Influence of the Embryo on the Marsupial Uterus

Abstract

I REPORT here evidence of a local morphogenetic action by the marsupial embryo or placenta on the uterus. The marsupial placenta is usually said not to be an endocrine organ and to have no influence on uterine changes during pregnancy. This assumption is based on the failure of pregnancy to extend the life of the active corpus luteum or to interrupt the oestrous cycle^1,2. The gravid uterus of macropodid marsupials becomes larger than the contralateral, non-pregnant uterus, but this has been attributed to the bulk of the embryo occupying it, although observations by Flynn³ suggest otherwise. Evidence is given below that the two uterine horns of the wallaby, Macropus eugenii, are distinct in a number of ways, and that it is the presence or absence of the embryo which determines the differences.