86 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
artery in the fourth abdominal segment. In the last 
segment an artery is given off internally to the intestine, 
on the ventral side of which it anastomoses with its fellow 
and the sub-intestinal artery. The abdominal artery 
finally terminates in the uropoda. 
The venous system is lacunar. A large thoracic 
sinus runs into the abdominal sternal sinus, from which 
five afferent branchial vessels arise; each of these 
bifurcates at the base of the branchial appendages, 
supplying the superior and inferior lobes of the branchiae. 
The vascular system of the branchiae. The branchiae 
are supplied by venous vessels from the abdominal sinus. 
The efferent branchial vessels open into the pericardium 
by way of the branchio-pericardial canals (Pl. II., fig. 16, 
br.p.c.). The circulation in the superior and inferior lobes 
of the abdominal appendages, both of which are respira- 
tory, is different. The interior of the inferior lobe of 
the branchiae (inf./am.) is fenestrated by an irregular 
system of lacunae, those of the outer side containing 
venous blood and those of the inner side arterial. On the 
other hand, the vascular system of the superior lobe (sup. 
lam.) is very definite and uniform throughout the five 
pairs. It consists of a venous portion (PI. IT., fig. 13, a.b.v.), 
which is ventral (looking at the gill from the anterior face) 
to the arterial system of vessels (e.b.v.). The individual] 
arteries and veins interdigitate in a very complete manner, 
and the vascular supply is very rich, as will be seen by 
reference to the figure (Pl. III., fig. 3). On this account, 
the superior gills cannot be looked upon as being merely 
opercular in function in this animal, but are certainly 
respiratory appendages of a very perfect nature. 
The blood is colourless and contains nucleated 
corpuscles which vary in size. As in most anthropods, it 
is very coagulable. 
