Akad. d. Wiss. zu Berlin. Von Joh. Muller, 1855, Pl. iii. fig. 3.
[32] Huxley, Introduction to the Classification of Animals, p. 45.
[33] Philosophical Transactions, 1865 and 1866.
[34] Loc. cit. Zweit. Abh. Pl. i., figs. 8 and 9.
[35] Thomson, on the Embryology of the Echinodermata, _Natural History Review_, 1863, p. 415. See also Agassiz, "Embryology of the Starfish,"
p. 62.
[36] A. Agassiz, Embryology of Echinoderms, p. 18.
[37] Hincks. British Hydroid Zoophytes, pp. 120-147.
[38] Zeits. fur Wiss. Zool. 1864, p. 228.
[39] Introduction to Entomology, 6th ed. vol. i. p. 61.
[40] Metamorphoses de l'Homme et des Animaux, p. 133. See also Carpenter, Principles of Physiology. 1851, p. 389.
[41] Darwin, Origin of Species, 4th ed. p. 532.
[42] Principles of Biology, vi. p. 349.
[43] For differences in larva consequent on variation in the external condition, see _ante_, p. 61.
[44] See Hincks. British Hydroid Zoophytes, P. lxii. Agassiz, Sea-side Studies, p. 43.
[45] See Newport, Phil. Trans., 1832.
[46] Linnean Transactions, 1862.
[47] Origin of Species, 4th ed., pp. 14 and 97.
[48] On the Alternation of Generations. By J. J. Steenstrup. Trans. by C. Busk, Esq. Ray Society. 1842.
[49] Zeit. fur Wiss. Zool. 1863.
[50] Mem. de l'Acad. Imp. de St. Petersbourg. vol. xv. 1870.
[51] Of course all animals in which the sexes are distinct are in one sense dimorphic.
[52] "There is no such thing as a true case of 'alternation of generations in the animal kingdom;' there is only an alternation of true generation with the totally distinct process of gemmation or fission."-HUXLEY _on Animal Individuality_, Ann. and Mag. of Nat. Hist.
June 1852.
[53] Prince Hohenstiel Schwangau, p. 68.
[54] Journal of the Royal Institution. April 1873.
[55] "Embryology of Echinoderms," l. c. p. 15.
[56] Mr. and Mrs. Agassiz: "Sea-side Studies," p. 139.
[57] l. c. p. 138.
[58] Wien. Zool. Bot. Gesells, 1869.
[59] Linnean Transactions, 1863.
[60] Linnean Transactions, 1866, vol. xxv.
[61] Linnean Transactions, vol. xxiv. p. 65.
[62] Siebold und Kolliker's Zeitschr. f. Wiss. Zool., 1864.
[63] Linnean Journal, vol. xi.
[64] Facts for Darwin, p. 120.
[65] A still nearer approach is afforded by the genus _Peripatus_, which since the above was written has been carefully described, especially by Moseley and Hutton. There are several species, scattered over the southern hemisphere. In general appearance they look like a link between a caterpillar and a centipede. They have a pair of antennae, two pairs of jaws, and (according to the species) from fourteen to thirty-three pairs of legs. They breathe by means of tracheae, which open diffusely all over the body.
[66] Unters. ub. die Entwick, und den Bau der Gliederthiere, p. 73.
[67] Linnean Transactions, v. xxii.
[68] Facts for Darwin, trans. by Dallas, p. 118. See also Darwin, "Origin of Species," p. 530. 4th ed.
[69] Mem. Peabody Academy of Science, v. I. No, 3.
[70] Wien. Zool. Bott. Gesells. 1869, p. 310.
[71] See also the descriptions given by Dujardin (Ann. des Sci. Nat.
1851, v. xv.) and Claparede (Anat. und Entwickl. der Wirbel osen Thiere) of the interesting genus _Echinoderes_, which these two eminent naturalists unite in regarding as intermediate between the Annelides and the Crustacea.
[72] "On a New Rotifer." _Monthly Microscopical Journal_, Sept. 1871.
[73] Generelle Morphologie, vol. ii. p. 79.
[74] Monographie der Moneren, p. 43.
[75] Gegenbaur. Grund. d. Vergleich. Anat. p. 210. See also Dr. M. S.
Schultze, Beitrage zur Naturg. der. Turbellarien. 1851. Pl. vi. fig. 1.
[76] Monographieder Moneren, p. 10.
[77] See Kauffmann, Ueber die Entwickelung and systematische Stellung der Tardigraden. Zeits. f. Wiss. Zool. 1851, p. 220.
[78] It is true that among the Insecta generally the first stages of development differ in appearance considerably from those above described; those of _Platygaster_, as figured by Ganin (ante Figs. 17-22), being very exceptional.