16 (INATS OR MOSQUITOES — CHAPTER I 



supernumerary transverse vein, which is considered by some 

 as merely the angulated origin of the third longitudinal. 



Doubtless in some cases, as in Miicidus, the third 

 springs from the second longitudinal very far out, but in 

 these cases the supernumerary is absent, and the middle 

 transverse, which m most mosquitoes connects the third 

 and fourth longitudinals, spans the entire space between 

 the second and fourth. The remaining cross vein, or 

 posterior transverse, connects the fourth with the anterior 

 branch of the fifth longitudinal. 



The relative length and position of these three last- 

 named cross veins is of great value in distinguishing species. 

 The branched portions of the second and fourth longitudinal 

 veins and tlieir unbranched portions, outside the transverse 

 veins, are often spoken of as the anterior and posterior 

 fourchettes and their stems, and the spaces enclosed within 

 the forks are commonly called the fork-cells. The relative 

 proportions of these are also valuable aids in classification. 



Some authors entirely eschew the use of numbers in 

 describing the longitudinal veins, and employ in their stead 

 certain special names. 



Where such are used, the first is commonly called the 

 "post-costal," the second the cubital, the third the sub- 

 marginal, the fourth the marginal, the fifth the brachial, 

 and the si.xth the anal, while Mr. Austen's eighth longi- 

 tudinal would be spoken of as the axillary. 



Ficalbi speaks of the tliird longitudinal vein as the 

 " vena interposita." 



The names of the remaining spaces, or " cells," can best 

 be followed by a careful study of fig. 4. 



For the rest, the incisura axillaris, a retiring angle in 

 the outline of the wing in its axillary border near the 

 base, and the alula, a lobe appended to the wing between 

 the axillary incision and its base, alone require special men- 

 tion. The latter, however, should not be confused with 

 the covering scale that lies above the halteres, as is a not 

 uncommon mistake. 



The legs of Diptera, like those of other Orders, consists of 

 four principal parts, the hips or cox(C, the thighs or femora, 



