4 INTRODUCTION 



Each branch of animals has bopii introduced by a familiar and 

 accessible type. Tire discussion of the type is intended (1) to expres-s, 

 in an organized form, the details of the work already supposed to 

 have been done in the laboratory and field, and (12) to bring out the 

 characteristics of the branch of which the type is an example. After 

 the different forms of the branch have been studied, their character- 

 istics are summed up, their adaptations to envircuirieiit and their 

 economic significance are discussed, and, lastly, a clear, concise classi- 

 fication of the group is given. In the main, the classification accords 

 with that given by Parker and Ilaswell. 



The author is greatly indebted to the following men who have read 

 and criticised parts of the manuscript, covering, in most cases, their 

 own special fields: Dr. Gary N. Calkins and Dr. Henry F. Osborn of 

 the American IMuseum of Natural History; Professors John Henry 

 Comstock and G. D. Harris of Cornell University; Dr. T. B. Palmer, 

 Dr. H. F. Merriam, Dr. Leonard Stejneger, Dr. Ch. Wardell Stiles, 

 and Dr. B. W. Evermann of Washington, D.C. ; Dr. J. G. Neediiam 

 of Lake Forest University; Dr. C. C. Nutting of Iowa LTniversity; 

 Professor J. S. Kingsley of Tufts College; and ^Ir. Edward Potts of 

 Philadelphia. It is to be distinctly understood, however, that these 

 men are in no way responsible for any part of the work. 



Most of the drawings were made by Miss ^Minnie Walker. Much 

 is due to her untiring enthusiasm and devotion for the completion of 

 the work. Several figures were redrawn from the " Standard Natural 

 History," a few from Packard's " Zoology," with the author's permis- 

 sion, several from the publications of the United States Geological 

 Survey, and Figs. 14-3 and 235 from Jordan and Kellogg's "Animal 

 Life." Figure 93 was kindly loaned by the Minnesota State Experi- 

 ment Station ; Fig. 201 is from a photograph by Professor H. Gar- 

 man ; Figs. 110, 138, and 199 were loaned by the Cornell Nature 

 Study Bureau; Figs. 99, 100, an.l 101 are after Snodgras; Figs. 95, 96, 

 97, and 98 were drawn by ]\Iiss Clara S. Ludlow, while agraduate 

 student in biology. Figure 8S is from a photograph by Professor J. H. 

 Comstock; Figs. 191 and 193 are from photographs by Dr. C. M. 

 Weed; Figs. 179 and 197 are from photograiihs by Dr." K. W. Shu- 

 feldt, while Figs. 118 and 119 are from pliotcgraphs by Mr. Victor 

 Lowe, Geneva, New York. Figure 4 was drawn from nature by my 

 wife, to whom acknowledgment is also due for information regarding 

 the etymology of many words, careful criticism of the manuscript, and 

 helpful suggestions concerning the subject -matter. The remainder 

 of the photographs, drawings, and diagrams are by the author. 



GLENN W. HERRTCK. 

 Agricultural Colleoio, Mississippi. 



