[7] First Principles, p. 396.
[8] First Principles, p. 167.
[9] First Principles, p. 176.
[10] Fragments of Science, vol. ii. p. 396.
[11] First Principles, p. 407.
[12] First Principles, p. 401.
[13] Ibid. p. 401-402.
[14] Reprint of a Lecture at the Royal Institution by Mr. Crooks, p. 2.
[15] Ency. Brit. art. ‘Biology,’ vol. iii. p. 679.
[16] Principles of Biology, vol. i. p. 481.