210 THE ORGANIZATION 



sac which lies on the right side of the inferior mid-line, and just 

 behind the heart. From this the intestine bends forward and 

 upward, and, passing under the right limb of the heart, rises (at 

 in) to the upper surface of the liver (Iv, lv l ), and terminates (an) 

 not far behind the neck, slightly to the left of the middle dorsal 

 line, and near the base of the funnel (/). 



The liver (Iv, lv l ) is an immense, elongate oval, brown mass, 

 which extends from the neck to the heart, and occupies nearly 

 the whole space between the upper and lower, and right and left 

 sides of the visceral mass in this half of the body. 



The circulatory system consists of a triple chambered heart, 

 and arteries and veins. The heart (h, h 1 , /i 2 , /i 3 ) lies at the pos- 

 terior end of the liver, (Iv,) and exactly in the middle line of the 

 body. The main chamber, the ventricle, (h 1 ,) is more elevated 

 than the two auricles, (h, h z , A 3 ,) on its right and left. In the pro- 

 cess of circulation, the blood issues from the ventricle and passes 

 into the great anterior (ao 2 , ao) and posterior (ao l ) arteries, the 

 first running along the lower side of the body close to the left 

 of the throat and into the head, and the second extending along 

 the upper face of the posterior visceral mass, and thence, after 

 dividing into numerous large and small branches, to the various 

 organs. From the tips of the various arterial branches the 

 blood escapes into return channels, and these coalescing into 

 larger vessels, the anterior (Ay 1 ) and posterior (hv) veins, the cir- 

 culating fluid is emptied into the right (h 2 , h 3 ) and left (h) auri- 

 cles. From these the blood is injected into the right and left 

 gills (g-l) through a vessel (pa, pa 1 ) which runs along the lower 

 edge of each, and branches within them in regular, parallel, trans* 

 verse channels. The blood, being thus aerated, is taken up by 

 the return currents in equally minute, parallel channels, and 

 poured into a larger vessel, (pv, pv l , pv*,) which, passing along the 

 upper side of each gill, empties its contents into the right and 

 left (at/w 1 ) sides of the ventricle; and thus the circuit is finally 

 completed. 



The gills, (gl,) which perform so important a part in this sys- 

 tem, are two elongate, leaf-shaped bodies, placed symmetrically, 



