Packard ] INSECTS OE THE POND AND STREAM. 155 
of the muscles of the body shows their wonderful adapta¬ 
bility for the production of these complicated movements. 
Many aquatic insects are either “side wheelers” or pro¬ 
pellers. The larval Ephemera, aided by the beautiful pad¬ 
dle-like tracheal gills fig. 123. 
along the sides of the 
body, moves through 
the water by a series 
of exceedingly grace¬ 
ful undulations; while 
the young Agrion pro¬ 
pels itself, partly at 
least, by its large 
terminal respiratory 
leaves. How by a 
strange economy of 
nature the dragon fly 
larva combines the 
functions of digestion, x 
locomotion and respi¬ 
ration in an organ 
which like a force 
pump ejects a power¬ 
ful stream, and like 
a flash propels the 
creature many times 
its own length over 
the bottom of its 
pond, we have seen 
above. 
Diplax larva; x, mass of tracheae. 
One important result of the metamorphosis of the young 
mosquito into a pupa is that it is promoted from a wriggler 
to a paddler, paddling being a higher mode of aquatic loco¬ 
motion. Our figure of the pupal mosquito shows in a rude 
■way the two beautiful, thin, rounded paddles at the end of 
27 
