214 Givynneth Buchanan: 



of coinmissurals in each seg'iiient, which pass to the ventral 

 vessel, sending a branch to the ventral body wall and posterior 

 septum of the segment on the way. In 4, 3 and 2, however, 

 the commissurals are very fine, and the vessel to the body wall 

 not apparent, thouirh in 3 there is a large development of 

 branches over the alimentary canal and gland. From 9-5 these 

 commissurals present a constriction, probably marking a valve, 

 about one-third of the distance along their length : and from 

 this point vessels arise running to the alimentary canal wall, 

 and in 5 to the hinder septum of the segment. 



In 10, 11 and 12 are a pair of hearts, thrown into folds l)y 

 strong connective tissue, and passing to join the ventral. They 

 are connected with the dorsal by a fine vessel at the posterior 

 part of each segment, but their main origin is from the well- 

 marked supra-intestinal, which arises in 12 and runs forward 

 to end over the alimentary canal in 7. It gives off well-marked 

 vessels to the alimentary canal in 12-7. which send branches 

 to the posterior mesentery of the segment, and join the lateral. 

 These branches to the mesenteries are more marked in the seg- 

 ments anterior to the hearts. 



The lateral is a well-developed vessel along the whole of its 

 length, taking origin in the first segment on the dorsal side of 

 the body, w^here it breaks up into very fine branches, one of 

 which connects with the dorsal on each side. It sends irregular 

 branches over the alimentary canal in 1, 2 and 3, and in 4 be- 

 comes larger, giving well-marked vessels to the posterior 

 septum. From 4 it runs backwards as a very distinct vessel, 

 whose branches to the hinder septa of the segments are very 

 large, and run in close connection with the lower parts of the 

 commissurals in 9, 8, 7 and 6. In 6 and 7 it is connected with 

 its fellow of the opposite side at the anterior end of the seg- 

 ment by a vessel below the alimentary canal (which sends a 

 branch to the anterior septum), and in 5 and 6 it gives branches 

 to this organ, while from 7-12 these are connected also with 

 the supra-intestinal, though there are also smaller branches 

 passing only to the lateral. In 10 the lateral passes below the 

 alimentary canal, and becomes the suh-intcxfi luil on each side, 

 receiving branches from the supra-intestinal in 10, II and 12, 

 and giving vessels to the posterior septum. It then runs on, 



