26 HOW INSECTS ARE CLASSIFIED 
Fie. 23.— Adult thrips, 
Euthrips tritici Fitch. 
Metamorphosis is incomplete. Both 
nymphs and adults are slender insects, pro- 
vided with sucking mouth parts. The adults 
have two pairs of peculiar wings, very nar- 
row, almost without veins, and fringed along 
the margins with a row of long hairs, set 
close together. The wings are laid along 
the back when not in use. In most species 
the adults are not more than one tenth or 
one twelfth of an inch in length. The an- 
tenne are comparatively short and simple. 
Usually the presence of these insects is 
recognized first by a whitening of the leaves 
Original. or a shriveling 
of other parts on 
which they happen to be feeding. Close 
examination will then reveal the tiny 
active insect itself. 
Hemiptera 
A large group, including the true 
“bugs,” characterized throughout by 
sucking mouth parts. 
Metamorphosis is incomplete. Active 
nymphs, which look more or less like the 
adults except that they have no wings, 
hatch from the eggs laid by the parent 
female. 
There are two large subdivisions in 
this order, the Homoptera and the Het- 
eroptera, distinguished from each other 
by the type of wings, and the manner in 
which the beak is attached to the head. 
Fic. 24.—A cicada. Sub- 
order Homoptera. Original. 
In the Homoptera the wings, four in number, are membranous 
throughout, and when the insect is at rest, usually are held in a slop- 
