306 



MR. H, H. STIRRUP ON" 



text-fig. 61 C shows three setse almost formed with the three old 

 setae close beside them. 



Blood-system. — The intestine is surrounded by a blood-sinus 

 which is in very close contact with the epithelial lining of the 

 gut. In segment 15 the dorsal portion of this blood-sinus 

 becomes swollen and is gradually pinched off to form a large dorsal 

 vessel. The fact that this dorsal vessel is postclitellar in origin 

 is an important generic character distinguishing the genus 

 Enchytrmus from most of the other genera in the family 

 Enchytraeidse. This dorsal vessel is continued forward until it 

 reaches segment 1. It then divides into two, each branch going 

 backwards to the ventral side and uniting to form the ventral 

 vessel. This ventral vessel continues, just ventral to the gut, to 

 the posterior end of the worm. Both dorsal and ventral vessels are 



Text-fiff. 61. 



Enchi/traus pellucidus. 



A. Three setae. B. Three new setse just being formed. 

 C, Three setae almost formed with the three old setae close to them. 



joined at intervals to the gut-sinus by small vessels (PI. XL VII. 

 fig. 10). There are three pairs of lateral vessels also in the 

 anterior blood-system ; two pairs are given ofi" close together and 

 join the two branches which form the ventral vessel, and one pair 

 is given ofi" just behind this and joins the ventral vessel proper. 

 Text-fig. 62 represents this anterior blood-system. 



The dorsal vessel, which is very large at its point of origin, is 

 partly covered with chloragogen-cells, which also extend round 

 the gut. At the point where the dorsal vessel arises, it swells 

 and contracts rhythmically, sending the blood forward. I have 

 seen no trace of the cardiac body, " a solid rod of cells attached to 

 the ventral side of the dorsal blood-vessel, and extending along 

 its whole length" (1, pp. 77-78), in Enchytrceus pellucidus. This 

 cardiac body was first described by Michaelsen in the genus 

 Mesenchytrceus. He suggested that this solid rod of cells served 

 to ease the contractions of the dorsal vessel. The blood is a 

 colourless fluid with no blood-corpuscles. 



