PLATE 12 



VIEWS OF SPECIMENS 10 AND 11 



10 a After fourteen days on white marble bottom. 



11 a After fifteen days on white marble bottom. (Both of these fishes appear 

 much too dark). 



116 Showing possible effects of black specks in the white field. 



10 6-11 c Showing condition of former fish, after thirteen days on the dark sand 

 as compared with the latter, which had just been transferred to this. 



10 c-11 d Taken on gray bottom (gray of the same shade as in ii). 



10 d After six days on jet-black (magnetite) sand, following long sojourn on 

 white and gray bottoms. 



10 e After blinding, during recently acquired dark condition, following long 

 sojourn on pale bottoms. The result is a return to the pale phase. 



11 e After eleven days on jet-black sand 



502 



