OTHER THEORIES OF SPECIES-FORMING. 261 



12 



Plate, L., "Uber die Bedeutung des Darwin'schen Selections- 

 prinzip," p. 193, 1903. 



13 Hutton, F. W., "The Place of Isolation in Or- 



Further refer- ic Evolution," Nat. Science, Vol. XI, pp. 240-246, 



ences to discus- ~ 

 sions of isolation. 



The not uncommon mating, in zoological gardens, 



of lions and tigers, with the production of healthy cubs, is a case 

 in point. 



15 This principle, strongly advocated by Romanes, seems first to 

 have been presented by Eimer in connection with his theory of 

 orthogenetic evolution. At least it enters into the make-up of the 

 Eimerian theory. See account of Eimer's theory in chapter x of this 

 book. 



1(1 Jordan, Karl, "Mechanische Selection," 1896; see also Peter- 

 sen, Wilh., "Entstehung der Arten durch Physiologische Isolirung," 

 Biol Ccntralbl, Vol. XXII, pp. 468 ff., 1902; also Vol. XXIV, pp. 

 423-431, 467-473. 1904. Author describes cases of marked differ- 

 ence in reproductive organs (includes primary and accessory parts) 

 of closely allied species of Lepidoptera. 



17 Snodgrass, R. E., "The Terminal Abdominal Segments of 

 Female Tipulidae," Jour. N. Y. Ent. Soc., Vol. XI, pp. 177-183, 1903; 

 "The Hypopygium of the Tipulidse," Trans. Amcr. Ent. Soc., Vol. 

 XXX, pp. 179-235, 1904; "The Hypopygium of the Dolichopodidae," 

 Proc. Cal. Acad. Sci., Ser. 3, Zool., Vol. Ill, pp. 273-285, 1904. 



18 Seebohm, H., "Physiological Selection," 1886. 

 Wallace, A. R.. "Darwinism," p. 180, 1891. 



Jordan, Karl, "Novitates Zoologies," pp. 426 ff., 1896. 

 Vernon, H. N., "Reproductive Divergence: An Additional 

 Factor in Evolution," Natural Science, Vol. XI, pp. 181-189, 1897. 



2 Jordan, Karl, "Reproductive Divergence: A Factor in Evolu- 

 tion?" Natural Science, Vol. II, pp. 317-320, 1897. 



3 Pearson, Karl. "Reproductive Selection," Natural Science, Vol. 

 VIII, pp. 321-325, 1896. 



24 Romanes. G. J., "Isolation in Organic Evolution," Monist, Vol. 

 VIII, pp. 19-38, 1897- 



25 Gulick, J. T., "Divergent Evolution through Cumulative Segre- 

 gation," Jour. Linn. Soc.. Zool., Vol. XX, pp. 189-274. 1888. 



26 Gulick, J. T., Jour. Linn. Soc., Zool, Vol. XX, pp. 202-211, 

 1888. 



27 Gulick, J. T.. "Evolution, Racial and Habitudinal," Pub. No. 

 25, Carnegie Institution of Washington, 1905. In this large paper 

 are to be found references to all of the author's important papers. 

 Some of these papers are reprinted (some completely, some in 

 part) in this monograph. 



19 



20 

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