CHANGES IN THE OVARY 157 



Loewenthal^ advanced the somewhat different theory that the 

 monthly bleeding is actually brought about by the death of the 

 ovum in .the uterus, the " decidua " of menstruation being produced 

 by the embedding therein of the unfertilised egg. No evidence has 

 been adduced in support of this view, which is evidently open to the 

 same objection as Sigismund's hypothesis. 



A further modification of the same theory has been advanced by 

 Beard,^ who expresses the belief that the process of menstruation is 

 of the nature of an " abortion of something prepared for an egg given 

 off at or after the close of the preceding menstruation, and [that] it 

 takes place because this egg has escaped fertilisation." "Prior to 

 the appearance of the menses the uterus has formed a decidua, 

 which is regarded as equivalent to that which would arise when a 

 fertilised egg became affixed- to the uterus." This theory also, if it 

 is to be entertained at all, necessitates the assumption that there is 

 no correspondence between the prooestrum in the lower Mammalia 

 and menstruation in the Primates, since the degeneration stage of 

 the prooestrum in the dog or ferret, for instance, can hardly be of the 

 nature of an abortion of something prepared for an ovum which was 

 discharged at the preceding "heat period" many months before. 

 The difficulty is further increased for those animals which experience 

 oestrus only once a year, or even less often, for it is improbable that 

 they ovulate more frequently than they come "on heat." Beard, 

 however, denies that there is any correspondence between " the heat 

 or rut of mammals " and menstruation in the higher forms, saying 

 that very little is required in disproof of the supposed relation. 



The theory that the whole prooestrous process, including both 

 the degeneration and the recuperation stages, is of the nature of a 

 preparation ^ on the part of the uterus for the reception of a fertilised 

 ovum is not opposed to any of the known facts. The process is 

 sometimes viewed as a kind of surgical " freshening " of the uterus, 

 whereby the ovum can be safely attached to the mucosa during the 

 healing stage. It is possible, however, that the changing of the 

 uterine tissue is not the least important part of the process. 



Emrys-Eoberts * has made the further suggestion that the secre- 

 tion of the uterine glands, together with the blood and other products 



' Loewenthal, " Eine neue Deutung des Menstruationsprocesses," Arch. f. 

 Qyndk., vol. xxiv., 1884. 



^ Beard, The Span of Oestation and the Cause of Birth, Jena, 1897. 



3 Kundrat and Engelmann, " Untersuchungen liber die Uterusschleinihaut," 

 Strieker's Med. Jahr., 1873. Lawson Tait, Diseases of Women, 1889. For a 

 further discussion of some of the theories regarding the purpose of menstruation, 

 see Heape, "The Menstruation of Semnopithecus entellus," Phil. Trans., B., 

 vol. clxxxv., 1894. 



* Emrys-Roberts, "A Preliminary Note upon the Question of the Nutrition 

 of the Early Embryo," Proc. Roy. Soc., B., vol. Ixxvi., 1905. 



