"Animal embryos" refers to the early stages of development of animals before they are fully formed. It is a term used to describe the beginning of life for animals, similar to how a baby starts as an embryo in its mother's womb. Full definition
It is especially important, he says, to close the loophole that leaves unregulated experiments with animal embryos that contain human cells. (sciencemag.org)
The trouble is that most of the «recipes» for these chemical «cocktails» were derived from studying animal embryos. (seeker.com)
Some of these possible animal embryos apparently record the early stage of cellular division. (fossilmuseum.net)