RETROSPECT AND CONCLUSIONS 159 



both in the south of England and as far away as Egypt apply the 

 same methods. 



To return to the carps it is found tliat the surface feeding mem- 

 bers of this family have the central acoustic area well developed, 

 A\hile the ground feeders have this area very small. The same 

 obstu'vation has been made on the fish which abound in the Macb-as 

 tanks as described by Bhimachar, and he adds further that those 

 fish which have a prominent central acoustic lobe have also an 

 accessory air-breathing organ. It maj' be mentioned here that the 

 recent work of Bull ]\Iamiing, Fritsch and others have put the 

 question of hearing in fish beyond dispute, and the minnow is noA\' 

 known to have a range of hearing as wide as that possessed by the 

 hunuin ear. 



We now come to the acoustic tubercles and shall endeavom- 

 to unravel its functions. Presumably if the central area is acoustic 

 in function, the lateral areas must be either connected with the 

 orientation of the body and so with the semi-circular canals, or 

 \\-ith the perception of waves received from the lateral-line organs 

 through the movement of the fluid in their canals. Recently a 

 Japanese observer has described experiments in which the effect 

 of ablation of the cerebellum was observed. These experiments 

 supported the view that the main body of the cerebellum is con- 

 nected with the registration of the position of the body in 

 space. 



The acoustic tubercles must, therefore, be chiefly receptors 

 for the sense organs of the lateral line. The question now arises 

 are there any examples of an exceptional development of the 

 acoustic tubercles and is such a condition associated with any 

 special habitat ? 



The examination of the brain of gadoids revealed the possibility 

 of such associated conditions being jDresent. The pattern of the 

 brain of gadoids is always of the same generalised type, the dif- 

 ferences being most noticeable in the lobes of the medulla oblongata 

 and in the size of the optic lobes. We have seen how enormous 

 is the size of the facial lobe in the rockling, and have associated this 

 development with the peculiar adaptation of the dorsal fin. But 

 this is not the only gadoid that has a marked and unusual develop- 

 ment of a sensory area. 



Molva elongata, one of the deep-sea lings, has exceptionally 

 large acoustic tubercles, as is shown in the plate of the gadoid 

 brains, and this development is associated with a bathysmal habitat, 

 and also with a predacious habit of feeding. If we consider what 

 we have described as the pattern of the brain of the deep-sea gadoid 



