54 
RES PI R A TION. 
them, freely communicating respiratory cavities, whilst 
the tracheae which issue from them are dilated into a 
series of funnels, which 
communicate with each 
other across the body by 
their finer ends. The air 
sacs of the drone are 
similarly placed, but those 
of the queen are consider- 
ably smaller, much of the 
space in the abdomen 
being, occupied by the 
large ovaries. 
As the abdomen of 
the bee is alternately con- 
tracted and extended, air 
is drawn into and forced 
out of these tubes through 
the spiracles. 
^ ^ ^ 1 he real use of the air 
sacs is, as Hunter supposed, to enable the insect to 
alter its specific gravity at pleasure by enlarging its 
bulk, and thus render it better able to sustain itself on 
the wing with but little muscular effort (Newport, ii6). 
In the act of respiration nearly all the muscles and 
nerves of each segment of the body are brought into 
constant action. Reaumur (139) found by his ex- 
periments that the anterior spiracles are the largest 
and most fully developed, and are the most important 
to the insect in the act of respiration. Each longi- 
tudinal extension of the segments of the abdomen 
