SEVEIvrTEEN-YEAR LOCUST — SNODGRASS. 
395 
pushed a long distance down into the sap-carrying tissues of the 
tree. Next the sap must be drawn up to the mouth. To serve this 
function two of the setae, the rear one of each Literal pair, are hol- 
lowed along their inner faces and united lengthwise by interlock- 
ing grooves and ridges. 
Thus a closed channel is 
formed between them, and 
it is through this tube that 
the sap reaches the mouth, 
going up probably by the 
mechanical force that 
makes all liquids flow up 
through hairlike tubes. 
The immature adult ci- 
cada has the mouth open, 
or easily opened ; but when 
fully matured the mouth is 
always tightly closed by 
the tongue {Ilphij) and its 
wings {a) which press 
firmly against the roof of 
the mouth. The middle 
pai-t of the tongue then fits 
snugly into a depression of 
the palate or epipharynx, 
as the roof of the mouth 
is called in insects. Hence, 
there would be no mouth 
opening at all if it were not 
for a small median groove 
on the front surface of the 
tongue. This groove is 
now converted into a tube 
which opens below at the 
pointed tip of the tongue, 
and above into the cavity of 
the pharynx. The pair of 
united setae carry the liquid 
food up to the mouth, but, 
right at the point of the tongue, they flare apart and embrace 
the tongue tip. This allows the liquid stream between them 
to pass on without interruption into the mouth pore through which 
it is sucked up into the pharynx. The sucking apparatus consists of 
the collapsed roof of the pharynx {e) which can be elevated by a 
Pig. 6. — Median vertical section through head of 
an adult cicada showing the sucliing pharynx 
(Phy) and the salivary glands (Gl, Gl). The 
liquid food goes up to the mouth between the 
second setae (2 Set), all being normally enclosed 
in the groove of the labium (Lb). The pharynx 
muscles (PhyMcI) contract and pull out the 
front wall (e) of the pharynx, thus suclcing in 
the liquid from between the bases of the setae 
through the mouth pore (Mth). When the 
muscles relax the pharynx wall (e) collapses 
again and forcesi the liquid up into the bulb 
iphy) from which it goes into the gullet ((E). 
The salivary duct (SalD) opens at the tip of 
the hypopharynx (Ilphy), the saliva being forced 
out by the salivary pump (SalPmp). Ft, dp 
and Lm are the front, clypeus and labram shown 
on figure 5, while o is the appondage of head 
plate B. Ti and Si are the dorsal and ventral 
plates of the first thoracic segment. 
