179] HEAD OF DIPTERA—PETERSOX 9 



ing a melting point of 62-64 C. was a sufficiently firm medium in which 

 to cut sections as thin as eight microns. Specimens stained in toto gave 

 the hest results. Delafield's haematoxylin required 24-48 hours, and 

 borax carmine 3-7 days. 



ACKNOWLEDGMENTS 



This investigation was carried on under the supervision of Dr. 

 A. D. MacGillivray, and to him I am greatly indebted for the sincere 

 interest shown and the many valuable suggestions received. Many speci- 

 mens, unobtainable in this vicinity, were secured from the collections 

 of the Illinois State Laboratory of Natural History, and for these I am 

 indebted to Professor S. A. Forbes. I am indebted to the Graduate 

 School of the University of Illinois for funds used in purchasing speci- 

 mens. I am also indebted to Mr. J. R. Malloch, of the Illinois State 

 Laboratory of Natural History, for the identification of all my material 

 and for specimens and many suggestions; to Mr. J. M. Aldrich for 

 species of Diopsidae, Phycodromidae, and Blepharoceridae ; to Professor 

 A. L. Melander for a species of Cyrtidae ; to Mr. 0. S. Westcott for a 

 species of Phycodromidae ; to Dr. P. S. Welch for a species of Simulii- 

 dae; and to Dr. 0. A. Johannsen for species of Dixidae and Blepha- 

 roceridae. I am also indebted to many others who furnished me with 

 unnamed material. 



MATERIALS 



The following list of insects includes all of the identified forms 

 studied. The families of Diptera to which these species belong are 

 arranged according to Aldrich 's ''Catalogue of North American Dip- 

 tera". The generic and specific names of all but a few species may 

 likewise be found in this catalog. 



Aldrich lists fifty-nine families; of these, one or more representa- 

 tives of fifty-three families have been studied. The following are not 

 represented: Orphnephilidae, Acanthomeridae, Nemestrinidae, Apio- 

 ceridae, Rhopalomeridae, and Nycteribiidae. The male and female of 

 each species have been observed except in a few cases ; in these the word 

 "male" or "female" after the species name indicates which sex has 

 been seen. Excepting one or two forms, the male and female have both 

 been drawn if they were decidedly different. If the two sexes are 

 similar, the figures were mostly made from the female. An asterisk 

 before the name of a species indicates that this form has been embedded, 

 sectioned, and studied. The figures following the various species refer 

 to the drawings made of the same. 



