62 The Life Story of the Fish 



pelled mainly by its dorsal fin, which waves so fast that it 

 looks like a whirling propeller. 



The conclusion which we cannot escape as the result of all 

 this discussion is the one which we touched on earlier, that 

 fins are not indispensable to most fish. The ventrals give the 

 secret away; the manner in which they shift about from one 

 part of the body to another, and vanish entirely in some 

 species, is clear proof that the fish does not know what to do 

 with them. Here is where those who believe in a wise and 

 far-seeing and all-providing directing Force have an oppor- 

 tunity for propaganda. The fish can get along without fins, 

 but the mammal cannot get along without limbs. Why, then, 

 was the fish given fins, unless it was prearranged In the 

 master plan that he should some day come out on land and 

 use them to walk with? 



It is a good argument. Its supporters may be right, and 

 certainly no one is in a position to go so far as to state flatly 

 that they are wrong. However, anyone wishing to give con- 

 sideration to the other side might point out that not much 

 foresight was shown in making preparations for that sacro- 

 iliac joint. He might suggest that perhaps it was because the 

 fish had fins that it was able to become a quadruped, rather 

 than that it was given fins in order to become a quadruped. 

 He might ask what part, if fins were given fish in prepara- 

 tion for quadruped use, the dorsal and anal played in the 

 plan. And this would bring him to the fin-fold theory, which 

 holds that fins came into being solely through the action of 

 the environment on the material. It holds that the earliest 

 fishlike creatures had no fins, but that, as they moved about, 

 the flow of the water against their soft bodies pressed out 

 ridges or keels along their upper and lower surfaces. One 

 ingenious experimenter has taken a penholder, coated it with 

 soft wax, and by moving it back and forth in the water pro- 

 duced just such "fin-folds." According to the theory, the 



