xviii ON THE TERMINOLOGY OF DIPTERA. 



Near the base of the fifth longitudinal vein rises the posterior 

 basal transverse vein (vena transversa basalis posterior s. venula 

 basalis posterior), usually a short transverse vein, running to the 

 sixth longitudinal vein, but frequently meeting it only in a later 

 part of its course at a very acute angle, or even reaching the bor- 

 der of the wing, without having met that vein; in all these cases it 

 divides all the space of the wing lying between the fifth and sixth 

 longitudinal veins into two parts. In several families there is, 

 immediately beyond this transverse vein, another vein, the posterior 

 intercalary vein (vena inter calaris posterior), which proceeds from 

 the fifth longitudinal vein and runs to the border of the wing ; 

 sometimes it meets the fifth longitudinal vein before reaching the 

 border. 



In that part of the wing which is behind the sixth longitudinal 

 vein, are spread the branches of the hindmost of the four trunks ; 

 it is entirely wanting in many Diptera, and exists in most of them 

 only in a rudimentary state; therefore generally only one branch, 

 or at the utmost two weak ones, not reaching the border of the 

 wing, are perceptible; they are called the axillary veins (vena ax- 

 illares). Where the hindmost trunk is well developed, these veins 

 become complete longitudinal veins; they best preserve the same 

 name, but may be numbered as the seventh, and, where two exist, 

 as the seventh and eighth longitudinal veins without any fear of 

 misinterpretation. In the case of such a great development of 

 this trunk, the foremost of the veins belonging to it is generally 

 connected near its base with the sixth longitudinal vein by a trans- 

 verse vein. 



It results, from the foregoing exposition, that the anterior part 

 of the wing is divided by the three longitudinal veins belonging to 

 the anterior main trunk, and the posterior by the three longitudi- 

 nal veins belonging to the posterior main trunk, each into three 

 sections, an exterior one, a middle, and an interior one, while the 

 three sections of the anterior part of the wing are separated from 

 those of the posterior part by a middle stripe or baud which ex- 

 tends from the base of the wing to its tip. It would be an easy 

 task to invent fit names for these principal parts of the surface of 

 the wing, from which convenient expressions would result for their 

 single parts or the cells of the wings. But it seems to me that 

 the introduction of such a new nomenclature would hardly promote 

 our principal end, the agreement of authors in the use of termino- 



