from The Century Dictionary and Cyclopedia
- Not having a placenta; aplacental, as the marsupials and monotremes. See aplacental.
Sorry, no etymologies found.
However, there are studies suggesting that at least some of the African HIV transmission due to non-placental, non-sexual causes is due to illegal abortion, and that this may be more important than ritual circumcision/female genital mutilation, also a known factor in transmission.
Subsequently, as the non-placental chorionic villi atrophy, their vessels disappear; and then the umbilical arteries convey the whole of their contents to the placenta, whence it is returned to the heart by the umbilical veins.
Among the former, the amphibian follows the fish, the reptile follows the amphibian, the mammal follows the reptile, and non-placental mammals are followed by the placental.
The non-placental mammals may have a different calculus for parental investment, and there are important mechanistic differences as well.
The multiplicity or loss of the vitellogenin (vtg) gene family in vertebrates has been argued to have broad implications for the mode of reproduction (placental or non-placental), cleavage pattern (meroblastic or holoblastic) and character of the egg (pelagic or benthic).
The greater part of the chorion is in contact with the decidua capsularis (Fig. 34), and over this portion the villi, with their contained vessels, undergo atrophy, so that by the fourth month scarcely a trace of them is left, and hence this part of the chorion becomes smooth, and is named the chorion læve; as it takes no share in the formation of the placenta, it is also named the non-placental part of the chorion.