HABITS AND LIFE-HISTORIES OF WOODLICE.
145
When the woodlice reach the age of maximum breeding
activity, the species T. pusillus, P. dilatatus, P. scaber and O.
asellus usually produce two separate broods in the same year ;
but the duration of the brood-pouch periods, as well as the
numbers of brood produced, were found to be invariably smaller
in the case of the second broods, hence in the table given below
the averages for the two successive broods are shown separately.
Returning now to the newly-laid eggs, the subsequent
development can be traced by gently raising the brood plates
of the mother at intervals of a few days, without causing any
apparent harm to the developmental process. Within the
translucent egg-membranes, tiny embryos can be seen gradually to
take shape, a series of stump-like limbs being the first organs
to make their appearance. After five weeks or so of embryonic
life (see table) the membranes burst, liberating the embryos
into the brood pouch, to commence a larval period. They are
curious little creatures at this early stage, having only six
thoracic segments and six pairs of jointed legs instead of the
usual seven of the adult. Furthermore, their bodies are not
yet completely segmented, and their heads are quite devoid
of the characteristic cephalic lobes of the adult. Their antennae,
too, are short, stumpy, and incompletely segmented at the
tips, whilst their eyes are mere groups of ommatidia, as yet
lacking the corneal facets which are characteristic of the Arthropod
eye. Their entire bodies have a soft, pearly-white appearance,
entirely devoid of any pigmentation, whilst the side-plates of
the thorax are almost transparent. In size they vary from one-
fifth to one-tenth of the adult in length, depending on the species,