THE BRITISH WOODLICE. It 
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, and 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. 92) 
FIG. 32. EMBRYO OF THE WOODLOUSE SHOWING THE previous to their junction. 
THREE DIVISIONS OF THE INTESTINE SEPARATELY 
DEVELOPED (Porcellio scaber), AFTER ROULE. 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, 
FIG. 33.—EMBRYO OF THE WOODLOUSE SHOWING TRACES In the last stages of 
OF THE SEGMENTS (Porcellio scaber). AFTER ROULE. the development the ap- 
pendages become larger 
still, the heayt 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 
MS intcnED (Porccllio scaber), arter nove, 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 
