be essentially similar. With all, as far as is at
present known, the germinal vesicle is the same; so that all organisms
start from a common origin. If we look even to the two main
divisions--namely, to the animal and vegetable kingdoms--certain low
forms are so far intermediate in character that naturalists have
disputed to which kingdom they should be referred. As Professor Asa Gray
has remarked, "the spores and other reproductive bodies of many of the
lower algae may claim to have first a characteristically animal, and then
an unequivocally vegetable existence." Therefore, on the principle of
natural selection with divergence of character, it does not seem
incredible that, from some such low and intermediate form, both animals
and plants may have been developed; and, if we admit this, we must
likewise admit that all the organic beings which have ever lived on this
earth may be descended from some one primordial form. But this inference
is chiefly grounded on analogy, and it is immaterial whether or not it
is accepted. No doubt it is possible, as Mr. G. H. Lewes has urged, that
at the first commencement of life many different forms were evolved; but
if so, we may conclude that only a very few have left modified
descendants. For, as I have recently remarked in regard to the members
of each great kingdom, such as the Vertebrata, Articulata, etc., we
have distinct evidence in their embryological, homologous, and
rudimentary structures, that within each kingdom all the members are
descended from a single progenitor.

When the views advanced by me in this volume, and by Mr. Wallace, or
when analogous views on the origin of species are generally admitted, we
can dimly foresee that there will be a considerable revolution in
natural history. Systematists will be able to pursue their labours as at
present; but they will not be incessantly haunted by the shadowy doubt
whether this or that form be a true species. This, I feel sure and I
speak after experience, will be no slight relief. The endless disputes
whether or not some fifty species of British brambles are good species
will cease. Systematists will have only to decide (not that this will be
easy) whether any form be sufficiently constant and distinct from other
forms, to be capable of definition; and if definable, whether the
differences be sufficiently important to deserve a specific name. This
latter point will become a far more essential consideration than it is
at pr