What don't female monotremes have?

Female monotremes are the only mammals which do not have nipples for the young mammals to suckle from. Monotremes, which are the echidnas and platypuses, feed their young on mothers' milk which is exuded from modified sweat glands, rather than from well-formed teats.

Female monotremes also do not have two external openings. They have just one external opening, the cloaca, for both waste elimination and for reproduction. The cloaca leads to the urinary, faecal and reproductive tracks, all of which join internally, and it is the orifice by which the female monotreme lays her eggs.