Placentation in the colugos Cynocephalus volans and Galeopterus variegatus (Dermoptera) and the transition from labyrinthine to villous placentation in primates

A choriovitelline placenta is not formed early in gestation nor is it present at term. Early in development invasive trophoblast spreads laterally to form a trophoblastic plate. We found evidence to support the idea that the colugo placenta is intermediate between the labyrinthine placenta of rodents and the trabecular type of Neotropical primates.