196 AN ESSAY ON THE DEVELOPMENT 
inous protecting margins, is led, as shown on PI. III, Fig. 10. A much better devel- 
oped organ, strongly resembling that in some of the Hemiptera, we find in the Asilidw 
(Pl. IH, Fig. 1”), and here also the salivary duct is obvious. The structure in Simu- 
uum has been already referred to, as has that in the Hmpidw. 
To recapitulate concerning the maxillee: The sclerites 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 flex the proboscis. 
It remains only to acknowledge the assistance received from my entomological 
friends. Dr. 5. 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 them the Simuliid already 
referred to. Mr. EH. 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 express my thanks. 
Concerning the figures—most of them are camera lucida drawings. A few are 
drawn from micro-photographs, assisted by the specimens themselves. The figures 
of transections are largely made from actual preparations; some are redrawn from 
other sources, while a few are ideal. 
