318 The Unity of the Organism 



ference? Degree of resemblance and that alone. Ho the 

 comprehensive and balanced study of rescmblances-and- 

 differences is far more important with the student of organic 

 groups than with the geneticist. The former must perforce 

 devote himself to resemblances more broadly and more deeply 

 than does the geneticist, and so is sure to have an ampler 

 mass of facts at his command. 



Looking at the phenomenon of heredity from the vantage 

 point now reached, a fact that cannot escape attention is 

 that the infinite number and kind of resemblances presented 

 by the living world co-exist with a likewise infinite number of 

 differences. This fact brings us to where we can state sharp- 

 ly the problem now before us : If the resemblances among 

 completed individual organisms are explained, as prevalent 

 theory holds them to be, by referring them to the chromo- 

 somes which constitute only a small fraction of the total 

 mass of organisms, and which have little observable variety 

 as compared with that among organisms, how have all the 

 differences among the organisms come about? Of the vast 

 total mass of material that enters into the make-up of living 

 nature and which is composed of chromosomes plus whatever 

 else the living body contains, how has the relatively small 

 mass of relatively undifferentiated chromatin produced the 

 great mass of relatively highly differentiated cytoplasm en- 

 tering into the tissues and organs? 



It should be stated at the outset that so utterly insignif- 

 icant is the positive evidence of the production of cytoplasm 

 by the chromosomes as compared with the evidence of the 

 fundamental coexistence and cointeraction of these sub- 

 stances, that very few biologists are so bold as to contend 

 that either ontogenetically or phylogcnetically are chromo- 

 somes literally first, and producers of other parts. The 

 extreme form of the germ-plasm theory probably implied 

 this, although Weismann never followed the logical conse- 

 quences of his speculations into phylogenctic history. 



