In most
birds and
reptiles, an egg (
Latin ovum) is the
zygote, resulting from
fertilization of the
ovum. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing
embryo. When the embryo is adequately developed it breaks out of the egg in the process of hatching. Some embryos have a temporary
egg tooth with which to crack or pip the eggshell or covering.
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