484 ' Comparative Animal Physiology 



in mammals. However, the same three bones are found in fishes, in which 

 they are known as the Weberian ossicles and connect the air bladder to the 

 inner ear. 



Fishes. In fishes only the vestibule and semicircular labyrinths are present, 

 and they have the dual function of determining equilibrium and of serving 

 as primitive auditory organs. There is no middle ear. The sacculus of the 

 trout is large, and there are three semicircular canals. The sacculus of fishes 

 generally has two small evaginations, the utriculus and the lagena. There are 

 usually statoliths in all three divisions, and these statoliths are especially well 

 developed in fish which produce sounds. The drumfishes, Aplodonitus and 

 Sciaena aquila, have large statoliths, and Sciaena has been reported as being 

 heard six feet above the water when it was swimming sixty feet below the 

 surface. The sounds of the drumfishes are produced by movements of the 

 air bladder, and since they are produced primarily by the males during the 

 mating season it seems very likely that they are perceptible to the females of 

 the same species. 



There has been much contradictory evidence concerning whether fish can 

 hear. Most of the negative evidence, however, is based on experiments in 

 which fish did not respond to sounds produced in air. This is often due to 

 the fact that the air-water surface is almost a perfect reflector for sound waves, 

 and therefore sounds produced above water are usually reflected rather than 

 transmitted to the water. A man swimming under water may not be able 

 to hear a pistol shot in air nearby, but he usually can hear sounds made by 

 someone kicking the bottom of a nearby boat, or sounds made by knocking 

 two rocks together under water. Likewise, sounds made by tapping the sides 

 of an aquarium may readily produce a response in fishes. 



Zotterman^^ measured a microphonic effect in the macular region of the 

 sacculus of the pike, Esox lucius, and of the burbot. Lota vulgaris. He stimu- 

 lated the ear with the tone produced by a 60 cycle tuning fork and recorded 

 a "macula effect" comparable to the microphonic effect in the mammalian 

 ear. He also recorded nerve impulses when the ear was rotated in one direc- 

 tion in the plane of a semicircular canal; with opposite rotation a response 

 occurred only at cessation. The existence of the macula effect demonstrates 

 that there is probably a mechanism for receiving sound of low frequencies. 



On the basis of behavior there is considerable evidence that fish have a 

 high ability to hear sounds in water. Parker'^"- '-^^ demonstrated that dogfish 

 are responsive to tapping of the aquarium, and that the reaction persists 

 after cutting of nerves to the skin and lateral line. Cutting of the eighth 

 cranial nerve, however, made the fish almost completely insensitive to sound. 

 In the squeteague QCynoscion') the same phenomenon could be demon- 

 strated."*^ Moreover, in Cynoscion the sacculus is separate from the utriculus 

 and semicircular canals, and Parker was able to show that after destruction 

 of the utriculus and canals the fish still responded to sounds, although it 

 lacked control of its equilibrium. Destruction of the sacculus alone was not 

 possible, but a pin thrust into the large saccular statolith greatly reduced sensi- 

 tivity to tapping. 



Bull,'^ by means of conditioned reflexes, has been able to demonstrate that 

 eels are sensitive to a submerged 342 cycle buzzer, and that wrasse will re- 



