26 



E. NOMURA.: 



wall of the segment and the sperm- sac, penetrates the posterior 

 septum and enters segment XI in the dorsal region. It runs straight 

 backwards, parallel to the body axis, and turning toward the ventral 

 side more or less suddenly at about the anterior one-fourth of the 

 segment comes to lie near the outside of the atrial portion of the 

 male duct. After giving off some more branches to the body wal] 

 the main part enters it at about 

 the posterior one -third of the 



segment, and on reaching the 

 posterior septum it turns sud- 

 denly to the dorsal side of the 

 body and is gradually resolved 

 into many branches. 



In each segment behind the 

 twelfth only one dorsal integu- 

 mentary vessel branches out 

 from the dorsal side of the 

 longitudinal main trunk. It runs 

 vertically upwards just in front 

 of the posterior septum, and 

 divides in the peritoneum into 

 two main branches which sub- 

 divide again and again. In the 



n.c p.v.Lv 



Fig. 22. 



Schematised cross section through the 

 anterior face of n posterior septum behind 

 segment XII, to show the unpaired dorsal and 

 posterior ventral integumentary vessels, x 100. 

 r.d.l.v — right branch of dorsal integumentary 

 vessel, ps— posterior sperm-sac, d.v — dorsal 

 vessel, b.n — intestinal vascular network, int 

 — intestinal canal, v.v — ventral vessel, n.c — 

 ventral nerve cord, p.v.l.v — posterior ventral 

 integumentary vessel. 



segments containing the genital sacs, each vessel passes through 

 the latter and richly supplies them on its way. 



b. The ventral integumentary vessels branch out always pairwise 

 from the ventral vessel and after running ventro- laterally a short 

 way enter the body wall on either side of the ventral nerve cord 

 (figs. 21, 22, 23). Two sets are generally found in each segment: 

 viz. the anterior and the posterior ; but in segments I — III, X and 

 in the hind part the anterior pairs are wanting. 



