DTJKHAM DIPTERA. 1 9 



(C.II.5). X.4. or simply X. The vein which joins the two 

 principal vein-systems near the middle of the 

 wing. It is always present, and generally 

 rests on V.4., or, when that vein is absent, on 

 V.5. It is often much inclined, and frequently 

 looks like the base of V.3, (See Plate IV. 1, 4, 5, 

 where the vein marked X is this X-vein, that 

 beyond, which looks like a X-vein, being re- 

 garded as the base of V.3. in this system, 

 which is distinctly artificial but useful). 

 X.5 1 or X.5. In. The X-vein uniting V.5. to V.4. near 

 to the base of the wing, and placed before or 

 only a little beyond X.4. 

 X.5 2 or X.5.0ut. The X-vein which unites V.5. to 

 V.4. on the apical region. One or both of the 

 X.5s may be absent. If only one be present, 

 it may be called simply X.5., or X.5 1 or X.5 2 

 according to whether its position is before, or 

 much beyond X.4. 

 X.6. The X-vein which unites V.6 and V.5, It is 

 often absent. 



Other X-veins are in like manner indicated 

 by the number of the vein on which they rest. 

 A Hang Vein or Appendix is a very short 

 incomplete branch, often recurrent, which 

 sometimes projects from the angle of a bent 

 long-vein, as in Plate V.7, where a recurrent 

 hang-vein is seen at the angle of V.3. a, or 

 as in Plate V.18, where one, not recurrent, 

 projects from the hinder side of V.4 4 . 

 v 6) The Cells or Areolets. — These bear the numbers of 

 the veins on which they rest, preceded by O. 

 The enclosed cell, which is often present near 

 the middle of the wing, and which may be either 

 0.4.b. or 0.5 2 , may also be indicated simply 

 by O. It is commonly called the discal or 

 discoidal cell. 



