CYCLIC CHANGES IN THE OVARY OF GUINEA PIG ol 
very small have reacheda large size. The new (eight days old) 
corpora lutea grow actively during this period and show frequent 
mitoses in lutein cells. The corpora lutea of the preceding ovula- 
tion (second generation) continues to shrink and show marked 
vacuolization of the lutein cells. If the second last ovulation were 
accompanied by pregnancy, the retrogressing corpora lutea were 
still larger. 
The third generation of corpora lutea was represented by atre- 
tic yellow bodies the age of which varied approximately between 
forty-eight and ninety-five days. 
OVARIES OF GUINEA PIGS TEN TO ELEVEN DAYS AFTER OVULATION 
We find good follicles without granulosa degeneration of small, 
medium and large size, besides various stages of granulosa degener- 
ation and of connective tissue atresia, early stages with beginning 
ingrowth of connective tissue included. In the granulosa of well 
preserved follicles mitoses are present as usual. 
At this stage —ten days after ovulation—the ovary presents 
again its normal aspect. The follicles have grown to a large size 
and undergo the ordinary retrogressive changes. The ten to eleven 
days old corpora lutea are well developed; in the centre a relatively 
small amount of connective tissue is present. Mitoses in the lu- 
tein cells are usually frequent; they occur perhaps also in endothe- 
lial cells of capillaries. The large majority of the vessels have a 
capillary character, but occasionally a vessel is seen with a double 
coat of cells. Marked signs of degeneration are absent, but a few 
slightly vacuolar lutein cells may occasionally be seen. 
The second generation of corpora lutea, originating in the sec- 
ond last ovulation, are small vacuolar bodies with much connective 
tissue and thick vessels. If, however, this second last ovulation 
had been followed by pregnancy, the retrogressing corpora lutea 
of the previous pregnancy are as yet much larger; the lutein cells 
have become very vacuolar; many thick vessels are present. In 
some of the vacuolar lutein cells yellow pigment appears. 
A third generation of corpora lutea is represented by yellow 
bodies. They are, however, not found in all ovaries. 
