Double-yolked pheasant eggs provide an insight into the control of albumen secretion in bird eggs

1. The possible role of the presence of the yolk in stimulating secretion of albumen was investigated. 2. Double-yolked and single-yolked pheasant (Phasianus colchinus) eggs were opened to determine the masses of the shell, albumen and yolk(s). 3. In double-yolked eggs, the two yolk masses were not significantly different. Albumen mass was increased above that expected from an egg with a single-yolk of comparable size but below that expected from an egg having a mass of the combined yolks. The mass of shell per unit area reflected the mass of the initial mass of the egg irrespective of the number of yolks. 4. The additional mass of albumen is unrelated to yolk or initial egg mass. It is postulated that in double-yolked eggs the oviduct is mechanically stimulated by the presence of both yolks, which empties the stores of water-soluble albumen proteins in the magnum wall. Such stores are insufficient to provide the same amount of protein for the two yolks.