[22] Similar conditions seem to have prevailed among the Proreptilia; but in those of their descendants which have specialized into Reptiles and Birds the basi-occipital element becomes more and more predominant in that formation which ultimately leads to the apparently single condyle. Hence it is misleading to divide the Tetrapoda into the two main groups of Amphi-and Mono-condylia, and therefrom to conclude that the two-condyled Mammalia are more closely related to the likewise amphicondylous Amphibia than to the so-called monocondylous Reptiles.
[23] 'Ergebnisse naturwissenschaftlicher Forschungen auf Ceylon,' vols. 4 and 5. (With an atlas of 84 plates; 1893.)
[24] 'Principles of Biology': 'The Factors of Organic Evolution'; 'The Inadequacy of Natural Selection.'
[25] Abridged from Haeckel's 'Systematische Phylogenie der Vertebraten,' § 14.
[26] That this great work is now comparatively rare, although still in the second-hand market, may perhaps be urged in excuse of the fact of so many attempts made by many authors, both professional and amateur, to find fault with or to explain the principles of adaptation, variation, heredity, cænogenesis, phylogeny, etc., in complete ignorance that all these and many more fundamental questions were fully discussed more than thirty years ago in the 'Generelle Morphologie.'
[27] James Croll: 'On Geological Time, and the Probable Date of the Glacial and Upper Miocene Period,' Philos. Magazine, xxxv., 1868, pp. 363-384; xxxvi., pp. 141-154; 362-386.
[28] William Thomson: 'On the Secular Cooling of the Earth,' Transact. R. S. Edinb., xxiii., 1864, pp. 157-169.
[29] 'Geological Time as indicated by the Sedimentary Rocks of North America.' Proc. Amer. Assoc. Adv. Sci., xlii., 1893, pp. 129-169.
[30] Henry Shaler Williams, 'Geological Biology.' New York, 1895.
Transcriber's Notes
Variations in spelling, punctuation and hyphenation have been retained except in obvious cases of typographical errors. Inconsistent hyphenation and spelling are as in the original. The layout of the chart Ancestral Tree of The Mammalia has been changed from the original to enhance clarity, the essential relationships have been preserved. The second reference to footnote 3, in the same paragraph as the first, has been left blind as it is redundant.