RESPONSIVE LIFE OF ORGANISMS 465 



for the conveyance of impulses — how manifold are the ways 

 these cells may react upon each other. How inconceivably 

 numerous are the by-paths of the brain . The mere mechani- 

 cal complexity of our thinking apparatus is beyond the com- 

 pass of our thought. 



Despite the differences in the mental powers of verte- 

 brates, the anatomical differences of the cortex are not very 

 great. Structurally the cortex of a rodent is very like that 

 of a man. The increase in number of cells is not proportion- 

 ate to the increase in size in the brains of the higher mam- 

 mals; the increase appears to be due rather to the more 

 extensive development of cell processes and of intercellular 

 substance, the cell bodies in the cortex of the brains of the 

 higher mammals being thus spaced farther apart. The 

 mechanism is therefore much more alike than we should 

 expect, judging by the great differences in mental capacity. 

 The analogy has been aptly drawn, that the structural 

 difference between a watch that will not keep good time, and 

 a perfect time piece may be very slight indeed. 



Such is the arrangement of neurones, that every part of 

 the cortex may receive impressions from other parts of the 

 nervous system and every part may give rise to outgoing 

 impulses. In other words, every point is a center of an 

 arc, with incoming and outgoing paths. The brain is, 

 therefore, essentially an integration of neurones, combined 

 in afferent and efferent intercommunication arcs. 



There are no very striking differences in structure in 

 different parts of the cortex, and this in spite of the fact 

 that the functional differences are more or less distinctly 

 localized. But our knowledge of these "centers" in the 

 cortex is very imperfect. Results have been most readily 

 arrived at in the case of the motor functions, because a 

 stimulus applied to a given part of the cortex may pro- 

 duce a visible response in muscular movement. By this 



