The Making of Species 



books which come under the third category have 

 the defects of extreme youth. De Vries has 

 discovered a new principle, and it is but natural 

 that he should exaggerate its importance, and see 

 in it more than it contains. But, as time wears 

 on, these faults will disappear, and the theory of 

 mutations will assume its true form and fall into 

 its proper place, which is somewhere between 

 the dustbin, to which Wallaceians would relegate 

 it, and the exalted pinnacle on to which De 

 Vries would elevate it. 



In the present state of our knowledge, books 

 of Class IV. are the most useful to the student, 

 since they are unbiassed, and contain a judicial 

 summing-up of the evidence for and against the 

 various evolutionary theories which now occupy 

 the field. Their chief defect is that they are 

 almost entirely destructive. They shatter the 

 faith of the reader, but offer nothing in place 

 of that which they have destroyed. T. H. 

 Morgan's Evolution and Adaptation, however, 

 contains much constructive matter, and so is the 

 most valuable work of this class in existence. 



Zoological science stands in urgent need of 

 constructive books on evolution books with 

 leanings towards neither Wallaceism, nor La- 

 marckism, nor De Vriesism ; books which shall 

 set forth facts of all kinds, concealing none, 

 not even those which do not admit of explana- 

 tion in the present state of our knowledge. 



vi 



