BLOOD-VESSELS. 



57 



fine network, but do not break up into parallel vessels as ora the gizzard. 

 In the two somites (13th and 14th) in front of the crop there are usually 

 two pairs of vessels running around the oesophagus. In the llth and 12th 

 somites a small branch is given off to each calciferous gland. The most 

 anterior pair of circular vessels are in the 6th somite, and are very small. 

 In front of this the dorsal vessel breaks up into the pharyngeal network. 

 In front of the llth somite there are three sub-intestinal vessels. The two 

 additional vessels lie, one on either side of the primary one and break up 

 into branches at the sides of the pharynx. The aortic arches empty into 

 the middle vessel, and at the point of junction there is a communication 

 with the lateral vessel of the corresponding side. 



Besides the dorsal and sub-intestinal vessels there are three other minor 

 longitudinal trunks (Fig. 26). Two of these are very small, and lie on 



S2, 



FIG. 36. Dorsal view of part of the ventral nerve-cord, showing the arrangement of 

 the vessels of the ventral region, ds, dissepiment ; si', sub-intestinal or ventral 

 blood-vessel ; sb.., sub-neural ; sp.?i., supra-neural. The sub-intestinal receives on 

 either side the ventro-laterals (r.Z) from the nephridia, of which it forms the ef- 

 ferent vessel (e.f). The sub-neural is joined on each side by a continuation of the 

 dorso-tegumenta/ry (d.t.); af, afferent branch to the nephridium (cf. Fig. 27). 



either side above the nerve-cord (p. 66), sending fine branches out from 

 each ganglion along the lateral nerves. These are the supra-neural trunks 

 (s.n.). The third longitudinal vessel (sub-neural) lies below the nerve-cord. 

 (See Fig. 26.) It receives on each side the termination of the dorso-tegu- 

 mentary vessel (d.t., Fig. 26) which in its course is connected with the 

 capillary networks of the body-wall and the dissepiment, and gives off a 

 large branch to the nephridium (cf. Fig. 27). 



