What is the reproduction of placentals marsupials and monotremes?

Answer 1

All three groups of mammals copulate. Male monotremes and marsupials have split penises with two functional heads (male monotremes also have two non-functional heads). They are used only for reproduction, as they urinate through the cloaca. Placental mammals have a single-headed penis that it used for both urination and reproduction. If the egg is fertilized, the embryo develops in the female's uterus. In monotremes, an eggshell forms around the embryo, and the female lays the egg, out of which the baby hatches. Marsupials give live birth, but the young are delivered prematurely. They must crawl up to the nipple (often inside a pouch) and attach to it. They do not detach for the first time until they are more fully developed. With the help of a more advanced placenta inside the uterus (marsupials have simpler placentas), placental mammals give live birth to more advanced young after a much longer gestation period. Female monotremes produce milk, but it simply passes through the skin; they have no nipples. Female marsupials and placental mammals have nipples, from which the babies suckle.