64 
AN EARLY HUMAN OVUM 
activity. The cellular “primitive” structure of the endometric stroma 
permits that special and ready reaction which constitutes the conservative 
function of the decidua, and by a recurrence of the menstrual cycle the 
mucous membrane is maintained in the necessary condition of immaturity. 
Accepting this interpretation of menstruation our Table II no longer 
presents the difficulties which it presents to the older views regarding the 
process. In the lower mammals ovulation takes place apparently during 
oestrus or in late pro-oestrum, and in most animals fertilization of the ova 
occurs forthwith. It is quite possible that in the human subject con¬ 
siderable delay may occur between insemination and ovulation on the 
one hand, and between insemination and fertilization, or the actual union 
of the male and female element on the other, as there is no fixed period 
corresponding to “ heat.” But it seems reasonable to suppose that the 
most favourable condition for successful impregnation lies in the occurrence 
of insemination and ovulation simultaneously, or at no great distance of 
time, and the occurrence of fertilization immediately the two elements 
meet, just as in the lower animals. 
Looking now at Table II, it is apparent on these premisses that 
fertilization of the twelve ova concerned must have taken place at wide 
intervals during the month, and comparing it with Table III it will be 
noticed that the first three must have been fertilized while repair was 
possibly not yet complete, and the next three clearly during the period 
of quiescence. Von Spee’s two ova may, and the last four certainly must, 
have been fertilized in the period of swelling, if we assume that the 
swelling continues in spite of the occurrence of fertilization. 
Most probably also ovulation corresponded more or less closely 
with fertilization, and occurred at intervals throughout the month, 
perhaps not even excepting the latter days of the actual period of 
menstrual discharge. A further inference is that ovulation and menstruation 
may, but do not necessarily, coincide. This is supported by the researches 
of Bland-Sutton on menstruation of Macaque monkeys and baboons, and of 
Heape on menstruation in Semnopithecus entellus and Macacus rhesus. 
They have shown that in these animals menstruation and ovulation do 
not necessarily coincide. Further, it is supported by the observations 
