PREFACE. V 



distinct and persistent for each group as are 

 the fossil types of each period revealed to us by 

 the latter ; and that the experiments upon domes- 

 ticated animals and cultivated plants, on which 

 its adherents base their views, are entirely foreign 

 to the matter in hand, since the varieties thus 

 brought about by the fostering care of man are 

 of an entirely different character from those ob- 

 served among wild species. And while their 

 positive evidence is inapplicable, their negative 

 evidence is equally unsatisfactory, since, however 

 long and frequent the breaks in the geological se- 

 ries may be in which they would fain bury their 

 transition types, there are many points in the 

 succession where the connection is perfectly dis- 

 tinct and unbroken, and it is just at these points 

 that new organic groups are introduced without 

 any intermediate forms to link them with the 

 preceding ones. In another series of papers, I 

 shall endeavor to show the futility of the argu- 

 ment so far as it is founded upon the r imperfec- 

 tion of the geological record. 



I would add one word upon the way in which 

 this volume has been prepared, since it has some 

 features requiring explanation, if not apology. 

 These chapters were first embodied in a course 



