_ Respiratory System. 69 
each side of the abdomen. These are armed with a com- 
plex valvular arrangement which excludes dust or other 
noxious particles. From these extends the labyrinth of 
air-tubes (Fig. 2, /,f,), which carries vitalizing oxygen 
into every part of the insect organism. As shown’ long 
ago by Leydig and Weismangn, these air-tubes are but an 
invagination of the derm of the insect. What is more 
curious, these trachez are molted or shed with the skin of 
the larve. In the more active insects—as in bees—the main 
trachez, one on each side of the abdomen, are expanded 
into large air-sacs (Fig. 2, f). Insects often show a 
respiratory motion, which in bees is often very marked. 
Newport has shown that in bees the rapidity of the respira- 
tion, which varies from twenty to sixty per minute, gauges 
the heat in the hive, and thus we see why bees in times of: 
severe cold, which they essay to keep at bay by forced 
respiration, consume much food, exhale much foul air and 
moisture, and are liable to disease. Newport found that 
in cases of severe cold there would be quite a rise of mer- 
cury in a thermometer which he suspended in the hive 
amidst the cluster. 
In the larval state, many insects breathe by fringe-like 
gills. The larval mosquito has gills in form of hairy tufts, 
while in the larval dragon-fly the gills are inside the rec- 
tum or last part of the intestine. The insect, by a muscu- 
lar effort, draws the water slowly in at the anus, where it 
bathes these singularly placed branchiz, and then makes it 
serve a further turn by forcibly expelling it, when the 
insect is sent darting ahead. Thus this curious apparatus 
not only furnishes oxygen, but also aids in locomotion. In 
the pup of insects there is little or no motion, yet import- 
ant organic changes are taking place—the worm-like, igno- 
ble, creeping, often repulsive larva, is soon to appear as the 
airy, beautiful, active, almost ethereal imago. So oxygen, 
the most essential—the size gua non—of all animal food is 
still needed. The bees are too wise to seal the brood-cell 
with impervious wax, but rather add the porous capping, 
made of wax from old comb and pollen. The pupz no 
less than the larve of some two-winged flies which live in 
water, have long tubes which reach far out for the vivify- 
