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should be ranked as species or varieties. 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
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
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
less than
amount of difference. |
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genera are related to each other, in the same manner as the varieties of any one species are related to each other. No
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. As Fries has well remarked, little groups of species are generally clustered like satellites around
other species. And what are varieties but groups of forms, unequally related to each other, and clustered round certain
is, round their
Undoubtedly there is one most important point of difference between varieties and species; namely, that the amount of difference between varieties, when compared with each other or with their parent-species, is much less than that between the species of the same genus. But when we come to discuss the principle, as I call it, of
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