EVOLUTION OF THE COLORS OF BIRDS. 49 



other not adaptive, must be abandoned, since the latter 

 does not exist in the second class." 



I have attempted to present a fair statement of both 

 sides of the case in this controversy in regard to the in- 

 heritance of acquired characters, and to all of the import- 

 ant arguments which have been adduced both pro and 

 con, illustrated by typical examples. It will be remembered 

 that the scepticism in regard to the possibility of ac- 

 quired characters being transmitted arose from the 

 theory of heredity enunciated by Prof. Weismann. A 

 study of the different theories of heredity disclosed the 

 fact that while Darwin's hypothesis of pangenesis, or 

 any subsequent modification of it, was a merely formal 

 and provisional scheme for explaining the supposed facts 

 of heredity, Weismann's theory of germ-plasm appears 

 to be a speculative deduction from real facts which the 

 facts themselves do not warrant. That consequently, 

 although this theory may be true, it appears rather vis- 

 ionary and certainly should not be unconditionally 

 accepted as true or even as a working hypothesis, unless 

 the facts dependent upon it can be thus best explained. 

 The practice of stretching facts to fit into a theory is a 

 habit which cannot be too strongly condemned. 



If Weismann's theory of germ-plasm is unproven 

 there is no apparent reason why acquired characters 

 may not be inherited. An examination of the testimony 

 on this point seems to indicate that both sides have cited 

 cases which did not prove their point. Many so-called 

 proofs which have been brought forward by the Neo- 

 Lamarckians in reality prove nothing, but, on the other 

 hand, some of the interpretations of the Neo-Darwin- 

 ians appear forced and illogical. 



It is obvious that a single established case of inherit- 

 ance of an acquired character would be sufficient to prove 

 the principle, however many other cases might be dif- 

 4 



