[Footnote 4: _Géographic Botanique_, p. 798.]
[Footnote 5: _The Origin of Species_, p. 53.]
[Footnote 6: _The Earth as Modified by Human Action_, p. 51.]
[Footnote 7: _The Origin of Species_, p. 56.]
[Footnote 8: See _Nature_, vol. xxxi. p. 63.]
[Footnote 9: _A Visit to South America_, 1878; also _Nature_, vol. xxxi. pp. 263-339.]
[Footnote 10: Still more remarkable is the increase of rabbits both in New Zealand and Australia. No less than seven millions of rabbit-skins have been exported from the former country in a single year, their value being £67,000. In both countries, sheep-runs have been greatly deteriorated in value by the abundance of rabbits, which destroy the herbage; and in some cases they have had to be abandoned altogether.]
[Footnote 11: Later observers have proved that two eggs are laid and usually two young produced, but it may be that in most cases only one of these comes to maturity.]
[Footnote 12: _Origin of Species_, p. 59. Professor A. Newton, however, informs me that these species do not interfere with one another in the way here stated.]
[Footnote 13: Winwood Reade's _Martyrdom of Man,_ p. 520.]
[Footnote 14: _Nineteenth Century,_ February 1888, pp. 162, 163.]
[Footnote 15: The Kestrel, which usually feeds on mice, birds, and frogs, sometimes stays its hunger with earthworms, as do some of the American buzzards. The Honey-buzzard sometimes eats not only earthworms and slugs, but even corn; and the Buteo borealis of North America, whose usual food is small mammals and birds, sometimes eats crayfish.]
