THE BRITISH WOODLICE. 7 
Circulatory system—The blood being aérated in the 
abdominal appendages, we find that the heart is situated towards 
the hinder end of the body (fig. 18). 
Three main arteries supply the 
thorax and head, while the 
blood is brought from the gills 
to the heart. 
Excretory system.—The ex- 
cretory organs consist of a (a) 
pair of so-called ‘shell glands,” 
which are considered to be the 
ae 
Nout 
: % 
R 
| Gaus | | 
cee ad 
Lijestive Glaiaets 
FIG. 17.—THE ALIMENTARY CANAL, 
(Oniscus asellus.) 
worms. In the woodlouse 
these excretory organs open 
on the second pair of maxillae. 
They are composed of a 
tube (sacculus) closed at one 
end and more or less bent upon 
itself (5, p. 261) which com- 
municates with a labyrinth that 
is provided with an excretory 
orifice. Matters are eliminated 
by the epithelial cells [the his- 
tology has been described and 
tubes or 
z | wm Orb ery 
mn 
VV 
Vi 
VP) ca yuh Cotter ace HEART 
Vil 
FIG, 18.—THE CIRCULATORY SYSTEM. 
(Ontscus asellus.) 
equivalents of the excretory 
nephridia of annelid 
figured in Ligidium hypnorum (66)], which are very large in Ligia 
oceanica. 
