The existing members of the order readily group themselves into five distinct families, the limits of which are perfectly clear. These are (1) _Bradypodidæ_, or Sloths; (2) _Myrmecophagidæ_, or Anteaters; (3) _Dasypodidæ_, or Armadillos; (4) _Manidæ_, Pangolins or Scaly Anteaters; and (5) _Orycteropodidæ_, Aard-varks or African Anteaters. The geographical distribution of these families coincides with their structural distinction, the first three being inhabitants of the New and the last two of the Old World. It has been usual to arrange these families into two large groups or suborders: (1) the Phyllophaga, leaf-eaters, also called Tardigrada, containing the _Bradypodidæ_ alone; and (2) the Entomophaga, insect-eaters, or Vermilingua, containing all the other families, from which sometimes the _Orycteropodidæ_ are separated as a third suborder under the name of Effodientia, or Tubulidentata. Such an arrangement is, however, an artificial one, founded on superficial resemblance. The bonds which unite the _Manidæ_ to the _Myrmecophagidæ_ are mainly to be found in the structure of the mouth, especially the extensile character of the tongue, the great development of the submaxillary glands, and the absence of teeth. These characters are exactly analogous to those found in the Echidna among Monotremes, the Woodpeckers among Birds, and the Chameleon among Reptiles,—the fact probably being that in countries where Termites and similar insects flourish various distinct forms of vertebrates have become modified in special relation to this abundance of nutritious food, which could only be made available by a peculiar structure of the alimentary organs. A close study of the more essential portions of the anatomy of these animals[90] leads to the belief that all the American Edentates at present known, however diversified in form and habits, belong to a common stock. Thus the _Bradypodidæ_, _Megatheriidæ_, and _Myrmecophagidæ_ are certainly allied, the modifications seen in the existing families relating only to food and manner of life. The ancestral forms may have been omnivorous, and gradually separated into the purely vegetable and purely animal feeders; from the former are developed the modern Sloths, from the latter the Anteaters. The Armadillos (_Dasypodidæ_) are another modification of the same type, retaining some generalised characters, as those of the alimentary organs, but in other respects, as in their defensive armature, remarkably specialised. The two Old World families _Manidæ_ and _Orycteropodidæ_ are so essentially distinct, both from the American families and from each other, that it may even be considered doubtful whether they are derived from the same primary branch of mammals, or whether they may not be offsets of some other branch, the remaining members of which have been lost to knowledge. Further remarks on this point are recorded under the description of the _Orycteropodidæ_.[91] _Family_ BRADYPODIDÆ.