CHANGES IN NON-PREGNANT UTERUS 107 



blood. Eventually regeneration sets in and the mucous membrane 

 undergoes recuperation. According to Hill and O'Donoghue the 

 changes which occur during pseudo-pregnancy are comparable to 

 those of the procestrum in the Eutheria in which animals the 

 cyclical events have been thrust forward to a much earlier stage 

 as compared with the marsupial. It has been pointed out, however, 

 that there is no necessity to take this view since the pseudo- 

 pregnant uterine phenomena of Dasyurm find their parallel in 

 the rabbit under experimental conditions, and normally in the 

 monoestrous dog l (see p. 98). 



A consideration of the facts set forth in this chapter should 

 leave one in no doubt regarding the essential similarity between 

 the menstrual cycle in the Primates, and the cestrous cycle in 

 the lower Mammalia. Those who have denied that there is any 

 correspondence between " heat " and menstruation 2 have laid stress 

 upon the assertion that whereas " heat " in the lower animals is 

 the time for coition, this act, as a general rule, is not performed 

 during menstruation. But, as was first pointed out by Heape, it 

 is the prooestrum alone and not the entire " heat period " (a term 

 used generally to include both prooestrum and oestrus) which is the 

 physiological homologue of menstruation ; and, moreover, the latter 

 process in many of the Primates is succeeded by a regular post- 

 menstrual cestrus. 



It is possible, however, that menstruation in man and monkeys 

 represents pseudo-pregnant destruction as well as prooestrous 

 degeneration, the complete cycle of changes being compressed into 

 one month, and unless some such explanation be adopted one must 

 suppose that the processes of pseudo-pregnancy are unrepresented 

 in the menstrual cycle. 



Nielsen 3 goes further and supposes that menstruation in man 

 does not represent the prooestrum at all, but corresponds to a later 

 phase in the cycle which must be identified with pseudo-pregnant 

 destruction, but the preponderating evidence is against this view. 



It has been shown that although the changes which occur in the 

 uterus during the cycle present a general similarity in the various 



1 Marshall and Hainan, loc. tit. In all these animals there are parallel 

 pseudo-pregnant changes in the mammary gland and in the development, 

 persistence, and retrogression of the corpora lutea (see below, pp. 371-373). 



2 Beard, in The Span of Gestation and the Cause of Birth (Jena, 1897), says, 

 " very little is required in disproof " of this correspondence. 



3 Nielsen, " Om Corpus Luteums Funktion og den Fysiologiske Korrelation 

 mellem Ovarier og Uterus," Den Kgl. Veterinaer og Landbohojskole Aarsslrift, 

 1921. According to this author, in the cow, sow, and the bitch, ovulation 

 seems to occur before or at the beginning of procestrum, but see below, 

 pp. 130-133. Compare Leo Loeb, Surg., Gyn., and Obstet., vol. xxv., 1917. 



