Sensory Discrimination: Hearing 129 



the fish, extending from head to tail, there is a row of 

 pores opening into a long canal, which at the head divides 

 into three branches, one going upward above the eye, a 

 second below the eye, and a third down toward the lower 

 jaw. The functions of these canals have given rise to 

 much discussion among zoologists, an exhaustive history 

 of which will be found in Parker's monograph entitled 

 "The Function of the Lateral-line Organs in Fishes." 

 Parker first proved experimentally that the canals played 

 no part in responses to the following stimuli : light, heat, 

 salinity of the water, food, oxygen dissolved in the water, 

 carbon dioxide, foulness of the water, hydrostatic pressure, 

 steady currents flowing through the water, and sound. 

 When, however, the water in the aquarium was made to 

 vibrate slowly, about six times per second, the fish made 

 certain characteristic reactions, differing somewhat for 

 the four or five species observed, but always failing to 

 appear when the lateral-line nerve was cut. Parker 

 concludes that "the stimulus for the lateral-line organs (a 

 water vibration of low frequency) is a physical stimulus 

 intermediate in character between that effective for the 

 skin (deforming pressure of solids, currents, etc.) and that 

 for the ear (vibrations of high frequency), and indicates 

 that these organs hold an intermediate place between the 

 two sets of sense organs named" (539). The ear is thus 

 regarded as actually derived from the lateral-line canal, 

 as this in turn was derived from the skin. We may suppose 

 that at least three different sensation qualities result from 

 stimulation of the skin, the canals, and the ear, where 

 hearing can be shown to exist. 



Hofer (326 a) criticizes these experiments on the ground 

 that when Parker cut the lateral-line nerves he also de- 

 stroyed the nerves supplying the skin of the head, a par tic- 



