MH: define as not part of embryo, or will not develop into embryo? MH: changed def to exclude cells so this class could be included in gross anatomical part. DOS: Changed to something that I think works for both vertebrates and invertebrates and that keeps the restriction to multicellular structures. Old def: "Anatomical structure that is contiguous with the embryo and is comprised of portions of tissue that will not contribute to the embryo.". One remaining question - perhaps zygote is too restrictive given that some organisms have parthenogenesis e.g. aphids?