| → distinct forms; 1872 |
| widely different forms, not connected by any intermediate links; 1866 1869 |
|
| → OMIT 1872 |
| for seizing the female, 1866 1869 |
|
| → OMIT 1872 |
| as if for compensation, 1866 1869 |
|
| ↑ 6 blocks not present in 1859 1860 1861 1872; present in 1866 1869 |
| Again, the males of another Crustacean, an Orchestia, occur under two distinct forms, with pincers differing much more from each other in structure, than do the pincers of most species of the same genus.
With respect to plants I have recently shown that species in several widely distinct orders
present two or even three forms, which are abruptly distinguished from each other in several important points, as in the size and colour of the pollen-grains; and these forms, though all hermaphrodites, differ from each other in their reproductive power, so that for full fertility, or indeed in some cases for any fertility, they must reciprocally impregnate each other.
Although the forms of the few dimorphic and trimorphic animals and plants which have been studied are not now connected together by intermediate links, it is probable that this will be found to occur in other cases; for Mr. Wallace observed a certain butterfly which presented in the same island a great range of varieties connected by intermediate links, and the extreme links of the chain closely resembled the two forms of an allied dimorphic species inhabiting another part of the Malay archipelago.
Thus also with ants, the several worker-castes are generally quite distinct; but in some cases, as we shall hereafter see, the castes are connected together by graduated varieties.
It certainly at first appears a highly remarkable fact that the same female butterfly should have the power of producing at the same time three distinct female forms and a male; that a male Crustacean should generate two male forms and a female form, all widely different from each other; and that an hermaphrodite plant should produce from the same seed-capsule three distinct hermaphrodite forms, bearing three different kinds of females and three or even six different kinds of males.
Nevertheless these cases are only exaggerations of the universal fact that every female animal
produces males and females, which in some instances differ in so
wonderful a
manner from each other.
|
|
| → OMIT 1872 |
| in their own country 1859 1860 1861 1866 1869 |
|
| → by means of intermediate links any two forms, 1872 |
| two forms together by others having intermediate characters, 1859 1860 1861 1866 1869 |
|
|
extraordinary cases
the males of certain Brazilian Crustaceans: thus, the male of a Tanais regularly occurs under two
→distinct forms;
one of these
has
and differently shaped
→OMIT
and the
→OMIT
has antennæ much more abundantly furnished with
Although in most of these cases, the two or three forms, both with animals and plants, are not now connected by intermediate gradations, it is probable that they were once thus connected. Mr. Wallace, for instance, describes a certain butterfly which presents in the same island a great range of varieties connected by intermediate links, and the extreme links of the chain closely resemble the two forms of an allied dimorphic species inhabiting another part of the Malay archipelago. Thus also with ants, the several worker-castes are generally quite distinct; but in some cases, as we shall hereafter see, the castes are connected together by finely graduated varieties. So it is, as I have myself observed, with some dimorphic plants. It certainly at first appears a highly remarkable fact that the same female butterfly should have the power of producing at the same time three distinct female forms and a male; and that an hermaphrodite plant should produce from the same seed-capsule three distinct hermaphrodite forms, bearing three different kinds of females and three or even six different kinds of males. Nevertheless these cases are only exaggerations of the common fact that the female produces offspring of two sexes which sometimes differ from each other in a wonderful manner. ↑
|
|
Doubtful
Species.
|
|
forms which possess in some considerable degree the character of species, but which are so closely similar to
other forms, or are so closely linked to them by intermediate gradations, that naturalists do not like to rank them as distinct species, are in several respects the most important for us. We have every reason to believe that many of these doubtful and
forms have permanently retained their characters
→OMIT
for a long time; for as long, as far as we know, as have good and true species. Practically, when a naturalist can unite
→by means of intermediate links any two forms,
he treats the one as a variety of the
ranking the most common, but sometimes the one first described, as the species, and the other as the variety. But cases of great difficulty, which I will not here enumerate, sometimes
in deciding whether or not to rank one form as a variety of another, even when they are closely connected by intermediate links; nor will the commonly-assumed hybrid nature of
|
