Kangaroos and Their Pockets

There are four different nipples in the pouch of the mother. The new-born sucks the nipple that issues a milk with just the right temperature and amount of fat for a new-born. The other three nipples, on the other hand, contain milk meeting the needs of an older baby. In a few weeks, the new-born stops suckling its nipple and finds another nipple from which issues a milk prepared for its own needs.