CHAPTER XI 



HISTORY OF THEORIES OF HEREDITY AND INHERITANCE 



" Like leaves on trees the race of man is found, 

 Now green in youth, now withering on the ground ; 

 Another race the following spring supplies, 

 They fall successive and successive rise." 



ILIAD (Pope's Translation). 



[The same may be said of the succession of theories of heredity, but, 

 in both cases, there is a persistent living tree, to whose growth all the 

 leaves contribute.] 



i. What is required of Theories of Heredity and 



Inheritance. 



2. The Old Theories of Heredity. 

 3. Theories of Pangenesis. 

 4. Theory of Genetic or Germinal Continuity. 



i. What is required of Theories of Heredity and Inheritance 



THE main object of a theory of heredity is to express in as 

 simple terms as possible the nature of the genetic relation which 

 binds generations together, and to interpret the facts of inheri- 

 tance in terms of this relation. 



The Uniqueness of the Germ -Cells. The first and chief pro- 

 blem is to account for the material basis of heredity i.e. in all 

 ordinary cases, for the germ- cells. What is their origin and 

 history ? what relation have they to the parental body which 

 bears them, from which they are liberated ? what relation have 

 they to the germ-cells of the body into which they develop ? Or, 

 more generally, hi what way are they peculiar ? how do they 



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