134 BRAIN AND BODY OF FISH 



scattered here and there. If we now examine a section posterior 

 to the above (Plate 25), we find that the special tissue of the acoustic 

 tubercle occupies but a small part of the periphery of the lobe and 

 that the lobe is made up of tissues of the central-acoustic type, fibres 

 which pass downwards and outwards to enter a gangloinic mass of 

 cells before joining the fibres of the eighth nerve. At this level the 

 tip only of the cerebellum appears, while below the somatic sensory 

 lobes are seen to meet in the middle line, although anteriorly these 

 lobes are separated, and form a widening of the rhomboid fossa. 



The importance of this special adaptation of the acoustic tubercles 

 must be emphasised. Here we find a typical section of a cerebellum, 

 separated from a highly differentated acoustic tubercle, the granular 

 areas of which meet medially and are joined up by a group of large 

 nerve cells. 



This area is again completely separated posteriorly from a 

 central acoustic area, in which there is no intermmghng of lateralis 

 nerve fibres. These three areas differing so markedly in structure 

 must clearly be endowed with separate functions, and their relation 

 to function can only be assessed by comparison with other teleostean 

 types. 



If we refer to the drawing of the brain of the herring, we see that 

 the central acoustic lobe forms a definite projection mesially and 

 that some fibres from it pass outwards to the acoustic tubercles, but 

 most of the fibres pass downwards and outwards to a ganglionic 

 mass before joining the eighth nerve ; in this family the central 

 acoustic lobe is the largest and most differentiated element in the 

 acustico-lateralis complex. If we now consider the minnow a fish, 

 which in the laboratory of Prof, von Friscli has revealed a nacute 

 perception of sounds, by means of a modified Pavlov technique of 

 conditioned reflexes, we find that it has a well-developed central 

 acoustic area, in which both cells and nerve fibres form a characteris- 

 tic pattern ; this we look upon as the central representation of the 

 auditory function. 



It may be noted in passing that the gurnard, a fish with a sound- 

 producing mechanism, has a similar central acoustic area to that of 

 the minnow. Von Frisch has also shown experimentally that the 

 saccule in the minnow is the peripheral sense organ for the perception 

 of sound waves. We must, therefore, associate the similar area in 

 the scabbard fish with audition. 



The work of certain Japanese investigators seem to confirm the 

 usually accepted view that the cerebellum proper is concerned with 

 equilibration. By a process of exclusion, therefore, we reach the con- 

 clusion that the enlarged lateralis area in the scabbard fish must be 



