EXTERNAL ANATOMY OF INSECTS. 471 
our friend Curtis have detected a seventh, as you see in 
his figure. From this account it appears, that the elon- 
gation of the organs of the Aphaniptera Order is at the 
expense of the dabium and its palpi. 
v. Rostellum.—So little is known of the composition 
of the next kind of imperfect mouth, that I need not en- 
large upon it. It is peculiar to the louse tribe (Pedicu- 
lide), and it consists of the tubulet (Zwbulus), and si- 
phuncle (Siphunculus). The former is slenderer in the 
middle than at the base and apex, the latter being tur- 
gid, rather spherical, and armed with claws which pro- 
bably lay hold of the skin while the animal is engaged in 
suction. When not used, the whole machine is with- 
drawn within the head; the siphuncle, which is the suc- 
torious part, being first retracted within the tubulet, in 
the same way as a snail retracts its ¢enfacula?. ‘This ap- 
paratus seems formed at the expense of all the other 
organs. 
There are some other kinds of imperfect mouth, 
which, though they seem not to merit each a distinet 
denomination, should not be passed altogether without 
notice. The first I shall mention is that of the family 
of Pupipara (Hippobosca L.). It consists of a pair of 
hairy coriaceous valves, which include a very slender 
rigid tube or srphuncle, the instrument of suction, which 
Latreille describes as formed by the union of two seti- 
form pieces >. In Melophagus, the sheep-louse, the union 
of the valves of the sheath is so short, that they appear 
like a tube; but if cut off they will separate, and show 
* Swammerdam Bibl. Nat. ¢. ii. f. 4. 
> N. Dict? d@ Hist. Nat. xxviii. 266. 
