Cock egg

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A cock egg, cock's egg, dwarf egg, or witch egg is a small usually yolkless egg.[1][2][3] Such eggs are sometimes also called wind eggs, but this term more often refers to eggs without a shell or with a soft shell and less often to eggs that are rotten or unimpregnated.[4]

A cock 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 as 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. This type of egg occurs in many varieties of fowl, including chickens (both standard and bantams), guineafowl, and Japanese (Coturnix) quail.


Since they contain no yolk and therefore cannot hatch, these eggs were traditionally believed to be laid by cocks.[3] This gave rise to the myth that when a cock's egg was hatched, it would produce a cockatrice, a fearsome serpent which could kill with its evil stare. According to the superstition, this could be prevented by throwing the egg over the family dwelling so it smashed at the other side without touching the roof.[3]

In other animals[edit]

Leatherback sea turtles are known to lay large clutches of viable eggs interspersed with yolkless eggs. This may be due to too much albumen, or it may function to separate viable eggs from each other and thereby improve gas exchange.[5]

The fossilized egg classified parataxonomically as Parvoblongoolithus may represent an instance of a yolkless egg in an unknown species of dinosaur.[6]


  1. ^
  2. ^ Rookledge, K. A.; Heald, P. J. (1996-06-25). "Dwarf Eggs and the Timing of Ovulation in the Domestic Fowl". Nature. 210 (5043): 1371. doi:10.1038/2101371a0. Retrieved 2008-10-25.
  3. ^ a b c "Cock's egg". Retrieved 2010-09-02.
  4. ^ Oxford Universal Dictionary
  5. ^ Lawver, D.R.; Jackson, F.D. (2014). "A Review of the Fossil Record of Turtle Reproduction: Eggs, Embryos, Nests and Copulating Pairs" (PDF). Bulletin of the Peabody Museum of Natural History. 55 (2): 215–236. doi:10.3374/014.055.0210.
  6. ^ Zhang, Shuakang; Jin, Xingsheng; O'Conner, Jingmai K.; Wang, Min; Xie, Junfang (2015). "A new egg with avian egg shape from the Upper Cretaceous of Zhejiang Province, China". Historical Biology. 27 (5): 595–602. doi:10.1080/08912963.2014.902451.