I2 20 BULLETIN OF THE BUREAU OF FISHERIES. 



normal one, for the normal fish almost invariably responded by a slight leap for- 

 ward to every tap, while the other fish only very rarely reacted. The same was 

 true when normal Fundulus heteroclitus were put in the aquarium and compared 

 with squeteagues whose ear-stones had been pinned. I therefore believe 

 that the larger otolith of the sacculus, the sagitta, is concerned with the sque- 

 teague's sensitiveness to sound, and further, for reasons already given, that it 

 has nothing to do with equilibrium or with muscle tonus. 



These conclusions are in accord with the observations of several other inves- 

 tigators. Thus, so far as hearing is concerned. Smith (1905) has pointed out 

 that in all sciaenid fishes which drum, as the squeteague does, the sagittas are very 

 large, but in Menticirrhus, which does not drum, these otoliths are relatively 

 small. Hence, the size of the otolith seems to be related to the drumming habit, 

 as might be expected if the otoliths are concerned with hearing. Further, Piper 

 (1906a) has demonstrated that a negative variation is observable in the eighth 

 nerve of Esox when that portion of the ear of Esox which contains the otoliths is 

 subjected to sound vibrations. From the standpoint of equilibrium Lauden- 

 bach ( 1 899) has already shown that the removal of the otoliths from the ears of 

 Siredon and the frog has no effect on the subsequent success of these animals 

 in keeping themselves upright, a state of affairs in agreement with my experience 

 in pinning down the otoliths in the squeteague. These observations therefore 

 confirm me in the belief that the sagitta of the fish's ear is in some essential way 

 concerned with the responses of these animals to sounds, as surmised by Scott 

 (1906), and has nothing to do with equilibrium or muscle tonus. So far as 

 equilibrium is concerned this conclusion is rather the reverse of what would be 

 anticipated, for in the invertebrates, at least, the otoliths have been clearly 

 shown to be concerned with equilibrium, and this function has been definitely 

 ascribed by Breuer (1891), Sherrington (1906), and others to these bodies in the 

 vertebrates; but this opinion is not supported by my observations. 



The sagittEe in the ears of vertebrates are certainly not merely tolerated 

 foreign bodies, as Ayers (1892, p. 309) has maintained, but, as has just been 

 pointed out, they are of real functional significance. How they act in the recep- 

 tion of sound is not known with certainty ; but since in the squeteague they have 

 a specific gravity of 2.84 and that of the whole head is about 1.8, it is quite 

 probable that when sound vibrations influence the normal fish they induce the 

 relatively lighter parts of the head, including the macula acustica sacculi, to 

 vibrate against the relatively heavier otolith; in other words, the otolith is a 

 relatively stable body against which the auditory hairs of the macula acustica 

 sacculi may strike. In my opinion sound stimulates the auditory hairs in some 

 such mechanical way as this. 



That the sagitta and its underlying sensory patch is not the only sound- 

 receptive mechanism in the squeteague may be inferred from the fact that after 



