| Placenta in STREPSIRHINI (Lemuroids, Lorisoids) | Placenta in HAPLORHINI (Tarsioids, Platyrrhines, Catarrhines) | |
| "Diffuse" (distributed all over the internal surface of the uterus) | "Discoidal" (confined to a disk, pancake-like in both size and shape) | |
| At the cellular level,
made of more layers ("epitheliochorial,"
with contact between fetal tissue and maternal epithelium) | At the cellular level,
a more intimate contact:
fetal blood vessels invade the endometrium and either intertwine with
maternal blood vessels ("endotheliochorial") or are bathed directly
in maternal blood ("hemochorial") | |
| "Non-deciduous"
and easily detached, so that no blood or uterine tissue is lost at birth | "Deciduous" (shed at birth)
because the fetal tissue rips out the endometrial tissue with considerable bleeding | |
| This type of placenta is a derived and very peculiar condition, found only in the Strepsirhini and in horses! | This type of placenta is primitive and is found in tree shrews (Scandentia) and several other primitive placental mammals. |