254 
CIRCULATION IN CRUSTACEA. 
ratus of a Lobster is seen in fig. 14 1, in which, a is the heart; 
b and c, the arteries to the eyes and antennae; d, the hepatic 
artery ; and e and f the arteries which supply the abdomen 
and thorax. The blood that has been propelled through these 
by the action of the heart, finds its way into the great venous 
sinus g g, which receives the fluid collected from all parts of 
the body ; from this it passes to the gills, h ; and thence it 
is returned to the heart by the branchial veins, i. Another 
view of a portion of the circulating apparatus is given in fig. 
142, which represents a transverse section of it in the region 
b ve c f vb 
st ce 
Fig. 142.— Branchial Circulation of Lobster. 
of the heart, with one pair of gills. The heart is seen at c; 
and from its under , side proceeds one of the arterial trunks 
which convey the blood to the system. Beturning thence, 
the blood enters the venous sinus s, which has an enlarge¬ 
ment at the base of each gill ; and this seems to act the part 
of a branchial heart, like the corresponding enlargement on 
the branchial vessels of the Cuttle-fish. From this cavity, it 
is carried by the vessel va into the branchiae b ; and after it 
has passed through the capillaries of the gill-filaments, it is 
collected by the vessels ve, which carry it to the branchial 
veins, vb, and thence to the heart. The general plan of the 
circulation in this class is shown in fig. 132. 
293. In the class of Insects we find a still greater incom¬ 
pleteness in the system of vessels for the conveyance of blood. 
Arterial trunks can only be traced to a short distance from 
the dorsal vessel, which answers the purpose of a heart; and 
the nutritive fluid which they convey is delivered into the 
channels or sinuses that exist among the different organs. 
