316 EDGAR ALLEN 
placed, and although the cumuli are still intact, the secondary 
liquor folliculi is present in them in small pools. The ova show 
resting nuclei centrally placed. The second set of follicles are 
medium sized and show only an early beginning of liquor forma- 
tion. ‘There are several atretic follicles present in various stages 
of granulosa degeneration. 
There are from twenty to thirty corpora lutea in this pair of 
ovaries, among which at least three sets can be defined. The 
most recent ones, ten in number, are superficially placed and 
quite large. ‘These corpora stain a light blue in contrast to the 
red-staining older sets. They are clearly defined from the 
stroma, and their constituent cells which are arranged in cords 
show distinct cell walls. Although the ovaries are hyperemic, 
there are few erythrocytes to be seen in these corpora lutea, which 
is in marked contrast to the small vessels crowded with erythro- 
cytes in the four-day corpora of the stage D animal described 
above. They must correspond, therefore, to the O period re- 
corded on the sixth day before death. The other two sets of 
corpora lutea are distinguishable chiefly by size, position in 
regard to the surface of the ovary, and proportionate ingrowth 
of stroma cells at their surfaces. The cytoplasm of the ‘luteal’ 
cells of both sets stains a blotchy red. There are a few intersti- 
tial cells in these ovaries. 
The early metoestrum 
Animal ¥*19, representing a typical M, stage, was one of three 
females of a litter of homozygous brown mice separated from 
males at the time of weaning, and examined daily for the appear- 
ance of her first oestrus. An open vagina was first noted on 
July 12th, at the age of three and one-half months, the membrane 
closing the orifice having ruptured during the night of the 11th. 
Routine smears were started on the 13th, and continued for 
forty days, during which time five complete cycles were recorded, 
making the average duration eight days. If, however, the first 
two longer periods are excluded, it brings this average down to 
seven days. At only one of these periods did she evidence 
external signs of oestrus. Previous ‘heat’ periods are recorded 
