They don't. Echidnas are monotremes, or egg-laying mammals. After mating, there is a gestation period for the egg of 23 days. During breeding season, the female develops a rudimentary pouch which is really just a flap of skin. When it comes time to lay her egg, she curls tightly into a ball and lays it directly in this pouch, where it is incubated for around 10 days. The young emerge blind and hairless, and stay in the pouch, suckling for two to three months.