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 Cyclo- 

 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 

 'feleostei (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. 



