16 NAOKI SUGITA 
On the basis of these rough data, the approximate age of the 
individuals in tables 1 and 2 can be inferred. 
To my regret, I did not obtain material under 17 grams in 
body weight. I could, therefore, not make a complete study of 
the postnatal growth of the cerebral cortex of the Norway rat 
from birth on and must in consequence be content to present in 
this paper the data beginning with material probably from 10 to 
12 days old. It may, however, be noted here, that, among the 
rats trapped, the following were evidently members of the same 
litter and still following the mother. 
(1) NXIa, NXIb, N XIc, N XId, with their mother 
N XX a, and three other young which were used for another 
purpose. 
(2) N XIi, N XI h, and four others. 
(3) ON XIN a. AN’ XI oy? IN) GI aN) OGY She N XIV a 
N XIV j, N XIV k. 
(4) N XIVe, N XIV f, and two others. 
(5) N X1IVa, N XIVb, N XIVc, N XIVd and two others, 
with their mother N XX b. 
This suggests that the Norway rats whose brain weighs less 
than 1.5 grams or whose body weighs less than about 40 grams 
are not yet independent of their mothers. 
III. TECHNIQUE 
For the technique of fixation and imbedding and the making 
and staining of the sections, the same procedures which have 
been already described (Sugita, ’17 a) were followed. ‘Thirteen 
different localities were measured on sections in three planes cor- 
responding to those used in the former study of the Albino cor- 
tex (cf. figs. 2, 4 and 6 in the paper cited). 
As to the cortical cell-lamination of the Norway rat, two sets 
of figures with explanations were given in the former paper (Su- 
gita, 717 a) reproduced from Lewis (1881) and Fortuyn (14) and 
to those I would like to call attention on this occasion. There 
does not appear to be any important difference between the 
Norway and the albino rats in the cell-lamination of the cerebral 
cortex. 
