Department of Zoology, Australian National University, Canberra 2600, Australia (Received 13 May 1974) CONTENTS PAGE Introduction 589 The oestrous cycle 590 Control of quiescence 592 Role of the corpus luteum 592 Lactational quiescence 592 Seasonal quiescence 592 Role of the pituitary 594 Patterns of breeding in Macropodidae 596 Control of pregnancy 599 The free vesicle stage 599 The control of diapause 599 Activation and maintenance of the embryo 599 Role of the uterus 602 Uterine secretions 602 Diapause and delayed implantation 604 Attachment stage 604 Determination of gestation length 605 Foeto-placental influence 605 Non-macropodid marsupials 606 The Macropodidae 607 Parturition 609 Role of the corpus luteum 609 Role of the pituitary 610 Conclusion 610 References 611 INTRODUCTION Two features distinguish reproduction in the Macropodidae from all other marsuppials. A period of embryonic diapause of variable duration may supervene after blastocyst formation, and the duration of pregnancy is