<P> An embryo is an early stage of development of a multicellular diploid eukaryotic organism . In general, in organisms that reproduce sexually, an embryo develops from a zygote, the single cell resulting from the fertilization of the female egg cell by the male sperm cell . The zygote possesses half the DNA of each of its two parents . In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism . The result of this process is an embryo . </P> <P> In humans, a pregnancy is generally considered to be in the embryonic stage of development between the fifth and the eleventh weeks after fertilization, and is expressed as a fetus from the twelfth week . </P> <P> First attested in English in the mid-14c., the word embryon derives from Medieval Latin embryo, itself from Greek ἔμβρυον (embruon), lit . "young one", which is the neuter of ἔμβρυος (embruos), lit . "growing in", from ἐν (en), "in" and βρύω (bruō), "swell, be full"; the proper Latinized form of the Greek term would be embryum . </P> <P> In animals, the development of the zygote into an embryo proceeds through specific recognizable stages of blastula, gastrula, and organogenesis . The blastula stage typically features a fluid - filled cavity, the blastocoel, surrounded by a sphere or sheet of cells, also called blastomeres . In a placental mammal, an ovum is fertilized in a fallopian tube through which it travels into the uterus . 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 eleventh week of gestation . However, animals which develop in eggs outside the mother's body, are usually referred to as embryos throughout development; e.g. one would refer to a chick embryo, not a "chick fetus," even at later stages . </P>

What is the main purpose of the last seven months of pregnancy