l6o Journal of Comparative Neurology and Psychology. 



2. The relation of the weight of the brain and of the spinal cord 

 to the body length. 



We shall consider each division of the central nervous system sep- 

 arately. 



(a) The relation of the weight of the brain to the body length. 



When the data on brain weight are plotted according to the body 

 length, we obtain the distribution of individual entries (196 males, 



TABLE 3. 



Calculated Brain Weights and Spinal Cord Weights According to Body 



Length in Mus Norvegicus Var. Albus. 



Data for Both Sexes Combined. 



* Since the formulas do not allow of extrapolation toward the lower end of the curve, the 

 averages of the observed values are here employed. 



137 females as shown on Chart III. The difference betAveen the two 

 sexes is slight, and in this instance therefore the data for both 

 sexes will be treated together. 



The theoretic ciir\'e which fits the means most closely has been 

 obtained in the following manner: — 



For the body lengths given in Table 3, the body weights were 

 calculated by formula (4) transposed as follows: — 



