TRACHEATA 369 
Hemiptera have a complete metamorphosis ; the adult male has 
one pair of wings, the anterior, the posterior being replaced by 
a pair of bristle-like processes, the ha/teres,as in the Diptera. 
No mouth is present. 
The female, after the first ecdysis, becomes almost stationary, 
she retains her proboscis, which is embedded in the tissues 
of the plant on which she lives, as a rule she loses her 
limbs, and almost all trace of segmentation; the successive 
skins that she casts either remain over her body forming a 
scale, or she secretes a waxy or woolly covering. The eggs 
are laid under the body of the mother, which ultimately dies, 
but remains as a covering for her offspring; under this the 
young may remain some little time before seeking a convenient 
place on their plant host to insert their own proboscis. 
Some of the Coccidae are of commercial value, Coccus cacti 
furnishes the pigment cochineal, and another species produces 
shellac. Most of the scale insects, however, are injurious to 
the plants upon which they live, and cause great loss to 
horticulturists and fruit-growers. Aspidiotus conchiformis is 
the well-known mussel scale on apple trees, etc., and A. aurantii 
attacks orange groves. 
Sub-order 3. Parasitica. 
CHARACTERISTICS. — These are wingless Hemiptera, commonly 
known as lie; they live as ectoparasites on the skin of 
mammals, sucking their blood. 
The proboscis is fleshy and unjointed, with, as a rule, a circle 
of recurved hooks round its base. There are two small simple 
eyes; the antennae have five joints. The legs arise from the 
edge of the prothorax; they terminate in a hooked claw, which 
works against a projection of the tibia; this forms an admir- 
able apparatus for clinging on to the hairs of their hosts. The 
young do not undergo any metamorphosis. 
Pediculus capitis is the head louse, and P. vestiimenti infests 
the body of all races of man. It is said that peculiar varieties 
infest the different races; thus those that live on negroes are 
nearly black, whilst the Chinese have a yellowish, and the 
natives of South Africa an orange variety. The genus which 
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