The allantois is composed of two layers, which form a closed sac in connection with the urachus, or the tube which extends from the fetal bladder through the umbilical cord.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
Covering the external face of the amnion and lining the inner face of the chorion is a double membrane, the allantois.
"Common Diseases of Farm Animals"
R. A. Craig, D. V. M.
These eggs are objectionable to the fastidious housewife, because of the appearing of the white and scummy looking allantois on the yolk.
"The Dollar Hen"
Milo M. Hastings