APPENDIX. 187 



be considered as varieties, where the differences of 

 food and of habits have occasioned, in a long course 

 of ages, differences of shape and colours, transmitted 

 to offspring in the same manner as in the variety 

 of dogs, which may all be referred to one primitive 

 type/' Now if the above quoted opinion be correct ; 

 and since it is certain that there is no real difference 

 between the sea or bull trout of the Coquet, and the 

 grilse which has been proved to be a young salmon 

 of the Tweed and the Tyne ; it would follow, that 

 the whole of the section, Truttce, of the genus 

 SALMO, including the salmon proper, forms but one 

 species; what are now described as species being 

 properly varieties. As it is known that the salmon 

 will breed with the grilse and the bull-trout, and 

 the two latter with the common or fresh water 

 trout ; it is, therefore, very likely that the several 

 varieties of the Truttce are capable of breeding 

 with each other, and of producing perfect fish 

 capable of breeding again. The carp and the trout 

 have been known to breed together, thus producing 

 a hybrid, which appears to be incapable of conti- 

 nuing a distinct variety, either from inability to 

 breed, or from its produce resuming the distinctive 

 character of a carp or a trout. The opinion of that 

 eminent physiologist, John Hunter, respecting that 

 which constitutes a distinct species, is as follows : 

 "The true distinction between different species of 

 animals, must ultimately, as appears to me, be 

 gathered from their incapacity of propagating with 

 each other an offspring capable again of continuing 



