Ontogeny, Genetic Control, and Phylogeny of Female Reproduction in Monotreme and Therian Mammals

Abstract

OverviewIn all living groups of mammals, prolonged protection of the developing young is a characteristic strategy of reproduction. Lactation, however, is the only uniquely mammalian characteristic, and all three groups have characteristic adaptations for achieving the transfer of energy from mother to young first via the uterus and placenta, and subsequently via the milk.In mammals the simple oviduct of lower vertebrates has differentiated into the uterus and vagina. There is a tendency toward fusion of the posterior end of the paired oviducts. The vagina remains paired in monotremes and marsupials, but is a single fused tube in all eutherians; the uterus may be paired, partly fused, or com..