248 NAOKI SUGITA 
ganglionaris (V) and especially the lamina multiformis (VI) 
grow much less rapidly. Chart 1 gives a comparison of the in- 
crease in the cortical thickness at corresponding localities (lo- 
cality ‘a’ of the mouse and locality III of the albino rat) in the 
albino rat and the mouse, the data being from Isenschmid (’11) 
and Sugita (’17 a). In the Albino the cortex attains nearly its 
full thickness at twenty days (weaning time), while in the 
mouse this stage was reached between twelve and seventeen 
days of age, very closely corresponding to the weaning time of 
m. 
m 
2.0 [ 
18 
B24 6 8 10 12 14 16 18 20 22 24 26 28 30 Ageindays. 
Chart 1 Giving the cortical thickness of the albino rat and of the mouse ac- 
cording to age. The data for the albino rat are taken from Sugita (717 a) at 
locality III measured on the sagittal section and the data for the mouse are 
taken from Isenschmid (’11) at locality ‘a.’ These two localities approximately 
correspond. 
the mouse, which is fifteen days. The remarkable phase during 
which the rapid increase in cortical thickness takes place in the 
Albino (first ten days after birth) cannot be clearly identified 
on the graph for the mouse cortex. It must be recalled, how- 
ever, that data on the mouse cortex have not been corrected for 
the action of the reagents, while the data for the rat have been so 
corrected. The outstanding fact, however, is that the cerebral 
cortex in both forms attains nearly its full thickness just before 
the weaning time. 
