ASSOCIATION AND COLOR DISCRIMINATION 445 



Parker ('03, '08, '10, '11) believes that certain sounds of low 

 vibration, like the discharge of a gun, are heard and that the 

 sacculus is the chief organ of hearing. 



According to Parker ('04), the lateral line organs are geneti- 

 cally related to the ear, and are not stimulated by light, heat, 

 salinity of the surrounding water, food, carbon dioxide, oxygen, 

 foulness of the water, currents, or sound, but by vibrations of 

 low frequency — about six per second. Since these organs appear 

 to be affected by such stimuli as disturbances caused by winds 

 and by bodies falUng into the water, they may be of significance 

 in orientation, but take no more part in equilibration than the 

 skin, and are less important in this connection than the eye and 

 ear. 



The sense of touch is well developed in fishes. Bateson ('89- 

 '90) states that the sole appears to use this sense in discovering 

 its food. Herrick ('03) finds that the gadoid fishes which he 

 observed detect their food by means of the tactile sense com- 

 bined with gustatory. 



Shelf ord and Allee ('13, '14) made elaborate experiments 

 showing that fishes may react in various ways to gradients of 

 dissolved gases, but no study was made of the sense organs con- 

 cerned. The resistance of fishes to different concentrations of 

 oxygen and carbon dioxide is discussed by Wells ('15). 



In a delicate and ingenious series of experiments, Lyon ('04) 

 proved that the reaction to current in the killifish, the scup, the 

 stickleback, and the butterfish is an optical reflex — as the fish is 

 carried down stream by current, the bottom of the stream ap 

 pears to move in the opposite direction; the fish has a tendency 

 to follow its passing field of vision, and consequently swims 

 against the current. 



Experiments to show that goldfish and Fundulus can find 

 their way through mazes are reported by Churchhill ('16) and 

 Thorndike ('11), respectively. 



Eigenmann ('00) shows that the integumentary nerves of the 

 bUnd fishes, Chologaster and Amblyopis, are sensitive to light. 

 According to Parker ('05, '09), the same is true of ammocoetes; 

 but no salt-water fishes which he observed possessed such photo- 



