PROBLEMS IN OBSTETRICS AND GYNECOLOGY 401 



body. But even if its origin be epithelial, it is equally remarkable 

 and unique that a glandular function should be carried on during 

 many years by a continued series of new formations in different 

 portions of an organ. 



In considering Fraenkel's hypothesis, various questions suggest 

 themselves for investigation. If the corpus luteum causes the 

 phenomena of menstruation, why is the latter function limited to 

 the primates? Born has pointed out that in all animals in which 

 there is a uterine insertion of the ovum there is a well-developed 

 corpus luteum, whereas in all other animals the latter is either 

 rudimentary or not developed at all. In all mammalians above 

 the monotremes the ovum is implanted in the uterus and the corpus 

 luteum is well developed. The absence of menstruation in the great 

 majority of these must either be due to some peculiarity of the 

 corpus luteum or to other unknown reasons. 



If the corpus luteum presides over the implantation of the ovum 

 through its internal secretion, does the latter influence the ovum 

 by passing to it through the maternal tissues (where presumably 

 it circulates) or is the ovum already influenced at the time it escapes 

 from the follicle? Fraenkel's experiments seem to negative the 

 latter hypothesis, for if the ovum reaches the uterus already charged 

 with the secretion, destruction of the corpora lutea in the rabbit 

 might not be expected to affect its implantation. It is therefore 

 more reasonable to suppose that contact with the uterine mucosa 

 in which the ovarian secretion circulates leads to the conditions 

 which determine the imbedding of the ovum. From histologic 

 studies it is now known that the implantation of the ovum in the 

 mammalia occurs after certain changes have taken place in it, that 

 in the vesicular stage there is a proliferation of the outer layer of 

 epiblast forming the trophoblast which has the power of attach- 

 ing itself to the uterine mucosa, of absorbing the latter and bur- 

 rowing into it. Is this power dependent upon the influence of a 

 circulating ovarian secretion? Hitherto it has always been be- 

 lieved that these changes were possessed by the ovum itself, for in 

 animals developed from ovums which find no resting-place in the 

 body the development of the ovum does not depend upon the ma- 

 ternal organism. 



It must, however, be believed that in the higher mammals, at 

 least, some special complementary characteristic must be found 

 in those areas of maternal tissue on which the ovum grows. In the 

 human female, for example, as I have already pointed out, a par- 

 ticular portion of the Miillerian tract, viz., the mucosa of the corpus 

 uteri, is the normal seat of implantation. The normal occurrence 

 of a decidual reaction in this area has already been noted. Is it 

 possible that this peculiar change is brought about by the ovarian 



