330 EDGAR ALLEN 
As to variation in the same litter, my material is too meager 
to warrant any statement. However, the following data con- 
cerning four albino mice from the same litter are of interest. 
These animals were examined for 146 days, making from twenty- 
four to thirty cycles for each animal. The average cycle length 
is as follows: 
TABLE 2 
ANIMALS 
53 W 53 WNL 53 WNR 533 E 
Average, total... fied... 2. 4.8 5.0 4.1 5.2 
Number of unusually long} 0 4 (9, 11, 11, | 1 (8 days) | 2 (0, 10 
CYGIOS 5. -2.43 a5 SARC ORE: cree 10 days) days) 
Average minus long cycles.....| 4.8 4.8 4.9 4.9 
Reference to the first line shows considerable variation, but 
if the seven longer cycles, which are approximately twice the 
average length, be excluded, there is a difference of only 0.1 
of a day, which is well within the limit of error. 
It is difficult to generalize on the variation with age of the in- 
dividual. The first and second cycles following puberty are 
usually longer than the average during later life. 
Four mice were kept in a cold room at a temperature varying 
from 40° to 55°F. for five weeks during the middle of summer to 
see if continued low temperature would retard the cycle. It 
resulted only in their building an elaborate, covered ‘house-nest’ 
in which they spent most of the time. The duration of their 
oestrous cycles was not affected. 
Tumors appeared in two mice which were undergoing routine 
examination, which was continued in one case until the tumor 
grew to an inconvenient size. The first cycle after the appear- 
ance of the tumor contained a seventeen-day dioestrous interval 
succeeded by a one-day oestrus. This was followed by an eight- 
day D interval, after which time she was mated. No pregnancy 
resulted. In this case sexual activity was at least greatly 
retarded. 
