BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 25, pp. 411-416 September 15, 1914 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



EECTIGEADATIONS AND ALLOMETRONS IN EELATION TO 



THE CONCEPTIONS OF THE "MUTATIONS OF WAAGEN/' 



OF SPECIES, GENEEA, AND PHYLA ^ 



BY HENRY FAIRFIELD OSBORN 



{Read before the Faleontological Society January 1, lOlJf-) 



CONTP]NTS 



Page 



General discussion ._. 411 



Discussion of the illustrative diagrams 413 



Space, geograpliic divergence, and evolution 414 



(ieograpliic distribution 416 



General Discussion 



The new problem raised in this contribution is that of the comparison 

 of a geologic ascending evolutionary series in time, like that of the titano- 

 theres, with a contemporaneous geographic series of species, subspecies, 

 and varieties which may be grouped within a single genus : In what re- 

 spects do the characters observed in a genus ascending and developing 

 in geologic time resemble or differ from the characters observed in a 

 genus distributed in geographic space? 



The superb materials assembled by Osborn with the cooperation of 

 William K. Gregory for the study of the titanotheres enable us to deter- 

 mine with precision that in a thne series there are two kinds of characters 

 in the hard parts of mammals, namely, aUometrons, or changes of pro- 

 portion, and recti gradations, or the appearances of absolutely new charac- 

 ters. For example, a new cusp or a new horn rudiment is regarded as a 

 rectigradation in its initial stage ; but when it takes on profound changes 

 of proportion in the course of evolution these changes are known as allom- 

 etrons. These characters appear to evolve under a different combina- 

 tion of causes. The accumulation of allometrons and rectigradations 

 marks the steps fjom "species" to "species" and the minute continuous 



Manuscript received by the Secretary of the Geological Society June 15, 1914. 



(411) 



