ABSTRACT
Menstruation, the shedding of the lining of the uterus is found in humans, chimpanzees, gorillas, orang-utans, gibbons, old and new world monkeys, the elephant shrew and in a species of bat (Dempsey, 1939; Graham, 1981). The reasons why these species use this ultimate form of tissue remodeling are unclear, but are probably related to the only obvious function of the endometrium, i.e. implantation. There seems to be a link between menstruation and hemochorial placentation in which a variable degree of trophoblastic invasion is tolerated by the maternal decidua, as species which use epithelio-chorial placentation do not menstruate (Enders, 1991).
