ght modifications of structure in some degree permanent; and
this assuredly we do see.

Secondly, areas now continuous must often have existed within the recent
period in isolated portions, in which many forms, more especially amongst
the classes which unite for each birth and wander much, may have separately
been rendered sufficiently distinct to rank as representative species. In
this case, intermediate varieties between the several representative
species and their common parent, must formerly have existed in each broken
portion of the land, but these links will have been supplanted and
exterminated during the process of natural selection, so that they will no
longer exist in a living state.

Thirdly, when two or more varieties have been formed in different portions
of a strictly continuous area, intermediate varieties will, it is probable,
at first have been formed in the intermediate zones, but they will
generally have had a short duration. For these intermediate varieties will,
from reasons already assigned (namely from what we know of the actual
distribution of closely allied or representative species, and likewise of
acknowledged varieties), exist in the intermediate zones in lesser numbers
than the varieties which they {179} tend to connect. From this cause alone
the intermediate varieties will be liable to accidental extermination; and
during the process of further modification through natural selection, they
will almost certainly be beaten and supplanted by the forms which they
connect; for these from existing in greater numbers will, in the aggregate,
present more variation, and thus be further improved through natural
selection and gain further advantages.

Lastly, looking not to any one time, but to all time, if my theory be true,
numberless intermediate varieties, linking most closely all the species of
the same group together, must assuredly have existed; but the very process
of natural selection constantly tends, as has been so often remarked, to
exterminate the parent-forms and the intermediate links. Consequently
evidence of their former existence could be found only amongst fossil
remains, which are preserved, as we shall in a future chapter attempt to
show, in an extremely imperfect and intermittent record.

_On the origin and transitions of organic beings with peculiar habits and
structure._--It has been asked by the opponents of such views as I hold,
how, for instance, a land carnivorous anim