In this scheme we see an expression of the fact that the Dogs (_Canidæ_) form a central group, from which the families of the Æluroidea--those to the left--diverge in one direction, and the families of the Arctoidea--those to the right--in the other direction. The Civets (_Viverridæ_) and the Weasel family (_Mustelidæ_), being the least modified of the Æluroid and Arctoid sections respectively, are placed at the bottom of the table, the Cats (_Felidæ_) and Bears (_Ursidæ_), being the most modified, are placed at the top. The two latter families, again, are placed at opposite extremities of the table, as far from one another as possible, to indicate the great gap which separates the digitigrade, short-skulled, active, carnivorous Cats, from the plantigrade, long-skulled, clumsy, herbivorous Bears. To be quite accurate, such a scheme should take account not merely of families, but of genera: in our table, for instance, there is nothing to show the immense amount of specialisation undergone by one section of the _Mustelidæ_--the Otters--to fit them for aquatic life; but such a detailed arrangement is quite beyond the scope of the present work. * * * * * In considering the chief forms of Carnivora existing at the present day, we have by no means exhausted this varied and interesting group, for a number of its members, the forerunners of those now living, have vanished from the face of the earth, and are known to us only by their bones, which we find here and there entombed in the strata of which the crust of our earth is composed. In the newest, that is the most recently deposited, set of strata, those which together form the beds of the Pleistocene period, we find a very curious change in the flesh-eaters inhabiting England. Instead of having nothing but Wild Cats, Wolves, and Bears--the only wild beasts known to have existed in the historical period--we have the enormous Cave Lion (_Felis spelæa_), besides the Cave Bear (_Ursus spelæus_), and the Cave Hyæna (_Hyæna spelæa_), the last being merely a variety of the Spotted Hyæna (_Hyæna crocuta_) of the present day. The presence of the first and last of these would seem to indicate that the climate of Britain was warmer in the Pleistocene period than it now is; but the presence of the Glutton, as well as of some non-carnivorous Arctic animals, tends to the other opinion, namely, that the climate of England was sub-Arctic. Very probably the Cave Lion and Hyæna were provided with thick woolly fur, and so, like the Mantchurian Tiger and the Northern Leopard (see pp. 34 and 42), enabled to bear a degree of cold experienced by but few of their relatives at the present day. [Illustration: SKULL OF MACHÆRODUS. (_After Gaudry._)]