52 MEMOIR OF BARON HALLER. 
important. It appears almost demonstrable that the 
embryo is found in the egg; and that the mother 
contains in her egg- vessel all that is essential to the 
chick. For the yolk is a prolongation of the intes- 
tinal canal of the chick ; the internal membrane of 
the yolk is continuous with the internal membrane 
of that canal ; and this canal is continuous with the 
lining membrane of the stomach, mouth, and skin : 
the external membrane of the yolk again is the ex- 
ternal membrane of the intestine expanded, and is 
continuous with the mysentery and peritoneum. 
The envelope which covers the yolk during the first 
days of incubation is a part of the skin of the chick ; 
and must always have covered it, though originally 
invisible, since the great size of the yolk, compared 
with the nascent chick, will not permit us to suppose 
that there could be found in the skin of this little 
being matter sufficient to supply an envelope, if this 
covering had not done it from all time. If the skin 
of the chick had been only proportionate to its own 
abdomen, it could never have covered the immense 
size of the yolk. 
If the yolk be a continuation of the skin and 
intestine of the chick, the chick must always have 
existed in it; but the yolk has always existed 
within the hen ; the chick then must have existed, 
though invisible, in its peculiar membrane the 
amnios, always apparently placed upon the yolk, 
though also invisible, on account of its minuteness 
and transparency. 
“ The venous figure,” he concludes, “ and the struc- 
