BLOOD-VESSELS. 



131 



breaks up into the pharyngeal network. In front of the llth somite there 

 are three sub-intestinal vessels, as shown in Fig. 76. The two additional 

 vessels lie on either side of the primary onq and break up into branches 

 at the sides of the pharynx. The aortic arches empty into the middle ves- 

 sel, 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. 77). Two of these are very small, and lie on 

 either side above the nerve-cord (p. 136), sending fine branches out from 



S.I. 



4- 03. 



~s.n. 



FIG. 76. 



FIG. 77. 



FIG. 76. Ventral view of part of the pharynx and oesophagus, showing the three sub-in- 

 testinal vessels in this region, the first pair of circular vessels, and the aortic arches, 

 a.o, aortic arches; ce, ossophagus; ph, pharynx; s.i, sub-intestinal vessel. 



FIG. 77. A portion of the ventral nerve-chain seen from above, and showing some of the 

 blood-vessels; d.d, dissepiments; I, lateral vessel from the sub-neural vessel; l.n, 

 lateral nerves proceeding from a ganglion; s.i, sub-intestinal vessel, showing along its 

 upper side the cut ends of short vessels which connect it with the sinus running along 

 the ventral side of the alimentary canal; s.n, supra-neural vessel; v.l, ventro-lateral 

 vessel. 



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

 (s.n). 



The third longitudinal vessel (sub-neural trunk) lies below the nerve- 

 cord. From it a pair of lateral vessels are given off in each somite just 

 behind the dissepiment (2, Fig. 77). A large branch from this vessel 

 (often more than one) runs backward to ramify on the body-wall. The 

 main trunk runs outward in the dissepiment and gives off numerous 

 branches to the adjoining nephridiuin (p. 132). 



