50 LEO LOEB 
since the beginning of degeneration the retrogressive changes have 
much advanced. The retrogressing corpora lutea of pregnancy of 
the corresponding generation are much larger at this period than 
the ordinary corpora lutea. 
In a certain number of ovaries we also find a further (third) 
generation of retrogressing corpora lutea, represented by yellow 
bodies. 
One corpus luteum deserves especial mention. In an ovary of 
a guinea pig which had ovulated approximately four and a half 
days before, five corpora lutea were found, four of whichshowing the 
typical structure. In the fifth of these corpora lutea, however, 
the lutein cells were arranged in the shape of glandular ducts. 
This condition has perhaps been produced through a dissolu- 
tion of the central cells. Otherwise the corpora lutea in this 
ovary were normal. 
The same typical changes in the follicles noticed in ovaries of 
this period after a preceding copulation and ovulation are also 
found in ovaries in which a spontaneous ovulation took place inde- 
pendently of a preceding copulation. As we stated above, such 
a spontaneous ovulation can be produced through an early exci- 
sion of the corpora lutea. The same follicular changes take place 
also in pregnant animals in which, through an excision of the cor- 
pora lutea about six to eight days after copulation, a spontaneous 
ovulation is produced approximately thirteen to fifteen days 
after the beginning of pregnancy, without the pregnancy being 
interrupted. 
We see therefore that these cyclical changes in the ovaries are 
essentially independent of copulation and of pregnancy and are 
directly connected only with ovulation. 
OVARIES OF GUINEA PIGS SEVEN AND ONE HALF TO EIGHT AND 
ONE HALF DAYS AFTER OVULATION 
At this stage of the sexual cycle we find good follicles of small, 
medium and large size with no, or only very little, granulosa 
degeneration. We also find follicles in connective tissue atresia. 
We see therefore that in approximately eight days follicles originally 
