185 Even after we have so narrowed the scope and sphere of natural selection, it is still hard to understand; for the causes of extinction are often wellnigh as hard to comprehend as are those of the origin of species. If we assert (as has been lightly done) that Smilodon perished owing to its gigantic tusks, that Teleosaurus was handicapped by its exaggerated snout, or Stegosaurus weighed down by its intolerable load of armour, we may be reminded of other kindred forms to show that similar conditions did not necessarily lead to extermination, or that rapid extinction ensued apart from any such visible or apparent disadvantages. Cf. Lucas, F. A., On Momentum in Variation, Amer. Nat. xli, p. 46, 1907.
186 See Professor T. H. Morganãs Regeneration (316 pp.), 1901 for a full account and copious bibliography. The early experiments on regeneration, by Vallisneri, Rûˋaumur, Bonnet, Trembley, Baster, and others, are epitomised by Haller, Elem. Physiologiae, VIII, p. 156 seq.
187 Journ. Experim. Zool. VII, p. 397, 1909.
188 Op. cit. p. 406, Exp. IV.
189 The experiments of Loeb on the growth of Tubularia in various saline solutions, referred to on p. 125, might as well or better have been referred to under the heading of regeneration, as they were performed on cut pieces of the zoophyte. (Cf. Morgan, op. cit. p. 35.)
190 Powers of the Creator, I, p. 7, 1851. See also Rare and Remarkable Animals, II, pp. 17ã19, 90, 1847.
191 Lillie, F. R., The smallest Parts of Stentor capable of Regeneration, Journ. of Morphology, XII, p. 239, 1897.
192 Boveri, EntwicklungsfûÊhigkeit kernloser Seeigeleier, etc., Arch. f. Entw. Mech. II, 1895. See also Morgan, Studies of the partial larvae of Sphaerechinus, ibid. 1895; J. Loeb, On the Limits of Divisibility of Living Matter, Biol. Lectures, 1894, etc.
193 Cf. Przibram, H., Scheerenumkehr bei dekapoden Crustaceen, Arch. f. Entw. Mech. XIX, 181ã247, 1905; XXV, 266ã344, 1907. Emmel, ibid. XXII, 542, 1906; Regeneration of lost parts in Lobster, Rep. Comm. Inland Fisheries, Rhode Island, XXXV, XXXVI, 1905ã6; Science (n.s.), XXVI, 83ã87, 1907. Zeleny, Compensatory Regulation, J. Exp. Zool. II, 1ã102, 347ã369, 1905; etc.