CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 43 
going changes in the ovaries; that merely a slow progress takes 
place in changes which had set inbefore delivery. We furthermore 
see that without copulation a spontaneous ovulation does not need 
to take place after delivery, notwithstanding the degenerative 
changes in the corpora lutea; that ovulation can, however, occur 
without copulation, and this seems to be the rule, if the male 
had been in contact with the female for some time after delivery, 
a copulation having been made impossible during this period of 
contact. 
OVARIES OF NON-PREGNANT GUINEA PIGS IN THE PERIOD 
DIRECTLY PRECEDING OVULATION 
This description applies to ovaries of guinea pigs which had 
copulated a few hours previously, in which an ovulation had how- 
ever not yet taken place—ovulation usually taking place approxi- 
mately six to ten hours after copulation. In another case we 
examined the ovaries of a guinea pig that was ready for copulation 
(‘in heat’) in which, however, an actual copulation had been pre- 
vented by occluding the vagina by means of a strip of plaster. 
The condition of the follicles in these ovaries was similar to the 
condition found in ovaries preceding and immediately following 
delivery; we find good follicles of small, medium and large size; 
mitoses are present in the granulosa of such follicles. The majority 
of the large follicles however show more or less degeneration of 
the granulosa, with the exception of the few large follicles which 
progressed to complete maturity; they showed the cytoplasmic 
changes described above. In these as well as in some other well 
preserved large follicles the theca interna appears somewhat 
hyperemic. We also find the various stages of connective tissue 
ingrowth and of the subsequent diminution in the size of the folli- 
cles (‘connective tissue atresia’) which we described in the case 
of the other ovaries. In this case we do not find corpora lutea of 
a preceding pregnancy, but corpora lutea of an ordinary ovarian 
period, not accompanied by pregnancy. These corpora lutea 
are much smaller than those of pregnancy; their lutein cells show 
vacuolization, indicating the beginning of retrogressive changes. 
Notwithstanding these retrogressive changes an occasional mitosis 
