Placenta

The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother’s blood supply. Placentas are a defining characteristic of eutherian or “placental” mammals, but are also found in some snakes and lizards with varying levels of development. Note, however, that the homology of such structures in various viviparous organisms is debatable and, in invertebrates such as Arthropoda, is analogous at best.