Abstract
Summary.: Data regarding the menstrual cycle of various Primates are summarized in Table II.In animals which undergo a sexual‐skin cycle the phase of swelling (folli‐cular phase) is generally longer and more variable than the phase of quiescence (luteal phase). This finding is related to the well‐established view that the luteal phase in the human menstrual cycle is generally less variable than the pre‐ovulation phase.Various issues concerning the sexual skin, including the sexual coloration of some male monkeys, are considered.