CONCLUSIONS. 179 



the place of their birth. The drift-wood which the Gulf 

 stream floats from the Gulf of Mexico even to the western 

 shores of Europe, is frequently perforated by the larvae of 

 insects, and may probably serve as depositories for the eggs 

 of fishes, Crustacea and mollusks. It is possible also that 

 aquatic birds may contribute in some measure to the diffu- 

 sion of some species of fishes and mollusks, either by the 

 eggs becoming attached to their feet, or by means of those 

 which they evacuate undigested, after having transported 

 them to considerable distances. Still, all these circum- 

 stances exercise but a very feeble influence upon the distri- 

 bution of species in general, and each country, none the less, 

 preserves its peculiar physiognomy, so far as its animals are 

 concerned. 



449. There is only one way to account for the distribu- 

 tion of animals as we find them, namely, to suppose that 

 they are autochthonal, that is to say, that they originated 

 like plants, on the soil where they are found. In order to 

 explain the particular distribution of many animals, we are 

 even led to admit that they must have been created at 

 several points of the same zone, as we must infer from the 

 distribution of aquatic animals, especially that of Fishes. 

 If we examine the fishes of the different rivers of the United 

 States, peculiar species will be found in each basin, associated 

 with others which are common to several basins. Thus, the 

 Delaware River contains species not found in the Hudson. 

 But, on the other hand, the pickerel is found in both. 

 Now if all animals originated at one point, and from a single 

 stock, the pickerel must have passed from the Delaware to 

 the Hudson, or vice versa, which it could only have been 

 done by passing along the sea-shore, or by leaping over large 

 spaces of terra firma ; that is to say, in both cases it would 

 be necessary to do violence to its organization. Now such 



