166 
J. P. HILL AND CHAS. H. o’dONOGHUE. 
and of ovulation to the cycle as a whole. Thus, taking oestrus 
as an easily recognisable and obviously equivalent event in 
the two cycles, we see that, whilst in the Marsupial, ovulation 
only occurs at an interval of some days after oestrus, in 
the Eutherian, ovulation either coincides with, or follows 
immediately after oestrus. We have emphasised this important 
difference by applying the term post-oestrus to the period 
intervening between oestrus and ovulation. 
Furthermore, there is a very striking discrepancy in the 
time of occurrence of the degenerative changes in the uterine 
mucosa in the two. In the marsupial, these succeed ovulation ; 
in the Eutherian they not only precede ovnlation, but also 
oestrus. This, we regard as the most striking difference in 
the two cycles. 
In the preceding pages we have produced evidence 
demonstrative of the essential similarity in Dasyurus of these 
degenerative changes in the pseudo-pregnant and post-partum 
uteri. Indeed, comparison of the entire series of changes in 
the organs directly concerned with and related to reproduction 
in females which have ovulated and have failed to become 
pregnant, and which we have already described (ante, pp. 21- 
28), with those seen in the same parts of the pregnant female, 
entirely justifies us in recognising the occurrence of what we 
have termed a period of pseudo-pregnancy in the oestral 
cycle of the marsupial and in affirming that that period repre- 
sents the phase of true pregnancy. 
That being so, the question arises. What part of the Eutbe- 
rian cycle corresponds to pseudo-pregnancy in the marsupial ? 
There can be little doubt but that the uterine degenerative 
changes seen during the pseudo-pregnancy period in the 
marsupial are equivalent to those which take place in the 
Eutherian uterus during pro-oestrus, a conclusion which we 
think, in view of the evidence herein presented, will meet 
with general acceptance. 
These pro-oestral changes in the Eutherian uterus con- 
dition the appearance in some members of the sub-class 
(e.g. Primates) of a sanguineous discharge — the menstrual 
