THE INADEQUACY OF "NATURAL SELECTION" 811 



causes in operation, though the matter is presented as though 

 there were. 



But passing over this, let us now represent to ourselves in 

 detail this process which Prof. Weismann thinks will, in thou- 

 sands of generations, effect the observed reduction of the eyes : 

 the process being that at each successive stage in the decrease, 

 there must take place variations in the size of the eye, some larger, 

 some smaller, than the size previously reached, and that in virtue 

 of the economy, those having the smaller will continually survive 

 and propagate, instead of those having the larger. Properly to 

 appreciate this supposition, we must use figures. To give it every 

 advantage we will assume that there have been only two thou- 

 sand generations, and we will assume that, instead of being re- 

 duced to a rudiment, the eye has disappeared altogether. What 

 amounts of variation shall we suppose ? If the idea is that the 

 process has operated uniformly on each generation, the implica- 

 tion is that some advantage has been gained by the individuals 

 having the eyes ^Vo less in weight ; and this will hardly be con- 

 tended. Not to put the hypothesis at this disadvantage, let us 

 then imagine that there take place, at long intervals, decreasing 

 variations considerable in amount — say -fa, once in a hundred gen- 

 erations. This is an interval almost too long to be assumed ; but 

 yet if we assume the successive decrements to occur more fre- 

 quently, and therefore to be smaller, the amount of each becomes 

 too insignificant. If, seeing the small head, we assume that the 

 eyes of the Proteus originally weighed some ten grains each, this 

 would give us, as the amount of the decrement of 4^, occurring 

 once in a hundred generations, one grain. Suppose that this eel- 

 shaped amphibian, about a foot long and more than half an inch 

 in diameter, weighs three ounces — a very moderate estimate. In 

 such case the decrement would amount to -j-jVt of the creature's 

 weight; or, for convenience, let us say that it amounted to T oVo> 

 which would allow of the eyes being taken at some fourteen 

 grains each.* To this extent, then, each occasional decrement 



* I find that the eye of a small smelt (the only appropriate small fish obtainable here, 

 St. Leonards) is about j\-$ of its weight ; and since in young fish the eyes are dispropor- 

 tionately large, in the full-grown smelt the eye would be probably not more than ^o o of 

 the creature's weight. On turning to highly-finished plates, published by the Bibliogra- 

 phisches Institut of Leipzig, of this perenni-branchiate Proteus, and other amphibians, I find 

 that in the nearest ally there represented, the caducibranchiate asolotl, the diameter of the 

 eye, less than half that of the smelt, bears a much smaller ratio to the length of the body; 

 the proportion in the smelt being ^ of the length, and in the axolotl about ■£% (the 

 body being also more bulky than that of the smelt). If, then, we take the linear ratio of 

 the eye to body in this amphibian as one half the ratio which the fish presents, it results 

 that the ratio of the mass of the eye to the mass of the body will be but one eighth. So 

 that the weight of the eye of the amphibian will be but xsVo °f toat °f tne body. It is 



