f the other members of the
family to which it belonged. There is, however, some difficulty on this
head, for it is necessary to suppose in some cases that ancient members
belonging to several distinct groups, before they had diverged to their
present extent, accidentally resembled a member of another and protected
group in a sufficient degree to afford some slight protection, this
having given the basis for the subsequent acquisition of the most
perfect resemblance.

ON THE NATURE OF THE AFFINITIES CONNECTING ORGANIC BEINGS.

As the modified descendants of dominant species, belonging to the larger
genera, tend to inherit the advantages which made the groups to which
they belong large and their parents dominant, they are almost sure to
spread widely, and to seize on more and more places in the economy of
nature. The larger and more dominant groups within each class thus tend
to go on increasing in size, and they consequently supplant many
smaller and feebler groups. Thus, we can account for the fact that all
organisms, recent and extinct, are included under a few great orders and
under still fewer classes. As showing how few the higher groups are in
number, and how widely they are spread throughout the world, the fact
is striking that the discovery of Australia has not added an insect
belonging to a new class, and that in the vegetable kingdom, as I learn
from Dr. Hooker, it has added only two or three families of small size.

In the chapter on geological succession I attempted to show, on the
principle of each group having generally diverged much in character
during the long-continued process of modification, how it is that the
more ancient forms of life often present characters in some degree
intermediate between existing groups. As some few of the old and
intermediate forms having transmitted to the present day descendants
but little modified, these constitute our so-called osculant or aberrant
groups. The more aberrant any form is, the greater must be the number of
connecting forms which have been exterminated and utterly lost. And
we have evidence of aberrant groups having suffered severely from
extinction, for they are almost always represented by extremely few
species; and such species as do occur are generally very distinct from
each other, which again implies extinction. The genera Ornithorhynchus
and Lepidosiren, for example, would not have been less aberrant had
each been represented by a dozen species, inst