THE CHAEACTEES OF THE DEEP-SEA FAUNA 75 

 and transmit their favourable variation in this respect 

 to their offspring, than their less fortunate neighbours. 

 Thus down to the depth of the limit of sunlight we 

 should expect to find, as we do find in fishes, large- 



eyed species. 



Beyond tlie limit of direct sunliglit the eyes would 

 be of very little use to tliem, the pigment would dis- 

 appear and the tissues become degenerate. This is 

 precisely, what has occurred in the genus Serolis. 



The disappearance of the sense of sight in the 

 animals of the deep sea is sometimes accompanied by 

 an enormous development of tactile organs. 



Thus, among fishes we find Bathypterois, a form 

 that possesses extremely small eyes, provided with 

 enormously long pectoral fin rays that most probably 

 possess the functions of organs of touch. 



Among the Crustacea we find the blind form, 

 Ga?ai/iofc^7itou,withanextraordinarydevelopment 



in length of the antenna, and Nematocarcinus. with 

 enormously long antennae and legs. 



The subject of the power of emitting phosphores- 

 cent light possessed by some deep-sea animals is much 

 more difficult to deal with. 



The presence of distinct organs in many of the 

 deep-sea fish that can only be reasonably interpreted 



