19t) AN ESSAY ON THE BEVELOrMElSTT 



inous protecting margins, is led, as shown on PI. Ill, Fig. 10. A much better devel- 

 oped organ, strongly resembling that in some of the Hemiptera, we find in the Asilidce 

 (PL III, Fig. 1''), and here also the salivary duct is obvious. The structure in Siiu"- 

 lium has been already referi-ed to, as has that in the Empidw. 



To recajiitulatc concerning themaxilhe: The scleritcs form three series, each of 

 which has its own possibilities of development. The lacinia never develope into any- 

 thing other than a chewing or piercing organ and always arises inside of the galea. 

 The galea varies in the direction of forming an enveloping organ for all the other 

 mouth parts, and the subgalea eventually unites along one margin for that purpose. 

 There is a tendency to develop a ridged membrane on the inner surface of the galear 

 joints which culminates in the pseudotrachea of the muscid labella. The palpifer has 

 a small range of development, from an unjointed, flexible, tactile organ, to a rigid, 

 piercing structure ; and as this becomes useless, to a process for the attachment of 

 muscles used to Hex the proboscis. 



It remains only to acknowledge the assistance received from my entomological 

 friends. Dr. S. W. Williston has from time to time sent me such specimens as I 

 thought might help me ; Mr. C. W. Johnson has given me numerous species of fami- 

 lies selected because of apparent differences in the mouth structure ; and to Mr. J. M. 

 Aldrich I owe many other species in some numbers, among tliem the Simuliid already 

 referred to. Mr. E. P. Fell kindly sent me specimens of Panorpa and Bittacus, which 

 enabled me to make a much more complete study of these insects than would have 

 been otherwise possible. To all these gentlemen, as well as to the others who have in 

 any wise aided me, I desire to exjjress my thanks. 



Concerning the figures — most of them are camera luckla drawings. A few arc 

 drawn from micro-photographs, assisted by the specimens themselves. The figures 

 of transections are largely made from actual preparations ; some are redrawn fi'om 

 other soui'ces, while a few are ideal. 



