the vascular fetal membrane that lies below the chorion and develops from the hindgut in many embryonic higher vertebrates (reptiles, birds and mammals)
2
A bar of cartilage at the base of the embryonic fins of some fishes
3
n an undifferentiated embryonic cell
4
of or relating to gills (or to parts of the body derived from embryonic gills)
5
n introduction during embryonic development of characters or structure not present in the earlier evolutionary history of the strain or species (such as the addition of the placenta in mammalian evolution)
