SEVEIs^TEEN-YEAR LOCUST- — SNODGRASS. 403 
space no thicker than a piece of paper in those indiA'iduals examined 
toward the end of their natural lives. The rectum {Red) lies in a 
freer space again behind the air chamber and above the reproductive 
organs {Epr). 
The great air chamber is a part of the respiratory system. It 
receives its supply of air directly through the spiracles of the first 
abdominal segment, which lie just before the drums in the male, 
as described by Vitus Graber in 1876. At least two tracheal tubes 
open from it on each side close to the spiracle, and its own walls 
are abundantly supplied with fine branching tracheae. It is pres- 
ent in the last pupal stage Avhere it is to be found at the 
time of emergence as a collapsed bag with rather thick walls 
lying lengthwise amongst the abdominal viscera (or at least it is 
thus in alcoholic specimens). It is distended in the imago when 
the latter first comes out of the pupal shell, and is present in both 
males and females, enlarging toward the end of adult life as the 
reproductive organs shrink into the rear extremity of the abdomen. 
In the young female, before egg laying has exhausted the ovaries, 
these organs occupy a much larger space at the expense of the air sac 
than they do toward the end of life. If the air chamber occurred in 
the male alone it would easily be explained as part of his musical 
equipment. The dry, hollow, thin-walled abdomen would be enthusi- 
astically described as a marvelous adaptation for giving resonance 
to the vibrations of the tympana. But the female contradicts this 
theory, unless it be that her body is set into sympathetic vibration 
by the song waves from the male. We shall probably have to fall 
back on the old prosaic explanation that bulk of bod}?^ is maintained 
with corresponding weight eliminated — a combination specially 
favorable to aerial life. 
In the narrow space about the sac there are, besides the alimentary 
canal, abundant strands of fat tissue, the heart, tracheal trunks from 
the spiracles and their numerous branches, nerves, and the muscles 
of the body wall. So, indeed, the cicada is a complete insect after 
all in spite of its deceptive appearance of emptiness. 
The central nervous system consists of four main ganglia, the two 
usual ones in the head, one in the prothorax (fig. 7, 1 Gng)^ and a 
larger one in the mesothorax {'B Gng). This explains why the loss 
of the abdomen is a matter of such little consequence to these insects, 
and also why the cicada appears to be such a perfect automaton. 
HATCHING. 
Knowing from printed records that the cicada eggs were due to 
hatch almost any time after the middle of July, the infested trees in 
the yard of the Office of Apiculture were daily inspected from the 15th 
