100 F. W. GAMBLE, M.SC, AND J. H. ASHWORTH, B.SC. 



intestine gives off in each somite a pair of branches which are attached 

 to the anterior face of the caudal septa, and which run downwards and 

 forwards to open into the ventral vessel (PL VII., Fig. 5). Of these 

 there may be twenty-seven to thirty pairs. In front of the caudal 

 region each of the last seven pairs of gills returns an efferent branch 

 to the dorsal vessel, and between these there are three or two pairs of 

 smaller branches which run round the alimentary canal from the 

 ventral vessel to open into the dorsal one. From the level of the 

 twelfth setae to the oesophageal pouches the dorsal vessel does not 

 receive any segmental vessels from the gills or nephridia, nor does it 

 open directly into the heart (Fig. 5). It merely receives numerous 

 branches from the gastric plexus. In front of the heart it receives on 

 each side a branch from the third nephridium and the fifth setigerous 

 sac ; a branch from the oesophageal pouches ; and one from the second 

 nephridium and fourth setigerous sac. It then runs on and, piercing 

 the third diaphragm, receives a branch running on the anterior 

 face of the diaphragm from the first nephridium and third 

 setigerous sac. On reaching the second diaphragm it receives a 

 branch, from the second setigerous sac, and after piercing the fiist 

 diaphragm receives a branch from the muscles forming the 

 buccal sheath. Thence the dorsal vessel breaks up into capillaries 

 around the buccal musculature, prostornium, and otocysts. From these 

 capillaries the ventral vessel takes its origin. It gives off a small 

 unpaired branch running in the first diaphragm and to its pouches ; 

 a paired branch arising about midway between the first and second 

 diaphragms to the neural vessels and second setigerous sac ; a single 

 small vessel supplying the second diaphragm and the neural vessels ; 

 an unpaired vessel to the third diaphragm, to the neural vessels in 

 that region, and to the first nephridia ; a pair of branches to the 

 neural vessels and second nephridia ; and lastly, a pair to the neural 

 vessels and third nephridia. From this point onwards the ventral vessel 

 supplies the setigerous sacs, body-wall, nephridia (if present), and gills, by 

 large segmental vessels. The ventral vessel is very large and turgid in the 

 gastric region, and is surrounded by tufts of dark brown chlorogogenous 

 tissue, which are also found in older specimens on the vessels running to 

 the body-wall. This chlorogogenous tissue is first seen on the ventral 

 vessel about the level of the eighth pair of setae. In the tail the 

 ventral vessel ends in the obliquely placed intestinal vessels which 



