THE AGE OF THE OVUM 
49 
therefore on the assumption that in the majority of instances insemination 
and ovulation nearly coincide, and for the sake of argument allow 24 hours 
for fertilization to occur. 
If we now deduct from the total interval of 16| days 24 hours for 
the period between insemination and fertilization, there remain 15-| days. 
The favourable state of preservation of the ovum, as already shown, 
precludes the possibility of its having been retained in the uterus for any 
length of time, and this is consistent with the fact that not more than 
36 hours elapsed between the first symptoms of abortion and its com¬ 
pletion. If it be assumed that development ceased soon after the 
commencement of abortion, at least 24 hours must be deducted at this 
end of the scale, and we have left a period of 14| days as the probable 
maximum age of the ovum. 
If the ao^e be calculated from the data regarding menstruation it 
O O O 
works out thus :—Menstruation should have occurred on October 25th, 
or 28 days after the date of the former period. Between this and the 
first symptoms of abortion 10 days intervened, making the minimum 
possible age of the ovum 10 days. If on the other hand the intermenstrual 
interval had equalised itself to the usual average of 26 days, the allowance 
on this occasion, seeing that the previous interval had been 25, should 
have been 27 days. On this basis the minimum possible age would come 
out as 11 days, or, according to the convention of His, 12 days. Now we 
know that degenerative changes commence some days before the appearance 
of the menstrual discharge. It therefore seems necessary to allow some 
time, probably as much as 3 days, during which the fertilized ovum 
exercises some influence over the uterus which results in the arrest of the 
destructive changes. This would bring the probable minimum age of the 
ovum up to 13 days. Taking all the factors into account, the absolute limits 
of age may be stated as from 12 to 15 days, but, as will be seen later 
when the data regarding other recorded ova are considered, a computation 
of from 13 to 14 days is probably correct. Moreover, it will be found 
to agree very well with such facts of comparative embryology as are 
applicable. 
The chronology of the early stages of development are most accurately 
G 
