CiONA. 3 



extends transversely into the centre of the chamber, 

 and the extremities diverge in the direction of the 

 dorsal margin, one passing upwards to the branchial 

 sac, the other downwards to the pyloric end of the 

 stomach. The upper extremity, as in Ascidia, divides 

 into three branches, two of which supply the dorsal 

 margin of the branchial sac, one upwards, the other 

 downwards, forming the great dorsal branchial channel; 

 the third supplies the test. The lower extremity of 

 the heart divides in the usual way into two branches 

 which ramify over the respective sides of the stomach. 

 The stem which goes to the left side gives off a branch, 

 which, turning backwards and upwards, goes along 

 with its fellow from the upper end of the heart to the 

 test. Another branch advances in the direction of the 

 oesophagus, and is apparently the equivalent of that 

 which goes to the ventral margin of the branchial sac 

 in Ascidia. 



Having thus far determined the circulatory organs, 

 there can be little doubt that the blood-system is as 

 complete in dona as it is in Ascidia, especially as 

 traces of the visceral and pallial plexuses have been 

 observed, and as the branchial suspenders are as 

 largely developed as they are in that genus. 



The digestive organs, as has been already stated, lie 

 below the branchial sac ; they are partially cut off 

 from the rest of the body by a membrane. The oeso- 

 phagus is considerably longer than it is in Ascidia, in 

 this respect agreeing with Pelonaia and Glavelina. It 

 is a rather wide tube, opening into the bottom of the 

 branchial sac close to its ventral margin. From the 

 oral orifice the oesophagus runs downwards, and then 

 bending backwards joins the anterior end of a well- 

 marked, globular, or ovate stomach, which lies across 

 the bottom of the abdominal chamber. The intestine 

 is a wide, even tube ; it leaves the opposite or dorsal 

 extremity of the stomach, and, bending upwards, 

 crosses a little above that organ towards the right side 

 of the body to the opposite or ventral margin, up 



