347 
during incubation in the common fowl. 
immediately after death become empty and the veins remain 
full, the vein from the vesicle, and that from the areola were 
the most conspicuous. 
In 18 days , the greater part of the yelk was drawn into the 
body. 
In 20 days, the chick was completely formed ; the yelk was 
entirely drawn in, and only some portions of the membrane 
of the vesicle appeared externally. The yelk passed into the 
intestine a little way above the openings of the coeca. 
Having traced the progress of the formation of the chick 
step by step, from the first appearance of the molecule found 
on the yelk before it leaves the ovarium to the complete evo- 
lution of all its parts, and its leaving the shell, I shall now 
take advantage of this investigation, which, illustrated as it 
is by Mr. Bauer's microscopical drawings, will stand long 
without a parallel. 
Although the processes by which the human foetus and 
that of quadrupeds are formed, differ in many essential par- 
ticulars from those employed in the bird, some circumstances 
are common to both ; one of these, the mode in which the 
vesicle bursts the membranes of the yelk is distinctly seen in 
the embryo in the egg hatched out of the body, and explains 
what takes place where the embryo is attached to the uterus, 
which otherwise could not have been ascertained. 
In a former paper, I have shown the formation of the ovum 
in the corpus luteum ; I have traced this ovum into the uterus, 
where it became concealed in the soft flocculent bed of efflo- 
rescent coagulable lymph prepared to receive it. That it is 
afterwards enveloped in this moss-like covering, has been 
demonstrated by my revered master in Human Anatomy, 
