No. 435.] SENSE OF HEARING IN FISHES. 



20I 



lateral-line organs. Thus the consideration of the sense of hear- 

 ing in fishes leads us to an understanding of a natural group of 

 sense organs whose genetic connections would never have been 

 suspected had we not been able to investigate them in these primi- 

 tive aquatic vertebrates, the fishes. 



Postscript. Since this lecture was prepared Professor Tull- 

 berg's interesting paper (1903) on the functions of the ears of 

 fishes has reached me. In this paper it is concluded (p. 20) 

 that the ears of fishes are not organs of equilibration and though 

 they may perhaps be to a certain extent organs of hearing, then- 

 original and principal function is to receive stimuli from the 

 movements of the surrounding water, especially from currents. 

 Vibrations probably stimulate particularly the maculae acusticae 

 of the utriculus, the sacculus, and the lagena ; currents affect 

 especially the crista? acusticae of the ampullae. Thus the ear is 

 held to be an organ directly concerned with the reactions of a 

 fish to a current of water (rheotaxis). 



My own experiments have been directed to test the sense of 

 hearing in fishes rather than to ascertain what other functions 

 the ears in these animals mav have, but some of my observations 

 bear on the questions raised by Professor Tullberg and [, there- 

 fore, call attention to them here. Professor Tullberg believes 

 that the ears of fishes are not concerned with equilibration 

 because the disturbances in the equilibrium of fishes that follow 

 many operations on the ears and that have been taken to indi- 



