III.] THE EARTHWORM. 26 1 



3. Still working from the side, carefully cut (with scissors) 

 into any three or four somitic constrictions of the 

 intestinal region, and without dissecting further ma- 

 nipulate the parts with forceps under water. Note 

 the relations of the mesenteric septa and nephridia, 

 as seen in the undisturbed condition (cf. Sect. E.) 

 and next examine in order 



a. The circular commissural vessels; one on either side 

 for each segment. They lie close under the body- 

 wall (to which they give branches) midway between 

 adjacent mesenteric septa, and connect the supra- 

 intestinal and sub-neural trunks. 



b. The excretory plexus. The posterior of the two 

 vessels from which this is derived springs from the 

 sub-neural trunk immediately adjacent to the ne- 

 phridium itself. The anterior one arises from the 

 supra-neural in the segment in front, and perforates 

 the mesenteric septum ventro-laterally. 



c. Remove a portion of the body-wall of this region, 

 and gently scrape away as much as possible of the 

 yellow-brown tunic of the intestine. There will 

 thus be brought into view the lateral intestinal 

 vessels ; two in number on either side in each seg- 

 ment. They arise from the supra-intestinal trunk 

 and break up into an alimentary plexus within the 

 walls of the digestive canal. A series of small 

 vessels will be seen to pass up towards these from 

 the sub-intestinal trunk. 



The blood-vessels described above can all be made 

 out by careful dissection. No mention has been 

 made of the delicate lateral-neural commissures, or 

 the smaller branches of the majority of the great 



