360 EXTERNAL ANATOMY OF INSECTS. 
A. Vacina (the Vagina). The jointed sheath of the 
Promuscis, representing the Labium in a perfect 
mouth *. 
B. ScaLpeiya (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 Mandibule », and the lower the Maz- 
le *. 
3. Prososcrs (the Proboscis). ‘The oral instrument of 
Diptera, in which the ordinary Trophi are replaced 
by an exarticulate sheath, terminated by Ladella, 
and containing one or more lancets covered by a 
valve’, It includes the Theca, and Haustellum. 
A. Tueca (the Theca). The sheath or case of the Pro- 
boscis, representing the Labium in a perfect mouth*. 
It includes the Basis, and Labella. 
a. Basis (the Base). The whole lower part of the Theca, 
from the mouth of the insect as far as the Labella, 
probably to be regarded as representing the Men- 
tum‘? 
b. LaBetua (the Ziplets). 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 * ? 
B. Hausrriium (the Haustellum). 'The instrument of 
suction contained in the Theca™. It includes the 
Valoula, Cultelli, and Scalpella. 
@ Prate VI. Fic. 7, 9. b’. De Tbe": * Thid. d’. 
4 Prate VIL. Fic. 5, 6. Mid: tb! f Ibid. Fic. 6. b’. 
8 Ibid.a. The Labella have been usually thought confined, or 
nearly so, to the genus Musca L.; but they may be traced in all ge- 
nuine Diptera, i. e. excluding Hippobosca L. 
h Ibid. Fre. 5. a/, c/, d’. 
