I04 



SEA AND LAND 



these light-givinc^ parts is probably the attraction of the 

 sexual mates of the creatures. In the utter darkness of the 

 ocean this indispensable end could be so well attained in no 

 other way ; even the fishes appear to have this beautiful pro- 

 vision for avoiding one of the most serious evils of the dark- 

 ness in which they are compelled to exist. 



It is evident that the fishes with large eyes would also 

 have a decided advantage in the pursuit of food, for their 



keen vision would 

 enable them to dis- 

 ,,^r3r!^ cern the glimmer 

 of the phosphor- 

 escent light for 

 some distance 

 through the still, 



A Member of the Genus Scopelus cleaT WatPT Thc 



Showing the large eyes common in fishes which swim in the depths rl iffinill-\7' nonipc in 



of the sea to which the light of the sun does not penetrate. The eyes J 



are probably specially adapted to perceiving the phosphorescent glow fl-,/^ rncp> nf tlTnc:F> 

 of various animals. 



fishes which under 

 the same general conditions of existence in darkness, com- 

 bined with the same need of food, and of finding their 

 mates, have not only failed to better their sight, but have 

 abandoned it altogether. There is, perhaps, no other simple 

 instance in which we may so well perceive the cardinal diffi- 

 culty which the extreme selectionist encounters in his effort 

 to explain all the complications of the organic world by the 

 single hypothesis of the survival of the fittest. Here are 

 two groups of like creatures introduced to the conditions of 

 utter darkness after long ages of experience in the realms 

 of light ; under circumstances which, so far as we can perceive, 

 are absolutely identical, the creatures enter upon v»'idely diver- 



