74 



THE FAUNA OF THE DEEP SEA 



explain why it is that we do not find more examples 

 of it. 



If the animals that now live in the depths of the 

 sea are descended from the shallow-water forms of 

 bygone epochs, they must have passed through many 



Fig. 4. — Semi-diagrammatic sec- 

 tion through the eye of Sero- 

 lis sehytJiei., a shallow-water 

 species (4-70 fathoms), c.lens; 

 V, crystalline cone; E, rhabdom; 

 N, nerve. (After Beddard.) 



Fig. 5. — Diagrammatic sec- 

 tion of the eye of Serolis 

 brovtlcijana, a deep-sea 

 species (400-1,975 fa- 

 thoms), showing the de- 

 generate character of the 

 eye. The corneal facets 

 c, and the crystalline 

 cones V, are the only 

 structures that can be re- 

 cognised. (After Beddard.) 



different habitats with diminished light until they 

 reached their present dark abode in the abyss. 



In every new region they came to, the forms with 

 larger and better eyes would be at an advantage in 

 the fainter light, and would be more likely to survive 



