174 THE GROWTH OF THE BRAIN. 



plexity in the encephalon is assumed to be necessary 

 for the maintenance of life. This minimum is pre- 

 sumptively represented by the least developed group of 

 microcephalies, yet even here the female brains are below 

 those of the males in weight, although it must be assumed 

 that in both the structural complexity is probably alike. 

 If this is so, the difference in weight between the two 

 groups must depend on the fact that the structural 

 elements in the encephalon of the female are smaller 

 than those in the male. What is true of this group is 

 probably true of the others, and the size of the nerve 

 elements rather than variations in their number is 

 therefore to be regarded as the principal factor in deter- 

 mining the difference in brain-weight. Size has a 

 double significance here. In the first place, the larger 

 cell has the larger proportion of unstable cytoplasm, 

 more stored energy. In the second, and this is a con- 

 dition peculiar to the nervous system, increase in size 

 accompanies increase in organisation ; but these points 

 will be taken up later. 



5. What value is to be given to the size of the brain in 

 different groups of animals ? As has been shown, small 

 dogs have smaller brains than large dogs, but in pro- 

 portion to the size of the entire animal, the smaller dogs 

 have the larger brains. The same is true of any other 

 similar group of animals. Moreover, the animals which 

 are absolutely the largest are in general the more intelli- 

 gent. The explanation appears to depend on the fact 

 that the mass of the individual elements is not propor- 

 tional to the mass of the body, so that if, for example, 

 the cell elements from a middle-sized dog be taken as a 

 standard, and those from the extreme forms be com- 

 pared with it, those from the smallest dogs will be found 

 proportionately large, while in the largest they are pro- 

 portionately small. Second, it depends on the fact that 



