But the three genera on the left hand have, on this same principle, much in common, and form a subfamily, distinct from that containing the next two genera on the right hand, which diverged from a common parent at the fifth stage of descent.

These five genera have also much in common, though less than when grouped in subfamilies; and they form a family distinct from that containing the three genera still further to the right hand, which diverged at an earlier period.

And all these genera, descended from (A), form an order distinct from the genera descended from (I).

So that we here have many species descended from a single progenitor grouped into genera; and the genera into subfamilies, families and orders, all under one great class.

The grand fact of the natural subordination of organic beings in groups under groups, which, from its familiarity, does not always sufficiently strike us, is in my judgment thus explained.