FISHES. 



331 



eye, is so similar to the rest of the skin, that we observe 

 hnes upon it, which form the same compartments as on the 

 body of the fish. Some fishes may be considered as blind, 

 as the Myxine coeca, in consequence of the uniform opacity 

 of the skin in passing over the eye. 



The form of the eye in this tribe of animals is nearly 

 that of a hemisphere, the plane part of which is directed 

 outwards, and the convex inwards. In the Ray, the supe- 

 rior part is also flattened, so that the vertical diameter is to 

 the transverse as 1 to 2. This flatness of the exterior part 

 of the eye is compensated by the spherical form of the 

 crystalline lens. This body is more dense in fishes than in 

 land animals *. 



• Monro found the crystalline lens of an ox to be 1104, while that of a 

 cod was 1165, water being reckoned at 1000. The crystalline lens projects 

 through the pupil, and leaves scarce any space for the aqueous humour. The 

 vitreous humour is proportionally small. The portion of the axis occupied by 

 each of the three humours of the eye, in the herring, for instance, may be 

 expressed in fractions, as follows: aqueous humour i, crystalline lens J 

 and the vitreous humour i . The spherical form of the crystalline lens has 

 been already stated ; but the following Table, from the observations of Pe- 

 tit and CuviER, will exhibit more clearly the proportion between the axis 

 and the diameter in a few species. 



The axis is to the diameter in the 



Salmon as 



Sword-fish, 



Shad, 



Pike, 



Barbel, 



Carp, 



Mackrel, 



Whiting, 



Shark, 



Ray, 



Herring, 



Tench, 



Ed, 



Conger, 



