Monotremes are the lowest mammals. Oviparous. The intestines and urogenital duct open into the cloaca and pass through the body through a common hole, hence the name "monopore". The mammary gland ducts open in the mammary gland areas on both sides of the abdomen without nipples; the body is covered with hair; the body temperature is low but has the ability to regulate body temperature. Such as platypus, echidna, etc., distributed in Australia and New Guinea.