19 



Spencer (1864). 



(Principles of Biology, Vol. i, pp. 179-183 and 209-292.) 



Theory of heredity part of philosophical system 

 of cosmic evolution. 



Polarity. 



Physiological unites. 



Germ cells collections of physiological unites. 



Any force affecting a part affects the whole. 



Acquired characters inherited. 



Darwin (1868). Provisional hypothesis of Pangen- 

 esis. 



Inheritance due to gemmules. 



Variation due to latent gemmules, to rearrange- 

 ment of gemmules, or to the inheritance of 

 the direct effects of the environment and of 

 use or disuse. 



Galton (1876). 



Pangenesis doubtful. 



Transmission of acquired characters doubtful, 



Continuity of the "Stirp." 



His (1875). 



Differentiation of areas. 



Unequal growth. 



Comparison with waves formed in liquids. 



Haeckel (1876). 



" Perigenesis of the plastidules." 

 Heredity is memory. 



