MODIFICATION OF THE EYE PEDUNCLES IN CYMONOMUS. 439 



On the Modification of the Eye Peduncles in 

 Crabs of the Genus Cymonomus. 



By 



£. Ray Laiikcstcr, M.A., LLr.D., F.R.S., 



Director of the Natural History Departments of the British Museum. 



Witli Plates 33 and 3i. 



My attention was drawn to the interesting subject which is 

 dealt with in the present article by a paragraph in Lord 

 Avebury's charming little book^ ' The Beauties of Nature.' 

 He there says (p. 331 of the last edition), " Sir Wyville 

 Thomson mentions a kind of crab (Ethusa granulata) 

 which, when living near the surface, has well- developed eyes; 

 in deeper water — 100 to 400 fathoms — eye-stalks are present, 

 but the animal is apparently blind, the eyes themselves being 

 absent ; while in specimens from a depth of 500 to 700 

 fathoms the eye-stalks themselves have lost their special 

 character, and have become fixed, their terminations being 

 combined into a strong pointed beak." When I came upon 

 this passage it occurred to me that possibly the crab was 

 large enough to form a suitable "exhibit" for the public 

 gallery of the Natural History Museum, and that if so the 

 three stages indicated in Lord Avebury's brief notice would 

 constitute a very intei'esting and striking demonstration for 

 the general public of the modification of the organ of sight 

 of Crustacea in relation to the presence or absence of light in 

 their environment. 



