Page:Natural History, Fishes.djvu/27

Rh nerves are very large, and distributed over a great extent of surface. Professor Owen concludes, from certain anatomical peculiarities, that some Fishes, as the Rays, which have the olfactory nerves greatly developed, "scent as well as smell; i.e., actively search for odoriferous impressions by rapidly changing the current of water through the olfactory sac." Many observations of living Fishes concur with deductions from structure to prove the exercise of smell. A Pike was seen to approach a dead Fish, but when within a foot of it, turned away, as if he had then become aware of what was the fact, that his supposed prey was stale. Mr. Couch observed, in a Stickleback, kept in a glass vase, that the nostrils opened and closed simultaneously with the action of the gill covers, and felt convinced that the water was received and rejected for the purpose of sensation. Mr. Jesse states that Fishes prefer paste and worms that have been prepared with particular perfumes.

No external ear, nor even an auditory orifice is detected in Fishes, yet there is a complex internal apparatus of large size, for the reception of sounds. In many species of bony Fishes there is a communication between the acoustic chamber and the air-bladder, of which we shall presently speak. Mr. Jesse has seen Fishes start at the report of a gun, when they could not see the flash; and several instances are on record of tame Fishes having been taught to come to the surface of the water at accustomed sounds.

From the density of the medium inhabited by