Vlll PREFACE 



that in the absence of monographic revisions of the species of 

 parasites noted any other method would have been indefensible 

 in a brief treatise. 



Abundant use has been made of figures to illustrate the forms 

 described. Most of the illustrations are new and many of them 

 drawn by the author of the chapter especially for this work. 



In chapter II certain figures and tables are taken with modi- 

 fications from Shelford's American Communities in Temperate 

 America by courtesy of the Geographic Society of Chicago and the 

 University of Chicago Press. 



It would be impossible to acknowledge all of the aid which has 

 been extended during the progress of the work. Valuable sugges- 

 tions from many sources have been freely extended us and as freely 

 utilized. 



To all of our colleagues who, in spite of multitudinous difficulties 

 and seemingly interminable delays, have worked so generously to 

 perfect their individual chapters the sincerest thanks of the editors 

 are due. Especial mention should be made of the numerous help- 

 ful suggestions and criticisms given outside their own chapters 

 during the preparation of the work by Professors E. A. Birge and 

 Frank Smith. Grateful acknowledgement is also due E. C. Faust 

 and H. G. May for aid in reading and checking proof. 



Finally, it is a pleasure as well as a duty to express our apprecia- 

 tion of the work of the publishers. Their forbearance and continued 

 kindly assistance during the long and difficult period of preparation 

 has made possible the completion of the work and its presentation 

 to the scientific worker in attractive form. 



