1 84 THE RIVER-SIDE NATURALIST. 



convinced that salmon see the fly when it is in a position 

 exactly over their heads. Actual observation soon taught 

 me that much. Often have I been looking through bino- 

 cular glasses and seen salmon behind perpendicular rocks 

 take notice of flies properly presented immediately above 

 them, the fisherman having payed out his line for the pur- 

 pose. What happens is this : if the fly is one they mean 

 taking, the dash after it is so instantaneous and sudden 

 that I have never once been able to see exactly what they 

 do. But if the fly is one they merely inspect and they 

 invariably do so unless they have been pricked or over- 

 thrashed they turn their heads sideways towards it, so 

 as to get a better view with one eye. So far as can be 

 judged from practical experience, I am also convinced that 

 salmon are apt to discriminate with astonishing precision 

 one coloured fly from another ; and, in my opinion, they 

 readily detect the least variation in the composition of a fly. 

 It must be well known to old and observant hands that the 

 small difference in size of a startling feather, such as that 

 of the jungle-fowl, affects the fish, and as frequently influ- 

 ences their movements." 



There is another organ in fish which, having a great 

 deal to do with the movements of many of them, is worth 

 a few moments' consideration the swimming or air bladder. 

 This is placed beneath the spine, and is firmly bound down 

 by the peritoneum. The outer coat is generally very 

 strong, and composed of a peculiar fibrous substance, which, 

 when obtained from some fishes, is the isinglass of com- 

 merce. It is lined internally with a very delicate and thin 

 membrane. The shape varies in different families. In the 

 perch it is a simple sac closed at both extremities. In the 

 carps it is divided into two portions an anterior and pos- 

 terior with a narrow constricted communication between 

 the two. But whatever may be the shape, it serves a 

 specific purpose, viz., to alter the specific gravity of the 

 fish, so that it may rise or sink in the water. By simply 

 compressing this bladder by approximating the walls of the 

 abdomen, or by means of a muscular apparatus provided 

 for the purpose upon a principle with which every one is 



