Vols. III., IV. (ff. i. + 526; i. + 603). "Principles of Biology" [1864, 1867]. In two volumes. At the end (f. 499) of the first is a letter to the North American Review.
Vol. X. (ff. i. + 1179) " Principles of Sociology," Vol. I. first edition [1876], but including ch. ix.-end, the publication of which was deferred till later editions.