CIRCULATION IN CEPHALOPODA AND CRUSTACEA. 253 
which we have seen in the class of Fishes. The auricle and 
ventricle of the heart are separated from each other; and 
whilst the latter remains in the position just described, the 
auricle occupies the place which the whole heart possesses in 
the class above. The course of the blood in these animals is 
shown in fig. 140; where c represents the ventricle or sys¬ 
temic heart, from which arises the aorta a, a , as, av, that 
supplies the body with arterial blood. The venous blood is 
returned through the great vein vc, covered with a curious 
spongy mass cs, the use of which is not known; this also 
receives the blood from the intestinal veins vv ; and it divides 
into two trunks which convey the blood to the gills or branchiae 
(br and hr), where it undergoes aeration. On each of these 
trunks is an enlargement, cb, which has the power of con¬ 
tracting and dilating, and thus of assisting the transmission 
of the blood through the arteries of the gills, a b. The blood 
is returned to the ventricle by the branchial veins, vb, on 
each of which there is another dilatation, bu, which might be 
regarded as analogous to the auricle of the other Mollusca, 
but that it is not muscular. Thus in the Cuttle-fish, the blood 
receives an impulse from the systemic heart, by which it is 
transmitted into the main artery; and when it returns by the 
systemic veins, it receives another impulse from the branchial 
hearts, before it passes through the gills;—an arrangement 
obviously analogous to that which we meet with in the highest 
Yertebrata. 
292. In the Crab and Lobster, and other animals of the 
class Crustacea, the blood for the most part follows the same 
e f i a d b c 
course as in the Mollusca, excepting that the heart contains 
but a single cavity. The arrangement of the circulating appa- 
