INTELLIGENCE AND BRAIN PATTERN 15 



if we come to study two familiar fomilics of flat-fish, the sole and the 

 plaice, it will be found that their hunting methods differ widely 

 and that this difference is reflected in their brain structure. The 

 sole is nocturnal in its habits, and it hunts by tapping the sand 

 in its search for Morms, just as the thrush does on the lawn in front 

 of your window, and it has an acute sense of smell, which is evidenced 

 by its elaborate nasal organ. Compared with the plaice its eyes are 

 very small. The conclusion is reached, therefore, that the sole 

 hunts by smell and touch. 



This is not the whole story, but it is sufficient for our present 

 purpose. The plaice on the other hand has large, prominent, and 

 movable eyes, and, as we shall find later, a marked sense of taste, 

 due to the presence of taste-buds, so we conclude that the plaice 

 feeds by sight and taste. Corresponding to the increased import- 

 ance of these different senses to these fish, the central areas in the 

 brain connected with the sense organs are enlarged, and thus a 

 definite type of brain pattern results. Other interesting correla- 

 tions between feeding habits and form of brain are to be observed 

 in the Cod family, in which there is a gradual change in the pattern 

 of the brain as we pass from the shell-fish eating members, through 

 the mixed feeders, to those purely predacious. The principle of the 

 enlargement of special sense areas in the brain in accordance with 

 an increase of function is also of service in elucidating problems like 

 the question of hearing in fish. Certain fish have elaborate mechan- 

 isms which are supposed to be accessory to the organs of hearing ; 

 if it is found that in these fish there is a special area more developed 

 than in fish devoid of these mechanisms, we may assume that this 

 area has some acoustic significance. Examples of this condition 

 are to be seen in the Carps and the Herring tribe among fishes 

 of the British Isles and seas, and in the interesting family of fish 

 kno^^"n as the Morm^Tidse of northern Africa. In fact, the com- 

 parative study of the brains of bony fishes is full of unexpected 

 revelations. So much may be said as an introduction to the subject 

 of brain form, in relation to hunting and feeding. Is there any 

 area in the brain that can be identified as associated with the function 

 of reproduction ? Modern research into the function of the pituitary 

 gland directs the attention to the condition of this gland in fish and 

 evidence will be brought forward to show that this gland undergoes 

 certain changes in those fish that are about to migrate for the 23ur- 

 poses of reproduction. 



The relation of form to function in determining the pattern of the 

 brain of a fish will be described in the following pages. In order to 

 help the reader to follow the argument it will be necessary to give 



