44 LEO LOEB 
can still be found in lutein cells. The corpora lutea of the second 
last ovulation have in the meantime been transformed into yellow 
bodies. Processes of degeneration have therefore set in in the 
corpora lutea of non pregnant as well as of pregnant guinea pigs 
before ovulation. These beginning degenerative changes do 
however not prevent the occurrence of a few mitoses in the cor- 
pora lutea of previously not copulated animals, while in the de- 
generating corpora lutea of pregnancy we have so far not been 
able to detect the presence of mitoses in lutein cells. 
OVARIES OF GUINEA PIGS WITHIN THREE AND ONE HALF DAYS 
AFTER OVULATION 
In connection with ovulation certain far reaching changes take 
place in the ovaries. All follicles, with exception of very small 
ones, degenerate. These changes set in with ovulation, or they 
may perhaps start somewhat earlier, namely, simultaneously 
with those processes that bring about ovulation. As we have 
pointed out above, the general degeneration of the follicular 
granulosa which we find directly after ovulation cannot yet be 
observed before ovulation. This sudden degenerative process is 
quite independent of copulation; we found that it can be produced 
through ovulation without a preceding copulation. We discovered 
experimental means through which we can produce a spontaneous 
ovulation without a preceding copulation. Such an ovulation is 
followed or accompanied by the same degeneration of the granu- 
losa. Moreover, if we keep a number of female guinea pigs separ- 
ated from the males and if we examine their ovaries after various 
periods of isolation, we find occasionally ovaries in which the 
rupture of follicles had taken place a few days before. In this 
case also the typical follicular degeneration takes place indepen- 
dently of a preceding copulation. 
Six and a half hours after a preceding copulation the ovaries 
showed, besides the presence of newly ruptured follicles, the follow- 
ing changes in the follicles: All, with the exception of very small 
follicles, show granulosa degeneration; in the large majority of the 
follicles almost the whole granulosa is found in a process of degen- 
eration. We also find follicles in the process of connective tissue 
