CHAPTER XVI 



HEARING, EQUILIBRIUM AND THE CEREBELLAR 



FUNCTIONS 



It has been the aim of this comparative study of the cerebellum 

 and acoustic tubercles, or more correctly the acoustico-laterahs 

 lobes, to disentangle the various functions of the nervous components 

 of this complex area. 



If it is found that certain areas in the cerebellum and acoustic 

 tubercles are enlarged in a particular fish, endowed with certain 

 habits or mode of life, and diminished in a fish that has not these 

 habits or mode of life ; it seems reasonable to associate this area with 

 a certain function, to which the habit or habitat gives the clue. 



For instance, if it is found that a surface-feeding fish has an 

 accessory air-breathing organ, and that this fish has an enlarged 

 area at the base of the cerebellum which is rudimentary or absent in 

 other members of the same family of fish, it is reasonable to associate 

 these two facts with a common factor, namely, the atmosphere, in 

 the one case the air is the medium for supplying oxygen and in the 

 other the vehicle for the perception of vibrations or sound ; in other 

 words respiration and audition ; and this is the case in certain 

 Indian fishes, as has been shown by Bhimachar, in which the 

 central acoustic lobe is well marked in proportion to the develop- 

 ment of an accessory air-breathing organ. When we examine these 

 facts closer we find that in jilankton-feeding animals such as the 

 herring, bleak, etc., there is a similar development of the central 

 acoustic area which in some fishes becomes a separate lobe. 



But before we proceed with this discussion of the acoustic area, 

 we propose to describe the microscopic structure of the acoustic 

 tubercles of the scabbard fish, a bathysmal fish, living at a depth of 

 600 to 1,G00 metres ; the naked eye appearance of these tubercles 

 has already been described, and they are typical of all the bathysmal 

 fishes we have had an opportunity to examine. 



If a section across the most prominent part of the large acoustic 

 tubercles be examined (Plate 26), it will be seen that the lateral 

 convexities consist of the typical small-celled tissue, so characteristic 

 of tliis area, in which the jDeripheral cells are found in small groups. 



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