146 On the Salmon Tribe. 



for a consequence of physical causes ; let us not say that 

 trouts resemble each other so much because they originated 

 under uniform conditions ; let us not say they have uniform 

 habits because there is no scope for diversity ; let us not say 

 they spawn during winter, and rear their young under snow 

 and ice, because at that epoch they are safer from the attacks 

 of birds of prey ; let us not say they are so intimately con- 

 nected with the physical world, because physical powers called 

 them into existence ; but let us once look deeper, let us re- 

 cognise that this uniformity is imparted to a wonderfully 

 complicated structure : they are trouts with all their admir- 

 able structure, their peculiar back-bones, their ornamented 

 skull, their powerful jaws, their moveable eyes, with their 

 thick, fatty skin and elegant scales, their ramified fin rays, 

 and with all that harmonious complication of structure which 

 characterizes the type of trouts, but over which a uniform 

 robe, as it were, is spread in a manner not unlike an almost 

 endless series of monotonous variations upon one brilliant 

 air, through the uniformity of which we still detect the same 

 melody, however disguised under the many undulations and 

 changes of which it is capable. 



The instincts of trouts are not more controlled by climate 

 than those of other animals under different circumstances. 

 They are only made to perform at a particular season, best 

 suited to their organization, what others do at other times. 

 If it were not so, I do not see why all the diiferent fishes, 

 living all the year round in the same brook, should not spawn 

 at the same season, and finally be transformed into one type ; 

 have we not, on the contrary, in this diversity under identical 

 circumstances, a demonstrative evidence that there is another 

 cause which has acted, and is still acting, in the production 

 and preservation of these adaptations ; a cause which endowed 

 living beings with the power of resisting the equalizing 

 influence of uniform agents, though at the same time placing 

 these agents and living beings under definite relations to each 

 other \ 



That trouts are not more influenced by physical conditions 

 than other animals is apparent from the fact that there are 

 lakes of small extent and of most uniform features, in which 



