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effect the necessary refraction of the rays in them 

 principally by the latter ; the iris, moreover, in 

 fishes, is almost entirely motionless, so that the 

 size of their pupil is always nearly the same. In 

 general they are destitute also of proper eye-lids ; 

 the eye-ball moving behind the common integu- 

 ments to which it is attached by very relaxed 

 cellular tissue as behind a piece of thin glass or 

 horn. In some few fishes, however, as the suri- 

 fish, Cuvier has found a regular circular eyelid, 

 the opening in which is contracted by a sphinc- 

 ter, arid expanded by five radiating muscles. 

 The direction of the eye- balls is usually out- 

 wards ; but in some few fishes, as the star-gazer, 

 it is upwards ; and in the plaice, flounder, dab, 

 halibut, turbot, &c., the eyes are placed both on 

 one side of the body an isolated instance, ac- 

 cording to Blumenbach, of a want of uniformity 

 in the two sides. The object, however, of such 

 an arrangement in this instance is obvious, for 

 as these animals, destitute as they are of an air- 

 bladder, are destined to continue always with 

 one side in the mud at the bottom of the water, 

 an eye on this side would have been superfluous 

 to them. The most singular situation of the eye- 

 ball, however, is that of the Surinam sprat, the 

 orbit extending in this fish, so far above the head, 

 that the eye, as the animal swims near the sur- 

 face, is partly in and partly out of the water ; 

 arid all its parts correspond with this strange 

 structure, the pupil being partially divided into 

 an upper and a lower portion, and the lens con- 



