DONALDSON-SCHOEMAKEK, NeiVOUS SystCVl of FvOgS. I3I 



grams respectively and an average of 16.2 grams, with an aver- 

 age brain-weight of 69.9 miHigrams. In the same manner the 

 weights of the three specimens of intermediate size in this table 

 give an average body-weight of 22. i grams with an average 

 brain-weight of 79.6 milligrams. The difference between these 

 two averages for body-weight is 36% of the smaller number, or 

 about midway between the two records in Table XIII. This 

 being the case and our previous statements being correct, it fol- 

 lows that the proportional value of the brain in the group with 

 heavier body-v^'eight should be less than in the group with the 

 lighter body-weights. The results can be best appreciated 

 when put in the form of a table. 



TABLE XV. 



Average Average Ratio of Milligrams of 



Body-weight. Brain-weight. Brain to Body-weight. 



Returning now to Table XIV we find the ratios of the 

 male to the female in R. temporaria, as 262 to 291, the lat- 

 ter being thus 1 1 % greater. The difference in the average 

 body weights is 29% (see Table XIII). Taking the data for 

 the males only of this species it appears, that within the limits 

 of two groups of males whose average body- weights are 16.2 

 grams and 22. i grams respectively, differing thus by 36%, the 

 ratios of brain- to body-weight are 231 to 277 (see Table XV), 

 giving a difference of almost 20% in the ratios or nearly twice 

 the difference claimed when the two sexes were contrasted. 

 We thus see that the males alone exhibit among themselves 

 a greater diminution in the relative weight of the brain than do 

 two lots of individuals grouped according to sex and differing by 

 nearly the same amount in body-weight. The suggestion from 

 this result as it stands, is that in the R. temporaria and escu- 

 lenta, as in our own R. virescens brachycephala, the female has 

 proportionately to the body-weight, a slightly heavier brain, 

 not a lighter one, as Fubini claimed. The point can however 

 hardly be positively decided from Fubini's data. 



