278 THE BRAIN OF QUADRUPKDS AND 



development, in reference to the amount of Intelligence 

 they are accustomed to display, several points have to 

 be borne in mind, which are too ai:>t to be overlooked. 

 Size of Brain, and with it convolutional complexity, must, 

 for instance, be closely related to the number and variety 

 of an animal's Sensorial Impressions — the raw material as 

 it were of Intelligence ; but it must be also largely depen- 

 dent upon the organism's power of evoking simple Move- 

 ments continuously or with great ene^'gy, as well as upon 

 its power of performing very varied or intricate Movements, 

 Herbert Spencer has called special attention to this latter 

 point of view.* 



The importance of taking into account the powers of 

 Movement possessed by the animal is fully borne out by the 

 fact that the Brain attains such a remarkable size in the 

 Shark, as well as in the Porpoise and the Dolphin — all of 

 them creatures whose Movements are exceptionally rapid, 

 continuous, and varied. The great increase in the size of 

 the Cerebellum in each of these creatures is, therefore, not 

 so surprising; but it seems very puzzling, at first sight, to 

 understand why this should be accompanied by a co-ordinate 

 increase in the development of the Cerebral Hemispheres. 

 For this, however, there are two causes, the one general 

 and the other more special. It is a fact generally observed, 

 that Sensorial Activity, and therefore Intelligent Dis- 

 crimination, increases with an animal's powers of Move- 

 ment ; and secondly, there must be special parts of the 

 Cerebral Hemispheres devoted to the mere Sensory Appre- 

 ciation of Movements executed. The nerve elements lying 

 at the basis of this latter appreciation, however they may 

 be distributed through the Hemispheres, would naturally 

 be the more developed (and, consequently, all the more 

 calculated to help to swell the size of the Cerebrum), in 

 * " Principles of Psychology," vol. i. p. 192. 



