452 



THE AMERICAN NATURALIST [Vol. LI 



their interdependence and coordination of function in 

 the organism. As remarked above the discovery of this 

 property of separability of characters was gradually 

 prepared for in various branches of biology. First, in 

 comparative anatomy, through the observations of the 

 laws of independent degeneration, balance and progres- 

 sion of adjoining parts; second, through embryogeny and 

 ontogeny, in the observation of the hastened or retarded 

 development of adjoining parts; third, through heredity, 

 as, for example, in the mosaic inheritance of Galton; 

 fourth, through paleontology and phylogeny, in the law of 

 acceleration and retardation of Hyatt and, through the 

 observations of many other paleontologists, concluding 

 with the detailed obsei^^ations of Osborn and Gregory. 

 But the property of separability first shone out clearly 

 and most brilliantly in the discoveries of Mendel in hered- 

 ity. 



This property of structural separability and inde- 

 pendence of evolution is closely connected with separa- 

 bilitij or independence of function. Thus separability 

 may distinguish a great number of cells and tissues which 

 are united by a single fiuiction. oi- separability may dis- 

 tinguish a single cell, for ('xaiiii»l(\ the single giant cells 

 of the spinal cord of (MTtain fislic- and amphibians. 



It is important, therefore, to realize that this property 

 of separability, the separability of biocliaracters, is now 

 observable under six classes of evidence. 



2. ]\roDES OF Skparabitjty of Biocharacters in Heredity, 

 IX Okxksis. IX Rate of Evolution 

 I. BiocJiarnrtrr ]ir ritiific separahUifij, unit or exclusive 



1. Ernh'urr of Calfon, etc., as to mosaic inheri- 



2. Chin-'irtry !>> rlf,Ni<' separahHity, under the sepa- 



rat.' 'SlctfiiMinei-" or "factor" hypothesis of 

 ?^l« n(h'i. r.ati-Dii, Morgan, etc., according to 

 which "hiocharacter" of the soma may 



spring from one or more "determiners" or 



