ATTl-BLADDER IN" NOTOPTEETJS BOUNEENSIS. 533 



not the Eishes deprived of tlie means by which the higher 

 Vertebrata are able to judge the direction, of the sound, viz., by- 

 turning the head (or external ears) to the right or to the left ? 

 It must also be kept in mind that it is always very difficult 

 thoroughly to understand that beings differently conditioned 

 know how to use the powers with which they are endowed, 

 especially when these powers are inferior to those bestowed 

 upon us." 



Sorenson's attempt to lessen the importance of what he terms 

 the only "real objection" to Weber's theory does not impress 

 one as being very successful. The capacity for appreciating the 

 direction of sounds, whether employed as a means of securing 

 prey, or escaping from enemies, or, as in the case of gregarious 

 Pishes, as a means of keeping together in shoals for breeding or 

 other purposes, must be of primary importance in any modifica- 

 tion of the auditory organ in the direction of giving to its 

 possessor exceptional powers of hearing. Fishes may have no 

 power of rotating or inclining the head, but it must not be for- 

 gotten that a slight deflection of the long axis of the body to the 

 right or left will at once enable the differeutial action of the two 

 auditory organs to come into play, and the Piah would be in a 

 position to appreciate the direction from which the sound is 

 travelling. An Ostariophysean, in so far as those parts of the 

 auditory apparatus which it possesses in common with all other 

 Fishes are concerned, is in much the same position as regards 

 the sense of direction. It is quite true that the two auditory 

 organs are in open communication by means of a sub-cerebral 

 transverse ductus endolymphaticus ; but it is also obvious, I 

 think, that the auditory organ, right or left, turned towards 

 the direction of the sound, will be stimulated appreciably sooner, 

 or it may be more forcibly, than its fellow, and hence the cog- 

 nizance of direction. Again, is it not possible, or even probable, 

 that sound-waves reaching the auditory organs simultaneously 

 by two distinct channels will have their effect nullified, and 

 the sense of direction seriously interfered with ? In fact it 

 seems extremely probable that sound stimuli which, according 

 to Weber's hypothesis, are received by the auditory organs 

 through the air-bladder and Weberian ossicles, would have 

 the eifect of confusing any sense of direction based upon 

 similar stimuli, generated by the same cause and at the same 

 moment, but pursuing, as in the generality of Fishes, the usual 



LINK. JOUKK. — ZOOLOaT, VOL. XSVII. 40 



