13 



THE FINS OF THE SALMON I D/E. 



A PAPER READ BY 



E. F. T. BENNETT, Esq., 

 May. 23/7/, igoo. 



An examination of the fins of a salmon open out a 

 multiplicity of questions so endless that it is possible only 

 in a short paper to call attention to their various forms, and 

 to suggest their different movements. 



The adipose fin set above the tail is apparently useless, 

 but serves to remind us that in ages long past it was a useful 

 fin, and that, as time went on and the character of the 

 waters inhabited by the fish changed, this fin was no longer 

 necessary, and so lost its original structure and power. 

 That it was a rayed fin once, there can be little doubt. 



The dorsal and anal fins act as a top and bottom keel, 

 and can each be erected or depressed at the will of the fish. 

 It will be noticed that a wavy motion is communicated to 

 the edge of the tough membrane that covers the framework 

 of these fins as well as of all the others. As this motion is 

 observable in the stillest water, we can see that it is the 

 result of a ceaseless nervous action that adapts the fins to 

 be constantly balancing the fish. 



The dorsal, anal, and adipose fins are all set vertically. 



The caudal fin is made up of two similar fins, and is also 

 set vertically. This fin is the only true propeller of the fish, 

 all the others being laid close to the body when great speed 

 is desired. In considering this fin as a propeller, it must be 

 borne in mind that a sinuous motion affects the whole after- 

 part of the fish, induced by the great muscles called the flesh 

 of the creature, which are stretched along its whole body 

 from the back of the head to the root of the tail. The action 

 of the tail is fairly well imitated by a sculling oar at the 

 stern of a boat. There are certain almost unless fish in 



