Monotremes are the only living mammals where females lay eggs instead of giving live birth. They produce sexually meaning they have two parents.Except during mating season, monotremes are solitary animals. Echidnas: Mating occurs in July or August during which time a single female is followed by up to ten males. A single egg is laid two weeks after copulation and hatches after ten days.
Platypus: A platypus lays her eggs on the bank of a stream, then curls around them to protect them and keep them warm. Echidnas lay a single egg in a temporary protective pouch on the mother's belly.
They produce milk for their offspring from mammary glands through holes in their skin. (They lack nipples) The offspring lick it off.
Monotremes fertilize internally after the sperm of the male enters the cloaca of the female (opening for the reproductive, urinary, and digestive systems). The embryo begins its development before the egg is laid.The egg stays inside the mother for twelve to twenty days. While the egg is still within the mother's oviduct (the tube leading from the ovaries to the cloaca), the tissues of the oviduct produce a shell onto the egg. The eggshell is soft, leathery, and porous. When the mother lays her egg, the embryo has developed the same amount as a newborn marsupial. After ten days of the egg's incubation, the young hatches by tearing the shell with a temporary egg tooth on its snout.