Number 45- September 28, 1917. 



OCCASIONAL PAPERS OF THE MUSEUM OF 

 ZOOLOGY 



UNIVERSITY OF MICHIGAN 



Ann Arbor, AIichigan. Puclisheo by the University. 



TPIE METHOD OF EVOLUTION IN THE 

 UNiONID^E-- 



By Bryant W'aeicer. 



After I had incautiously and some\vhat improvidently, per- 

 haps, accepted the invitation of the chairman to take part in the 

 discussion this afternoon, I began to consider what there was 

 to say upon the subject that had been assigned to me. At the 

 outset it seemed that there was a certain element of uncer- 

 tainty, what we lawyers call a latent ambiguity, as to what was 

 meant by "method of evolution." Assuming the existence of a 

 primitive, simple, homogeneous type of any class of animal 

 life, which in the course of time has become changed into a 

 series of similar, yet diverse, types of greater complexity of 

 organization, does the "method of evolution" refer simply to 

 the changes in the organism itself from simplicity to com- 

 plexity, or does it mean those external forces, which, exerted 



* Read at a symposium on the method of evolution before the zoological sec- 

 tion of the Michigan Academy of Science, March 28, 1917- 



