328 LAKE SUPERIOR. 



mouth is large, their jaw strong, their teeth powerful, to enable them 

 to secure with ease the scanty prey with which they meet in these 

 deserts of cold water, and nevertheless, though we cannot but be 

 struck by the admirable reciprocal adaptation between the structure 

 of the northern animals and the physical condition in which they 

 live, let us not mistake these adaptations 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 connected 

 with the physical world, because physical powers called them into 

 existence ; but let us at once look deeper ; let us recognize that this 

 uniformity is imparted to a wonderfully complicated structure ; they 

 are trouts with all their admirable structure, their peculiar back 

 bones, their ornamented skull, their powerful jaws, their movable 

 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 rooe, 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 organiza- 

 tion, what others do at other times. If it were not so, I do not see 

 why all the different 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 an- 

 other 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 ? 



