74 THE EARTHWOKM 



nucleus and nucleolus, form a layer on the ventral and lateral 

 surfaces of the cord. 



I. The Blood-vessels. 



These are readily recognised by the deeply staining blood - 

 clots with which they are filled. The larger vessels have 

 muscular walls. 



1. The dorsal vessel lies in the body-cavity above the intes- 



tine. It is of large size, and has masses of ' hepatic ' 

 cells at its sides. Large lateral vessels, as well as 

 vessels from the typhlosole, all surrounded by ' hepatic ' 

 cells, may be seen in some sections opening into the 

 dorsal vessel. 



2. The sub-intestinal vessel lies between the nerve-cord 



and -the intestine, and is connected with the latter 

 by a median sheet of vascular connective tissue. 



