Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Monotreme
The key anatomical difference between monotremes and other mammals gives them their name; "monotreme" means “single opening” in Greek, referring to the single duct (the cloaca) for their urinary, defecatory, and reproductive systems. Monotremes, like reptiles, have a single cloaca; marsupials also have a separate genital tract; whereas most placental mammal females have separate openings for reproduction (the vagina), urination (the urethra), and defecation (the anus). In monotremes, only semen passes through the penis; urine is excreted through the cloaca. The monotreme penis is similar to that of turtles, and is covered by a preputial sac.