148 Journal of Comparative Neurology. 



Intellectually, however, a child of this earlier age, is very 

 immature, yet our general theory demands that the growth in 

 intelligence should be accompanied by an increase in cortical 

 complexity, which, if other things were equal, would mean an 

 increase in mass. 



In this case, the correlation has not been statistically de- 

 monstrated, though in consideration of the small number of 

 records, this is not even presumptive evidence that such a cor- 

 relation does not exist, and it is here intended to point out 

 merely the reason why the demonstration is difficult. 



The psychological changes between the sixth year and ma- 

 turity are most naturally assumed to depend on changes in the 

 cerebral cortex. But the entire mass of these cell bodies is 

 probably less than i 3 grms. , and the normal growth of these 

 must be completed by a weight of substance which is but a 

 small fraction of this initial mass ; hence such changes in the 

 cortex must be very small so far as the mass of material in- 

 volved in enlarging the cell bodies is concerned. There is with- 

 out doubt an enlargement of axones during this period, as the 

 studies of Kaes^ and Vulpus" on progressive medullation show, 

 but even this is not great enough to counterbalance the other 

 causes of variation ; and for these reasons, the enlargement has 

 escaped demonstration by the method of weighing. 



A similar explanation is offered for our failure to find the 

 left hemi-cerebrum heavier than the right, although it is agreed 

 that the left is physiologically the more important, and 

 hence should be structurally more complex, and by inference, 

 heavier. ^ 



In this last instance, the independent increase of the ax- 

 ones might mask, on the right side, any deficiency in the mass 



* and 2. P. 241. 



^ The weight relations of the two hemicerebrums are given on pp. 184 and 

 185. Tables 43 and 44. 



