34 NAOKI SUGITA 
which weighs 16 to 20 per cent less. With this relation in view, 
I reduced by 18 per cent—which is the mean value of 16 to 20 
per cent (see table 9)—the weight of the Norway rat brains in 
table 7, and assumed that I thus obtained brain weights which 
represent the corresponding brain weights of the albino rat in 
respect to the cortical development. I have plotted the values 
for the actual cortical thickness on the reduced brain weights by 
mm 
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Chart 9 Giving a comparison of the thickness of the Norway cortex with that 
of| the albino cortex, on brain weight. °¢ °N General average thickness of the | 
Norway cortex according to the actual brain weight group. - - - - - AL General 
average thickness of the Albino cortex according to the brain weight group. 
Smoothed. Taken from chart 9 of the second paper of this series. *—*—® 
N’ General average thickness of the Norway cortex entered according to the re- 
duced brain weight representing the albino brain weight of the corresponding age. 
the dot and dash line in chart 9, in which the smoothed graph for 
the cortical thickness of the albino rat is represented by a dotted 
line. Glancing at the chart, my assumption appears to be jus- 
tified as both the graphs for the reduced Norway and the Albino 
are found to run a similar course. This relation is acceptable, 
since, as shown in the tables given by Donaldson and Hatai (11), 
and also by Miller (11), the relative weight of the brain in the 
mature albino rat is 12 to 16 per cent less than in the Norway rat 
of like body weight, and, furthermore, the relative weight of the 
