152 
Beekeeping 
(ftnnux 
dioxid enter the tracheal branches and are expelled through 
the spiracles. The more complex compounds are eliminated 
in the process of excretion. 
The tracheal system of the bee is shown sufficiently in 
the accompanying il¬ 
lustration (Fig. 79) so 
that a detailed de¬ 
scription is unneces¬ 
sary. The abdomen 
contains the unusu¬ 
ally large tracheal 
sacs ( TraSc ) connected 
with each other by 
ventral commissures 
( TraCom ). They are 
also connected with 
tracheal sacs of the 
thorax. From the 
most anterior spiracles 
of the thorax are 
heavy trunks to the 
air sacs of the head, 
above the brain. The 
tracheal system of the 
bee is more elaborate 
than that of most 
other insects and prob¬ 
ably in no other 
species is there more 
free access of oxygen 
to all parts of the 
body. 
The pumping of the 
air through the body is accomplished by the respiratory 
movements of the abdomen, consisting of a lengthening 
and shortening of the abdomen and a slight dorso-ventral 
movement. The muscles of the abdomen which function 
Flo. 79. — Tracheal system of worker with 
dorsal sacs and trunks removed, from above. 
