fortunately evolution is under this suspicion. The most 

 fundamental and far reaching conceptions that science has 

 achieved are ruled out of some science courses if they fail 

 to seem to be of immediate interest to the student. Into 

 the merits of such ruling there is not space here to enter. 

 There is only space to say that such very brief treatment 

 of evolution as is presented herewith may find place even 

 in courses in which the weeding out of the "abstract" has 

 been very thorough. For, after all, evolution has prac- 

 tical aspects which cannot be denied, and these are empha- 

 sized in this little book. 



The text is organized into what have been tested and 

 found to be serviceable "assignment units"; short chapters 

 which may also be welcome to the general reader. 



CHAPTER TITI^ES 



1 What is Evolution? 



2 Periods in Its Study. 



3 The Facts That Suggest It. 



4 Explanations of Evolution. 



5 Environment. 



6 Lamarck. 



7 Darwin and DeVries. 



8 Causes of Natural Selection. 



9 Evidences of Natural Selection. 



10 Objections to Natural Selection. 



11 Mutation. 



12 Objections to Mutation. 



13 Orthogenesis. 



14 The Problem of Heredity. 



15 Machinery of Heredity. 



148 



