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76 REPRODUCTION AND LIFE HISTORY. 
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Heredity may be defined as the relation of genetic 
continuity between successive generations, and inheritance 
as all that the organism is or has to start with in virtue 
of this hereditary relation. Development is the expression 
or realisation of the heritable qualities. which have their 
physical basis in the germ cells, and it presupposes an ap- 
propriate environment of nutrition and “liberating stimuli,” 
—‘ nurture” in the widest sense. What the organism 
becomes is the resultant of two components, inherited 
“nature” and external “nurture.” 
