EYES AND EYELIDS. 65 



apart as to be even directed slightly downwards. 

 But of all anomalies presented by the position of 

 the eyes of fishes, none is so extraordinary as that 

 of the Pleuronectes (such as turbot, flounders, soles, 

 &c.) in which the visual organs are placed, as it 

 were, one above the other, and both upon the same 

 side of the head. In certain species of eels and 

 Siluri, they are so small as to be scarcely visible ; 

 while in other groups, such as Priacanthus and 

 Pomatomus, they surpass in porportional diameter 

 whatever is known of the same organs in the higher 

 classes. It may indeed be said, in general, that 

 the eye of fishes is large, and that its pupil especi- 

 ally, is broad and open, a character probably con- 

 nected with the necessity of collecting whatever 

 dubious rays of light may penetrate the obscure 

 depth of waters. Fishes have no true eyelids. 

 The skin always passes over the eye, to which it is 

 slightly adherent ; and is for the most part suf- 

 ficiently transparent for the passage of the solar 

 rays. In some species, such as eels, it passes over 

 without the slightest fold or duplication ; while in 

 a few, for example, Gastrobranchus ccecus of Bloch, 

 it continues so opaque as entirely to conceal the 

 eye. In others, as the familiarly known herring 

 and mackerel, it forms an adipose fold both before 

 and behind ; but these folds are fixed, and being 

 unprovided with muscles, have no mobility. Sharks 

 have an eyelid, somewhat more moveable, on the 

 inferior margin of the orbit. The globe of the eye, 

 although furnished as in man with six muscles, is 

 scarcely moveable by voluntary action. One of 



