This sub-order contains only one family, which is considered to be the
last and lowest group of the _Hemiptera_, of which it may be regarded
as a very degenerate form. The insects have no wings, and live upon the
blood of other animals.
_Family 1, Pediculidæ._--The "Lice" are a very extensive family,
but at present not very well known. Almost every mammal has a louse
peculiar to itself.
[Illustration: Fig. 119.--Pediculus Capitis (Mag.)]
Three species infest man. The Head Louse (_Pediculus capitis_), found
on the head, especially in children. The Body Louse (_Pediculus
vestimenti_), found in the clothes; and the Crab Louse (_Phthirius
inquinalis_), a broader and shorter insect, found in the hair on the
face and body of uncleanly persons.
The lice infesting different races of men differ in colour--thus, those
found on niggers are black; and those on Europeans are whitish.
Other species of lice infest the dog, cat, pig, mouse, elephant,
monkey, etc.
The _Pediculidæ_ undergo no metamorphoses.