ions, and the mere putting together and
separating objects more or less alike.

But I must explain my meaning more fully. I believe that the ARRANGEMENT
of the groups within each class, in due subordination and relation to
the other groups, must be strictly genealogical in order to be natural;
but that the AMOUNT of difference in the several branches or groups,
though allied in the same degree in blood to their common progenitor,
may differ greatly, being due to the different degrees of modification
which they have undergone; and this is expressed by the forms being
ranked under different genera, families, sections, or orders. The reader
will best understand what is meant, if he will take the trouble of
referring to the diagram in the fourth chapter. We will suppose the
letters A to L to represent allied genera, which lived during the
Silurian epoch, and these have descended from a species which existed at
an unknown anterior period. Species of three of these genera (A, F, and
I) have transmitted modified descendants to the present day, represented
by the fifteen genera (a14 to z14) on the uppermost horizontal line. Now
all these modified descendants from a single species, are represented as
related in blood or descent to the same degree; they may metaphorically
be called cousins to the same millionth degree; yet they differ widely
and in different degrees from each other. 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 the 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 organic
beings belong to Silurian genera. So that the amount or value of the
differences between organic beings 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. All the modified
descendants from A will have inherited something in common from their
common parent, as will all the descendants from I; so will it be with
each subordinate branch of descendants, at each successive period. If,
however, we choose to suppose that any of the descend