HEMIPTERA . 
iS7 
which are of small size. In our largest species the body 
measures only about one-fourth inch in length, and usually 
these insects are very much smaller. 
The body is usually more or less pear-shaped. The 
winged forms have two pairs of delicate, transparent wings. 
These are furnished with a few simple veins, but the vena¬ 
tion is more extended than in either of the two following 
families. The first pair of wings is larger than the other, 
and the two wings of each side are usually connected by a 
compound booklet. The beak is three-jointed, and varies 
greatly in length; sometimes it is longer than the body. 
The compound eyes are prominent, and ocelli are also 
usually present. The antennas are from three to seven 
jointed. On the back of the sixth abdominal segment there 
is, in many species, a pair of tubes, through which a wax¬ 
like material is excreted. In some genera these organs are 
merely perforated tubercles, while in still other genera they 
are wanting. 
The substance known as honey-dew is excreted from 
the posterior end of the alimentary canal. It is sometimes 
produced in such quantities that it forms a glistening coat¬ 
ing on the leaves of the branches below the plant-lice, 
and stone walks beneath shade-trees are often densely 
spotted with it. This honey-dew is fed upon by bees, wasps, 
and ants. The bees and wasps take the food where they 
find it, paying little if any attention to its source; but the 
ants recognize in the plant-lice useful auxiliaries, and often 
care for them as men care for their herds. This curious re¬ 
lationship will be discussed farther under the head of Ants. 
It is easy to see what benefit ants derive from this asso¬ 
ciation with plant-lice, and how they should learn that it is 
worth while for them to care for their herds of honey pro¬ 
ducing cattle. Little has been done, however, to point out 
the great benefit that accrues to the plant-lice from this re¬ 
lationship. It seems fair to assume that the plant-lice are 
greatly benefited, else why has the highly specialized appa- 
