| → their sexual characters, 1859 1860 1861 1866 1869 |
| these 1872 |
|
| → parts of their structure. 1859 1860 1861 1866 1869 |
| respects. 1872 |
|
| → in illustration two instances, the first 1859 1860 1861 1866 |
| two instances in illustration, the first 1869 |
| in illus- tration the two first instances 1872 |
|
| → of the subject: 1859 1860 1861 1866 1869 |
| OMIT 1872 |
|
|
in giving to the species of the same group a greater amount of difference in
→their sexual characters,
than in other
→parts of their structure.
|
|
| It is a remarkable fact, that the secondary
differences between the two sexes of the same species are generally displayed in the very same parts of the organisation in which the
species of the same genus differ from each other. Of this fact I will give
→in illustration two instances, the first
which happen to stand on my list; and as the differences in these cases are of a very unusual nature, the relation can hardly be accidental. The same number of joints in the tarsi is a character
common to very large groups of beetles, but in the Engidæ, as Westwood has remarked, the number varies greatly; and the number likewise differs in the two sexes of the same
in
hymenoptera, the
of
the wings is a character of the highest importance, because common to large groups; but in certain genera the neuration differs in the different species, and likewise in the two sexes of the same species.
Lubbock has recently remarked, that several minute crustaceans offer excellent illustrations of this law. "In Pontella, for instance, the sexual characters are afforded mainly by the anterior
and by the fifth pair of legs: the specific differences also are principally given by these organs." This relation has a clear meaning on my
→of the subject:
I look at all the species of the same genus as having as certainly descended from
progenitor, as have the two sexes of any one
species.
whatever part of the structure of the common progenitor, or of its early descendants, became
variations of this part would, it is highly probable, be taken advantage of by natural and sexual selection, in order to fit the several species to
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