254 DIVERSIONS OF A NATURALIST 



units to nearly 2000. Idiots have abnormally small 

 brains which are often deformed. We leave them aside 

 for the moment. Healthy European adults have been 

 measured with a brain of only 1000 units. Australian 

 " black-fellows " have,, it seems, in some cases a brain 

 which measures as little as 900 units, but in others 

 it reaches 1500. The skull of the fossil man from 

 Pleistocene (possibly Pliocene) gravels in Java (known 

 as Pithecanthropus) had a capacity of only 900 units. 



If we suppose (as it is legitimate to do) that some 

 specimens of the gorilla may have a brain a third larger 

 than the average we get 670 units for the biggest gorilla 

 brain, and if we similarly assume that the primitive 

 human race of the Java gravel varied to the same 

 extent — namely, by a third more or less around 900 as 

 the normal — we find that the greatest size of the gorilla 

 brain overlaps the smallest of the Javan Pithecanthropus, 

 whilst the largest of that race would overlap not only 

 the Australian but the smaller-sized brains of Europeans. 

 Hence, if we accept, as we must, the fact that the brain 

 of man and the man-like apes naturally varies greatly 

 in volume in different individuals, there is no absolute 

 gap in regard to size between the higher races of man 

 and the apes. The difference is bridged over by the 

 lower races of man and the exceptional individuals of 

 apes. 



A remarkable feature in regard to man's brain is its 

 growth. Since it is contained in a bony box, which in 

 the adult is firmly ossified and incapable of expansion, 

 it is obvious that the brain, too, must cease growing 

 when the bony box has closed in. In the apes this 

 occurs at an earlier age than in man. The brain-box 

 has its sides and roof constituted by a number of plate- 



