276 »B. W. A. HEBDMAN ON BBITISH TTJNICATA. 



Mg. 1. 



Diagrams showing course of the alimentary canai : fig. 1, in Ciona \ 



Corella ; fig. 3, in Ascidia. ce, oesophagus ; st, stomach ; i, flexure of in- 

 testine ; r, rectum ; br, branchial sac : h, heart. 



If we now, the mouth and anus being fixed, draw the intes- 

 tinal loop (i) directly anteriorly until the whole alimentary canal 

 is on the left side of the branchial sac, we get the relation of 

 parts characteristic of Ascidia, as shown in fig. 3. The heart 

 now lies at the ventral edge of the posterior end, the intestine 

 turns anteriorly, and is in its entire extent anterior to the heart. 

 If we return to fig. 1, the arrangement in Ciona, and again 

 draw the intestinal loop forwards, but this time to the right of 

 the branchial sac, we produce the configuration shown in fig. 2, 

 and characteristic of Corella. Here the heart, having remained 

 on the stomach-wall, has become anterior to the intestiue, and is 



