occasion a sudden change in another organ; (4). Cross 

 fertihzation and hybridism. AJ^^yi h^t-^uh-^'^ 



It is clear that with reference to the factors of evolu- 

 tion Eimer is, and perhaps not unreasonably, an eclectic, 

 whose aim is to do justice to the predecessors of Darwin 

 as well as to Darwin himself. His antagonism to Darwin 

 and Weismann in this work is still quite moderate, al- 

 though even here it appears with sufficient clearness that 

 selection and the struggle for existence, the two principles 

 peculiarly characteristic of Darwinism, do not give rise to 

 new species, but can at best only sepai^ate and differentiate 

 species already existing. 



The second part of Elmer's work dealing with the ori- 

 gin of species, which appeared after an interval of ten years, 

 bears the title: "Orthogenesis of Butterflies." The Origin 

 of Species, II. Part (2 tables and 235 illustrations in the 

 text). Leipzig, 1897. In this book substantially the same 

 thoughts occupy the mind of the author as in the former 

 volume, but in many respects they are more mature, and 

 conspicuously more definite and precise. The most salient 

 features are the following: 



1. Eimer establishes his theory by means of very 

 minute observations on a definite species of animals, viz., 

 butterflies. 



2. He attributes evolution almost exclusively to de- 

 velopment along definitely determined lines. 



3. He proves the utter untenableness of Darwinian 

 principles and repudiates them unqualifiedly. 



71 



