My wife recently broke three eggs into the frying pan in quick succession, and all were double-yolked. Does this mean there would have been three sets of chicken twins?
鈥� Double-yolked eggs are the result of two ova coming from the ovary within a very short time. This occurs more frequently in young birds approaching their peak laying, but it is unusual to find them in standard eggs graded for sale because double-yolkers are usually removed and sold for special culinary purposes.
It is feasible, if rare, for an egg with two ova to be fertilised. If this does happen, a number of factors make it very unlikely that either chick would survive. The larger the egg, the smaller the ratio of surface area to volume, so oxygen exchange across the shell would be compromised and the chicks would be competing for the same supply.
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If the two chicks were to survive long enough to hatch, they would both need to break into the air cell contained within to take their first breaths. They would then have to get out of the shell.
Chicks usually do this by putting their head under one wing and using this as a fulcrum, and they need to be able to turn a full circle as they chip away at the shell with their 鈥渆gg tooth鈥�. This would be nearly impossible with two chicks in the shell, because they would obstruct one another.
One can seldom say never, but it would be highly unlikely for two viable chicks to hatch out of one egg.
Kim Critchley, Clarence Park, South Australia
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