84 



GNATS OR MOSQUITOES — CHAPTER VI 



fashioned astopractically defy draughtsmanship, so that they 

 can only be represented in diaf^rannnatie form. 



The upper Hp, or labrinn, springs from a bulbar enlarge- 

 ment of the front of the face, placed between the bases 

 of the antennti). This bulb is flexible and elastic, and the 



Fig. 19. — Semi-diagrammatic representation of Serial Preparations of 

 THE Anterior part op the Head and Proboscis, x 150 diams. 



A, median sagittal section of root of proboscis, showing the entry of the 

 salivary duct into the floor of the base of the hypopharynx, with the valvular 

 fold and its muscles, by whicli the duct is opened and closed. B, transverse 

 section opposite the point of entry of the salivary duct, and the roots of 

 the palpi. C, transverse section of the proboscis, near its base. D, trans- 

 verse section of the middle of the proboscis. In the above figures: — 

 a, labrum ; b, mandible ; c, labium ; d, buccal bulb ; /, salivary duct ; Ic, 

 hypoi^haryux ; mx, maxilla; m.at., muscle opening the salivary valve; m.rt., 

 muscle closing salivary valve; Di.jjr. Ibr., protrusor muscle of labrum; m. rt. 

 Ibr., retractor muscle of labrum; t.o., taste organ (?) ; q, tracheae; .r, root of 

 palp. 



whole of its median plane is occupied by a fan-shaped 

 muscle, taking origin from its upper surface ; the fibres 

 converging to be inserted into a thickening of the chitine 

 at the base of the actual labiuui; while, on either side of 

 this retractor, a number of antero-posterior transverse fibres 

 fill up most of the remaining space. By the action of the 



