CHAPTER XX 

 RETROSPECT AND CONCLUSIONS 



The interesting connections of brain pattern with the diet and 

 habitat of fish can now be reviewed. 



In cyprinoids the association of diet with brain pattern is very 

 clearly seen in the enlarged vagal lobes and facial lobes of the 

 bottom feeding fish, and the differences of size of these lobes accord- 

 ing to the habit of extracting nutriet material from mud, or groping 

 and grubbing on stony or gravelly bottoms. There is reason to 

 beheve that the enlargement of the vagals is due to the palatal 

 organ, which is an adaptation for sorting, sifting, retaining, or 

 rejecting food particles ; there is also strong evidence that the 

 enlargement of the facial lobes is due to the presence of barbels 

 which are supplied with taste-buds, as the facial nerve divides 

 within the brain into two branches leading to anterior and posterior 

 areas of the lobe of varying size, according the imjDortance of 

 the barbels : when we come to the next group which are surface 

 feeders we find that sight is a very important sense in hunting and 

 therefore the optic lobes are prominent, while the vagals and facials 

 are small. But in the highly speciahsed planlvton feeders, like the 

 bleak and engraulicypris, the naked eye appearance of the brain is 

 remarkably altered in type, as the facial lobes do not appear on the 

 sm-face and can only be demonstrated in serial sections, when it is 

 found to be completely overlapped by the somatic-sensory lobes ; 

 and, further, a special area at the base of the cerebellum becomes 

 very prominent, and being associated with audition we have ven- 

 tured to call it the central acoustic lobe. This lobe is present to a 

 lesser extent in the fish belonging to Group II, but in the purely 

 ground feeders it is rudimentary. Bhimachar has also shown 

 that cyprionodont fish, living at the surface of the water, have 

 the medulla oblongata narrow, without prominent vagal and facial 

 lobes, and that there has been developed a conspicuous central 

 acoustic area. 



THE BRAIN PATTERN IN GADOIDS 



In this family the relationship of brain pattern to diet and 

 habitat is more complex. In the first group, according my classi- 



152 



