THE BRITISH WOODLICE. 49
appendages have made their appearance and the mesoderm,
(which has grown considerably, to form the beginnings of the
muscles) has sent prolongations into each of them. About this
time, spaces (see fig. 31) are formed in the muscular mesoderm
which are all that remain of the true body cavity characteristic of
animals above the level of the jelly-fish, arid in these spaces
the blood ultimately cir-
culates.
The body next alters
somewhat in shape and
the three divisions of the
intestine approach one
another (see fig. 32)
previous to their junction.
As may be imagined dur-
ing these processes the
food-yolk has gradually
been used up and the
space which it occupied
taken by the internal
organs, which we have
mentioned.
In the last stages of
the development the ap-
pendages become larger
still, the heart makes its
appearance, segmentation
of the body is completed,
and except that the
seventh pair of walking
legs are as yet rudimen-
tary the Woodlouse is
completed. It is only
after hatching that the
pair of legs mentioned, attain to their normal length.
The process of segmentation of the egg and the formation of
its layers lasts about a fortnight, while the completion of the
development proceeds much more rapidly, for another three
weeks bring it to an end.
After the first moult or change of skin the last pair of