i62 'Journal of Comparative Neurology and Psychology. 



body weights used were those calcuhited by formula (4), and then 

 the theoretical curve which fits these results most closely has been 

 obtained by the use of the formula (3). (Donaldson, '08.) 



y = .585 log' (x + 21) — 0.795 (3) 



where y represents the weight of the spinal cord and x the weight 

 of the body. 



This curve apparently forms a straight line, though in reality it 

 is a trifle convex towards the base line. 



From the correlation table based on groups dilfering by 10 mm. 

 in body length and .04 gms. in spinal cord weight, we obtain a co- 

 efficient of correlation which is .99, being almost f»erfect. 



It will be seen from the foregoing that the weight of the spinal 

 cord can be inferred from the body length with a high degree of 

 accuracy. 



In this connection an application of the foregoing data can be 

 made at once. It was noted in a previous paper (Donaldson, '08, 

 p. 3G0) that for rats of the same body weight, but of different sex, 

 the central nervous system in the male was slightly heavier than in 

 the female. The question naturally arises, therefore, whether there 

 is any somatic character with which this diiference in the weight 

 of the central nervous system according to sex can be connected. I 

 shall endeavor to show that in the sex difi^erence in body length we 

 find such a character. 



It has been ])ointed out in the present paper (p. 158) that for 

 the same body weight the males have a slightly greater body length 

 than the females. It will be of interest, therefore, to determine 

 whether this diiference in body length is sufficient to account for 

 the difference in the weight of the central nervous system. 



It is to be remembered in this connection that when males and 

 females of like body weights are compared, the brain in the male 

 is absolutely heavier, but the spinal cord is absolutely lighter. (Don- 

 aldson, '08.) 



The relative difference is slightly greater in the case of the spinal 

 cord, but the absolute mass of the brain is so much greater than that 

 of the cord that as a final result the entire central nervous system 

 is found to be heavier in the male. 



