ENTEROPNEUSTA 589 



boscis pores when the organ contracts. From the glomerulus the 

 blood is gathered into two vessels which lead backwards one on each 

 side to a ventral vessel below the gut. From the dorsal vessel is 

 supplied a plexus in the wall of the alimentary canal, including the 



Fig. 442. A zooid of Rhabdopleura normani removed from its tube and seen 

 from the right-hand side. From Lang. An. anus; arm. arms; M. position 

 of mouth; por.' position of collar pore; pro. proboscis; stk. stalk; trk. trunk. 



bars between the gill openings. From this plexus blood passes to the 

 ventral vessel. The blood flows forwards in the dorsal vessel and 

 backwards in the ventral. 



The sexes are separate. The gonads are mere sacs lying at the sides 



