812 THE POPULAR SCIENCE MONTHLY. 



would profit the organism. The economy in weight to a creature 

 having nearly the same specific gravity as its medium, would be 

 infinitesimal. The economy in nutrition of a rudimentary organ, 

 consisting of passive tissues, would also be but nominal. The 

 only appreciable economy would be in the original building up of 

 the creature's structures ; and the hypothesis of Weismann im- 

 plies that the economy of this thousandth part of its weight, by 

 decrease of the eyes, would so benefit the rest of the creature's or- 

 ganization as to give it an appreciably greater chance of survival, 

 and an appreciably greater multiplication of descendants. Does 

 any one accept this inference ? 



Of course the qualifications of data above set down can be only 

 approximate ; but I think no reasonable changes of them can alter 

 the general result. If, instead of supposing the eyes to have dis- 

 appeared wholly, we recognize them as being in fact rudimentary, 

 the case is made worse. If, instead of two thousand generations, 

 we assume ten thousand generations, which, considering the prob- 

 ably great age of the caverns, would be a far more reasonable 

 assumption than the other, the case is made still worse. And if 

 we assume larger variations — say decreases of one fourth — to occur 

 only at intervals of many hundreds or thousands of generations, 

 which is not a very reasonable assumption, the implied conclusion 

 would still remain indefensible. For an economy of ^-g- part of 

 the creature's weight could not appreciably affect its survival and 

 the increase of its posterity. 



Is it not then, as said above, that the use of the expression, 

 " natural selection," has had seriously perverting effects ? Must 

 we not infer that there has been produced in the minds of natu- 

 ralists, the tacit assumption that it can do what artificial selection 

 does — can pick out and select any small advantageous trait ; while 

 it can, in fact, pick out no traits, but can only further the devel- 

 opment of traits which, in marked ways, increase the general fit- 

 ness for the conditions of existence ? And is it not inferable that, 

 failing to bear in mind the limiting condition, that to become es- 

 tablished an advantageous variation must be such as will, other 

 things remaining equal, add to the prosperity of the stirp, many 

 naturalists have been unawares led to espouse an untenable hy- 

 pothesis ? — Contemporary Review. 



[To be concluded.] 



a liberal estimate, therefore, to suppose that its original weight in the Proteus was yoW o( 

 that of the body. I may add that any one who glances at the representation of the axolotl, 

 will see that, were the eye to disappear entirely by a single variation, the economy achieved 

 could not have any appreciable physiological effect on the organism. 



