[24] "Proceedings of American Academy of Arts and Sciences," vol. xiv, May, 1878.
[25] Fol., "Archives des Sciences," vol. xiv, p. 84, 1885; "Science," vol. vi, p. 92, 1885.
[26] Of course, this is a purely imaginary case. The conditions of development of the eggs of higher animals forbid continuous watching the process. Yet we do observe in different individuals all these stages in mammals as well as other animals.
[27] These baleen plates are not modifications of teeth, as might at first be supposed, but rather of the transverse gum-ridges found on the roof of the mouth of many mammals, and conspicuous in the horse.
[28] "Proceedings of the California Academy of Science," vol. v, p. 152. 1873.
[29] For fuller discussion of this subject, see "Bulletin of the California Academy of Science," No. 8, 1887, and "American Journal of Science," for Dec., 1887.
[30] "Origin of Races of the Dog." "Annals and Magazine of Natural History," vol. xvii, p. 295. 1886.
[31] Mr. Galton ("Nature," August 26, 1886) has used a diagram similar to the above (which I first used in 1879) to illustrate the law of sexual attraction and repugnance.
[32] This subject is more fully discussed by the author in an article entitled "Genesis of Sex," in "The Popular Science Monthly," vol. xvi, p. 167, 1879.
[33] For examples of this the reader is referred to Cope, "Bulletin of the National Museum," No. 1; and to Coues's "Key to North American Birds," last edition.
[34] "Monatsbericht d. k. Preuss. Akademie d. Wissenschaft zu Berlin," for July, 1866.
[35] "Genesis of Tertiary Species of Planorbis at Steinheim." A. Hyatt, Anniversary Memoir of the Boston Society of Natural History, 1880.
[36] In a letter to the author, dated February 13, 1887, Prof. Cope says: "Such transitions of species are clearly indicated in the _Oreodontidæ_, where such different forms as _O. gracilis_ and _O. Culbertsoni_ are connected by intergradations."
[37] "American Naturalist," 1873; "Popular Science Monthly," June, 1873.
[38] For a fuller development of this subject the reader is referred to an article by the author, entitled "Critical Periods in the History of, and their Relation to, Evolution" ("American Journal of Science," vol. xiv, p. 99, 1877).