Eggs are laid by female animals of many different species, including
birds,
reptiles,
amphibians,
mammals, and
fish, and have been eaten by humans for thousands of years. Bird and reptile
eggs consist of a protective eggshell, albumen (
egg white), and vitellus (
egg yolk), contained within various thin membranes. The most popular choice for egg consumption are
chicken eggs. Other popular choices for egg consumption are
duck,
quail,
roe, and
caviar.