CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 59 
OVARIES OF GUINEA PIGS TWENTY-SIX TO FORTY DAYS AFTER 
OVULATION 
In five animals in which, in order to prevent pregnancy, both 
(and in one case one) of the Fallopian tubes had been ligated 
within twenty-six hours after copulation, and in which at a later 
operation incisions had been made into the uterus, no new ovu- 
lation had taken place at the time of the examination, twenty- 
six to thirty-four days after copulation. The corpora lutea 
(twenty-six to thirty-four days old) showed very marked retro- 
gression; they were very vacuolar; their size was always diminished 
especially after thirty-two to thirty-four days, but differed some- 
what in individual cases. Some corpora lutea formed small 
bodies containing very dense fibrous tissue in the center and en- 
closing in the periphery a relatively small number of very vacuolar 
cells. Other corpora lutea were still somewhat larger and con- 
tained a.few better preserved cells. 
Besides the retrogressing vacuolar corpora lutea some atretic 
yellow bodies could be found in some cases; they were remnants 
of corpora lutea at least fifty days old. In two other ovaries a 
spontaneous ovulation had taken place recently and the condition 
of the follicles was in accordance with the age of the new corpora 
lutea. Here also the thirty to thirty-two days old corpora lutea 
of the preceding ovulation were very vacuolar and contained blood 
vessels with a thick coat and much dense fibrous tissue. 
OVARIES OF A PREGNANT GUINEA PIG APPROXIMATELY THIRTY- 
FIVE TO FORTY DAYS AFTER COPULATION 
In these ovaries we found good follicles of small, medium and 
large size without granulosa degeneration and with mitoses in 
granulosa cells; other follicles showed various stages of granulosa 
degeneration and of connective tissue atresia. Mitoses were 
absent or diminished in number in follicles in which granulosa 
degeneration existed. 
In addition to the ordinary large follicles mature or almost 
mature follicles were seen in which the cytoplasm of the cells was 
well developed, and in which the granulosa contained only very 
