40 THE BRITISH WOODLICE.
terminal part, or flagellum, and a basal part, the peduncle (fig. 3).
The number of joints in these structures, which varies in different
genera and species, forms a useful classificatory character, and
the relative length of the component parts is of considerable
value in distinguishing species.
There are four pairs of mouth appendages—namely the jaws
or mandibles (fig. 5), the first maxillae (fig. 6), the second maxillae
(fig. 7), and the maxillipeds (fig. 8). When the head is examined
from the underside the last of these organs will be seen first,
covering in the others.