→ which have suffered much extinction; but 1861 1866 1869 1872 |
but 1859 1860 |
|
→ OMIT 1860 1861 1866 1869 1872 |
as is proclaimed by the canon, "Natura non facit saltum," 1859 |
|
→ of 1859 1860 1861 1866 1869 |
in the same community of 1872 |
|
→ in the same community of ants; 1859 1860 1861 1866 |
ants in the same community; 1869 |
ants; 1872 |
|
→ distinct trees 1866 1869 |
trees 1859 1860 1861 |
distinct kinds of trees 1872 |
|
→ are crossed reciprocally,— 1866 |
are crossed reciprocally; 1859 1860 1861 |
reciprocally,— 1869 1872 |
|
→ in no respect from each other 1866 1869 |
from each other in no respect 1872 |
|
It is, no doubt, extremely difficult even to conjecture by what gradations many structures have been perfected, more especially amongst broken and failing groups of organic
→which have suffered much extinction; but
we see so many strange gradations in nature,
→OMIT
that we ought to be extremely cautious in saying that any organ or instinct, or
whole
could not have arrived at its present state by many graduated steps. There are, it must be admitted, cases of special difficulty
the theory of natural selection; and one of the most curious of these is the existence
→of
two or three defined castes of workers or sterile
→in the same community of ants;
but I have attempted to show how
can be mastered. |
|
With respect to the almost universal sterility of species when first crossed, which forms so remarkable a contrast with the almost universal fertility of varieties when crossed, I must refer the reader to the recapitulation of the facts given at the end of the
chapter, which seem to me conclusively to show that this sterility is no more a special endowment than is the incapacity of two
→distinct trees
to be grafted
but that it is incidental on
differences
the reproductive systems of the intercrossed species. We see the truth of this conclusion in the vast difference in the
the same two species
→are crossed reciprocally,—
that is, when one species is first used as the father and then as the
from the consideration of dimorphic and trimorphic plants clearly leads
the same conclusion, for when the forms are illegitimately united, they yield few or no seed, and their offspring are more or less sterile; and these forms
the same undoubted
differ
→in no respect from each other
except in their reproductive organs and functions. |
|
fertility of varieties when intercrossed and
|