440 CHARACTERS OF INVERTEBRATE ANIMALS 



gland opens into the stomach. The excretory organs are in the 

 form of a pair of funnel-shaped tubes, which, like the nephridia 

 of a segmented worm (p. 425), place a spacious body-cavity in 

 communication with the exterior. The central nervous system 

 essentially consists of a ring surrounding the gullet, and thickened 

 above into brain- and below into other ganglia. (The upper part 

 of the ring is not shown in fig. 271, a.) 



