class="figsubvt c7"> FIG. 6.—THE FIRST
MAXILLAE.
(Oniscus asellus.)

FIG. 7.—THE SECOND
MAXILLAE.
(Oniscus asellus.)

FIG. 8.—THE FUSED
MAXILLIPEDS.
(Oniscus asellus.)

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.

FIG. 9.—THE "UPPER LIP.
(Oniscus asellus.)

FIG. 10.—THE "LOWER LIP.
(Oniscus asellus.)

FIG. 11.—A TYPICAL THORACIC SEGMENT.
(Oniscus asellus.)

FIG. 12.—THE FIFTH THORACIC SEGMENT OF A FEMALE.
(Oniscus asellus.)

When we examine the abdomen, we find that the appendages are plate-like, with the exception of the last pair (fig. 13), and they all agree in having two divisions, an arrangement which would prove awkward in limbs used for walking or feeling.

FIG. 13.—THE UNDERSIDE OF THE ABDOMEN OF A FEMALE.
(Oniscus asellus.)]

FIG. 15.—THE FIRST ABDOMINAL APPENDAGE OF THE MALE.
(Oniscus asellus.)

The inner plate (or endopodite) is in structure a gill, but the blood that passes through it, is enabled to take up oxygen from moist air, while the outer division (or exopodite) acts as a protecting cover (fig. 14). In Porcellio, air-tubes (tracheae) may be present (see below).

In the male, the first two pairs of abdominal appendages are specially modified, the inner divisions (endopodites) being long and pointed (figs. 15 and 16). The last pair, or tail appendages, in the male are often considerably larger than in the female, and the form of these structures is sometimes of value in classification.