What is the animal body is divided into three parts?

The primary and most well-known traits that taxonomists use to divide mammals into three groups are the method of reproduction and the method of caring for the young. Monotremes lay eggs and have no nipples (all other mammals do). Marsupials give live birth to premature young, which must crawl to the nipple (often inside a pouch) and attach to it (they detach later when they are more fully developed). Placental mammals keep the young in the uterus for a longer time. A more advanced placenta inside the uterus is used to transfer nutrients from the mother to the baby and to transfer waste products from the baby to the mother (through their respective blood streams). Placental mammals' young are born more developed. They suckle, but do not need to attach to the nipple. There are many other traits used to divide mammals into the three groups, such as details of bones, details of genital organs, internal body temperature, parts of the brain, and so on.