Heredity as a form of motion, or as memory. 



Spexcer (1864), polarity of the physiological units. 

 Congenital variations diK' to changes in polarity. 

 Inheritance of acquired characters thus ex- 

 plained. 



Nageli {1884), morphogenic stimuli transmitted 

 through micellar threads. 



Haeckel (1876), branched wave motion, perigen- 

 esis of the plastidules. Heredity is memory. 



Okr (1893). Heredity is habit. 



Cope. 



Objections to these theories. 



a. Their fanciful character. 



b. All founded on the supposed inheritance of 

 acquired characters. 



c. Absence of mechanism. 



Pangenesis. 



Democratus (400 B. C). Seed of animals formed 

 by contributions from all parts of tlie body. 



BuFFON (1720-1793). 



Darwin (1868). Pangenesis of gemmules. 

 Latent gemmules. 

 Acquired characters inherited. 



Galton (1872). Great number of gemmules. 

 Their imaginary character. 

 Experiments on rabbits. 

 Acquired characters seldom inherited. 



Brooks (1876, 1883). Modified pangenesis. 



New gemmules formed only under unfavorable 

 conditions. 



Hybrid gemmules induce variation. 



Latent gemmules in egg, new gemmules in sper- 

 matozoon. 



Acquired characters not inherited. 



