21 



Sexual reproduction. 

 The idioplasm in heredity. 

 Variation. 

 The nucleus as the bearer of heredity. 

 O. Hertwig (1875, 1884, 1886). 

 Strasburger (1884). 

 kolliker (1886). 



BOVARI (1886). 



E. B. Wilson (1895). 



Roux (1881, 1885+). 



Struggle of the elements within the cell. 



Struggle of the cells. 



Morphogenic effect of functional stimuli. 



Heredity due to transmission of chemical com- 

 position. 



The mosaic theory. 



Weismann. Earlier theories (1883, 1885, 1886, and 

 1887). 



All inheritance of acquired characters denied. 



Theory of gemmules unnecessary and improbable. 



Continuity of germ-cells disproved. 



Germ-tracts. 



Position of the idioplasm in the nucleus. 



Distinction between germ idioplasm, or gcrtii- 

 plasin, and somatic idioplasm. 



Improbability of the backward development of 

 somatic idioplasm into germ-plasm. 



Continuity of the germ-plasm. 



