CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 56 
sizes without granulosa degeneration,’ and follicles of large and 
also of medium size in various stages of granulosa and connective 
tissue atresia. 
In the ovaries of the guinea pig in which a spontaneous rupture 
of follicles was imminent, the twenty-two days old corpora lutea 
also showed the signs of early degeneration; some of the cells 
were still good, but the majority were vacuolar. 
In the guinea pigs, in which a spontaneous ovulation had not yet 
taken place, the corpora lutea of the last ovulation were also in a 
process of degeneration, which was especially marked during the 
later stages, twenty-four to twenty-six days after ovulation; here 
the vacuolization was very pronounced, and occasionally con- 
nective tissue began to grow into the periphery of the corpus 
luteum. The vessels of these corpora lutea were very thick. In 
some other ovaries, especially in those examined twenty and 
twenty-one days after ovulation, the number of relatively well 
preserved cells was still greater. On the whole the number of 
mitoses found in lutein cells at this period is distinctly diminished. 
The older generations of corpora lutea are represented by atre- 
tic yellow bodies, which are however not present in all animals. 
In one case a corpus luteum was present that originated as a result 
of an ovulation that took place approximately ninety-three days 
before and was accompanied by pregnancy. In this cases twenty- 
seven days after delivery very little of the lutein tissue was left, 
the blood vessels had very thick coats, and the fibrous tissue of 
the remnant of the corpus luteum was very prominent. 
If the ovulation which took place twenty to twenty-seven days 
before were followed by a pregnancy, no new spontaneous ovula- 
tion took place. The conditions of the follicles was the same as in 
those guinea pigs in which the last ovulation was not followed by 
pregnancy and in which no new spontaneous ovulation had as yet 
taken place. The corpora lutea of pregnancy of this period showed 
much less vacuolization, although a slight amount of it may have 
been present, especially in the periphery of the corpus luteum. 
Mitoses were more common in these corpora lutea of pregnancy 
than in the ordinary corpora lutea of the same period. Their 
size was also greater. 
JOURNAL OF MORPHOLOGY, VOL. 22, NO. 1 
