PERCENTAGE OF WATER IN BRAIN AND CORD 101 
It is evident from the foregoing that the variability in the per- 
centage of water is somewhat greater in the case of the males 
than in the case of the females. When the corresponding mean 
values for the variability of the brain are compared with those 
for that of the cord we find that the values for the male cord 
are about 3.4 times that for the brain and the values for the 
female cord about 2.6 times. 
Among the 19 male groups examined there were 9 which con- 
tained from 1 to 4 litters, composed of three or more individ- 
uals. In all there were 21 litters. 
The average variability in the 9 age groups in which the 21 
litters occurred was 
¢ = 0.80 + 0.091 C=h0s == 05120 
while the average of the variabilities of the 21 litters taken 
from these 9 age groups was 
Ge — sor = 10.04 C— 0.46 = 0.11 
Thus among the males the variability within the litters was 
only about one half of that found for the age groups. It seems 
not improbable that myelin formation, which is so much more 
active in the cord than in the brain, may also be relatively 
more variable in the cord and thus contribute to the higher 
variability of this organ in general, and of the cord of the male, 
in particular. 
Among the females there were 7 age groups which contained 
from 1 to 3 litters composed of three or more individuals. In 
all there were 12 litters. The average variability of the 7 age 
groups in which the 12 litters occurred was 
¢ = 0.72 + 0.094 Creve aks 
While the average of the variabilities of the 12 litters was 
¢ = 0.31 = 0.08 C042 —= 0:01 
Again the litter variability is less than one half of that for the 
groups from which the litters were taken. 
