FISH IN GENERAL. 75 



and closely approximated, in others they are far apart, and 

 directed even somewhat downwards ; but the most extraor- 

 dinary positions are those noticed in pleuronectes, where both 

 are placed on the same side of the head, one above the other. 

 In some species of the eel and silurine genera, they are so dimi- 

 nutive, as scarcely to be seen, in others, as is the case with 

 priacanthi and pomatomi, they are of a diameter proportion- 

 ably larger than in any other known animal. In general fish 

 have large eyes, and in particular the pupil is very broad and 

 open, such as we would expect it to be for creatures who 

 require great powers of vision, in the deep where light pene- 

 trates scantily. 



The eye has no real eyelids, the skin passing over it, mostly 

 in a transparent form, to admit light, is occasionally opaque, 

 as in the cecilioe and gastero-branchi, and conceals the vestige 

 of the eye altogether. It is without a fold upon the eyes of 

 eels, but forms a kind of adipose doubling before and behind 

 on those of mackerel and herrings. In sharks the fold is 

 more moveable, and in diodon luna it is puckered round the 

 eye, and inwardly furnished with fibres, forming a kind of 

 sphincter, counteracted by others in a radiating direction. 



The eye-ball is capable of little motion ; as in man, it is 

 furnished with six muscles, four direct and two oblique ; but 

 the superior oblique wants the pulley to change its direction 

 as in quadrupeds, and the funnel shaped muscle is also 

 wanting. The vacant space between the orbit, the muscles, 

 and the eye-balls, is occupied by a soft cellulosity, replete 

 with gelatinous fluid, but there is no lachrymal gland, or 

 puncta, which, in truth, would be superfluous to animals whose 

 eyes are constantly bathed by the element they inhabit. Rays 

 and sharks have the eye-ball fixed upon a moveable carti- 

 laginous pedicle. The anterior surface of the eye is generally 

 plain, or but slightly convex, and the aqueous humour not abun- 

 dant; the rest of the ball is more or less spherical, only some- 



