SPACE, GEOGRAPHIC DIVERGENCE, AND EVOLUTION 



415 



mental or ontogenetic species," "sub-species," "races," "varieties," distinguished 

 by different coloring, habits, proportions ( "allometrons" ) , and perhaps by 

 "rectigradations." 



It follows that to institute a true comparison between a geographic 

 series and a geologic series precisely the same metliods of ohservaiion 

 should be employed. Direct measurements of length and breadth should 

 be recorded from which indices (proportions of single structures like the 

 skull) and ratios (proportions between different parts like the upper and 

 lower segments of limbs) should be established. 



It is already known that allometrons, . or changes of proportion, in 

 every part distinguish the various geographic species and subspecies of 

 Ursus, for example, as studied by Merriam, the changes technically 

 known as dolichocephaly, brachycepbaly, dolichopy (or elongation of the 

 face), brachyopy (abbreviation of the face), brachypody (abbreviation 

 of the feet), dolichopody (elongation of the feet), brachymely (abbre- 

 viation of the limbs), dolichomely (elongation of the limbs), occur in 

 zoologic series in their incipient stages exactly as they occur in paleonto- 

 logic series. The only distinction is that in paleontologic series they may 

 be followed, through vastly greater periods of time in all the stages from 

 incipiency to the various climaxes. 



For example, the ten phyla of titanotheres described in the preceding 

 contribution are distinguished by progressive changes of proportion in 

 different directions. Thus one phylum is progressively brachycephalic 

 until it reaches an extreme in which the. breadth of the head is as great 

 as the length ; another phylum is progressively dolichocephalic until the 

 liead reaches a long, attenuated form. 



Table III. — Showing that geographic or space distribution and geologic or time 

 distribution may tal'C place coincidently from a central stem form A during 

 such an epoch as the post-Glacial. 



YEARS. 



4fr(ino- ,. . 





a 













k / 



\ / 



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^. 



> 



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3ft OOO 













9.nnnn __ 













1 r.^oon . 













1(1 (\c\rf 













K rldf> ^ r 



^^ 



b Ti 



- 



\ f 



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J - i 



3 ....... ( / 



A ; 1 



D 



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