THE OPINIONS OF NEO-LAMARCKIANS. 527 



tion of the causes of variation. Nor is it pretended for 

 a moment that use and disuse are the sole or even the 

 chief factors in variation." 



European authors, partly from their less favorable 

 situation for the obtaining of paleontologic evidence, 

 have not contributed as much as Americans to the 

 doctrine of bathmogenesis. Nevertheless, in England 

 Spencer, Cunningham, Henslow, and others have sus- 

 tained this doctrine, and in France Giard and Edmond 

 Perrier, and in Germany, Semper, Eimer, and others, 

 who lean principally in their writings to its physio- 

 genetic aspect. Says Eimer : 1 



"According to my conception, the physical and 

 chemical changes which organisms experience during 

 life, through light or want of light, air, warmth, cold, 

 moisture, food, etc., and which they transmit by her- 

 edity, are the primary elements in the production of 

 the manifold variety of the organic world, and in the 

 origin of species. From the materials thus supplied, 

 the struggle for existence makes its selection. These 

 changes, however, express themselves simply as 

 growth." 



Nageli discards completely the agency of natural 

 selection, and sees an internal " Principle of Improve- 

 ment" as the active agent in evolution. He appar- 

 ently includes both statogenesis and bathmogenesis in 

 his conception. 2 He says : 



"Such internal causes must necessarily be sup- 

 posed merely on the ground that modifications or vari- 

 ations of the phyla do actually take place in definite 

 directions, are not irregular. The internal causes effect 



1 Organic Evolution, English Translation, 1890, p. 22. 



2 Mechanische physiologische Abstammungslehre, C. V. Nageli, Munich, 

 1884. 



