A yolkless egg is a small egg with no

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...

, sometimes produced by a

pullet The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adul ...

that has only just started laying. These eggs are common and usually pose no harm. The eggs can also be called fart eggs, cock eggs, fairy eggs, dwarf eggs, and witch eggs. The name wind eggs is also sometimes used, 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 unfertilized.Oxford Universal Dictionary

Cause

A yolkless egg is most often a

's first egg, produced before her laying mechanism is fully ready. In a mature hen, a yolkless 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. In cases of an egg that contains a small particle of grayish tissue instead of a yolk, this is what has occurred. This type of egg occurs in many varieties of

fowl Fowl are birds belonging to one of two biological orders, namely the gamefowl or landfowl (Galliformes) and the waterfowl (Anseriformes). Anatomical and molecular similarities suggest these two groups are close evolutionary relatives; together ...

, including

chicken The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adu ...

s (both standard and bantams),

guineafowl Guineafowl (; sometimes called "pet speckled hens" or "original fowl") are birds of the family Numididae in the order Galliformes. They are endemic to Africa and rank among the oldest of the gallinaceous birds. Phylogenetically, they branched ...

, and

Japanese Japanese may refer to: * Something from or related to Japan, an island country in East Asia * Japanese language, spoken mainly in Japan * Japanese people, the ethnic group that identifies with Japan through ancestry or culture ** Japanese diaspor ...

(''Coturnix'') quail.

Etymology

Since they contain no

and therefore cannot hatch, yolkless eggs were traditionally believed to be laid by

cock Cock or cocks most commonly refers to: * Cock (bird) or rooster, a male of any bird species * Cock (slang), a slang term for the penis Cock or cocks may also refer to: Names * Cock (surname) * Cocks (surname) Places * Cocks Glacier, Ross ...

s. This gave rise to the myth that when a cock's egg was hatched, it would produce a

cockatrice A cockatrice is a mythical beast, essentially a two-legged dragon, wyvern, or serpent-like creature with a rooster's head. Described by Laurence Breiner as "an ornament in the drama and poetry of the Elizabethans", it was featured prominently i ...

, 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 on the other side without touching the roof.

In other animals

Leatherback sea turtle The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtles and the heaviest non-crocodilian reptile, reaching lengths of up to and weight ...

s are known to lay large clutches of viable eggs interspersed with yolkless eggs. This may be due to too much

albumen Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms a ...

, or it may function to separate viable eggs from each other and thereby improve gas exchange. The fossilized egg classified parataxonomically as ''

Parvoblongoolithus ''Parvoblongoolithus'' is an oogenus of fossil dinosaur egg whose small size and unusual shape suggest the possibility that it is a cock egg, dwarf egg. Distribution The sole known ''Parvoblongoolithus jinguoensis'' specimen was found in the Uppe ...

'' may represent an instance of a yolkless egg in an unknown species of

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

References

Eggs {{poultry-stub