106 ACQUIRED CHARACTERS sec. 



Salmo lacustris, as compared with the brook trout, Sahiio 

 fario. The epicure easily distinguishes the one from the 

 other. The hake trout has coarser flesh than the brook trout, 

 and also tastes somewhat peaty. The two forms also show 

 differences in the colour and marking of the skin, but the 

 specific distinction is generally founded principally on the 

 dentition of the vomer. Quite recently, Professor Klunzinger 

 has, certainly with reason, publicly embraced the view long ago 

 put forward by me, that both fishes are but one species. From 

 the influence of different habitats, the one living in lakes, the 

 other in the rapid waters of mountain brooks, they have become 

 so different that the}^ have been taken for distinct species, 

 notwithstandino- that it has ever been of the neatest difficulty 

 to discover any really definite distinction between them. 



In a similarly slight degree does the salmon-trout Salmo 

 trutta differ from the lake and brook trout, so that we must 

 regard, with Klunzinger, this also as a " biological species." 



The comparison of the American fauna with the European 

 shows a large number of curious parallel forms, i.e. several of 

 our species of animals have representatives in Xorth America 

 which are very similar to them, but which have so many 

 peculiar characters that they are described as distinct species, 

 or at least form distinct varieties. Thus the reindeer : Cervus 

 tarandus and C. caribou, Aud. and Bachm. ; Canis lupus, of 

 which orientalis as our, occidentalis as the American wolf 

 are distinguished ; Ursus arctos our brown bear, and Ursus 

 americanus and ferox in North America ; Cervus elaphus, 

 our stag, and C. canadensis, the Wapiti stag ; Bison europffius 

 and B. americanus, etc. 



These relations of forms can only be explained on the 

 ground that the faunae of America and Europe were once 

 united by the connection of the two continents, and that they 

 have gradually formed two distinct groups from the difference 

 of the environment. It is also certain, as I have before men- 



