SEVENTEEN-YEAR LOCUST — SNODGRASS. 393 
as a distinct species or only as a variety of the larger form. The 
two kinds occur together, but they are>not known to intermarry; 
they occasionally intergrade in size, and no constant physical differ- 
ences have so far been found between them. 
It was formerly supposed that the cicadas take no food during the 
brief time of their adult life, but we now know, from the observations 
of Mr. W. T. Davis, Dr. A. L. Quaintance, and others, and from a 
study of the stomach contents recorded in this paper, that they do 
feed abundantly by sucking the sap from the trees and bushes on 
which they live. The cicada is a large relation of the aphids, the 
scales, and other insects of the sucking order, and like them has a 
beak for piercing the plant tissues and drawing the sap up to its 
mouth. But, unlike the aphids and scales, the cicadas seldom cause 
any visible damage to the plants by their feeding. Perhaps this is 
because their attacks last such a short length of time and come at a 
season when the trees are at their fullest vigor. 
The details of the head structure and the exposed parts of the 
beak are shown in figure 5, A, which is a side view drawn from the 
head of a fully matured adult, detached from the body by the torn 
neck membrane (r/ih) with the long slender beak (Lh) projecting 
below. The cicada has no jaws. Its mouth is shut in between a 
large front lip {dp), and the base of the main part of the beak {Lh), 
which is really the prolonged lower lip, or labium. The narrow 
spaces on the sides between the bases of the lips are closed by the 
soft, slender pieces marked Lm and c. 
If these outer parts can be separated, we find some other very 
important parts hidden from view within them. But it is difficult 
to separate them on the hardened head of a fully matured specimen. 
However, if we take an insect in the act of emerging from its pupal 
skin, when it is still soft, the parts are easily spread out, exposing 
all the structures shown in figure 5, B. In the front half of the 
space between the lips {Clp and Lh) there is exposed a large tongue 
{ILphy), the hypopharynx, which is connected by a flaring wing («) 
on each side with the first side plate {A) of the head. Between this 
tongue and the front lip {Clp) is an open cleft {Mth) which is the 
cicada's mouth. It opens into the pharynx, whose roof {e) bulges 
in and almost fills its cavity. The lobe {h) behind the tongue is the 
same thing as h on figure A, being merely a downward extension of 
the second side plate {B) of the head, and carries the soft appendage 
(c), already noted, at its lower end. Between this lobe {h) and its 
mate on the opposite side of the head are two deep pouches, from each 
of which there issues a pair of long, slender, bristlelike rods {1 Set 
and 2 Set), which are called the setae. (Only the left pair is shown 
in the drawing.) 
