FISHES. 



531 



what anglers now know to be true, that these 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 found, has no exterior opening. It forms a 



e' 



Fig- 352. Teeth of the Bream. 



Fig. 351. A Fish's Eye. 



/, crystalline lens ; etf, cornea ; h, posterior 



chamber ; c, optic nerve. 



Fig. 353. Teeth of the Carp. 



cavity in the interior of the cranium, which is far from presenting the 

 complicated structure of the ear in mammals and birds. In spite, 



* 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 accom- 

 modated 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. 



