Female monotremes lack a uterus and vagina. Instead, they have a cloaca with one opening, like the cloaca's of reptiles and birds. The opening is used to excrete wastes as well as lay eggs.
Monotreme eggs have a leathery shell, like the eggs of reptiles. The eggs are retained inside the mother’s body for at least a couple of weeks. During that time, the mother provides the eggs with nutrients. Platypus females lay their eggs in a burrow. Echidna females have a pouch in which they store their eggs. Female monotremes have mammary glands but lack nipples. Instead, they “sweat” milk from a patch on their belly.
