THE BRITISH WOODLICE. 41
A small median plate attached to the front of the head has
been called "the upper lip" (fig. 0), while inside the mouth
appendages is a little bilobed structure
"the lower lip" (fig. 10).
Before leaving the external features
of the head, we must allude to the
pair of eyes which are usually present,
though never raised on stalks. In
the Common Wood-louse (Oniscus
asellus, from which all our figures to
illustrate structure have been made),
as in many other species, the eyes are
compound (fig. 4), but in some forms
these are simple.
Each of the seven joints of the
thorax bears a pair of walking legs
(fig. 11), and in the female at the time
when the eggs are laid, a pair of
plates (fig. 12) arises on segments
II. to V. These plates together
form a brood pouch, in which the eggs are carried (fig. 12)
until they are hatched, and in which the young ones remain
for some time afterwards.