[40] “On the Caves of Gibraltar,” ‘Transact. Internat. Congress of Prehist. Arch.’ Third Session, 1869, p. 54.
[41] Quatrefages has lately collected the evidence on this subject. 'Revue des Cours Scientifiques,’ 1867-1868, p. 625.
[42] Owen, ‘On the Nature of Limbs,’ 1849, p. 114.
[43] Leuckart, in Todd’s ‘Cyclop. of Anat.’ 1849-52, vol. iv. p. 1415. In man this organ is only from three to six lines in length, but, like so many other rudimentary parts, it is variable in development as well as in other characters.
[44] See, on this subject, Owen, ‘Anatomy of Vertebrates,’ vol. iii. pp. 675, 676, 706.
[45] See the evidence on these points, as given by Lubbock, ‘Prehistoric Times,’ p. 354, &c.
[46] ‘L’Instinct chez les Insectes.’ ‘Revue des Deux Mondes,’ Feb. 1870, p. 690.
[47] ‘The American Beaver and his Works,’ 1868.
[48] ‘The Principles of Psychology,’ 2nd edit. 1870, pp. 418-443.
[49] ‘Contributions to the Theory of Natural Selection,’ 1870, p. 212