The animals most familiar to us, our domestic cattle and our dogs and cats, all belong to a group of animals technically termed _mammals_, from the circumstance that the females have milk-glands (or _mammæ_), by which they nourish their young. The name "beasts" may be set apart for the brute animals belonging to this group; but they do not altogether form it, since man himself--the most individually numerous of all the large animals--is, structurally considered, also a mammal.
For various reasons, which will appear later, the domestic cat (which is a member of the genus _Felis_) may serve as an instructive, as it is a familiar, example of a highly-organized mammal. Allied to the cat, and formed on so completely the same model as hardly to differ, save in size and colour, are the lions, tigers, leopards, jaguars, pumas, ocelots, lynxes, and wild-cats of different kinds. What are commonly called pole-cats are not really cats, but belong to a different "family;" while civet-cats are not cats in the strict sense of that term. Civet-cats pertain to a group of beasts called _Viverrines_ (_Viverridæ_), to which all ichneumons and mongouses (which appear to have been the domestic cats of the ancient Romans) as well as the bone-eating hyænas also belong.
The viverrines and the cats, however, together form one great family to which the scientific name _Felidæ_ has been assigned. The pole-cats, together with the ermine, ferret, weasel, marten, sable, skunk, badger, the otter and the bear, raccoon, coati-mondi, with the kinkajoo, panda, &c., all belong to another family. Of this family the bears are the largest in size, and constitute a small group or "genus" called _Ursus_, whence the whole family bears the designation _Ursidæ_.
Our dogs (genus _Canis_) are, as every one knows, first cousins to jackals and wolves and near allies of the different species of fox, the whole forming a family--_Canidæ_.
The otter has been already referred to, and it may be thought that mention of the seals and sea-lions has been unintentionally omitted. But the seals and sea-lions, in spite of a certain slight resemblance to otters, due to similarity of habit, are not really near allies of the latter. They (_i.e._, seals and sea-lions), together with the walrus, form, indeed, a very distinct family, which is termed _Phocidæ_, because its type, the common seal, belongs to a subordinate group, or "genus," named _Phoca_.