CHAPTER VII 



Theories of Heredity. — Spencer's 

 Physiological Units 



Relations between theories of evolution and theories of hered- 

 ity. — The various hypotheses as to the structure of the 

 protoplasm. — Micromerists and organicists. — Uniform par- 

 ticles and representative particles. — Physiological units 

 typical of the former. — Their properties; an explanation 

 of biological phenomena. — The persistence of force and the 

 instability of the homogeneous. — Other hypotheses. 



FROM the foregoing we can see how closely the 

 question of the phylogenetic evolution of living 

 things is related to the question of their individual de- 

 velopment, of the transmission of their characters to 

 their progeny and of the appearance in them of new 

 characters. It is through inheritance that variations 

 become constant and characteristic of a species instead 

 of remaining individual and temporary. Certain the- 

 ories of evolution are therefore indissolubly allied 

 with certain conceptions of hereditary transmission. 



A noteworthy feature of the various hypotheses 

 advanced on the subject of heredity is that they solve 

 at the same time two radically different problems, the 



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