506 THE OCEAN WORLD. 



microscopic crystals, presents the appearance of a gold or silver-coloured 

 coating, which gives to the iris that extraordinary brilliancy which 

 belongs to the fish's eye. The crystalline lens is voluminous, spherical, 

 and diaphanous. When the fish is cooked, the crystalline lens con- 

 stitutes that opaque and hard white substance which often comes 

 under the teeth in eating fish of a certain size. Cuvier suspected, 



what anglers now know to be true, that those 



active chasseurs of the deep saw far and very 



clearly.* 



If fishes have great eyes, they have, on the 



other hand, very small ears. This organ, it is 

 Fig. 344. Teeth of the Bream. f oun(ij hag no ex t er i or opening. It forms a cavity 



in the interior of the cranium, which is far from presenting the com- 

 plicated structure of the ear in mammifers 

 and birds. In spite, however, of the imperfect 

 structure, fishes are sensible to the least 

 noise. In consequence, silecce is a rigorous 

 law with the fisherman. 



The dimensions of the mouth and teeth 



Fig. 345. Teeth of the Carp. ^ ^ yariable ^ figheg . thege organg ^ 



in proportion to their voracity, which in many of these beings is 

 very great. The form and development of the buccal pieces are also 

 very various. Some species are toothless, but in most fishes the 



* Dr. Fripp's theory of the properties of the fish's eye is very plausible. 



1st. That the fish's eye in its normal state is arranged for the vision of near objects, 

 and that the great refractive power of a prolate spheroid lens, such as exists in the 

 fish, is adequate to the production of a picture at short focal distances, even with rays 

 of light passing through so dense a medium as water. 



2nd. That there is no accommodation of the fish's eye for extended limits of vision. 



3rd. That the passive state of the fish's eye, being that in which it is enabled to 

 see objects near and at moderate distance, no active or physiological change for 

 accommodation of sight for distant objects takes place or seems necessary. 



The dioptric arrangement, being the reverse of that which obtains in animals where 

 "accommodation" is observed, and in whom the passive state is that of vision, arranged 

 for distant objects, while the active state is that of vision accommodated at will for 

 near objects. 



4th. That the vascular distribution of the choroid vessels has no relation to any 

 movement of the lens or change of its shape, but is arranged to meet the changes of 

 static condition of the circulating fluid, and of dynamic force exerted by the heart 

 under varying pressure from without ; and that by such an arrangement, protection to 

 the delicate tissues of the eye is afforded by a compensating balance between the 

 tension of the blood within the vessels and the external pressure exerted upon them. 



