The Destiny of Man. 47 



volition begin with this retention of a sur- 

 plus of molecular motion in the high- 

 est centres. As we survey the vertebrate 

 sub -kingdom of animals, we find that as 

 this surplus increases, the surface of the 

 highest centres increases in area. In the 

 lowest vertebrate animal, the amphioxus, 

 the cerebrum and cerebellum do not exist 

 at all. In fishes we begin to find them, 

 but they are much smaller than the optic 

 lobes. In such a highly organized fish as 

 the halibut, which weighs about as much 

 as an average-sized man, the cerebrum is 

 smaller than a melon -seed. Continuing 

 to grow by adding concentric layers at 

 the surface, the cerebrum and cerebellum 

 become much larger in birds and lower 

 mammals, gradually covering up the optic 

 lobes. As we pass to higher mammalian 

 forms, the growth of the cerebrum be- 

 comes most conspicuous, until it extends 

 backwards so far as to cover up the cere- 

 bellum, whose functions are limited to the 

 conscious adjustment of muscular move- 



