EYES OF DEEP-SEA ANIMALS 1 03 



seems good reason to hope that in time we may win from the 

 deep the nearest living representations of many creatures 

 which once occupied a large place in the seas, but now have 

 abandoned the fields of more active combat, which are usu- 

 ally the seat of the greatest advance. 



In the profounder seas the invertebrate life appears to 

 have a larger share than is secured by the vertebrate, or back- 

 boned animals ; yet there are a number of fishes known in 

 these depths, and it seems likely that these tenants of the 

 deep sea may be numbered by thousands of species. Among 

 the finned tenants of the deeper parts of the ocean, we find 

 some startling departures from the types with which we 

 are familiar in coastal waters. In general shape they differ 

 little from their kindred which dwell in the sunlit shallows. 

 The differences are largely in the mechanism of the senses, 

 especially of the eyes. These organs undergo surprising 

 variations with reference to the enduring of the darkness of 

 these deeps. In certain of the species the sight not only 

 fails, but the visual apparatus entirely disappears ; in others 

 the eyeballs become very much enlarged and the nervous 

 apparatus increased ; they are evidently arranged to catch 

 mere glimpses of light. As it is certain that no trace of sun- 

 light can ever penetrate through the deep which overlies the 

 realm where these animals dwell, the adaptation of these eyes 

 to the needs of difficult vision at first appeared to be a very 

 inexplicable matter. Some recent discoveries provide us with 

 what seems to be an adequate explanation of the enigma. 

 It has been found that certain of the denizens of the deep 

 sea-floors have phosphorescent parts of their bodies which 

 serve to crive lieht in the manner in which it is yielded by 

 the familiar fire-flies and glow-worms. The end secured by 



