Anatomical and functional differences in the placenta of primates.

The mammalian placenta is the most important fetal organ, assuring a variety of physiologic functions for the fetus that vary with different stages of embryonic development. There is an amazing variety of form and function in placentas of different mammals whose possible evolutionary significance has been alluded to by a number of reviewers. It was Grosser’s (1972. p. 170) contribution, however, that first drew attention to the principal microscopic features of the placental “barrier,” from epitheliochorial to hemochorial. This concept has allowed a more systematic approach to an understanding of the physiology of transplacental traffic. In his extensive review of placentation of man and mammals, this author could describe only few definitive studies on nonhuman primate placentas but remarked that “the captive reproduction of primates, currently attempted with ample funds in the USA, promises new insights.” Indeed, much has been learned about some aspects of primate placentation since then; most remarkable has been the understanding we have about Cercopithecids because of their value to biomedical research. Nevertheless, there are huge gaps in our anatomical and physiological knowledge of this organ in most other primates. This is particularly true of the mature placenta because of the almost regular placentophagy, the rarity of some primates, and also because of a widespread lack of interest in the pathophysiology of this organ. The most comprehensive recent account of the early developmental stages of many primate species is that of Luckett (1974). This contribution also makes reference to most earlier