The forms descended from A, now broken up into two or three families, constitute a distinct order from those descended from I, also broken up into two families.

Nor can the existing species descended from A be ranked in the same genus with the parent A, or those from I with parent I.

But the existing genus F14 may be supposed to have been but slightly modified, and it will then rank with the parent genus F; just as some few still living organisms belong to Silurian genera.

So that the comparative value of the differences between these organic beings, which are all related to each other in the same degree in blood, has come to be widely different.

Nevertheless, their genealogical ARRANGEMENT remains strictly true, not only at the present time, but at each successive period of descent.