394 FISHES CHAP. 
cylinders, each terminating in a strongly convex cornea (Fig. 
227). The eyes are directed either upwards or forwards, 
and, as their long axes are parallel in either’ position, it 
is probable that these Fishes are capable of binocular vision. 
In the young of certain Teleosts occurring in the Antarctic 
and Indian Oceans the large eyes are situated at the ex- 
tremities of extraordinary long stalks extending from ‘the sides 
of the head. 
In the quasi-parasitic Cyclostome, JMyxine, and in many 
Teleosts belonging to widely different families, which live at 
great depths in the sea or 
inhabit subterranean waters, 
the eyes suffer from disuse 
and degenerate in structure. 
The influence of a deep-sea 
habitat on the eyes of Fishes 
is somewhat varied. The 
eyes are often small. <A few 
abyssal Fishes are totally 
blind, and no external trace 
of eyes can be seen (Fig. 
430). In such Fishes com- 
' pensation is often afforded 
Fic. 226.—Vertical section of the eye of Salmo ; 
fario (semi-diagrammatic). arg, Argentea ; by an extraordinary develop- 
ch, choroid ; ch.gld, choroid gland ; cz, ment of tactile organs in 
cornea ; cp.hal, campanula Halleri ; 77, iris ; ‘ = 
/, lens ; opt.nv, optic nerve ; pg, pigmentary the form of long barbels, or 
layer ; pr, processus falciformis ; rt, retina ; of trailing filaments derived 
sel, sclerotic. (From Parker and Haswell.) Sues, 
from the median or the paired 
fins (Fig. 371, B). Many deep-sea forms possess eyes of the 
normal size, or even exceptionally large eyes, probably because 
either they occasionally migrate towards the surface, or else they 
possess phosphorescent organs and are able to see by the aid of 
the light they themselves emit. A blind Siluroid (Amiurus 
nigrilabris) frequents the cave streams of Pennsylvania, and 
many members of the same family which live in muddy waters 
have very small or even minute eyes. One of the Gobies (7yphlo- 
gobius),” which buries itself in the sand, or is found under stones in 
the holes of a burrowing Crab on the coast of California, is also 
scl cp.hal 
! Chun, Aus den Tiefen des Weltmeeres, Jena, 1900, p. 534. 
° Ritter, Bull. Mus. Comp. Zool. xxiv. 1893, p. 51. 
