ler genera; for wherever many closely related species (i.e., species
of the same genus) have been formed, many varieties or incipient species
ought, as a general rule, to be now forming. Where many large trees
grow, we expect to find saplings. Where many species of a genus have
been formed through variation, circumstances have been favourable
for variation; and hence we might expect that the circumstances would
generally still be favourable to variation. On the other hand, if we
look at each species as a special act of creation, there is no apparent
reason why more varieties should occur in a group having many species,
than in one having few.

To test the truth of this anticipation I have arranged the plants of
twelve countries, and the coleopterous insects of two districts, into
two nearly equal masses, the species of the larger genera on one side,
and those of the smaller genera on the other side, and it has invariably
proved to be the case that a larger proportion of the species on the
side of the larger genera presented varieties, than on the side of the
smaller genera. Moreover, the species of the large genera which present
any varieties, invariably present a larger average number of varieties
than do the species of the small genera. Both these results follow when
another division is made, and when all the least genera, with from only
one to four species, are altogether excluded from the tables. These
facts are of plain signification on the view that species are only
strongly marked and permanent varieties; for wherever many species of
the same genus have been formed, or where, if we may use the expression,
the manufactory of species has been active, we ought generally to find
the manufactory still in action, more especially as we have every reason
to believe the process of manufacturing new species to be a slow one.
And this certainly holds true if varieties be looked at as incipient
species; for my tables clearly show, as a general rule, that, wherever
many species of a genus have been formed, the species of that genus
present a number of varieties, that is, of incipient species, beyond the
average. It is not that all large genera are now varying much, and are
thus increasing in the number of their species, or that no small genera
are now varying and increasing; for if this had been so, it would have
been fatal to my theory; inasmuch as geology plainly tells us that small
genera have in the lapse of time often inc