96 HENRY H. DONALDSON 
To bring together the observations and comments on cranial 
capacity which have just been presented, it appears that while 
the European Norways areshown to be distinct from the European 
Albinos as regards their cranial capacity, yet the interpretation of 
the direct observations is necessarily so modified by the shrinkage 
of the crania that in the case of any particular series, we can infer 
only in a general way from the cranial capacity to the brain weight. 
CONCLUSIONS 
1. In the case of the wild Norway rat, which entered western 
Europe about the beginning of the eighteenth century, and the 
eastern United States about 1775, the observations on the con- 
stitution of the populations, the general body form, the weight of 
the central nervous system and the cranial capacity, show that 
‘it is at the present time essentially similar in these respects in the 
two continents. 
2. The observations on the albino rat from different stations 
indicate that this variety is also essentially similar in the two 
continents. Therefore there is no evidence to support the view 
that the Albino was derived from a strain of the Norway hav- 
ing a relatively small central nervous system. 
3. Logically this result does not preclude the possibility of such 
an origin, but it does indicate on the other hand the absence of 
present evidence in favor of it. 
4. That the Norway rats from the three stations in Europe are 
very similar to the Philadelphia Norways, despite the difference 
in station and the wandering of those that have crossed the sea, 
is probably due to the fact that the series of rats which have here 
been compared represent those which kept close to man, and all 
of which lived among food conditions and other surroundings 
characteristic of large cities; conditions and surroundings which 
are much the same in western Europe and eastern America. 
A like explanation applies also to the similarity found among the 
Albinos from these two regions, and perhaps even more forcibly, 
as the treatment of these caged animals probably represents a 
still more uniform environment than that which the Norways 
experience in their wild life. 
