Embryonic Development

The zygote formed as a result of syngamy is activated to divide, entering a sequence of developmental stages. Cleavage produces a solid ball of blastomeres, the morula, which hollows out during blastulation into the blastocyst; the blastocyst then implants into the uterine endometrium, after which gastrulation converts the simple two-layered embryonic disc into a three-layered (trilaminar) embryo made up of ectoderm, mesoderm and endoderm — the three germ layers from which all the tissues and organs of the body will eventually arise. …