ON MONOPYLEPHORUS L1MOSUS. 



25 



points, which lie just behind the swellings of the dorsal vessel and 



in front of the posterior septum of each segment. 



In segments VI— X (fig. 20) each vessel is much dilated; 



the left one starts from the dorsal side and the right one from the 



ventral side of the longitudinal heart, owing to the displacement of 



the dorsal vessel. After undergoing a 

 few windings in the ccelom the integu- 

 mentary vessels enter the body wall 

 about midway between the dorsum and 

 the ventrum, just in front of the posterior 

 septum, and divide into the capillary 

 network of the integument (fig. 21). 



Of these dilated vessels the pair in 

 segment X are somewhat different from 



IV 



v 



VI 

 VII 

 VIII 



IX 

 X 



XI 



l.d.l.v 



r.d.l.v 



Fig. 20. 

 Dorsal view of the anterior 

 part of the body, showing the 

 blood-vessels ; from a living speci- 

 men, x 30. d.v — dorsal vessel, v.v 



p.v.l.v 



Fig. 21. 



Schematised cross section to show the dorsal 

 dilated and the posterior ventral integumentary 

 vessels. xlOO. d.v — dorsal vessel, v.v — ventral 

 vessel, int — intestine, bn — intestinal vascular 

 layer, 1. d.l.v and r.d.l.v. — left and right dorsal in- 

 tegumentary vessel, p.v.l.v — posterior ventral 

 integumentaly vessel. 



— ventral vessel. 



the others. Each vessel here starts on its winding course like 

 others, but its main part, after giving off some branches to the body 



