342 EDGAR ALLEN 
Marshall (’14) believes he has experimentally disproved the 
ripening follicles as a factor in the mechanism of cyclic sexual 
changes. For criticisms of this work the reader is referred to 
Stockard and Papanicolaou (’17) and Robinson (20). It seems 
to the writer that Marshall’s conclusions are not justified. Mar- 
shall falls back on the ovarian interstitial tissue as the cause of 
oestrus. Interstitial tissue in the ovary is a very ill-defined, 
intangible substance. Any cells not connective-tissue cells 
appearing between the follicles may be called interstitial. If 
they bear a resemblance to secreting cells they may be called 
typical interstitial cells. They are believed by most investiga- 
tors to be epithelial in nature and to have an origin similar to 
that of the ova and the follicle cells. The interstitial cells in 
the mouse ovary are chiefly peripheral in distribution and not to 
be confused with those appearing in many forms in the theca 
of atretic follicles or originating from old corpora lutea after 
connective-tissue ingrowth. There seems to be no _ periodic 
hypertrophy of these cells such as would be expected if they 
were the cause of cyclic oestrous changes in the genital tract. 
3. The corpora lutea. As has already been pointed out, the 
corpora lutea, have had attributed to them the following func- 
tions, the inhibition of ovulation even in non-pregnant animals 
and the cause of degenerative menstrual changes in the uterus 
of primates, and metoestrous changes in the uterus and vagina 
of other mammals (by analogy), and, finally, the source of a 
protective influence on the vaginal and uterine mucosae. 
In mice in which ovulation does not occur spontaneously, and 
consequently in whose ovaries there are no corpora lutea, the 
normal oestrous cycle goes on regularly. In mice that ovulate 
spontaneously several healthy sets of corpora lutea are present 
during the whole cycle. There seems to be no escape from the 
conclusion that in the oestrous cycle in the mouse (unaffected by 
pregnancy) the corpus luteum has no primary causative function. 
Since the evidence seems to discredit both interstitial tissue 
and corpora lutea as causative factors in the phenomena of the 
normal oestrous cycle, the follicles are the only remaining ova- 
rian possibility. 
