68 SCIENCE SKETCHES. 



correspond to our closet-formed definition of its 

 species must therefore be a " hybrid " with some 

 other. There is no evidence worth mentioning, 

 known to me, of extensive hybridization in a state 

 of nature in any group of fishes. This matter is 

 much in need of further study; for what is true of 

 the species in one region, in this regard, may not 

 be true of others. The species of trout, also, may 

 perhaps hybridize, while Salmo salar and the 

 species of Oncorhynchus certainly do not. Dr. 

 Giinther observes : 



"Johnson, a correspondent of Willughby, had already 

 expressed his belief that the different salmonoids inter- 

 breed ; and this view has since been shared by many who 

 have observed these fishes in Nature. Hybrids between 

 the sewin (Salmo trutta cambricus} and the river- trout 

 (Salmo far to) were numerous in the Rhymney and other 

 rivers of South Wales before salmonoids were almost ex- 

 terminated by the pollutions allowed to pass into these 

 streams, and so variable in their characters that the pas- 

 sage from one species to the other could be demonstrated 

 in an almost unbroken series, which might induce some 

 naturalists to regard both species as identical. Abundant 

 evidence of a similar character has accumulated, showing 

 the frequent occurrence of hybrids between Salmo fario 

 and S. trutta. ... In some rivers the conditions appear 

 to be more favorable to hybridism than in others, in which 

 hybrids are of comparatively rare occurrence. Hybrids 

 between the salmon and other species are very scarce 

 everywhere." 



The black-spotted trout, forming the sub-genus 

 Salar, differ from Salmo salar and Salmo trutta in 

 the greater development of the vomerine teeth, 



