282 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



2. On each side of the ventricle is a large transparent 

 auricle, which receives the blood from the bases of the 

 gills and drives it into the ventricle. 



3. Carefully study the pulsation of the heart. The 

 auricles swell irregularly and become filled with the trans- 

 parent, colorless blood from the gills, and they then 

 contract, slowly and irregularly, while the ventricle 

 becomes distended. A slow wave of contraction then 

 runs from one end of the ventricle to the other, and forces 

 the blood into the aorta. 



4. Notice that the pericardium is also filled with blood. 



5. Open the ventricle, and notice the lip-like valves, 

 which prevent the blood from returning to the auricles. 



0. The venous sinus and the renal organs. 



Cut the intestine, and the auricles, so that they may be 

 removed from the pericardium, thus exposing its floor, 

 and the organs which lie below it. 



1. The venous sinus is a long chamber, with a transpa- 

 rent roof, which lies along the middle line of the floor of 

 the pericardium, into the cavity of which it opens, near 

 its anterior end, by a single median aperture. 



2. On each side of it is one of the renal organs, or 

 organs of Bqjanus. Each of these is a long tube, doubled 

 upon itself so as to form an upper and a lower chamber. 

 The upper chamber lias thin, transparent walls, and is 

 known as the non-glandular portion (Fig. 145, '). Its 

 anterior end bends downward, and opens at / in Fig. 145, 

 into the cloacal chamber. The lower chamber has thick, 

 dark-colored, folded walls, and is known as the glandular 

 portion of the organ. At its anterior end it opens into 

 the cavity of the pericardium (Fig. 145, ?*'), at i. Ante- 

 riorly, the cavity of the non-glandular portion is separated 

 from that of the glandular portion, but posteriorly the two 

 communicate with each oilier. 



