THE EARTHWORM AND ANNELIDS IN GENERAL 173 



tudinal vessels, five in number, extend from the anterior to the 

 posterior end of the body; these are connected with one another 

 and with various organs by branches more or less regularly 

 arranged. 



(1) The largest and most important of the longitudinal trunks 

 is the dorsal or supra-intestinal (Fig. 88, sp.), which runs along 

 the dorsal surface of the alimentary canal, from the posterior 

 end of the body to the pharynx. 



(2) Just beneath the alimentary canal lies the ventral or sub- 

 intestinal trunk (sb.). This likewise extends from the posterior 

 end of the body to the pharynx, where it divides into many small 

 branches. 



(3) The sub-neural trunk (sn.) traverses the entire length of the 

 body on the under side of the ventral nerve cord. 



(4 and 5) The lateral-neural trunks (nl.) lie one on either side 

 of the ventral nerve cord; they are smaller than the other longi- 

 tudinal trunks. 



The branches from the longitudinal trunks in the anterior part 

 of the body differ from those in the region of the intestine. A 

 pair of short thick tubes connect the dorsal with the ventral 

 vessels in each of the five segments from VII to XI. These are 

 known as hearts (tit.) because of their power of contractility. 

 Small branches from the hearts supply the septa immediately 

 posterior to them (Fig. 88, A). In somite X, two intestino- 

 tegumentary vessels (Fig. 88, it. in A and B) arise, one on either 

 side of the dorsal trunk. Each extends anteriorly, sending a pair 

 of branches to the oesophagus in every segment from X to VI, 

 and receiving branches from the integument and nephridia in the 

 same somites. The ventral trunk gives rise in each segment to 

 two vessels, one going to the nephridium, the other to the body 

 wall (Fig. 88, D). The sub-neural receives vessels from the in- 

 tegument. 



In the region of the intestine the dorsal is connected with the 

 sub-neural trunk in each segment by a pair of parietal vessels 

 (Fig. 88, co. in C and D). The latter receive branches from the 



