64 THE SALMON. 



then, so to speak, come all at once ; from which two 

 facts, we submit, it is a fair inference that the one is an 

 adult fish, capable of ascending at any time, and that 

 the other is a young fish which first attains to the 

 capacity of ascending at that season at which its ascent 

 is practically found to begin. Or put it thus the 

 difference in the time of ascent points to the inference 

 that salmon are the produce of several years, and grilse 

 of only one year. It may be possible to dispute the 

 inference ; but it is necessary, to a fair discussion of the 

 question, that these facts should be looked at, and, if 

 possible, fitted with some other explanation. 



It is the chief defect of Mr. Mackenzie's argument, 

 that he not only overlooks these and similar facts, but 

 founds upon assumptions to the contrary. Thus, he 

 begins by saying, that " a grilse's instincts, in some 

 respects, are different, though its habits are precisely the 

 same ;" a proposition which, if it does not contradict 

 itself, is at least contradicted by what follows : " Ex- 

 perience shows us that salmon, impelled by their in- 

 stinct, leave the sea for their home, or rivers in winter 

 and spring, whereas the grilses do not leave the sea for 

 the rivers until summer ; clearly showing that the one is 

 a spring, and the other a summer fish." How the two 

 fish thus described can be spoken of as being of " pre- 

 cisely the same habits," is perplexing ; yet, though it 

 might seem at first sight that the greater the difference 

 of habits the better for Mr. Mackenzie's theory of two 

 different species, it is yet a fact that, in the above pas- 

 sage, he under-states, as well as mis-states, that differ- 

 ence. The difference is not that the salmon is " a spring 



