DEEP-SEA FISHES 



399 



ants. Ichthyologists are coming to believe that the ubiquitous cod family 

 originated from the grenadiers or 'rat's-tails' — developing a brand-new 

 tail fin, and coming back up onto the continental shelf. If any blind 

 abyssal fishes should return to shallow water, they could take up only 

 habitats in which their blindness was no handicap. It is barely possible 

 that the reef brotulids, and those which have gotten into caves (p. 388), 

 were blind before ever they parted company with their many relations 

 which are still on the ocean floor. 





,-<-5J 



■(0^(^y-i^ 





:C'%^^s^-^-^-':S--^.^:' 



.■0'. 



Fig. 135 — Retinae of bathypelagic teleosts. 



a, a stemoptychid, Argyropelecus hemigymnus. X 420. After Contino. 

 Lampanyctus joubini. x 500. After Verrier. 



myctophid, 



In large-eyed deep-sea fishes, everything possible has been done to in- 

 crease the sensitivity of the eye to light. The pupil and lens are relatively 

 and absolutely enlarged, cones have been largely or wholly eliminated 

 from the retina, and the rods have been stretched to great lengths (Fig. 

 135) and enormously multiplied. The retinas of Etmopterus and the 

 chimaeras have ten or more times as many rods per unit area as do those 



