322 



THE EYE IN EVOLUTION 



is devoid of muscles and the pupil is slightly oval with the long axis 

 vertical, moving only passively when the lens moves in accommodation. 

 The retina is typically teleostean, and contains double cones (Fig. 374) ; 

 there are, however, no twin cones nor an area centralis. The optic 

 nerve is of the teleostean type, with a broad ribbon of nerve fibres 

 folded over itself in pleats within the tubular sheath. 



ANOMALIES IN THE EYES OF FISHES 



In a group so heterogeneous as the Fishes it is not surprising that 

 many modifications to the general form arise ; some of the most 

 important of these deserve a passing note. 



THE TUBULAR OR TELESCOPIC EYE 



We have already seen that lack of illumination in the abyssal 

 depths has led to the development of an immensely large lens to 



Figs. 376 to 379. — The Tubular Eyes of Deep-sea Fish. 

 Figs. 376 and 377. — The Hatchet Fish, Argyropelecus. 



Fig. 376. — In the larva the eve is directed forwards. 



Fig. 377. — In the adult the eyes are tubular and uijward-looking ; the body 

 is covered with luminous organs giving the scales a silvery gleam 

 (compare Fig. 892) (after Goode and Bean). 



Fig. 378. — Stylophorus paradoxus. An 

 inhabitant of the deep Atlantic. The 

 eyes are directed forwards and 

 sligVilly upwards (after Goode and 

 Bean, 1896). 



Fig. 379.— The giant-tailed fish, 

 Giganturus chuni. An inhabitant of 

 the deep Atlantic. The eyes are 

 directed straight forwards (from the 

 Valditia Reports). 



