ON THE BRAIN WEIGHTS OF RATS DESCENDED FROM 
THE CROSS BETWEEN THE WILD NORWAY 
(MUS NORVEGICUS) AND THE DOMESTICATED 
ALBINO (MUS NORVEGICUS ALBINUS) 
SHINKISHI HATATI 
The Wistar Institute of Anatomy 
TWO CHARTS 
The present study was undertaken to determine the in- 
fluence of the parental brain weight on that in the offspring. 
For this purpose wild norway rats (Mus norvegicus) were crossed 
with their domesticated variety, the albino rats. The main 
advantages in employing these animals are two: 1) these two 
forms interbreed readily in confinement (Hatai, ’07) and 2) the 
brain weight in the Norway is considerably heavier (about 
14 per cent in the adults) than that of the Albino of the same 
body weight or length (Donaldson and Hatai, ’11). It was 
thought possible that the respective brain weights might be 
inherited as Mendelian characters and thus enable us to differ- 
entiate the Norway type from the albino type among the de- 
scendants. At the same time we encounter in such a study 
sevelrul drawbacks: 1) the fact that we do not possess any data 
by which to estimate the probable effect of domestication on the 
Norway rats during the experiment and 2) that we do not know 
the effect of close inbreeding on the weight of the brain under 
the changed conditions for the Norway. 
The lack of these data naturally limits our interpretation of 
the results. Nevertheless the results thus far obtained seem 
to indicate rather clearly that the brain weights in the hybrids 
lie practically midway between those in the parents. Thus the 
inheritance of brain weight in this experiment appears to be an 
example of ‘blending inheritance’ and it is the object of the pres- 
sent paper to give the evidence for this conclusion. 
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THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 6 
