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THE AMERICAN NATURALIST [Vol. XLIX 



development in successive generations. For example, a 

 rectigradation like the hypocone may become more dis- 

 tinct, a change of proportion like brachycephaly may be- 

 come more pronounced in successive generations. Yet 

 there are a number of additional contrasts between the 

 proportional and certain numerical characters, a few of 

 which may be enumerated : 



Proportional characters = Alio- Orthogenic numerical characters — 

 metrons Rectigradations 

 Alloinetrons give rise to analo- Rectigradations give rise to 

 gies, never to homologies: they homologies, strictly speaking ho- 

 are quantitative and intensive and momorphic structures; they are 

 not numerical ; . closely related neomorphs, new outgrowths, nu- 

 forms give rise to different al- merically new characters; similar 



he same allometrons; allometrons tween the members of related 

 -both harmonic and disharmonic phyla; they are comparatively in- 

 -frequently accompany changes frequent phenomena ; they are not 



i be produced experi 



saltum; the closer 



4. Differences of Opinion as to the Origin of Netv 

 Numerical and Proportional Characters 



In my opinion, which is not shared by all my co-workers, 

 rectigradations and allometrons are qualitatively differ- 

 ent characters and are attributable to different combina- 

 tions of causes. For example, the additional cuspules on 

 the teeth of Cams, Alopex and Vulpes are typical recti- 

 gradations; they are "characters" qualitatively different 

 from the dolichocephaly of Vulpes or the relative brachy- 



