90 



THE EYE IN EVOLUTION 



Figs. 64 to 67. — Pigmentary Changes with Light Intensity 

 IN A Sea-urchin. 



Fig. 65. 



X / 



Fig. 66. 



Fig. 67. 



To show the variation of pigmentation in a young specimen of Diadema 

 antiUarum. In the hght-adapted phase the animal appears uniformly black 

 owing to the dispersion of melanin pigment (Fig. 64). In the dark-adapted 

 phase the melanin recedes from the aboral surface leaving beautifully defined 

 patterns of white lines and a ring, an effect due to the concentration of 

 pigment (Fig. 65). 



In older specimens, the changes are less marked (Figs. 66 and 67) 

 (N. Millott). 



