If worms then ori- 

 ginate within the body, how do they originate ? — what are the 

 obstacles in the way of our adopting the theory of spontaneous 

 generation 7 In the first place, if they can be formed by the 

 mere combination of inorganic elements, we may well ask, why 

 they should be furnished with reproductive organs ? No such 

 creations or combinations have ever been observed, and therefore 

 the fact of their occurrence is a matter of mere supposition. The 

 only argument on which this hypothesis may be said to rest, is 

 our ignorance of the precise mode of their origin, and derives no 

 support from analogy. 



If this theory be true, it is difficult to explain why the law 

 should be confined to the lower classes of animals, and not also 

 extend to the higher. By some fortuitous concourse of atoms, 

 we should expect, occasionally, to see a man, a quadruped, or a 

 bird, spring up from some dunghill, or fermenting vat ; but this 

 is a phenomenon which even Ovid never dreamed of. 



The production of certain species of vegetables was once as 

 difficult 10 explain, as it now is to account for the origin of intes- 

 tinal worms ; but late investigations have removed these difficul- 

 ties, and shov/n that they are propagated in the usual manner by 

 seed or reproductive granules. Thus it is observed that white 

 clover is ready to spring up on soils which have been rendered 

 alkaline by the strewing of wood-ashes, or the burning of weeds; 

 ground newly turned up by the plough is found to produce plants 

 dissimilar to any in their neighborhood ; parasitic ^w^« sprout up 

 upon decaying organized substances, and even in the interior of 

 cheese, &c. Dr. Good remarks that he "has seen a hop-ground 

 completely overrun and desolated by the Aphis humuli, or hop 

 green-louse, within twelve hours after a honey-dew (which is a 



