406 BIOLOGY AND ITS MAKERS 
5. Weismann adopts and extends the principle of 
natural selection. Germinal selection is exhibited 
in the germ-plasm. 
IV. De Vries’s Theory of Mutations. 
t. The formation of species is due not to gradual 
changes, but to sudden mutations. 
2. Natural selection presides over and improves varia- 
tions arising from mutation. 
Among the other theories of evolution that of Eimer is 
the most notable. He maintains that variations in organisms 
take place not fortuitously or accidentally, but follow a per- 
fectly determinate direction. This definitely directed evolu- 
tion is called orthogenesis. He insists that there is con- 
tinuous inheritance of acquired characters, and he is radically 
opposed to the belief that natural selection plays an important 
part in evolution. The title of his pamphlet published in 
1898, On Orthogenesis and the Impotence of Natural Selection 
in Species-Formation, gives an indication of his position in 
reference to natural selection. A consideration of Eimer’s 
argument would be beyond the purpose of this book. 
The cause for the general confusion in the popular mind 
regarding any distinction between organic evolution and 
Darwinism is not far to seek. As has been shown, Lamarck 
launched the doctrine of organic evolution, but his views did 
not even get a public hearing. Then, after a period of tem- 
porary disappearance, the doctrine of evolution emerged 
again in 1859. And this time the discussion of the general 
theory centered around Darwin’s hypothesis of natural selec- 
tion. It is quite natural, therefore, that people should think 
that Darwinism and organic evolution are synonymous terms. 
The distinction between the general theory and any particular 
explanation of it has, I trust, been made sufficiently clear in 
the preceding pages. 
