4 MODES OF RESEARCH IN GENETICS 



other individuals. This resemblance marks the 

 end stage of heredity regarded as a process. It is 

 unnecessary to cite detailed instances to prove 

 how extraordinarily minute and specific this 

 resemblance ordinarily is, in respect of some 

 one or more characteristics of the individual. 

 Such facts are matters of common knowledge. 



B. Gametogenesis. The intervention of a rela- 

 tively undifferentiated stage {the germ cell) in the 

 cycle of reproduction of the individual. 



In higher organisms ordinarily each time an 

 individual reproduces itself it does so by means of 

 a single cell, which separates completely from the 

 other cells which together make the individual. 

 After separation this cell may for a time derive 

 its nourishment from the individual which pro- 

 duced it, but morphologically and physiologically 

 the completely formed gamete is essentially a 

 separate and independent entity, with certain 

 limitations as to the possibility of its continued 

 independent existence. 



Gametogenesis is clearly one of the most funda- 

 mental parts of the hereditary process for two 

 reasons : first, because the gametes are the 

 essential links in the preservation of physical 

 continuity in the genetic series ; and second, be- 

 cause, since all gametes formed by the same in- 

 dividual are demonstrably not absolutely alike 

 in respect of their hereditary qualities, the distri- 

 bution of the different hereditary qualities amongst 



