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THE DIPTERA 



4. The Radius 2+3 {Second Longitudinal). — Commences in the middle of 

 the wing, and shortly divides into two branches (Radius 2+3), enclosing a 

 piece of the wing called the first submarginal cell. 



5. The Radius 4+5 {Third Longitudinal Vein). — Commences in the middle 

 of the wing and runs to the margin. 



6. The Media {Fourth Longitudinal Vein). — Runs from the base of the 

 wing to the margin, but forks (Media i + 2) to enclose the second posterior cell. 



7. The Cubitus {Fifth Longitudinal Vein). — Runs from the base and forks 

 (Cubitus 1 + 2) to enclose the third posterior cell. 



8. The Anal 1+2 {Sixth Longitudinal Vein). — Runs a curved course from 

 its margin. 



In some mosquitoes there is a second anal vein (seventh longitudinal vein), 

 but more often this is only indicated by a fold or incrassation. There may 

 be a vena spuria or marking between the cubitus and the anal vein. 



9. Transverse or Cross Veins. 



{a) The Humeral, between the Costa and Subcosta. 



ib) The Radial, between Radius 2+3 and Radius 4+5 (second + third 



longitudinal veins) . 

 (c) The Radio-medial, between the Radius and Media (third + fourth 



longitudinal veins). 

 {d) The Medio-cubital, between the Media and the Cubitus (fourth + 



fifth longitudinal veins). 



These veins mark out the following cells : — 



I. The Costal cell, between Costa and Subcosta, but subdivided by the 

 humeral vein. 



2. Subcostal (Mediastinal) cell, between Subcosta and Radius i. 



3. Marginal cell, between Radius i and Radius 2+3. 



4. First Submarginal cell, between Radius 2+3. 



5. Second Submarginal cell, between Radius 2+3 and Radius 2+5. 



6. First Posterior cell, between Radius 4+5 and Media. 



7. Second Posterior cell, between Media 1 + 2. 



8. Third Posterior cell, between Media and Cubitus. 



9. Fourth Posterior cell, between Cubitus 1+2. 



10. Anal cell, between Cubitus and Anal i. 



11. Axillary cell, between Anal 1+2 and Anal 3, when present. 



12. Spurious cell, behind Anal 3, when present. 



13. Anterior Basal cell, bounded anteriorly ' by the Radius i, posteriorly 

 by the Media, and externally by the Radial transverse vein. 



14. Posterior Basal cell, bounded anteriorly by the Media, and posteriorly 

 by the Cubitus, and externally by the Medio-cubital vein. 



The wing has scales on all its veins, except the cross and the spurious veins, 

 which are arranged in two ways: (i) Two rows of fiat scales on each vein; 

 (2) lateral scales along each vein. 



Generally these scales in the Anophelinse are lanceolate, or long and narrow, 

 but one genus, Cycloleppteron, has large inflated scales. It will be found that 

 scales vary much in the different genera and species, the principal forms of 

 which may be gathered from the following: The posterior margin of the 

 wing carries a fringe consisting of scales arranged as follows: (i) Flat scales; 

 (2) long lanceolate scales; (3) short lanceolate scales alternating with the 

 long lanceolate scales. 



Abdomen. — There are eight segments in the abdomen, each of which consists 

 of a dorsal plate, the tergum, and a ventral plate, the sternum, joined together 

 by a pleural membrane, on which lie the abdominal spiracles, said to number 

 six or eight by different observers. 



On the posterior end of the terminal segment are the external genital 

 organs. In the male these consist of a pair of large basal lobes, each termin- 

 ating in a clasp segment armed with a claw, thus forming the clasper. The 

 arrangements of the male genitalia vary so much that they have been used as 

 a method of classification. Therefore it is necessary to explain in a general 

 way the terms used with regard to the various parts which may be found. 



