630 THE AMERICAN NATURALIST. [VOL XXXII. 
believe to be its proper place among the other factors of 
organic evolution. 
2. The renascence of Lamarckism under the name of Neola- 
marckism, being Lamarckism in its modern form. This school 
relies on the primary factors of evolution, on changes in the 
environment, such as the agency of the air, light, heat, cold, 
changes in climate, use and disuse, isolation, and parasitism, 
while it regards natural, sexual, physiological, germinal, and 
organic selection, competition or its absence, and the inherit- 
ance of characters acquired during the lifetime of the indi- 
vidual, as secondary factors, calling into question the adequacy 
of natural selection as an initial factor. 
3. The rise of the Neodarwinian school. While Darwin 
soon after the publication of the Origin of Species somewhat 
changed his views as to the adequacy of natural selection, and 
favored changes in the surroundings, food, etc., as causes of 
variation, his successors, Wallace, Weismann, and others, believe 
in the “all-sufficiency”’ of natural selection. Weismann also 
invokes panmixia, or the absence of natural selection, as an 
important factor; also amixia, and denies the principle of 
inheritance of acquired characters, or use-inheritance. 
4. A third school or sect has arisen under the leadership of 
Weismann, who advocates what is in its essence apparently a 
revival of the exploded preformation, incasement, or “ evolu- 
tion ” theory of Swammerdam, Bonnet, and Haller, as opposed 
to the epigenetic evolutionism of Harvey, Wolff, Baer, and the 
majority of modern embryologists. On the other hand, there 
are some embryologists who appear to accept the combined 
action of epigenesis and evolution in development. 
5. Attention has been concentrated on the study of varia- 
tions and of their cause. Opinion is divided as to whether 
variation is fortuitous, or definite and determined. Many now 
take exception to the view, originally held by Darwin, that 
variations are purposeless and fortuitous, believing that they 
are, for example, dependent on changes in the environment 
which were determined in early geological periods. For 
definite variation, Eimer proposes the term orthogenesis. 
Minute variations dependent on climatic and other obscure 
