Changes in Generative Organs, etc. , of Non-Pregnant Dog. 555 



have shown that ovulation, when it occurs in Man, probably takes place 

 shortly after the menstrual period is over. It is usually stated (cf. 

 Halliburton's 'Handbook of Physiology') that the corpus luteum spurium 

 in Man is in a condition of retrogession at the end of one month, being 

 smaller then than after a period of three weeks. It has been established by 

 Heape and other investigators that menstruation in the Primates is the 

 homologue of the pro-oestrum in the lower Mammalia. Nevertheless, it 

 seems possible, in the light of the facts described in this paper, that the 

 menstrual cycle is a process of greater complexity than most authorities 

 have supposed, and that the destruction stage corresponds partly to the 

 later portion of the pseudo-pregnant period of the Dog, when the corpus 

 luteum no longer exerts an anabolic influence upon the reproductive organs. 

 If this surmise is correct, it helps to reconcile the two seemingly divergent 

 views as to the homologous stages of the cycle, namely, the view of Heape, 

 according to whom the pro-cestrum and menstruation are identical (a view 

 taken in previous papers by Marshall), and the theory put forward by 

 Beard, and adopted in more recent publications by Grosser, Hitschmann 

 and Adler, and Hill and O'Donoghue, according to whom the menstrual 

 process represents the removal of a preparation made for a fertilised ovum 

 which failed to arrive, or a degeneration of uterine tissue which was unable 

 to fulfil its purpose. In this connection it is interesting to note that, 

 according to Hitschmann and Adler, the premenstrual uterus in Man 

 undergoes changes which are similar in character to those observed in the 

 pregnant uterus. It seems possible, therefore, to regard menstruation in 

 Man as representing pseudo-pregnant destruction as well as pro-oestrous 

 degeneration, owing to the whole cycle of changes having been compressed 

 into one month. Indeed, unless some such explanation as this be adopted, 

 one must suppose that the processes of pseudo -pregnancy are unrepresented 

 in the menstrual cycle, and that the corpus luteum spurium in the Primates 

 exerts little or no influence. 



Since the retrogressive changes in the uterus of Dasyurv.s, the Rabbit and the 

 Dog in the later part of pseudo-pregnancy are correlated with the degenera- 

 tion of the so-called corpus luteum spurium, it seems reasonable to suppose 

 that the retrogression of the corpus luteum verum at the close of gestation 

 may be one of the factors involved in those destructive changes which are 

 associated with parturition. 



It has been pointed out that the comparatively long persistence of the 

 corpora lutea spuria and their influence upon the uterus and mammary 

 glands in bitches are probably associated directly with the moncestrous 

 habit. In most polycestrous animals the corpus luteum is believed to 



