304 HENRY H. DONALDSON 



The postnatal asymmetries which appear to arise largely from 

 use in man (Gaupp, '09) are not evident in the rat, and there 

 is nothing systematic in the slight deviation which we have 

 observed for the values of symmetrical bones. But it seems not 

 improbable that the weight of the skeleton is very responsive to 

 nutritional conditions, even when these vary only within limits 

 usually considered normal. 



The capacity of the mammalian skeleton to respond in this 

 way would seem to be indicated by the changes in skull and face 

 measurements of the descendants of immigrants to the United 

 States, shown by the observations of Boas ('11) and is implied 

 by the use of the Bertillon system of measurements for identifi- 

 cation ('93)- — a system founded on the idea of variability within 

 the race. 



From all this it follows that the tables here given must be 

 expected to furnish standard values only for albino rats reared 

 under conditions very similar to those applying to the rats used 

 for the tables, and the skeletons of which have been prepared in a 

 similar manner, while for rats otherwise reared our tables furnish 

 merely reference values with which the new data may be com- 

 pared. How the feral Norway rat, living under the usual con- 

 ditions, will differ from the domesticated Albino here studied in 

 these skeleton characters we do not yet know, but one set of 

 observations (Donaldson '12) shows the cranium to be heavier 

 in the Norway than in the Albino. 



Finally, it is not without interest to note that some characters 

 of the human body which meet with aesthetic approval, and which 

 depend on the proportions of the skeleton — the small head, well- 

 formed mandible, length of limbs, and small feet and hands — are 

 all of them characters which represent completed growth in both 

 man and the rat, and thus in approving of them in man, we 

 approve not only of constitutional vigor, but also of characters 

 which man shares with other mammals. 



