56 LEO LOEB 
follicles which we mentioned above. In the ovaries of pregnant 
animals of this period we may also find mature follicles, the granu- 
losa cells of which have more cytoplasm that stains red with eosin. 
Such follicles show less granulosa degeneration and a decrease in 
thenumber of mitoses is visible in the granulosa cells. Some degen- 
eration of granulosa cells may however occur in these follicles and 
their further fate will still have to be determined. 
The corpora lutea of pregnancy (first generation) are well pre- 
served. Fine vacuoles may however be present, especially in 
the peripheral lutein cells. Mitoses are also present. They do 
not show such pronounced signs of retrogression, as occur in cor- 
pora lutea of non-pregnant animals of this period. 
OVARIES OF GUINEA PIGS TWENTY TO TWENTY-SEVEN DAYS 
AFTER OVULATION 
At this period the proportion of animals in which a spontane- 
ous ovulation had taken place, notwithstanding the separation of 
females and males, is much greater than in the preceding period. 
Among twenty-two guinea pigs a spontaneous ovulation had taken 
place in eight, while in the fourteen other females no rupture of 
follicles had as yet occurred. In at least one and possibly in more 
of these fourteen guinea pigs a rupture was however imminent, 
as indicated by the presence of mature, red-staining follicles. In 
those animals in which ovulation had taken place within the last 
few days the follicles were in the condition corresponding to that 
stage after ovulation. The corpora lutea that originated as a 
result of the ovulation twenty to twenty-six days previously 
showed marked degeneration; the cells were vacuolar; in one case 
the lutein cells formed a hyaline material in which the vesicular 
nuclei were imbedded. Mitoses were present in only one case, in 
which the rupture had taken place apparently within the last 
twenty-four hours, but even vacuolar cells may divide mitotically. 
Many blood vessels have thick cellular coats and the blood vessels 
in general do not seem to be patent. 
In all the other guinea pigs in which a new rupture of follicles 
had not yet taken place the follicles behave approximately in the 
same manner as in the previous stage; we see follicles of various 
