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TR OEEO 
PREFACR. XXIX 
Throughout the above period the nucleus has gone 
on increasing in size, but at the time of fecundation, 
it is invariably enclosed and concealed by both coats 
when the two exist. But it undergoes no further 
change for some period. 
An ovulum at the time of fecundation will general- 
ly be found to consist of an outer coat open at its true 
apex, the opening varying in size, but always less than 
the diameter of the ovula; an inner cellular coat, ge- 
nerally thinner than the outer, prolonged beyond the 
nucleus into a hollow neck, the apex of which is 
open and more or less dilated, either (and perhaps ge- 
nerally,) about on a level with the opening of the outer 
coat, or projecting beyond it to a variable distance ; and 
a central cellular body the nucleus. generally ovate, 
its apex being more laxly cellular than the remainder, 
and occasionally projecting into the neck of the inner 
or when this does not exist of the outer integument 
and in this case very much resembling a coat itself. 
At this period the ovula may be entirely cellular or 
it may be partly supplied with vessels, but I shall 
refer to this more fully when I speak of the raphe. 
'The nucleus will at this period almost always be found 
to have a central discolored nucellus, or frequently 
an excavated cavity of varying dimensions. The above 
discoloration or rather opacity is invariably the pre- 
cursor of the cavity that is about to be formed, and 
indicates the situation as well as the direction in 
which it will be formed. This cavity is always? form- 
ed from below upwards. 
Allthe subsequent changes at least those of any 
importance, are carried on within the nucleus. They 
