220 THE THEORIES OF EVOLUTION 



fall to the bottom and remain on one side the rest of 

 their lives. The side on which they rest being de- 

 prived of light remains uncoloured. At the same 

 time the eye on the lower side passes gradually around 

 or through the forehead to join its fellow on the upper 

 side. Cunningham took young fish two-thirds of an 

 inch or so in length, but having begun to undergo their 

 metamorphosis, that is, already accustomed to lying 

 on one side. The pigment was already abundant on 

 the upper side while the lower side remained uncol- 

 oured. He put those fish into an aquarium lighted 

 from below by means of mirrors and covered with an 

 opaque lid, shutting off all light from above. Several 

 other fish taken from the same school were kept under 

 normal conditions for comparison. 



A month and a half after Cunningham examined 

 the two lots and found very little difference between 

 them; in the one as in the other the lower side was 

 greyish white. Pigment did not appear in the fish 

 under observation, although they were placed under 

 conditions which should have caused it to appear. A 

 certain distribution of pigment cells determined in the 

 ancestral series by external conditions was maintained 

 by heredity. 



Later on, however, actual conditions seemed to as- 

 sert their influence. Two months afterward, when the 

 death of the fish put an end to the observations, Cun- 

 ningham noticed in a number of individuals a few 



