110 



GENERAL ZOOLOGY 



The difficulty in adopting this principle as an explanation 

 of the way in which evolution has taken place lies in the fact 



already mentioned in 

 the discussion of 

 characters acquired 

 through use or dis- 

 use, that it is not 

 yet entirely clear that 

 changes occurring 

 during the lifetime 

 of the individual are 

 transmitted to the 

 next generation. 



The Mutation 

 Theory. It will be re- 

 membered that Dar- 

 win laid stress upon 

 indefinite, or fluctu- 

 ating, variations as 

 furnishing the greater 

 part of the material 

 for selection. The mu- 

 FIG. 57. Pupse of Black Swallow-l^ai! Butterfly tation theorv stands 



Showing influence of color of near-by object on the in sharp Contrast with 

 color of the pupa. Photographed from life. About .-, -, ,- ,, 



three quarters natural size the Selection theory 



(From Hunter's Studies in Insect Life) in emphasizing the 



heredity transmission 



of definite variations. With the mutation theory is particularly 

 associated the name of Hugo de Vries, a Dutch botanist living 

 in Amsterdam, Holland. He was led to express the princi- 

 ple from his studies of the variations of a species of even- 

 ing primrose introduced from America and found growing in 

 waste places in Hilversum, near Amsterdam. It should not 

 be overlooked that William Bateson, of Cambridge, England 



