680 



THE EYE IN EVOLUTION 



Opisthoproctus 



direction ; they thus retain an extensive panoramic field at the 

 expense of a much larger blind area below, where, resting on or skim- 

 ming near the bottom, vision is in any event useless (Fig. 816). In 

 other upward -looking fishes such as the stargazer (Astroscopus, 

 Uranoscopus, etc.) and some abyssal types such as Opisthoproctus, the 

 dorsal binocular field may vary between 25° and 40° or even more 

 (Fig. 901). A few pelagic and surface fishes have their eyes canted 

 downwards to joroduce a small ventral binocular field within which 

 much of their predatory interests lie (the needle-fish, Belone ; the 

 flying-fish, Pantodon). 



Fig. 818. — The Pipe-fish, Stnonathus. 



Showing the frontally directed eyes to allow accurate binocular vision 

 in the region of the upturned jaws (seen in profile in the lower figure). 



Few fishes have forward-looking eyes ; such a configuration occurs in some 

 deep-sea Teleosts provided with tubular eyes {Qiganturus, etc.),^ but this overlap 

 of two small fields is probably a device to improve sensitivity in the darkness 

 of the abyss (Weale, 1955). A frontal direction of the eyes with well-developed 

 binocularity may, however, be adopted for reasons of space -perception in 

 the jaipe-fish, Syngnathiis (Fig. 818), As this fish lies immobile on the bottom 

 it catches its prey by opening its jaws just as its victim floats above its mouth ; 

 the forward-looking eyes with their temporal foveas should allow accurate 

 binocular vision in the region of the upturned jaws which protrude far forwards 

 at the end of the elongated snout. 



BINOCULAR FIELD 



Fig. 



28- 

 BLIND AREA 



819. — The Binocular Field of the Lizard, Lacebta. 

 1 p. 322, Fig. 379. 



