66 The Natural History of the Salmon, 



genera. Whenever the zoologist observes two 

 forms, distinguished by peculiarities of organization, 

 such as cannot be conceived to be the effects of an 

 external or internal cause, disappearing with the 

 disappearance of that cause, and which forms have 

 been propagated and are being propagated uni- 

 formly through all generations within the limits of 

 our observations, and are yet most probably to be 

 propagated during the existence of mankind, he is 

 obliged to describe these forms as distinct, and 

 they will commonly be called species." ^ 



From so great an authority as Dr. Gunther, it 

 would seem almost presumptuous to differ ; yet prac- 

 tical experience and more extended observations 

 will certainly tend to lessen, and not increase, the 

 number of species of the genus Salmo. 



Dr. Francis Day, a very close observer and a very 

 practical ichthyologist, in stating the various cha- 

 racters which have been relied on to distinguish the 

 different species enumerated by various authors, 

 writes as follows : — 



" Having enumerated the character stated to be 



^ It is well to know what is now usually meant by the term 

 species, and Dr. Gunther defines it as above. Formerly, 

 species signified an individual form with distinct and per- 

 manent characters ; but what is termed species now, would 

 be much simplified under the term, variety ; and so get rid 

 of a number of useless names, which confuse and mislead 

 the non-scientific naturalist. 



