158 BRAIN AND BODY OF FISH 



and an eminent physiologist told how he had removed the cere- 

 bellum of fish without any effect on its equilibrium. 



In reference to these remarks we find, that the classic text- 

 book on physiology by Michael Foster devotes 32 pages to the 

 cerebrum and only one to the cerebellum. It is usually taught 

 that the cerebellum is associated with the co-ordination of move- 

 ments, and this view is based on the effects produced by extirpation 

 of portions of the cerebellum ; it has also been observed that lateral 

 lesions and incisions produce a greater effect than medial or sym- 

 metrical ones. But clinical evidence in man is conflicting, as cases 

 have been recorded, in which extensive disease has existed without 

 any obvious disturbance of the co-ordination of movements. 



It must be remembered that the acoustico-lateralis system is 

 only developed fully in fish, and consists of three branches connected 

 with roots of the seventh nerve, the eighth or auditory nerve, and 

 the vagus lateral-line branch, and that the fibres of all these nerves 

 are derived from nerve-cells in the acoustico-lateralist area of the 

 medulla. We shall consider first the central acoustic area III. 



It was observed in the coiu"se of a systematic examination of 

 the brains of Cyprinoids that Engraulicypris and Bleak had minute 

 facial lobes only evident by examining serial sections, and that they 

 possessed a well-marked central acoustic lobe or area. Associated 

 with these facts, it is to be noted that they are surface feeders ; 

 in fact, Engraulcypris behaves like a clupeoid fish and as its name 

 impHes is an anchovy-carp. The next quest was the investigation 

 of the facial lobe of the herring, a typical plankton feeder. Tliis 

 has a well-marked central lobe, in the position of a facial lobe, but 

 really due to a median backward projection of the cerebellum and 

 its microscopic structure is like that of an invaginated central 

 acoustic area ; the eighth nerve can be traced to its lateral margins. 

 The evidence seemed to point to an auditory function. It did not 

 appear likely that this specialised area could be connected with the 

 lateral line organs as the herring has no lateral line, but only a few 

 sense organs on the head, one in particular being closely connected 

 with the posterior and anterior spherical air-vesicles which form the 

 accessory auditory organ of this fish. 



It was argued that if a central acoustic area was really auditory 

 in function those fish which are known to produce sounds, such as 

 the gurnards, would have this area well developed; sound pro- 

 duction without auchtion would appear to be a useless accomplish- 

 ment. Certain fish, such as the mullet, are very susceptible to 

 sounds, and fishermen make use of this characteristic reaction in 

 their methods of fishing, and it is interesting to note that fishermen 



