12 NAOKI SUGITA 
differences in the cerebral cortex. Consequently, it became 
desirable for me to compare in these two forms, one wild and 
aggressive and .the other gentle and domesticated, the course 
of the growth of the cerebral cortex. 
Using my previous studies on the Albino (Sugita, ’17a) and 
on the form of the Norway brain (Sugita, 718) as a paint of de-_ 
parture, I will present in this paper the data on the cortical thick- 
ness of the Norway rat and will compare these with the data 
for the Albino. In this comparison of the brains of the two 
forms, the data, other than those on cortical thickness, are all 
quoted from Donaldson and Hatai (’11, 715). 
Il. MATERIAL 
The Norway rats used in this study, were all supplied through 
the courtesy of The Wistar Institute and were trapped alive in 
Philadelphia and its vicinity, between April and November, 
1916. There were 36 males and 18 females, representing every 
stage of growth between 17 and 394 grams in body weight. 
In the preparation of the material and the arrangement of the 
data, the same methods as those described in my former study 
on the Albino (Sugita, ’17a) were followed. For the discrimi- 
nation of a Norway group from an albino group of the same 
tabular number, the Norway records carry the capital letter N 
before their group number. 
The following tables, tables 1 and 2, give the sex, body and 
tail lengths, and body and brain weights of the Norway rats 
used in this study, grouped according to their brain weights and 
averaged for each group. Table 1 contains the material used 
for the sagittal and frontal sections and table 2 that for the 
horizontal sections. 
Comparing the body measurements of this series with those 
given in table 85 in “The Rat’? (Donaldson, ’15), it is found 
that the average values for my material by groups correspond 
fairly well with the table values. 
The increase in the body measurements of the Norway rat 
according to age is imperfectly known, so that we can not in- 
fer the age from the body measurements with any exactness. 
