G55 



in the Snakes and the snake-sliaped Slow Worm, but the deviation 

 is here still greater on account of a second cause. 



The results obtained in this way seem to prove with certainty 

 the existence of a law that can be applied to all Vertebrates, indi- 

 cating the relation between quantity of brain and size of body. 



In species of Vertebrates that are equal in organisation {si/ste- 

 matically), in their modus of living and in shape, the iveights of the 

 brains are proportional to the ■'"'/o power of the toeights of the bodies. 



Before we try to discover the meaning of this law, it is 

 important to determine the value of the exponent of correlation for 

 the brainweight of large and small individujxls in one and the same 

 species. The differences of size of the body are, in most cases, com- 

 paratively much less here than those between the species mutually, 

 and we are generally obliged to take averages of a great number 

 of individuals, to make the ei'rors attending each special observation 

 balance as much as possible against one another. With the exception 

 of such species as the Dog, having many races of very different 

 sizes, the best evidences can consequently be found for Man. 



The result 1 obtained in this respect for Man, in 1898, was com- 

 pletely contradictory to what I found for different species of Mammals.^) 

 The exponent of correlation proved to be an entirely different one. 

 For obvious reasons we cannot dispose, with regard to Man, for this 

 calculation of sufficient evidence, relating to normal weights of the 

 body belonging individually to the weights of the brain. In order 

 to be able to compare these quantities, we may follow two 

 indirect ways. In the first place it is possible to calculate the weight 

 of the brain of living Man. According to (he method of Welcker, 

 which has proved to be very trustworthy, I calculated the weights 

 of the brains of four groups, each of 10 strong, healthy, and not fat 

 young men, from the dimensions and shapes of their heads, which 

 evidences Otto Ammon had been kind enough to provide me with. 

 It had been ascertained for those 40 men that they did not grow 

 any more. They were all small farmers and day-labourers from 

 Baden. In this way I found an exponent of correlation of about 

 0.25, the value 0.245 (of two of the six combinations possible) is 

 probably more correct. 



Taking the second way I calculated r from the directly determined 

 weights of the brains of Englishmen (Londoners) with average 

 weights of bodies of men of the same social class, according to the 



1) Ueber die Abhangigkeit des Hirngewichles von der Körpergrösse beim Mensclien. 

 Arcliiv fur Aniliropologie. 4'. Bd i2ö. Het'l 4. BiMuuschvvcig 1898, p. 423-441. 



42* 



