214 METAMORPHOSIS AND 



would appear impossible to believe that the action of 

 light was the cause of the development of pigment on 

 the lower sides of normal specimens in my experi- 

 ments. To some it may be so, but in my own 

 opinion the one fact is as certain as the other. I 

 believe the two facts can be reconciled. I had one 

 specimen of Plaice in the living condition which had 

 the middle third of its upper surface white, and 

 the whole of the lower side white as usual. This 

 specimen was kept for 4J months with its lower 

 surface exposed to light and the upper side shaded. 

 At the end of that period there were numerous small 

 patches of pigment scattered over the lower side 

 principally in the regions of the interspinous bones, 

 above and below the lateral line. In the area of the 

 upper side, which was originally unpigmented, there 

 were also numerous small pigment spots. I believe, 

 therefore, that in this case there were determinants 

 for absence of pigment not only on the lower side but 

 on part of the upper side also, and that so long as 

 light was excluded from the lower side the patch on 

 the upper side remained unpigmented in sympathy. 

 When the congenital tendency of the determinants 

 on the lower side was overcome by the action of light, 

 the white patch on the upper side also began to 

 develop pigment. 



Lastly, I may refer again to the specially abnormal 

 Turbot mentioned above. In this case the lower side 

 was over the greater part pigmented and the upper 

 side white, and this would appear to contradict the 

 conclusion just drawn concerning the piebald Plaice. 

 But this Turbot was only 4*4 cm. long, and is the 

 only case known to me where so much of the lower 

 side was pigmented with the upper side almost 



