THE UNITY OF THE ORGANISM 



Chapter XIV 



EVIDENCE FROM METAZOAN GERM-CELLS THAT 

 SUBSTANCES OTHER THAN CHROMATIN 

 ARE THE PHYSICAL BASES OF 

 HEREDITY 



Evidence from Spermatozoa 



f N our discussion we will be guided by the principle laid 

 down earlier and followed throughout our treatment 

 of heredity in the Protozoa, namely, that descriptive onto- 

 genesis brought to bear on the actual transformations which 

 result in the production of specific organs and parts, is the 

 final tribunal for the determination of what substances are 

 hereditarily formative. The first inquiry will be whether 

 there exist among the metazoa single-cell organs or parts 

 which when fully formed exhibit species characters in the 

 sense of taxonomic biology. If such elements do exist, ob- 

 servation on the constituents of the undifFerentiated cells 

 which take part in the transformations, obviously may be 

 expected to give us the information sought as to what 

 substances are formative. 



Spermatozoa Subject to Heredity as Well 'as "Bearers of 



Heredity" 



The comparative anatomy and comparative ontogenesis 

 of the male germ-cells among animals, which have been pur- 

 sued with great assiduity and skill during recent decades, 



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