6 NAOKI SUGITA 
brains of the same age be compared, the Norway brain weight 
is 20 to 25 per cent higher than the albino brain weight, when 
the albino brain weight is taken as the standard. For the pur- 
pose of comparison in their developmental stages, I have as- 
sumed that the Norway brain would correspond to an Albino 
brain whose weight is 18 per cent less than the Norway brain 
weight of like age. Here the Norway brain weight is taken as 
the standard. The evidence for this conclusion will be given in 
detail in a later paper which discusses the thickness of the cortex 
in the brain of the Norway rat. 
A comparison of the Norway brain with that of the Albino 
may be made in two ways; by a comparison of brains of like 
weight or by a comparison of brains of like ages. In Chart 2, 
the diameters of the cerebrum in the Norway rat are compared 
with those in the albino rat. In part A of this chart, the data for 
the Norway and the albino rats were entered according to the 
observed brain weights, and in part B of the same chart, the 
same linear measurements for the Norway as used in part A are 
entered above brain weights which are 18 per cent below the 
observed Norway brain weights and which in turn represents the 
weights for the albino brains of like age with those of the Norway 
rat. The corresponding brain weights of the Norway and of the 
albino rats at the same age are given in table 3 A. It is assumed 
that the albino brain weight is 82 per cent of that for the Norway. 
If, as shown in part A of Chart 2, the comparison is made 
between the brains of the two rats using similar brain weight 
groups, W. B in the Norway cerebrum surpasses W. B in the 
Albino on the average by 0.4mm. L.G is quite equal in both 
the rats for brains weighing 1.1 to 1.6 gms, after which stage it 
is clearly greater for the Albino. Hf. is on the average slightly 
in favor of the Norway. 
If, on the other hand, as shown in | part B of the chart, a Nor- 
way cerebrum be compared with an Albino cerebrum of the 
same age (over 10 days), the Norway cerebrum has a greater 
W. B than the Albino, by about 1.00 mm., and also a greater 
L.G. The excess of L. G in the early age is on the average 0.7 
mm., but this difference decreases as the age advances, owing to 
the more rapid growth of the albino cerebrum in this dimension. 
