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ENTOMOLOGY FOR MEDICAL OFFICERS 



longitudinal is very short and takes off from the 2nd at a 

 right angle; the 4th and Sth longitudinal veins both 

 bifurcate ; there is no posterior cross-vein, and so no discal 

 " cell " ; both of the basal " cells " are long ; there is no 

 posterior basal cross-vein, and so no enclosed anal " cell." 



Pig. 7.— Wiag of Mosquito. 



It should be mentioned that in the wings of some flies 

 faint traces of a longitudinal vein, or even of two may be seen 

 behind the 6th. 



The abdomen is compact, but the segments are usually 

 distinct. The number of visible segments varies from 4 to 

 8 or (rarely) 9. When the number of visible segments is 

 small, it is generally the case that several inconspicuous 

 posterior segments are present (and, perhaps, are introverted, 

 or telescoped inwards) to form in the female an ovipositor, 

 and in the male a part of the inseminating apparatus, or 

 hypopygiuni (vtto = beneath ; Truy?; = rump). 



Integument of Diptera. — The chitinous cuticle is often 

 beset with hairs, or bristles, or sometimes with scales. In 

 addition to this general investment, which may be either 

 thick or sparse, there sometimes occur definitely placed 

 bristles of larger size which have received special names 

 according to their situation. Among these the following 

 may be mentioned as their names, perhaps, are not self- 

 explanatory : (12) vibrissa — these are two strong bristles 

 sometimes found near the upper angles of the mouth-cavern, 

 one on either side ; {b) dorso-central — these are bristles some- 

 times inserted in rows in the field of the mesonotum ; (c) 

 sternopleural— these are large bristles sometimes found on 

 the pleural plate that lies immediately above the middle 

 legs ; (d) kypopleural^smzXlet bristles sometimes inserted in 



