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 L67,000.