92 PARKER— A CRITICAL SURVEY OF 



ject is thrown under suspicion and it, therefore, remains to discuss 

 this problem from the standpoint of the few cases of positive evi- 

 dence. 



These few instances cover a considerable range of fishes. They 

 begin with Ammococtes which is apparently not responsive to ordi- 

 nary noises (de Cyon, 1878, p. 93) though it will react by a winking 

 movement of its oral hood and by curving its body when the wall 

 of its aquarium is struck by a swinging pendulum. After cutting 

 the eighth nerves, these responses can be called forth only by a 

 stroke at least three times as strong as in the previous instance, thus 

 showing that the ear is decidedly more sensitive to this stimulus 

 than the other receptors in the body, very probably those in the 

 skin (Parker, 1910a, p. 470). 



Mustehis exhibits conditions very similar to those in Ammococtes. 

 It is not responsive to tones (Parker, 1903a, p. 62) and to ordinary 

 noises (Lafite-Dupont, 1907), but it reacts with a sudden jump 

 forward or a quivering of the pectoral fins to a pendulum stroke on 

 the wall of its aquarium (Parker, 1909, 191 ia_, p. 48). On cutting 

 the eighth nerves, three times the former stimulus was required to 

 call forth the response previously noted. This fin-movement re- 

 mained normally elicitable in fishes whose skin had been desensitized 

 by combined nerve-cutting and treatment with cocoaine, but disap- 

 peared entirely from them on cutting their eighth nerves. Thus 

 Mustelus is responsive through the ear, and less so through the 

 skin, to the noise produced by a stroke on the wall of its aquarium. 



Among teleosts three cases call for consideration : Fundulus, 

 Carassins and Amiurus. The grounds for concluding Ihat Fundulus 

 (Parker, 1903a) and Carassius (Bigelow, 1904) hear have already 

 been briefly stated in the earlier part of this paper. Each fish re- 

 sponds by at least fin-movements to the tones of a tuning-fork and 

 to other sounds. These responses cease in part or wholly on cutting 

 the eighth nerves. They are not greatly reduced by very extensive 

 nerve-cutting through which much of the skin can be rendered 

 insensitive. The responsiveness of the fishes under these conditions 

 shows that the operation of cutting the eighth nerve cannot be re- 

 garded as the occasion of the decline in sensitivity of the particular 

 group in which this operation was carried out but that this decline 



