[39] Mr. Darwin, in the last (fifth) edition of "Natural Selection," 1869, p. 102, admits that all sexual differences are not to be attributed to the agency of sexual selection, mentioning the wattle of carrier pigeons, tuft of turkey-cock, &c. These characters, however, seem less inexplicable by sexual selection than those given in the text. [40] I am again indebted to the kindness of Mr. A. D. Bartlett, amongst others. That gentleman informs me that, so far from any mental emotion being produced in rabbits by the presence and movements of snakes, that he has actually seen a male and female rabbit satisfy the sexual instinct in that presence, a rabbit being seized by a snake when _in coitu_. [41] "Habit and Intelligence," vol. i. p. 319. [42] The reader may consult Huxley's "Lessons in Elementary Physiology," p. 204. [43] "Natural Selection," p. 350. [44] Bivalve shell-fish are creatures belonging to the oyster, scallop, and cockle group, _i.e._ to the class Lamellibranchiata. [45] The attempt has been made to explain these facts as owing to "manner and symmetry of growth, and to colour being incidental on the chemical nature of the constituents of the shell." But surely beauty depends on some such matters in _all_ cases! [46] It has been suggested in opposition to what is here said, that there is no real resemblance, but that the likeness is "_fanciful!_" The denial, however, of the fact of a resemblance which has struck so many observers, reminds one of the French philosopher's estimate of facts hostile to his theory--"Tant pis pour les faits!" [47] Fifth Edition, p. 236. [48] Mr. Smith, of the Entomological department of the British Museum, has kindly informed me that the individuals intermediate in structure are very few in number--not more than five per cent.--compared with the number of distinctly differentiated individuals. Besides, in the Brazilian kinds these intermediate forms are wanting. [49] By accidental variations Mr. Darwin does not, of course, mean to imply variations really due to "chance," but to utterly indeterminate antecedents. [50] "Origin of Species," 5th edition, p. 235. [51] _I.e._ warm-blooded animals which suckle their young, such as apes, bats, hoofed beasts, lions, dogs, bears, weasels, rats, squirrels, armadillos, sloths, whales, porpoises, kangaroos, opossums, &c. [52] "Journal of Anatomy and Physiology" (1868), vol. ii. p. 139. [53] See "Ann. and Mag. of Nat. Hist." for August 1870, p. 140. [54] See "Proceedings of the Royal Institution," vol. v. part iv. p. 278: Report of a Lecture delivered February 7, 1868. Also "Quarterly Journal of the Geological Society," February 1870: "Contributions to the Anatomy and Taxonomy of the Dinosauria." [55] "Proceedings of Geological Society," November 1869, p. 38. [56] The archeopteryx of the oolite has the true carinate shoulder structure. [57] "Proceedings of the Royal Institution," vol. v. p. 279.