233 



structure and functions of other organs, and on other not easily 

 measurable factors which determine the c e p h a 1 i s a t i o n of the 

 central nervous system. When we compare Man with animals of 

 the same body weight, when, in other words, we eliminate the factor 

 body weight, we see that he far surpasses all fhe animals. He 

 possesses three times the brain weight of a species of anthropoid 

 apes of the same weight and more than six times that of an equally 

 heavy gazelle. We may also say that the coefficient of cephalisation 

 it of Man is three times as great as that of Anthropoid Apes and 

 more than six times as great as that of the Gazelle. 



We may assume equal cephalisation for the Cat and the Tiger, 

 and yet we see the body weight increase in a ranch greater pro- 

 portion than the brain weight. The same fact is found on comparison 

 of the Mouse with the Rat, of tiie Pigmy Antilope with the Beisa- 

 Antilope etc. Evidently the weights of brain and body, also with 

 equal development of that organ, are not simply proportional to 

 each other. The laige species of the same genus, and also the large 

 adult individual of the Domestic Dog species always has less brain 

 weight in ratio to the body weight than the small species and the 

 small adult individual. On account of the equality of the densities, 

 the volumes may be substituted for the weights, and it is, therefore, 

 possible that another measure of the body than the volume, for 

 instance the surface, which is proportional to the 2/3 power of the 

 volume, — for which the weight P of the large animal may be put, 

 and the weight p of the small one, — determines the quantity of brain 

 — volume or weight — of the species. A priori it seems, indeed, that 

 there is a good deal to be said for this view, for the sensuftl areas, the 

 physiological cross-sections of the muscles, which determine muscular 

 force, the superficial extent of the body, on which metabolism 

 depends, are proportional to the surface of the body. The brain 

 weights ^ and e of two animals differing only in body weight, but 

 with for the rest quite identical organisation, may always be put 

 E = xP' and e = itp'' ; then the exponent of relation r, indicating 

 the power of the body weight with which the brain weight increases 



or decreases,, can be calculated trom the equation r =z — —^— 



log P — log p 



E 

 and X = -— will be found. 



Twenty-five years ago, making use of the observations of weight 

 published by Max Wkber *) a year before, I found thus ^9 as mean 



^) Max Weber, Vorstudien iiber das Hirngewicht der Saugethiere, in Festschrift 

 fur Carl Gegenbaur, p. 105— 123. Leipzig 1896. 



