vii. 15 HEARING OF FISHES 217 



particularly well. In these fishes the receptors are in the inferior part 

 of the ear (saccule and lagena, Fig. 134). The sagitta carries a special 

 wing projecting into the cavity and is so suspended as to serve to 

 amplify vibrations. Near to it is 

 a thin portion of the wall of the 

 sac, which would favour the 

 passage of variations of pressure 

 transmitted to the endolymph by 

 the ossicles. 



These Ostariophysi respond to 

 sounds between about 60-6,000 

 vibrations/sec. After removal of 

 the pars inferior responses con- 

 tinue only up to 120/sec. If the 

 air bladder is punctured a min- 

 now can still respond, but only 

 up to 3,000/sec and with a sen- 

 sitivity diminished by more than 

 fifty times. 



Minnows can be trained to 

 discriminate between warbled 

 notes separated by I tone. Non- 

 ostariophyse fishes have mostly 

 a much lower upper limit of 

 hearing and lower capacity for 

 discrimination. The Mormyridae 

 (p. 254), however, approach the 

 minnows in this respect and here 

 there is a special isolated portion 

 of the air bladder within the otic 

 bone. 



In the best cases the sense of 

 hearing of fishes thus approaches 

 that of man, in spite of the 

 absence of a coiled cochlea and 



basilar membrane with fibres of different lengths. Clearly the discrimi- 

 nation of tones cannot here depend upon differential resonance as the 

 theory of Helmholtz requires. In spite of the considerable powers 

 of pitch discrimination there is little evidence of capacity to localize 

 sounds except when they are loud and near. 



Sch. 



Fig. 135. Position of ear in Ostariophysi 



and its relation to the Weberian ossicles, 



which are shown in black. 



C.tr. transverse canal between the two sacculi; 

 //. brain; /. 'incus'; L. lagena; M. 'malleus'; 

 S. sacculus; Sch. swim-bladder; S.i. sinus impar 

 (perilymphatic space); St. 'stapes'; U. utriculus. 

 (From V. Frisch.) 



