lo PRIMARY FACTORS OF ORGANIC EVOLUTION. 



tion, as friction, impact, and strain, as an efficient 

 cause of evolution. ^ This demonstration led me to the 

 necessary inference that when the agency directive of 

 motion is consciousness, this also has been an impor- 

 tant factor of evolution, in demonstration of the sup- 

 position of Erasmus Darwin.^ Hyatt has demonstrated 

 first on paleontologic evidence, the inheritance of a 

 mechanically acquired character. Important contribu- 

 tions to corresponding histories of the Mollusca have 

 been made by Hyatt,^ Dall,* Jackson,* and Beecher.^ 

 Many other contributions, into which the paleontologic 

 evidence does not enter, have also been made by vari- 

 ous authors in Europe and America. 



The authors quoted up to this point had all as 

 sumed that the progress of evolution depends on the 

 inheritance by the offspring of new characters acquired 

 by the parent, and had believed that such is the fact 

 in ordinary experience. In 1883, Weismann, in an 

 essay on heredity, announced the opinion that charac- 

 ters acquired by the body could not be transmitted to 

 the reproductive cells, and could not therefore be in- 

 herited. This doctrine rests on the relation of the 

 germ-cells to those of the rest of the body, which is 

 expressed in the following language of his predecessor 

 Jaeger: "Through a great series of generations the 



l"The Origin of the Hard Parts of Mammalia," American Journal of 

 Morphology, 1889, p. 137. 



2 Origin of the Fittest, 1887, p. 357. 



3"Phylogeny of an Acquired Characteristic," Proc. Amer. Philosophical 

 Society, 1893, p. 349; "The Genesis of the Arietidse," Memoirs Mus. Compar. 

 Zo5logy, Cambridge, Mass., i88g, XVI., No. 3. 



4DalI, W. H., "The Hinge of Pelecypods and Its Development, Amer. 

 Jour. Sci. Arts, 1889, XXXVIII., p. 445. 



6 Jackson, R. T., " Phylogeny of the Pelecypoda, the Aviculidae, and Their 

 Allies," Memoirs Boston Society Natural History, i8go, IV., p. 277. 

 ^American Journal Sci. Arts, 1893. 



