466 EXTERNAL ANATOMY OF INSECTS; 
mandibulate Orders ?. It consists of three joints, the last 
of which is formed by the liplets (Zabella). Those in 
the Muscid@ are large, turgid, vesiculose, and capable of 
dilatation; in the Bombylide and other tribes they are 
small, slender, long and. leathery, and sometimes re- 
curved. ‘The second joint or stalk, which may be said 
to represent the mentum, the liplets being properly in a 
restricted sense the analogue of the dabium, its sides being 
turned up, forms a longitudinal cavity, which contains 
the haustellum. ‘The upper piece of this, the valvula, is 
long, rigid, and very sharp, representing the dabrum °. 
Beneath this cover, in the above cavity, are the lancets ; 
which, as far as they are at present known, vary in num- 
ber and form: sometimes there are jive of them, some- 
times four, sometimes fwo, and sometimes, it should seem, 
only one*. Inthe gnat (Culex) they are finer than a 
hair, very sharp, and barbed occasionally on one side ‘; 
in the horse-fly (Tabanus) they are flat and sharp like 
the blade of a knife or lancet *. In this tribe the upper 
pair, or the knives (Cultellz), represent the mandibles ; 
the lower pair, or the lancets (Scalpella), usually. pal- 
pigerous, the mazxille; and the central one the tongue. 
In the horse-fly Reaumur has figured only four, exclu- 
sive of the labrum and labium ; but in a specimen I have 
preserved there appear to be five, one of which, as 
slender as a hair, I regard as the analogue of the 
~ ®* Prare VIL Fie. 5, 6. a’. > Ibid. 
e Reaum. iv. ¢. XVI. Fre. 13. z. 
¢ Authors are not agreed as to the precise number of lancets con- 
tained in a gnat’s proboscis. Swammerdam affirms there are siz, in- 
cluding the labrum. i. 156. b. ¢. xxxii..f. 3. Reaumur could find only 
jive. iv. 597—. t. xii. f. 10. And Leeuwenhoeck only four. 
* Prate VII. Fic. 5. 
