A COMPARISON OF THE EUROPEAN NORWAY AND 
ALBINO RATS (MUS NORVEGICUS AND MUS. NOR- 
VEGICUS ALBINUS) WITH THOSE OF NORTH 
AMERICA IN RESPECT TO THE WEIGHT OF THE 
CENTRAL NERVOUS SYSTEM AND TO CRANIAL 
CAPACITY 
HENRY H. DONALDSON 
The Wistar Institute of Anatomy and Biology 
FIVE FIGURES 
In a paper recently published (Donaldson and Hatai, ’11) the 
fact that the domesticated albino rat (Mus norvegicus albinus) 
of our laboratory colony has a relatively smaller central nervous 
system than the wild Norway (Mus norvegicus) from which it 
is derived, has been presented and examined in some detail. 
This difference between the two forms has been known to us for 
several years and ever since it was first appreciated we have been 
in search of a satisfactory explanation for it. 
In the paper just cited, the conclusion is reached that this 
difference represents one effect of domestication on the albino 
rat, but in order to justify this conclusion, it will be necessary not 
only to analyse domestication into its main factors, but also to 
test other explanatory suggestions which have been made. 
One such suggestion is to the effect that the small relative 
weight of the central nervous system in the domesticated Albino 
is due to the fact that the Albino has been derived from a strain 
of the wild Norway in which the central nervous system was 
also relatively small. It was to test this suggestion that the 
present study has been made. 
At the same time we recognize that this question represents 
one aspect only of the larger problem of the possible variations 
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