80 , PARKER— A CRITICAL SURVEY OF 



ity of fishes to associate, showed that goldfishes could be taught to go 

 for food to one or another part of an aquarium depending on the 

 sounding of a high- or a low-pitched bell, a result favorable rather 

 than otherwise to the opinion that goldfish hear. 



Without knowledge of the work of Haempel (1911) and of 

 Korner (1916) Parker and Van Heusen (1917) undertook the study 

 of the responses of Amiurus to sound and other mechanical stimuli. 

 They were influenced in this by the hardiness of Amiurus and by 

 the observation of Maier (1909) that this fish responded to a 

 whistle. As in Parker's former experiments, attempts were made 

 to eliminate the ears, the lateral-line organs, and the skin. In two 

 of these operations new methods were devised. In excluding the 

 ear nothing better was found than cutting the eighth nerve. After 

 the operation the necessary incisions on the head quickly healed and 

 the fishes lived well. Following the tests, fishes that had been 

 thus operated upon were dissected to ascertain that the eighth nerves 

 had actually been cut, an almost invariable result. In the elimina- 

 tion of the lateral-line organs those of the trunk were rendered 

 inoperative by cutting the lateral-line nerves near the gill clefts and 

 those of the head by destroying individually the forty-eight organs 

 of that region. This was done by means of an electric depilating 

 needle. Histological examinations of the spots thus treated showed 

 in the preliminary tests the complete destruction of these organs. 

 Finally, the skin was rendered non-receptive by painting it with a 

 20 per cent, solution of magnesium sulphate, which was allowed to 

 act for five minutes. The skin of a fish so treated remained insensi- 

 tive to mechanical stimulation for an hour to an hour and a half. 



In preparing fishes for experimental tests they were always 

 previously blindfolded by having a pair of thin leather goggle- 

 shaped shields placed over the eyes and held there by a few stitches 

 taken in the skin. Because of its gregarious habits Amiurus was 

 always tested in pairs, single fishes being much less satisfactory for 

 experimental work than two. In accordance with the states of 

 their sense organs eight groups of fishes were used: first, normal 

 fishes with skin, lateral-line organs, and ears intact; second, fishes 

 with skin and ears intact but lateral-line organs eliminated; third. 



