ON THE TERMINOLOGY OF DIPTERA. XV 



(hypopygiwm), in the female the organ for laying the eggs (ovi- 

 positor) the former, if they have the form of pincers and are not 

 bent under the belly, are called the pincers (forceps), the latter 

 according to its form either the borer (terebra) or the style (stylus). 

 Both organs are of the greatest importance in the distinction of 

 species in many families, and their structure being generally very 

 complicated and varying much in different families, deserves a most 

 attentive study. 



The neuration of the wings of Diptera forms so essential a foun- 

 dation of their systematical arrangement and is so useful for the 

 distinction of species, that its thorough knowledge and a scrupulous 

 and accurate denomination of its single parts and of their mutual 

 arrangement is quite indispensable. Our first and most important 

 task will be to ascertain which parts of the neuration of the wings 

 correspond to each other in the different families, since this is the 

 only way to obtain a terminology in which corresponding things 

 are designated by the same names, and which, therefore, is not 

 liable to misinterpretation. 



At a first and superficial glance, the neuration of the wings shows 

 so different a structure in the various families of Diptera, that it seems 

 impossible to reduce it to a common type. But, on a closer examina- 

 tion, we find that we can make out without much difficulty a common 

 type existing in its greatest simplicity and plainness in the Muscidse. 

 The framework of the whole neuration of the wings is formed by 

 the longitudinal veins (vents longitudinales), which are connected 

 with each other by the transverse veins (vence transverse s. venulce). 

 The longitudinal veins spring from four trunks, issuing from the 

 base of the wings; the first and fourth trunks being the least de- 

 veloped, the second and third must be taken for the main trunks, 

 and consequently the longitudinal veins originating from them, for 

 the main longitudinal veins of the wing. To the anterior of these 

 two main trunks belong three longitudinal veins, the foremost of 

 which runs first parallel to the anterior border of the wing and 

 joins it at a greater or less distance from the tip of the wing ; it 

 is called the first longitudinal vein (vena longitudinales prima). 

 The second longitudinal vein proceeds from the first generally be- 

 fore the middle of the wing, and reaches the anterior border of the 

 wing nearer to the tip. In a similar way the third longitudinal 

 vein has, again, its origin from the second. To the second main 

 trunk also belong three longitudinal veins, which are counted 



