442 SUB- PHYLUM HEMICHORDA. 



a pair of lateral gill-slits The gonads lie between anus and pharynx 

 Buds are given off from a lateral stalk. 



(2) Rhabdopleura 



-This genus is found at considerable depths in the North Sea and 

 Atlantic. Like Cephalodiscus^ the individuals are minute and stalked, 

 and occur in a colony ; in this case, however, they remain attached to 

 one another by a common stolon, instead of being united only by an 

 investment. The proboscis or buccal shield makes a thin annulated 

 tube within which the polyp moves up and down. In the head region 

 there are two hollow lateral arms bearing numerous ciliated tentacles, 

 which have a skeletal support. The gut, as in Cephalodiscus, has a 

 U-shaped curvature and an anterior diverticulum (" notochord"). 

 There are five ccelomic cavities, and two collar-pores. There are no 

 gill-slits. 



