154 ACQUIRED CHARACTERS SEC. 



The causes of this effect of practice lie firstly in the in- 

 creased supply of blood which it produces, and secondly in 

 the more delicate adjustment of nervous and muscular action. 



That characters acquired through use or disuse are in- 

 herited, and must therefore aid in the formation of new species, 

 can, I believe, be proved more easily than any other of the 

 propositions I am maintaining. If I were to bring together 

 all the facts which could be used as evidence on this point, I 

 should never come to the end of them, for I should have to 

 refer to all the facts of comparative anatomy and physiology. 

 But I intend to show in particular that use and disuse by 

 themselves must lead to the formation of new permanent 

 characters, without the aid of selection, for even this I hold 

 to be a physiological necessity. 



Lamarck long ago explained the degeneration of the eyes 

 in animals living in darkness by disuse. 



But how are eyes evolved ? 



The pigment-spots which at the present day are the only 

 representatives of these organs in many animals show evi- 

 dently the first stage of their evolution. 



The stimulus of light acting upon spots of the outer skin 

 specially suited for seeing, i.e. for " feeling at a distance," has 

 produced a deposition of pigment in these spots, because they, 

 originally endowed only with the sense of touch, have con- 

 stantly been directed towards the light in order to receive 

 the more delicate stimulus of the ether waves. Pigment 

 cannot have been the primitive organ of sight, nor can it at 

 present, in any instance, be itself such an organ. But pigment 

 is so far absolutely necessary for sight that it serves to separate 

 the rays of light falling on the nerve-endings. Pigment is 

 deposited around primitive tactile cells, and separates each 

 one from its neighbours, or it is deposited in some of the 

 touch -cells, leaving one free here and there. The touch-cells 



