44 SALMONID^. 



founded upon facts that cannot err, upon deductions drawn 

 from differences of anatomical structure, permanent from gene- 

 ration to generation, and liable to no modification by the 

 change of external circumstances. 



This it is which renders the structure of the fins, the shape of 

 the gills, the system of the teeth, and other matters of the 

 same kind, which pass wholly unnoticed by tlie clod-hopping 

 hunter^ of all importance in distinguishing one species from 

 another ; while the size, the weight, the colour and number of 

 the spots, things to which he will point as decisive with all the 

 pig-headed presumption of self-conceited ignorance, are of little, 

 if any weight, as varying in individuals, and not transmitted, 

 like to like, through generations. 



Almost all the really distinct species of the Salmonidce are 

 distinguished principally one from another by the form of the 

 head and the structure of the gills in the first degree, and by 

 the dental system in the second. Any permanent and unvarying 

 difference in these, coupled to other variations of colour, form, 

 habit, or the like, which might otherwise be deemed casual, 

 being held sufl&cient to constitute a distinct species. 



Many discoveries have been made through these means of late 

 years ; many varieties, which were formerly supposed to be truly 

 distinct, having been proved to be identical; and many new 

 species discovered — the tendency of the Avhole having been to 

 simplify and to diminish the number of species, in the upshot, 

 and thereby to decrease the labours of the student, and to 

 facilitate the acquisitions of science. 



Much, however, yet remains to be done, as will be rendered 

 evident by the consideration that, even in so circumscribed a 



