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- 



