204 



OF THE BLOOD AXD CIECULAT10X. 



Auricle. 



Lesser circulation. 



lying along the spine, and byits branches is distributed through- 

 out the body. Fig. 220 is a plan of this type of circulating 

 organ. 



[ 368. In the 

 mollusca the heart 

 consists of a ven- 

 tricle and an au- 

 ricle, as in fishes ; 

 Heart. but it differs in 



this, that it is 

 destined to pro- 

 pel the blood 

 the sys- 



Ventricle. 



"Veins 



^Dorsalartery. 



through 



Veins. 



Greater circulation. 

 Fig. 220. Circulation in fishes. 



through the gills, 

 as in that class. 



[Fig. 221 repre- 

 sents the circula- 

 ting organs of the 

 Doris; the heart 

 consists of a ven- 

 tricle (a), from 

 whence arises the 



aorta (6), which sends branches to all parts of the body ; and a 

 single or double auricle (c), in which the veins (d) of the bran- 

 chial organs (e) terminate, the branchiae being developed in the 

 form of external vascular tufts. The blood purified in these or- 

 gans is conveyed to the heart, and transmitted by arteries through 

 the body ; it is collected by the radicles of the veins, which 

 terminate in a large trunk (f). By this vena cava it is dis- 

 tributed through the gills (<?), and from these organs it is re- 

 turned to the heart. In the CEPHALOPODA the circulation 

 through the gills is aided by branchial ventricles, situated at 

 the bases of these organs, but in other respects their circu- 

 latory apparatus resembles that of the mollusca in general. 



[ 369. In the Crustacea (fig. 222), the circulation is after 

 the type of the mollusca. The heart (a) consists of a ven- 

 tricle only, from which several arteries arise ; the opthalmic 

 (b), the antennal(c), the hepatic (d), the superior abdominal (e), 

 and the sternal (/*). After having circulated through the body, 

 the blood is collected in certain reservoirs (g g), which take the 



