Nearly allied to the sloths were certain huge beasts, now extinct, which formerly inhabited the same Continent--such as the _Megatherium_ and _Mylodon_, which rivalled or exceeded our largest rhinoceroses in bulk. They fed on the same food which nourishes the sloth, but obviously the branches of no tree could sustain such monsters. They obtained their leafy pasture, therefore, by a different method. Rearing themselves on their massive hind legs and powerful tail, as on a tripod, they embraced the trees with their vigorous arms, and swayed them to and fro, till the tree embraced was prostrated, and literally fell a prey to their efforts. These bulky creatures were protected against that danger which such a mode of life rendered imminent by a specially strong skull structure, which enabled them to bear a broken head with but little inconvenience. In the same region of the earth are found the ant-eaters and armadillos, and more or less allied to them are the pangolins (_Manis_) of Africa and Asia. The horny scales which cover the bodies of the last-named animals caused them for some time to be associated with reptiles rather than with beasts, though they are true and perfect mammals. Lastly must be mentioned the aard-vark (_Orycteropus_) of South Africa. All these creatures, from the sloths to the aard-vark, are commonly associated together in an order which is termed _Edentata_. The whole of the orders of mammals yet mentioned agree in certain important details with respect to their reproductive processes, as well as in certain smaller anatomical peculiarities, and the whole of the creatures included within these orders are (and will be) often spoken of as _Placental Mammals_. The only beasts which it yet remains to speak of are grouped in two other orders. The first of these is called the order _Marsupialia_, and comprises all opossums (_Didelphys_), kangaroos (_Macropus_), phalangers (_Phalangista_), the Tasmanian wolf (_Thylacinus_), the dasyures (_Dasyurus_), the bandicoots (_Perameles_), and their allies. With the exception of the true opossums (_Didelphys_), all the members of the order are found in Australia or its vicinity, and nowhere else in the present day; although, as we shall better see hereafter, Europe once possessed animals closely allied to Australian forms of to-day--notably to a pretty little quadruped which bears the generic name _Myrmecobius_. As last of the class of beasts, we have two extremely exceptional mammals (both found only in the Australian region), the duck-billed platypus (_Ornithorhynchus_), and the _Echidna_. The first of these, as its name implies, has a muzzle quite like the bill of a duck, with a squat, hairy body, and short limbs. The echidna is covered with strong, dense spines, and has a long and slender snout. These creatures together form the order _Monotremata_--an order which differs very much more from any other Mammalian order than any of the other orders of mammals differ one from another.