ON MONOPYLEPHOEUS LIMOSUS. 



27 



The vessels which form the ventral integumentary network in 

 segment I branch ont from the ventral vessel at the middle of 

 segment II and enter the body wall just in front of the ventral 

 seta-bundles of the latter segment. 



In segment II they start from the main trunk and enter the body 



wall just in front of the setal zone of segment III. It is worthy of 



note that in this segment the ventral vessel is sometimes cleft in two. 



In segments III they start and enter the body wall just in 



front of the posterior septum. 



In those segments in which two sets of these vessels are present, 

 the posterior pair lie just in front of the posterior septum, while 

 the anterior pair, which are mostly larger than the posterior, always 



lie in the anterior region of the 

 segment ; in segments IV and V 

 the latter start just in front of the 

 setal zone, in segments VI — X at the 

 middle of the segment, and in 

 the segments behind the twelfth 

 they lie rather near the anterior 

 septum. 



In the hindermost segments of 

 the body there is only one set of 

 ventral integumentary vessels, which 

 start and enter the body wall just 

 as in segment III. 



c. The integumentary vascular 

 networks are formed by the capillaries arising from the dorsal 

 and ventral integumentary vessels. The dorsal and the posterior 

 ventral integumentary vessels divide repeatedly (fig. 22), while 

 the anterior ventral integumentary vessels have a main trunk, which 

 runs dorso-ventrally along the curve of the body wall on either 



a.v.l.v n.c 



Fig. 23. 



Schematised cross section through 

 an anterior segment to show the anterior 

 ventral integumentary vessel. xlOO. 

 d.v — dorsal vessel, b.n — intestinal vas- 

 cular network, int — intestine, v.v — 

 ventral vessel, n.c -nerve cord, a. v.l. v. — 

 anterior ventral integumentary vessel. 



