EXTERNAL ANATOMY OF INSECTS. 361 



A Vagina (the Vagina). The jointed sheath of the 

 Promuscis, representing the Labium in a perfect 

 mouth a . 



B Scalpella (the Lancets). Four pieces adapted for 

 perforating the food of the insect, which when 

 united form a tube for suction. The upper pair 

 represent the Mandibulaj b , and the lower the Max- 

 illa? c . 



3. Proboscis (the Proboscis). The oral instrument of 

 Diptera, in which the ordinary Trophi are replaced 

 by an exarticulate sheath, terminated by Labella, 

 and containing one or more lancets covered by a 

 valve d . It includes the Theca, and Haustellum. 



A Theca (the Theca). The sheath or case of the Pro- 

 boscis, representing the Labium in a perfect mouth e . 

 It includes the Basis, and Lobelia. 



a Basis (the Base). The whole lower part of the Theca, 

 from the mouth of the insect as far as the Lobelia, 

 probably to be regarded as representing the Men- 

 turn ? 



b Labella (the Liplets). A pair of tumid lobes, often 

 corrugated and capable of tension and relaxation, 

 which terminate the Theca, and perhaps represent 

 the termination of the Labium s ? 



B Haustellum (the Haustellum). The instrument of 

 suction contained in the Theca h . It includes the 

 Valvula, Cultelli, and Scalpella. 



a Plate VI. Fig. 7, 9. b'. b Ibid. c'. c Ibid. d'. 



d Ibid. VII. Fig. 5, 6. e Ibid. b'. f Ibid. Fig. 6. b. 



8 Ibid. a. The Labella have been usually thought confined, or 

 nearly so, to the genus Miisca L. ; but they may be traced in all ge- 

 nuine Diptera, i. e. excluding Hippobosca L. 



h Plate VII. Fig. 5. a', c', d'. 



