NATURAL HISTORY OF THE SALMON. 77 



where is the evidence for saying that grilse are small in 

 the beginning of the season, large in the middle, and 

 small again at the close ? Mr. Mackenzie may be in 

 possession of such evidence, but he has kept it to him- 

 self. We also have some evidence on the point, of which, 

 in no expectation of gratitude, we shall give him the 

 benefit. On a series of years, the average weight of 

 the grilse captured on the Tweed fisheries was in the 

 month of June, 3 Ib. ll|-oz. ; July, 4 Ib. 5 oz. ; August, 

 4 Ib. 15 oz. ; September, 5 Ib. 12| oz. ; October, 6 Ib. 

 llf oz. These figures are refutatory of the statement 

 that grilse diminish in weight towards the end of the 

 season, though we are aware that it may, and sometimes 

 does happen, that there are great temporary variations, 

 caused by the differences of seasons affecting the tem- 

 perature of the atmosphere and of the water ; as, for 

 instance, in a warm summer the grilse of July or August 

 will be larger than in a cold summer. But the state- 

 ment, even if correct, would not help Mr. Mackenzie, nor 

 injure us. If it were true that grilse fluctuated in size 

 during the season, and were even smallest in the latest 

 months, the fact would prove nothing in favour of the 

 fish being a distinct species, and nothing against, but 

 rather something in favour of, their being adolescent 

 fish, born in one year, though with a difference of weeks 

 as to birth, and of various circumstances as to growth. 

 What we do see is, that (at least in the case of Tweed) 

 grilse go on increasing gradually in size to the end of 

 the fishing- season ; that increase, such as it is, being, we 

 maintain, caused mainly by many of the late-comers 

 having had a more protracted residence in the sea, where 



