So far as we have hitherto proceeded, by examining objects in comparative anatomy which from their magnitude can not be misunderstood, we have been led to conclude that, independently of the system of parts marvellously combined to form the individual animal, there is another more comprehensive system, which embraces all animals; and which exhibits a certain uniformity in the functions of life, however different in form or bulk the creatures may be, or to whatever condition of the globe they may have been adapted. We have seen no accidental deviation or deformity, but every change has been for a purpose, and every part has had its just relation. We have witnessed all the varieties moulded to such a perfect accommodation, and the alterations produced by such minute degrees, that all notion of external and accidental agency must be rejected.

We might carry our demonstration downward through the lower classes of animals; for example, we might trace the feet of insects from their most perfect or complex state, till they disappear; or, observing the changes in another direction, we might follow out the same parts from the smallest beginning to the most perfect condition of the member, where we see the thigh, leg, and tarsus of the fly. We might distinguish them at first as the fine cirri, like minute bristles, which, on the bodies of worms take slight hold of the surface over which they creep.