NATURAL HISTORY FISH. 241 



excluded from the egg, may be considered in 

 the tadpole state as fish ; and you would not 

 find their singular metamorphosis without in- 

 terest. Or I could detail to you the true 

 histories which naturalists have given of the 

 habits of snails and earthworms, and of the 

 sexual relations of these apparently con- 

 temptible animals; — but this is too delicate 

 a subject to dwell on. Even the renewing 

 or cluinge of shell in the crawfish, when 

 it falls in its soft state an easy prey to fish, 

 is a curious inquiry not only for the phy- 

 siologist, but likewise for the chemist. On 

 these points, I must request you to refer to 

 writers in Natural History: yet I shall per- 

 form my promise, and say a few words on 

 winged insects, which, in their origin and 

 metamorphosis, offer the most extraordinary 

 known miracles perhaps of terrestrial natures. 

 You must be acquainted with the origin of , our 

 common house flies ? 



Phys. — We know, that they spring from 

 maggots, and that both the common and blue 

 bottle fly deposit their ova in putrid animal 

 matter, where the eggs are hatched and pro- 



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