130 The Life Story of the Fish 



used in hearing: the tense air-bladder would be well adapted 

 to receive vibrations coming through water, and would use 

 the ossicles to transmit them to the ear. 



The opponents were quick to point out that while this 

 might be all very well when the air-bladder was fully ex- 



C<ip3ule 



Wehtrian Ossic/es 

 Backbone 



Figure i6. DIAGRAMMATIC REPRESENTATION OF THE AIR- 

 BLADDER AS A SENSE ORGAN IN THE CARP 



After Thilo. 



panded, as in the diagram on the right in the figure, it would 

 not work at all when the air-bladder, in the course of its 

 hydrostatic duties, reached the shrunken state shown on the 

 left. In that state, not only would the membrane of the blad- 

 der be so relaxed as to be no use in receiving sound-waves, 

 but the ossicles would cease to press against the ear, and 

 would be unable to transmit them. To these people it was 

 evident that the system was a device to keep the fish in- 

 formed as to its relative depth by the increase or decrease 

 of the pressure transmitted by the ossicles from the air- 



