EXTERNAL ANATOMY. 9 



carried right round the wing uninterruptedly, without any 

 distinct or sudden termination near or just beyond the tip, as in 

 some families of NEMATOCERA. 



The auxiliary vein is the first vein below the costa, and generally 

 ends, in the TIFTJLID^E, between the middle (or just before the 

 middle) and about three-fourths the length of the wing. It is 

 connected with the costa quite near its base by a short upright 

 cross-vein, the latter known as the humeral cross-vein. The 

 auxiliary vein is often known as the subcostal, which is perhaps a 

 better name, but since in studying TIPULID^E the works of Osten 

 Sacken must be consulted, his name for this vein is adopted in 

 preference. 



The next vein is a much longer one, running parallel with the 

 auxiliary vein and ending some little distance beyond it ; this is 

 the 1st longitudinal vein. It either turns up rather suddenly at 

 the tip into the costa, as is generally the case in the LIMNOBIIXJG, 

 or turns distinctly down at the tip into the 2nd longitudinal 

 vein, as is usually the case in the TIPULINJB. In some few cases 

 it fades away at the tip without turning either up or down. The 

 auxiliary vein often lies so closely in front of the 1st longitudinal 

 vein as to be imperceptible unless carefully looked for. In some 

 few genera these two veins are actually united (Toxorhina, Styt-in- 

 gomyia), and in these cases the 1st longitudinal vein, as the 

 united veins are invariably called, generally approximates gradually 

 to the costa, finally becoming merged in it, and not turning dis- 

 tinctly up or down at the tip as in the typical forms. The 

 auxiliary vein and the 1st longitudinal are, in the TIPULID.B, 

 nearly always connected by a short cross-vein known as the sub- 

 costal cross-vein, which is most frequently situated towards the end 

 of the auxiliary vein, but sometimes occurs a little before or after 

 the origin of the 2nd longitudinal vein. Considerable importance 

 attaches not only to the actual length of the auxiliary vein, but to 

 the relative position of the subcostal cross-vein, although exceptions 

 occur, even in otherwise closely allied genera (in the ERIOPTEBIXI, 

 for instance). 



The 2nd longitudinal vein emerges from the first, usually some- 

 where near the middle of the latter, sometimes in a straight line 

 at a more or less acute angle, but more often in a gentle or 

 distinct curve. When the 2nd longitudinal vein is "simple" 

 (that is to say, not forked) there is only one submarginal cell ; * 

 when the 2nd vein is forked there are two, and this character is 

 of paramount importance, being the very first one employed in 

 separating the subfamilies ; and on it depends the terminology 

 of many or the cells.t The portion or section of the 2nd 



* Vide p. 13 for description of ceils. 



t The principal exception in Oriental genera is G&nomyia, in which some 

 species have but one whilst others have two submarginal cells. This instability 

 is very exceptional as a generic character (Gonomyia). 



