CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 69 
more solid and mitoses are still present. If no new ovulation have 
taken place, degeneration becomes more marked after twenty days; 
twenty-four days after ovulation we noticed a small amount of 
connective tissue growing into the periphery. At this period the 
number of mitoses is already diminished. In cases in which, 
between the eighteenth and twenty-sixth day after ovulation, a 
new rupture of follicles sets in, the degenerative processes are 
still more marked; mitoses may still be seen in the course of the 
first day after rupture of the follicles, but they disappear after- 
wards and the degenerative processes progress. The vacuoliza- 
tion of the lutein cells increases, the corpora lutea shrink, the con- 
nective tissue becomes gradually hyaline and is relatively pre- 
ponderating in quantity over the lutein cells. About six days after 
the new ovulation (in approximately twenty-six days old corpora 
lutea) yellow pigment may be seen for the first time in the vacuo- 
lar lutein cells. Eight days after the new ovulation the corpus 
luteum is much shrunken, and ten to eleven days after the new 
ovulation corpora lutea approximately thirty-one to thirty-two 
days old have been reduced to small vacuolar bodies, around 
which a strong connective tissue capsule may appear. Corpora 
lutea thirty-three to forty days old (twelve to nineteen days 
after new ovulation) still, represent vacuolar bodies; but now 
gradually the transformation into a yellow body sets in. Corpora 
lutea about forty-five days old have the appearance of yellow 
bodies and they may probably persist as such for a long time, 
after the third ovulation has taken place. Thus three generations 
of corpora lutea may be present side by side in the same ovary. 
c. Corpus luteum of pregnancy. The corpus luteum of pregnancy 
differs from the ordinary corpus luteum in the longer duration of 
mitotic division, and the delay in retrogressive changes. Although 
slight vacuolization may be noticeable at relatively early stages, 
the corpora lutea of pregnancy are still in a good condition thirty- 
five to forty days after ovulation and they may still show mitoses 
at this period. Towards the latter part of pregnancy however 
degenerative processes set in, vacuolization and loss in staining 
power of the nuclei, and other changes, are noticeable. Mitoses 
could not be seen at this stage, and they appeared to be absent 
