[10] _Biol. Bull._, XVIII, 1910, p. 285. [11] This description does not quite agree with the representation of the larvae in Pl. 17 of the book _Evolution in the Genus Leptinotarsa_ for there the larva of _undecimlineata_ is shown as white in the second stage, but yellowish in the third stage; perhaps there is an error in printing. [12] _Biol. Bull._, XX, 1910, p. 67. [13] As to the interrelations of these three forms, Tower states (1906, p. 18) that _angustovittata_, which he reared from _undecimlineata_, is intermediate between it and _signaticollis_. Compare Stål, "_Monogr. des Chrysomélides_," 1862, p. 163; and Jacoby, _Biol. Centr. Amer. Celeopt._, vi, Pt. 1, p. 234, Pl. xiii, fig. 20; Tab. 41, fig. 15; _ibid._, Suppl., p. 253. All these forms are evidently very closely related, and the delimitation of species is quite arbitrary. Jacoby indeed suggests that _undecimlineata_ may be a variety of _decemlineata_. [14] Gortner, _Amer. Nat._, Dec., 1911, XLV, p. 743. [15] _Mutations, Variations, and Relationships of the Oenotheras_, Carnegie Institution Publication No. 81, 1907, pp. 61-64. [16] Macdougal, D. T., "Alterations in Heredity induced by Ovarial Treatments", _Bot. Gaz._, vol. 51, 1911, p. 241. [17] Payne, Fernandus, _Biol. Bull._, XVIII, 1910, p. 188, and _ibid._, XXI, 1911, p. 297. [18] See especially, _Mutation et Traumatismes_, Paris, Felix Alcan, 1908. [19] J. H. Powers, "Morphological Variation and its Causes in _Amblystoma tigrinum_." _Studies from the Zoological Laboratory. _ The University of Nebraska, No. 71, 1907. [20] In connexion with this case I would refer the reader to some remarkable observations of Dr. T. A. Chapman on various types of larvae which he reared from the moth _Arctia caja_ (_Ent. Rec._, IV, 1893, p. 265, and following parts). From a single mother he raised a great diversity of forms, some which fed up rapidly and passed through their development without assuming certain stages, and others which were, as he called them, "laggards," moulting more times than their brethren and developing at a much slower rate. It is greatly to be hoped that such a case may be critically investigated by analytical breeding. CHAPTER XI. STERILITY OF HYBRIDS. CONCLUDING REMARKS. When we consider the bearing of recent discoveries on those comprehensive schemes of evolution with which we were formerly satisfied, we find that certain details of the process are more easy to imagine. We readily now understand how varieties once formed, can persist, but at the same time difficulties hitherto faced with complacency become formidable in the light of the new knowledge. So generally is this admitted by those familiar with modern genetic research that most are rightly inclined to postpone the discussion. The premisses, indeed, on which such a discussion must be based are almost wholly wanting.