Monotremes

Monotremes (Monotremata), the single order of the sub-class Prototheria ( Ornitltodclphia of De Blainville). The animals of this order - the lowest of the Mammalia, are restricted to the Australian region, and resemble the Sauropsida (Birds and Reptiles) in having a cloaca or common passage into which the urinary, genital, and food canals open, whence the name Monotremata. De Blainville's name refers to the resemblance between the female reproductive organs and those of birds. There are but two families: Ornithorhynchidae and Echidnidas. [Ornithorhynchus, Echidna.]" These animals are oviparous, and the mammary glands, which are of a different type from those of higher Mammals, open by a mere slit on each side of the abdomen. The eggs resemble those of birds in that part of the yolk nourishes the embryo.