oved, and preceding
forms. I request the reader to turn to the diagram illustrating the
action, as formerly explained, of these several principles; and he
will see that the inevitable result is that the modified descendants
proceeding from one progenitor become broken up into groups subordinate
to groups. In the diagram each letter on the uppermost line may
represent a genus including several species; and all the genera on this
line form together one class, for all have descended from one ancient
but unseen parent, and, consequently, have inherited something in
common. But the three genera on the left hand have, on this same
principle, much in common, and form a sub-family, distinct from that
including 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, though less, in common; and they form a family distinct from
that including the three genera still further to the right hand, which
diverged at a still 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 are included in, or subordinate to,
sub-families, families, and orders, all united into one class. Thus, the
grand fact in natural history of the subordination of group under group,
which, from its familiarity, does not always sufficiently strike us, is
in my judgment fully explained.

Naturalists try to arrange the species, genera, and families in each
class, on what is called the Natural System. But what is meant by
this system? Some authors look at it merely as a scheme for arranging
together those living objects which are most alike, and for separating
those which are most unlike; or as an artificial means for enunciating,
as briefly as possible, general propositions,--that is, by one sentence
to give the characters common, for instance, to all mammals, by another
those common to all carnivora, by another those common to the dog-genus,
and then by adding a single sentence, a full description is given
of each kind of dog. The ingenuity and utility of this system are
indisputable. But many naturalists think that something more is meant
by the Natural System; they believe that it reveals the plan of the
Creator; but unless it be specified whether order in time or space,
or what else is meant by the plan of the Creato