238 
INSECTS. 
their bodies ; others, whose wings are of that exqui- 
site fineness that the least friction would tear them, 
have two strong scales which they raise and fall like 
a pair of wings : but these are no more than a case 
for the real ones. You will find beetles, may-chaf- 
fers, and Spanish flies, furnished with these cases. 
You may also observe numbers who have only two 
wings, but under these you will perceive as many 
bladders, or hollow vessels, which are thought by 
some to be a couple of weights, or a kind of counter- 
poise, by the assistance of which the insect supports 
itself against the agitation of the air, and continues 
in an equilibrium, like a rope-dancer who poises 
himself with a pole that has a weight of lead at each 
extremity; though perhaps these hollow vessels 
may answer the purpose of castanets, which the in- 
sects strike against their wings either for their di- 
version, or to make themselves known to each other 
by the buzzing sound. 
Every insect is generated, like other animals, 
from a germ which contains the insect in miniature. 
This germ is at first wrapped up in a single or 
double covering, which opens when the animal has 
acquired strength enough to break through it. If 
the little creature escapes from its enclosure at the 
birth, and comes into the world completely formed, 
and like its dam, this latter is said to be viviparous. 
Of this species are the palmer and the aphis , so 
common upon rose trees, besides many others that 
are to be found on different plants. But when the 
female parent produces her young in a hard enclo- 
