54 LEO LOEB 
and follicles in various stages of granulosa degeneration and of 
connective tissues atresia. We may also find large mature follicles. 
In how many cases these latter are present, will still have to be 
determined. In such animals a rupture of follicles is imminent. 
In three guinea pigs a spontaneous ovulation had taken place 
at this period, notwithstanding the absence of male guinea pigs. 
In such cases young corpora lutea were found and, accordingly, a 
condition of the follicles characteristic of a period directly follow- 
ing ovulation. In the large majority of cases however a spontane- 
ous ovulation did not take place in ovaries at this period of the 
sexual cycle. In such cases the follicles showed the character 
described above. 
The corpora lutea of the first generation, which originated as 
a result of the last ovulation, show more or less signs of beginning 
retrogressive changes as indicated by fine or coarse vacuoliza- 
tion of the lutein cells. The intensity of this degenerative change 
varies is different ovaries. On the whole the retrogressive changes 
seem to be more marked in the nineteen days than in the sixteen 
days old corpora lutea; but variations seem to occur, even in cor- 
pora lutea of the same age. The vacuolization is usually most 
marked in the periphery and progresses toward the center. Other 
lutein cells are still more solid and mitoses in lutein cells can be 
seen in the majority of the corpora lutea of this period. In cases 
in which mature follicles are present and a spontaneous rupture 
of follicles is therefore soon to be expected, the corpora lutea 
show much vacuolization; but here also mitoses are still present in 
lutein cells. 
In some cases the retrogressive changes are still further ad- 
vanced and a connective tissue capsule may appear in the peri- 
phery of the corpus luteum. The marked vacuolization of peri- 
pheral lutein cells may be accompanied by a diminution in the 
lumen of blood vessels. Vessels with coats consisting of several 
rows of cells are seen regularly in these corpora lutea. The con- 
nective tissue in the center of the corpora lutea is usually dense and 
relatively small in amount. 
In those cases in which a new spontaneous ovulation had taken 
place the vacuolization of the corpora lutea had still further pro- 
