http://en.wikipedia.org/wiki/Egg_yolk
snip:
"Double-yolk eggs occur when ovulation occurs too rapidly, or when one yolk becomes joined with another yolk. These eggs may be the result of a young hen's reproductive cycle not yet being synchronized."
snip:
"Some hens will rarely lay double-yolked eggs as the result of unsynchronized production cycles. Although heredity causes some hens to have a higher propensity to lay double-yolked eggs, these occur more frequently as occasional abnormalities in young hens beginning to lay. Usually, a double-yolked egg will be longer and thinner than an ordinary single-yolk egg. Double-yolked eggs usually only lead to observed successful hatchlings under human intervention, as the chickens interfere with each other's hatching process and die"
(But even more interesting, in my opinion, are eggs with no yolks):
snip:
"Eggs without yolk are called "dwarf" or "wind" eggs.[8] Such an egg is most often a pullet's first effort, produced before her laying mechanism is fully ready. In a mature hen, a wind egg is unlikely, but can occur if a bit of reproductive tissue breaks away, stimulating the egg producing glands to treat it like a yolk and wrap it in albumen, membranes and a shell as it travels through the egg tube. This has occurred if, instead of a yolk, the egg contains a small particle of grayish tissue. An archaic term for a no yolk egg is a "cock" egg.[9] Since they contained no yolk and therefore can't hatch, it was traditionally believed that these eggs were laid by roosters."
= new reply since forum marked as read
