[156a] “Origin of Species,” ed. vi., p. 107.
[156b] Ibid., ed. vi., p. 166.
[157a] “Origin of Species,” ed. vi., p. 233.
[157b] Ibid.
[157c] Ibid., ed. vi., p. 109.
[157d] Ibid., ed. vi., p. 401.
[158a] “Origin of Species,” ed. i., p. 490.
[161a] “Origin of Species,” ed. vi., 1876, p. 171.
[163a] “Charles Darwin,” p. 113.
[164a] “Animals and Plants under Domestication,” vol. ii., p. 367, ed. 1875.