PREFACE vii 



where they may be obtained. This list of publica- 

 tions has been arranged according to the method 

 now in general use among zoologists; the author's 

 name and the date of the appearance of the contri- 

 bution in question are bracketed in the text wher- 

 ever it has been considered necessary, and reference 

 to the list at the end of the book will reveal the 

 full title and place of publication of the work, thus 

 avoiding cumbersome footnotes. The figures that 

 have been copied or redrawn are likewise referred 

 in every case to the original source. Many of them 

 have been taken from the writer's previous publica- 

 tions and a few have been made especially for this 

 work. The writer has likewise drawn freely upon the 

 text of his original investigations already published. 



Ann Arbor, Michigan, 

 April 16, 1914. 



