20 NORTH AMERICAN DIPTERA. 



(trypanosomiasis), likewise resulting from the predatory 

 bites of the tsetze fly, are among the most virulent or 

 widespread diseases of mankind. Perhaps we may justly 

 say that the order, so far as man is concerned, is the 

 most pestilential of all animal life. 



In the larval condition the habits of flies are even more 

 diverse than are those of the adult insects. Brief refer- 

 ences to the larval habits will be found in the discussion 

 of the families. Suffice it here to say that the larvae or 

 'maggots' of diptera are, for the most part, vegetable 

 feeders, but not a few feed upon living or decaying ani- 

 mal matter; and many are parasitic within the bodies of 

 other insects, whether larvae or adults, snails, reptiles, 

 birds and mammals, and possibly also amphibians and 

 fishes. 



MORPHOLOGY OF DIPTERA. 



In the following pages I endeavor to give such defini- 

 tions and descriptions of the mature insect as will enable 

 the student to understand and appreciate, not only the 

 present work, but all other systematic works upon dip- 

 tera. I have not thought it desirable to consider at length 

 many interesting subjects connected with them, such as 

 their internal anatomy, embryology, larval habits, etc., 

 as being rather apart from the chief object of the work 

 an introduction or aid to the study of systematic dipter- 



ology. 



HEAD. 



The head in diptera is very variable in shape, reaching 

 its most remarkable development in the Diopsidse and 

 Nycteribiidse. It is frequently more or less spherical, 

 but usually the posterior surface or occiput is flattened . 

 or concave, giving a more hemispherical appearance. 

 The face is rarely produced into an elongated rostrum 

 or snout, and the front part may be produced into a con- 

 ical prominence. Its relative size is also variable, some- 



