Origin of Species Variorum

→ 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

→ ants in the same community; 1869

in the same community of ants; 1859 1860 1861 1866

ants; 1872

→ distinct trees 1866 1869

trees 1859 1860 1861

distinct kinds of trees 1872

→ reciprocally,— 1869 1872

are crossed reciprocally; 1859 1860 1861

are crossed reciprocally,— 1866

→ 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

beings;

beings,

→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

any

the

whole

being,

structure,

could not have arrived at its present state by many graduated steps. There are, it must be admitted, cases of special difficulty

opposed to

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

females

female

→ants in the same community; but I have attempted to show how

this

these

difficulty

difficulties

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

ninth

eighth

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

together,

together;

but that it is incidental on

constitutional

....

differences

confined to

the reproductive systems of the intercrossed species. We see the truth of this conclusion in the vast difference in the

result,

results

when

of crossing

the same two species →reciprocally,— that is, when one species is first used as the father and then as the

mother.

mother:

Analogy

analogy

from the consideration of dimorphic and trimorphic plants clearly leads

us to

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

belong to

the same undoubted

species,

species

and

....

differ →in no respect from each other except in their reproductive organs and functions.

The

Although the

fertility of varieties when intercrossed and