28 BRITISH FRESH-WATER FISHES 
lakes and rivers can close an eye from the day it is hatched 
from the egg till the hour of its death. Man has been 
described as an animal that weeps, and makes others to weep ; 
but a fish can shed no tears, having no lachrymal duct. Never- 
theless, in the majority of fishes the eye is a very complex 
and highly developed organ. To compensate for the absence 
of eyelids, the skin of the head covers the eye, becoming 
perfectly transparent where it passes over the orb. Moreover, 
the cornea, or exposed part of the orb, is flat, instead of convex 
as in terrestrial vertebrates, and therefore less liable to receive 
external injury; but in the general arrangement of the 
component parts—pupil, iris, crystalline lens, sclerotic coat, 
vitreous humour, and retina—the eye resembles those of the 
higher animals. Dr. Giinther has shown by a vertical section 
magnified 350 times that the retina of a perch is not less 
complex than that of one of the higher mammals, composed 
of nerve cells, granular layers, and a layer of rods and cones, 
occupying the same relative positions to each other as they 
do in the human eye, and bearing similar proportion to each 
other. The presence of the rod-and-cone layer seems to 
justify the assumption that perch have a well-developed percep- 
tion of colour.* It should be mentioned as an interesting 
point in comparative anatomy that in the sub-class of Cyc/lo- 
stomata (lampreys), the optic nerves pass from the brain to 
the eyes without crossing—the right lobe being connected 
with the right eye and the left lobe with the left eye. In 
Teleostei (perch, etc.) they are crossed, the nerve from the right 
* The colour sense in fish has been the subject of much controversy 
among anglers, some of whom are anxiously particular about the precise 
hues acceptable to surface-feeding fish, My own experience goes to 
convince me that salmon, and even highly-educated chalk stream trout, are 
singularly indifferent to the colours of flies offered to them, taking a scarlet 
or blue fly as readily as one closely assimilated to the natural insect. 
Probably the position of the floating lure, between the fish’s eye and the 
light, interferes with any nice discrimination of hue from reflected rays. 
