The Factors of Organic Evolution

by Herbert Spencer

[5]. A Manual of the Infusoria, by W. Saville Kent. Vol. i, p. 232.

[6]. Ib. Vol. i, p. 241.

[7]. Kent, Vol. i, p. 56.

[8]. Ib. Vol. i, p. 57.

[9]. The Elements of Comparative Anatomy, by T. H. Huxley, pp. 7-9.

[10]. A Treatise on Comparative Embryology, by F. M. Balfour, Vol. ii, chap. xiii.

[11]. Sachs, p. 210.

[12]. Ibid. pp. 83-4.

[13]. Ibid. p. 185.

[14]. Ibid. p. 80.