. The origin and evolution of life, on the theory of action, reaction and interaction of energy. The same is true of the widely separated lines of descendants from the mas-todons, elephants, and rhi-noceroses. This law ofuniform evolution and ofthe development inde-pendently in descendantsfrom the same ancestors ofclosely similar charactersis confirmed in Osbornsstudy of the evolution ofthe titanotheres (Fig. 127).In these animals, whichhave been traced throughdiscoveries of their fossilremains over a period oftime extending from thebeginning of the LowerEocene to the beginningof the Middle Ol
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. The same is true of the widely separated lines of descendants from the mas-todons, elephants, and rhi-noceroses. This law ofuniform evolution and ofthe development inde-pendently in descendantsfrom the same ancestors ofclosely similar charactersis confirmed in Osbornsstudy of the evolution ofthe titanotheres (Fig. 127).In these animals, whichhave been traced throughdiscoveries of their fossilremains over a period oftime extending from thebeginning of the LowerEocene to the beginningof the Middle Oligocene,inclusive, is exhibited anearly continuous,^ un-broken transformationfrom the diminutive Eoti-tanops of the Lower Eoceneto the massive Brontothe-rium of the Lower Oligocene, the latter form being so far asknown the most imposing product of mammalian evolution, 1 The continuity is broken by the extinction of one branch and the survival of an-other.^ It IS a continuity of character rather than of lines of descent. In some casesthere is a continuity both of characters and of Fig. 128. Stages in the Evolution of theHorn in the Titanotheres. This shows that these important weapons ariseas rectigradations, /. c, orthogenetically andnot as the result of the selection of chance orfortuitous variations. Horns, large, 4, Bron-totheriinn platyccras, Lower Oligocene; horns,small, 3, Protitanothcrium emarginaliim, UpperEocene; horns, rudimentary, 2, Manteoccrasmanteoceras, Middle Eocene; hornless stage,I, Eotitanops horealis, Lower Eocene. Models in the American Museum of NaturalHistory, prepared for the author by Erwin CHANGES OF PROPORTION 265 with the exception of the Proboscidea. Every known step inthis transformation is determinate and definite, every additionalcharacter which has been observed arises according to a fixedlaw and not according to any principle of chance. In theeleven principal branches which radiate from the earliest knownforms {Eotltanop
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