Now Fries has remarked in regard to plants, and Westwood in regard to insects, that in large genera the amount of difference between the species is often exceedingly small.

I have endeavoured to test this numerically by averages, and, as far as my imperfect results go, they confirm the view.
I have also consulted some sagacious and experienced observers, and, after deliberation, they concur in this view.

In this respect, therefore, the species of the larger genera resemble varieties, more than do the species of the smaller genera.

Or the case may be put in another way, and it may be said, that in the larger genera, in which a number of varieties or incipient species greater than the average are now manufacturing, many of the species already manufactured still to a certain extent resemble varieties, for they differ from each other by a less than the usual amount of difference.
Moreover, the species of the larger genera are related to each other, in the same manner as the varieties of any one species are related to each other.

No naturalist pretends that all the species of a genus are equally distinct from each other; they may generally be divided into sub-genera, or sections, or lesser groups.