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 br), 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 

 Vertebrata. 



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 



Fig. 141. CIRCULATING APPARATUS OF LOBSTER. 



course as in the Mollusca, excepting that the heart contains 

 but a single cavity. The arrangement of the circulating appa- 



