26 SALMON FISHING IN THE TWEED 



The salmon has a peculiar formation of the eye, 

 the crystalline lens having the fibres of which it is 

 composed arranged as in the annexed sketch A, the 

 line m n being horizontal on one side, and vertical 

 on the other ; whereas in many of the trout species 

 the fibres are arranged as at C, crossing one another, 

 or rather meeting at two opposite poles, like the 

 meridians of a globe, the line joining the two poles 

 being the axis of vision of the eye. 



" After examining the lenses of the parr you sent 

 me," says Sir David Brewster in a letter now before 

 me, " I found the structure to be exactly the same 



as that of the salmon. I have frequently had 

 occasion to mention the proofs that you gave me 

 of the identity of the parr with the salmon, and to 

 mention my own experiments on the lenses as 

 confirmatory of your opinion that the parr and the 

 salmon are one and the same species." 



Salmon begin spawning as early as September, 

 and continue to do so throughout the winter 

 months ; December, January, and February being 

 the principal ones for that operation. They con- 

 tinue on the spawning ground, or rade, as it is 

 termed in Scotland, also during the spring months, 

 though in diminished quantities. I myself have 

 caught full roeners, as they are called, in the month 

 of May in the Tweed. Now we know from the 



