Final answer:
Female monotremes lack teats and secrete milk from mammary glands onto their skin, differing from other mammals who have nipples. They also lay leathery eggs and have a cloaca.
Step-by-step explanation:
In monotremes, females lack teats and secrete milk from mammary glands directly onto their skin, where the young lap it up. Monotremes, which include species such as the platypus and echidnas, are unique among mammals as they lay leathery eggs and use a cloaca for excretion and reproduction, unlike other mammals that have separate openings. These primitive mammals provide an interesting comparison to more derived mammal species in terms of reproductive and lactation strategies.