How do monotremes raise their young?
The only known monotremes, platypuses and echidnas, raise their young differently.
Platypuses are one of two types of mammals which lay eggs. Unlike the echidna, the other egg-laying mammal (or monotreme), the platypus does not develop a temporary pouch to incubate the eggs.
The mother platypus prepares a chamber at the end of a burrow especially for the purpose of protecting the young. After she lays one to three eggs, which have already developed within her body for 28 days, she curls her body around the eggs to incubate them for another ten days.
After hatching, the mother platypus feeds her young on milk secreted from glands, rather than from teats. The young are blind, hairless and completely vulnerable. They are suckled by the mother for 3-4 months, during which time she only leaves them to forage for food. As she leaves the burrow, the mother platypus makes several thin plugs made of soil along the length of burrow; this helps to protect the young from predators which would enter the burrow during the mother's absence. When she returns, she pushes past these plugs, thereby forcing water from her fur and helping to keep the chamber dry.
The male platypus does not take any part in raising the young platypuses.
During the breeding season, a female echidna develops a rudimentary pouch - just a flap of skin - on its abdomen. The female echidna manages to lay a single egg in its pouch, and incubates the egg there. When the young hatches, it is fed on mother's milk which seeps from milk glands, not teats like other mammals.
Once the young begin to develop their sharp spines, they are transferred to a burrow. They remain in the burrow, not the pouch, to continue their development. This is their most vulnerable stage, as snakes often enter the burrows and eat the young.