Framework 59 



medium through which he has to push himself, and of the 

 fact that amphibians and reptiles, which are looked on as 

 higher animals, cannot go as fast, thirty miles an hour is not 

 so bad for the poor fish after all. 



It was formerly held that the caudal fin, at the end of the 

 fish's tail, was its most important instrument in swimming. 

 The idea seemed plausible, and was for a long time accepted 

 by many people. Then there came a man who wondered. 

 He took two identical fish. From one he amputated the 

 caudal fin. This may sound like a serious operation, but it is 

 in reality very simple, for fishes' fins do not bleed, and all 

 that is necessary is to take a pair of scissors and trim off the 

 undesired part, just as you trim excess material off a piece 

 of cloth. He placed them both, the fish with and the fish 

 without a tail fin, at one end of a tank, and slapped the tank 

 sharply with his hand to frighten them. Both scurried off 

 for all they were worth, and they reached the other end of 

 the tank at precisely the same instant. The caudal fin may 

 make it easier for the fish to swim, but it is the muscular 

 action of the body which really accomplishes the result. 



To determine the importance of the other fins, he carried 

 out similar experiments. It had been stated that the dorsal 

 and anal act as keels, to keep the fish straight up. He cut 

 off both of these, and found that while the fish rolled a 

 little at first, it soon learned to get on without them. He then 

 cut all the fins off, and found that even in that denuded 

 state the fish could navigate. He did find, though, that the 

 pectorals and ventrals play a part in maneuvering. In straight 

 swimming they are folded back; when the fish wants to make 

 a quick stop, it opens them out, and they act as brakes. When 

 it wants to turn, it uses them on one side or the other as 

 rudders or pivots. The primitive fish, like the salmons and 

 the tarpon, have not much control over the brakes. They 

 are apt to swerve aside to avoid an object, instead of coming 



