22 



Development a process of epigenesis. 



Variation due to the direct effect of external 

 conditions upon the germ (1883). 



Variation in higher organisms due principally 

 to the mingling of diverse germ-plasms in sex- 

 ual reproduction (1886). 



First polar spindle removes the ovogenic idio- 

 ■ plasm (1887). 



Second polar spindle removes half of the ances- 

 tral germ-plasms. 



De Vries (1889). Intracellular pangenesis. 



Pangenes (gemmulcs). 



Reserve pangenes in nucleus, active pangenes in 

 cytoplasm. 



Protoplasmic net-work and inheritance of ac- 

 quired characters denied. 



Variation due to, — modification, change in pro- 

 portion, alteration in arragement, or unequal 

 division, of pangenes in germ-cells. 



Continuity of germ-plasm. 



Independence of hereditary characters and the 

 necessity for separate factors. 



Control of the cell by the nucleus and the ne- 

 cessity for material particles. 



Weismann. Later theory (189 1, 1893). 



Development a process of evolution. 



Continuity of the germ-plasm. 



The mingling of gerni-i)lasms in sexual repro- 

 duction, A nipli iiii iv IS. 



Each ancestral germ-i^lasni a distinct unite, the 

 id 



