DEEP-SEA FISHES 



401 



ma) , the juvenile eye is normal or nearly so in form, and slowly becomes 

 tubular during growth (Fig. 137). 



In some forms {e.g., Dolichopteryx, Argyropelecus, Opisthoproctus — 

 Figs. 137, 138a), the optic axis of the adult eye points straight upward. 

 Here, the lens has moved dorsad and looks through transparent sclera, 

 not true cornea, the iris and the superior ciliary body disappearing to 



Fig. 137 — Development of the tubular eye of Argyropelecus hemigymnus. 

 X 14. After Contino. 



a, 7.5mm. larva — 'praescopic' stage (the eye aims forward), b, 10.3mm. metamorphosing 

 larva — lens commencing its dorsad migration, c, 10.0mm. metamorphosing larva — lens 

 continuing migration, d, 7.5mm. postlarval growth-stage — ^final condition (the eye, now 

 tubular, aims upward); the ventral, pigmented organs are photophores. 



allow this. The chief retina, remaining in the floor of the tube, represents 

 the original inferior periphery of the retina. The optic nerve thus comes 

 away from the mesial edge of the definitive retina, not from its center. 

 A portion of the original superior retina often remains, applied to the 

 lens as an accessory retina (Fig. 136), which is most useful for vision at 

 a distance (see p. 257). The lens becomes so large that the iris is elim- 

 inated, the lens itself serving as a pupil. There is little or no possibility of 



