preceded in early Tertiary times by others which were more or less intermediate in structure. This is not the case as regards hats. Bats, as soon as they appear at all, appear as thoroughly and as perfectly organized bats as are those living among us now.
This leads us to speculate upon questions of origin; but, before so doing, let us see that we have a clear idea of what a bat is, and can give a good definition of it.
In order that we may have this clear idea, we must consider for a few moments zoological classification.
The whole group of animals is fancifully termed the animal kingdom, in contradistinction to the world of plants—the vegetable kingdom.
Fig. 7.—Skeleton of Flying-Fox. Side-View of Sternum.
This vast mass of animals is subdivided into a number of very large groups, each of which is a called a sub-kingdom. Thus, we have the sub-kingdom to which we ourselves belong—the vertebrate sub-kingdom; the sub-kingdom of insects, etc.; that of snails, cuttle-fishes, etc., and so on.
Each of these various sub-kingdoms is again divided into certain subordinate, but still very large groups, each of which is called a class.
Thus, the sub-kingdom Vertebrata is made up of the class of man and beasts, that of birds, that of reptiles, that of frogs, toads, and efts, and that of fishes.
