To the many who have aided the authors in the years past, by suggestions and by sending specimens and other materials, sincerest thanks is tendered. This is especially due to their colleagues in the Department of Entomology of Cornell University, and to Professor Charles W. Howard, Dr. John Uri Lloyd, Mr. A. H. Ritchie, Dr. I. M. Unger, and Dr. Luzerne Coville. They wish to express indebtedness to the authors and publishers who have so willingly given permission to use certain illustrations. Especially is this acknowledgment due to Professor John Henry Comstock, Dr. L. O. Howard, Dr. Graham-Smith, and Professor G. H. T. Nuttall. Professor Comstock not only authorized the use of departmental negatives by the late Professor M. V. Slingerland (credited as M. V. S.), but generously put at their disposal the illustrations from the MANUAL FOR THE STUDY OF INSECTS and from the SPIDER BOOK. Figures 5 and 111 are from Peter's "Der Arzt und die Heilkunst in der deutschen Vergangenheit." It should be noted that on examining the original, it is found that Gottfried's figure relates to an event antedating the typical epidemic of dancing mania. WM. A. RILEY. O. A. JOHANNSEN. CORNELL UNIVERSITY, January, 1915. ADDITIONS AND CORRECTIONS vi line 11, for Heilkunft read Heilkunst. 18 line 2, for tarsi read tarsus. 32 line 21, and legend under fig. 23, for C. (Conorhinus) abdominalis read Melanolestes abdominalis. 47 legend under figure for 33c read 34. 92 line 22 and 25, for sangiusugus read sanguisugus. 116 legend under fig. 83, for Graham-Smith read Manson. 136 line 10, from bottom, insert "ring" after "chitin". 137 line 3, for meditatunda read meditabunda. 145 line 7, from bottom, for Rs read R_5. 158 line 20, for have read has. 212 after the chapter heading insert "continued". 219 line 10, from bottom, for Cornohinus read Conorhinus. 266 line 1, fig. 158j refers to the female. 272 line 5, insert "palpus" before "and leg". 281 line 6, for discodial read discoidal. 281 last line, insert "from" before "the". 284 line 5, for "tubercle of" read "tubercle or". 305 lines 19, 28, 44, page 306 lines 1, 9, 22, 27, 30, page 307 line 7, page 309 lines 8, 11, for R_{4+5} read M_{1+2}. 309 legend under fig. 168 add Bureau of Entomology. 312 line 36, for "near apex" read "of M_{1+2}". 313 running head, for Muscidæ read Muscoidea. 314 line 29, for "distal section" read "distally M_{1+2}". 315 legend under fig. 172, for Pseudopyrellia read Orthellia, for Lyperosia read Hæmatobia, for Umbana read urbana. 323 and 325 legends under the figures, add "After Dr. J. H. Stokes". 328 line 7 from bottom for Apiochæta read Aphiochæta. CONTENTS CHAPTER I INTRODUCTION 1-5