I3 2 Evolution and Adaptation 



surfaces of each layer slowly changing in form. Further we 

 must suppose that there is a power, represented by natural 

 selection or the survival of the fittest, always intently watch- 

 ing each slight alteration in the transparent layers ; and care- 

 fully preserving each which, under varied circumstances, in 

 any way or in any degree, tends to produce a distincter 

 image. We must suppose each new state of the instru- 

 ment to be multiplied by the million ; each to be preserved 

 until a better one is produced, and then the old ones to be 

 all destroyed. In living bodies, variation will cause the 

 slight alterations, generation will multiply them almost infi- 

 nitely, and natural selection will pick out with unerring skill 

 each improvement. Let this process go on for millions of 

 years; and during each year on millions of individuals of 

 many kinds ; and may we not believe that a living optical 

 instrument might thus be formed as superior to one of glass, 

 as the works of the Creator are to those of man." 

 We may conclude in Darwin's own words : — 

 " To arrive, however, at a just conclusion regarding the 

 formation of the eye, with all its marvellous yet not abso- 

 lutely perfect characters, it is indispensable that the reason 

 should conquer the imagination ; but I have felt the difficulty 

 far too keenly to be surprised at others hesitating to extend 

 the principle of natural selection to so startling a length." 



The electric organs, present in several fish, offer a case 

 of special difficulty to the selection theory. When well 

 developed, as in the Torpedo and in Gymnotus, it is conceiv- 

 able that it may serve as an organ of defence, but in other 

 forms the shock is so weak that it is not to be supposed that 

 it can have any such function. Romanes, who in many ways 

 was one of the stanchest followers of Darwin, admits that, so 

 far as he can see, the evolution of the electric organs cannot 

 be explained by the selection theory. Darwin offers no 

 explanation, but bases his defence on the grounds that we do 

 not know of what use this organ can be to the animal. 



