Bird eggs are laid by the females and range in quantity from one to up to seventeen. Clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been fertilized; it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are sometimes called wind-eggs.
Eggs of various birds, labelled (Trinity College Zoological Museum, Dublin)
Guillemot eggs
Almost spherical bird egg (Senegal parrot)
Long, "elliptical" bird egg (Common murre)
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the animal hatches.
Eggs of various birds, a reptile, various cartilaginous fish, a cuttlefish and various butterflies and moths. (Click on image for key)
Six commercial eggs — view from the top against a white background
Salmon eggs in different stages of development. In some only a few cells grow on top of the yolk, in the lower right the blood vessels surround the yolk and in the upper left the black eyes are visible.
Diagram of a fish egg: A. vitelline membrane B. chorion C. yolk D. oil globule E. perivitelline space F. embryo