CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 49 
number is decreased. Follicles in an advanced state of connective 
tissue atresia are frequent. 
The character of the follicles at this period-of the sexual cycle 
is the same in cases in which the last ovulation was preceded by 
delivery, in which, therefore, in the previous period of the sexual 
cycle a pregnancy was present, and in other cases in which the 
previous period of the sexual cycle had not been complicated by 
pregnancy. We see therefore that within six days quite small 
follicles, possessing only a very small follicular cavity, grow and 
reach medium size. During this period the granulosa of medium 
sized follicles did not degenerate, and no large follicles had as yet 
developed. We find therefore principally, besides the follicles 
with preserved granulosa, follicles in an advanced state of con- 
nective.tissue atresia. 
Six days after ovulation we find the corpora lutea of the last 
generation (corpora lutea six days old, asfollows: The center of 
the corpus luteum is filled by a more or less loose connective tissue. 
Mitoses are present in the lutein cells as well as in the endothelial 
cells of the capillaries. Almost all the vessels have a capillary 
character. They penetrate into the central connective tissue. At 
that period vessels with two coats (intima and muscle coat of the 
media) can be observed for the first time, although they become 
more frequent at a somewhat later period. 
In guinea pigs in which a pregnancy and delivery preceded the 
- last ovulation, the corpus luteum of the preceding pregnancy 
shows marked signs of degeneration. Especially the peripheral 
cells are frequently coarsely, while the more centrally situated 
cells are more finely vacuolar; but even in the latter the proto- 
plasm stains less with eosin and the nuclei are slightly chromatoly- 
tic; the cells appear distinctly pale. The vessels are very thick and 
at certain places in the periphery the connective tissue of the neigh- 
borhood seems to begin to grow into the peripheral parts of the 
corpus luteum. 
The ordinary corpora lutea of the second generation (not accom- 
panied by pregnancy) show marked vacuolization; they diminish 
in size and in one case yellow pigment developed in a few of the 
vacuolar cells. Therefore in the course of five to eight days 
