Order DIPTERA. 



This order contains the flies, always recognizable by having two wings only, 

 the secondaries being reduced to little knobs or halteres. The head is separated 

 from the thorax by a distinct narrow neck, and the antennae are either quite 

 long or very short and aristate. The mouth is formed for scraping or sucking 

 or both, never for biting, in the adult stage. The larvae vary greatly in form, 

 but are usually either very slender and elongate or maggot-like in form. The 

 metamorphosis is complete, and the change between larva and adult is more 

 radical than in any other insect. 



The flies contain many injurious or annoying forms, and a few that are bene- 

 ficial because as scavengers they remove or hasten the decay of large animals. 



Our collections are small and most of those listed here have been collected or 

 named by Mr. C. W. Johnson, of the Wagner Free Institute, Philadelphia, Pa. 

 Mr. Johnson has also prepared the following list in this order in its entirety, 

 and should be considered authority for all notes not otherwise bracketed. The 

 descriptive remarks under family headings and the economic suggestions are 

 my own. 



Mr. Johnson writes in explanation and acknowledgment as follows : 



" It has given me great pleasure to assist Prof Smith in preparing this list of 

 Diptera. The work on my own part consists of a record of all the species col- 

 lected in various portions of the State since I took up the study of this order in 

 the Spring of 1891. All data, therefore, unless immediately followed by the 

 name of the collector, are my own. I regret the unsatisfactory condition of the 

 Cecidomyidce, Sarcophagidcs and Anthomyidce ; but it seems impossible, at the 

 present time, to do better. Careful collecting in all portions of the State at 

 various seasons will probably show that the present list, which numbers about 

 1,200 species, will represent only about two-thirds of the actual number found 

 within the State. 



"I here wish to express my sincere thanks to Mr. D. W. Coquillett for his 

 ever kind assistance in determining the species in the more difficult families ; 

 also to Prof. J. M. Aldrich and Prof. W. M. Wheeler for determining the Doli- 

 chopodidce, and to Dr. G. de N. Hough for classifying the Muscidce. Dr. E. G. 

 Love and Mr. M. S. Crane kindly sent their entire collection to me for study, 

 while Messrs. S. T. Kemp, C. T. Greene, H. S. Viereck, H. W. Wenzel, Chas. 

 Liebeck, Philip Laurent, Philip Nell, H. Hornig, Dr. H. Skinner and others 

 have contributed many additional species. 



"CHAS. W. JOHNSON. 



*' Wagner Free Institute of Science, Philadelphia, Pa." 



(617) 





