ficulties in the
way of the theory. It is to show that such difficulties do not exist,
and in the full conviction that an adequate knowledge of the facts of
variation affords the only sure foundation for the Darwinian theory of
the origin of species, that this chapter has been written.

FOOTNOTES:

[Footnote 16: _Foraminifera_, preface, p. x.]

[Footnote 17: _United States Geological Survey of the Territories_,
1874.]

[Footnote 18: _Proceedings of the Entomological Society of London_,
1875, p. vii.]

[Footnote 19: _Ann. des Sci. Nat._, tom. xvi. p. 50.]

[Footnote 20: See _Winter Birds of Florida_, p. 206, Table F.]

[Footnote 21: See Table I, p. 211, of Allen's _Winter Birds of
Florida_.]

[Footnote 22: _Proc. Zool. Soc._, 1864, p. 64.]

[Footnote 23: J.A. Allen, on Geographical Variation among North American
Mammals, _Bull. U.S. Geol. and Geog. Survey_, vol. ii. p. 314 (1876).]

[Footnote 24: _Proc. Zool. Soc. Lond._, 1864, p. 700, and 1868, p. 28.]

[Footnote 25: See _Trans. Entomological Society of London_, 1887, p.
24.]

[Footnote 26: _Nature_, vol. xix. p. 554.]

[Footnote 27: _Nature_, vol. xvi. p. 163; and vol. xi. p. 227.]

[Footnote 28: _Ibid._, vol. xxxi. (1885), p. 533.]

[Footnote 29: _Nature_, vol. xxvi. p. 81.]

[Footnote 30: _Animals and Plants under Domestication_, vol. ii. p.
258.]

CHAPTER IV

VARIATION OF DOMESTICATED ANIMALS AND CULTIVATED PLANTS

The facts of variation and artificial selection--Proofs of the
generality of variation--Variations of apples and
melons--Variations of flowers--Variations of domestic
animals--Domestic pigeons--Acclimatisation--Circumstances
favourable to selection by man--Conditions favourable to
variation--Concluding remarks.

Having so fully discussed variation under nature it will be unnecessary
to devote so much space to domesticated animals and cultivated plants,
especially as Mr. Darwin has published two remarkable volumes on the
subject where those who desire it may obtain ample information. A
general sketch of the more important facts will, however, be given, for
the purpose of showing how closely they correspond with those described
in the preceding chapter, and also to point out the general principles
which they illustrate. It will also be necessary to explain how these
variations have been increased and accumulated by artificial selection,
since we are thereby better enabled to understand the actio