48 BRAIN AND BODY OF FISH 



the Weberian ossicles with the saccule by means of certain ducts 

 which lead to a space called the " atrium sinus imparls." But it 

 will be interesting to quote some conclusions arrived at by Sorensen : 



" I. — The wall of the air-bladder is capable of vibrating syn- 

 chronously with rapidly recurring sound waves. 



" II. — The tripus is thrown into vibrations when the wall of 

 the bladder is vibrating. 



" III. — All movements, also, vibrations of the tripus are trans- 

 mitted, by means of the tight inter-ossicular ligament, to the rest 

 of the Weberian ossicles and in this way to the atriun sinus imparls. 



" IV. — The tones of the air-bladder can be transmitted to the 

 water without losing much in strength, and if so, vice versa, sound 

 waves can be transmitted from without to the air-bladder." 



Recently, Prof. K. von Frisch has shown by experiments that 

 have been conducted on the principle of Pavlov's conditioned reflexes 

 that the minnow has a range of hearing as wide as has the human 

 ear. But we are the more indebted to him for putting on an experi- 

 mental basis, the fact that the swim-bladder has an important 

 share in the hearing of those fish with a Weberian apparatus. He 

 tested the range of hearing in minnows both before and after removing 

 the swim-bladder and found that hearing remained in those fish 

 which had had the swim-bladder removed, but that it was iveakened. 

 " We see, therefore, that those fish in which the swim-bladder is 

 connected with the labyrinth by Weberian ossicles, have an apparatus 

 through which the acuteness of hearing is increased." 



We are now able to tiu'n to the discussion of the methods of 

 feeding of the fourth group of Cyprinoids as typified by the African 

 fish Engraulicypris and the bleak, which, as far as we were able to 

 judge, were mostly dependent on sight in the search for food. When 

 the serial sections of the roach and Engraulicypris were described 

 in a previous chapter there was noted a central area of round cells 

 with interlacing transverse fibres at the base of the cerebellum 

 connected laterally with the acoustic tubercles ; this we termed the 

 central acoustic area. When we come to discuss the auditory organ 

 of the herring and its central representation in the brain it will be 

 possible to give more fully the arguments in favour of adopting this 

 term and of associating this with audition. 



It has already been i)ointed out that Engraulicypris has a rudi- 

 mentary facial lobe, and that the gustatory function must be smaU ; 

 that it has large optic lobes and that it has a surface habitat and is a 

 jjlankton feeder. The study of its central acoustic area, however, 

 seems to indicate that hearing may be of importance in regard to its 



