· is triggered by fertilisation.
· can be divided into three main stages:
· division of the zygote
· into daughter cells.
· embryo (at the end of this stage) = blastula
· arrangement of embryonic cells
· into three germ layers (ectoderm, mesoderm + endoderm).
· embryo (at the end of this stage) = gastrula.
· formation of organs + organ systems.
· each germ layer àgives rise to different organ systems.