Embryo

frog embryos
Embryos (and one tadpole) of
the wrinkled frog (Rana rugosa).

An embryo is an animal or a plant in its earliest stage of development.

The embryo of vertebrates is defined as the stages between the first division of the zygote (a fertilized ovum) until it becomes a fetus. An embryo is called a fetus at a more advanced stage of development and up until birth or hatching. In humans, this is from the eighth week after fertilization onward.

In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem (see hypocotyl), and root (see radicle), as well as one or more cotyledons. Once the embryo begins to germinate — grow out from the seed — it is called a seedling.

See also : In Vitro Fertilization -- embryology