| → in those cases in which 1859 1860 1861 1866 1869 |
| when 1872 |
|
|
Many
of
the
Species the
Larger
Genera
resemble
Varieties
in
being
very
closely,
but
unequally,
related
to
each
other,
and
in
having
restricted
ranges.
|
| There are other relations between the species of large genera and their recorded varieties which deserve notice. We have seen that there is no infallible criterion by which to distinguish species and well-marked varieties; and
→in those cases in which
intermediate links have not been found between doubtful forms, naturalists are compelled to come to a determination by the amount of difference between them, judging by analogy whether or not the amount suffices to raise one or both to the rank of species. Hence the amount of difference is one very important criterion in settling whether two forms 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. |
|
| Moreover, the species of the
genera are related to each other, in the same manner as the varieties of any one species are related to each other. No
|
