OX THE TERMINOLOGY OF DIPTERA. 



Diptera have so much in common with other orders of insects 

 that the terms applied to the latter, which I may consider as gen- 

 erally known, may frequently be used for the former. I have there- 

 fore merely to explain those terms which, on account of the peculiar 

 organization of Piptera, are either applied solely to the insects of 

 this order or are used in a more or less modified sense. It is well 

 known, how little the various authors agree in the choice of these 

 terms, and how many of them seem to find pleasure in departing 

 as much as possible from the terms used by their predecessors. 

 This is a great evil, aggravating the difficulty of understanding 

 Dipterological publications, and impeding the progress of Dipter- 

 ology. It would take too much space to explain all the terms 

 used by different authors, and I confine myself to those only which 

 seem the most necessary and which I have used in this publication. 

 The following considerations have guided me in their choice. I 

 think it a duty of a later author to accommodate himself to the 

 usage of his predecessors, especially those who have written stand- 

 ard works, and at the same time to reconcile them as much as 

 possible where they differ from each other. The indispensable 

 innovations should be introduced only gradually and in conformity 

 with the established usage, since in such matters an agreement about 

 the terms chosen is more important than the mode of selecting 

 them. Mcigen, Wiedemann, and Fallen in earlier times, Zetter- 

 stedt and Macquart more recently, have in that respect a claim to 

 our attention. It has therefore been my object to assume the 

 position of an arbiter between them, and to avoid such terms as 

 depart entirely from the adopted usage, except in cases in which I 

 might differ so much from my predecessors as to become unintel- 

 ligible if restrained by their terminology. 



The head has a hinder plane opposite to the thorax, called ocei- 



