442 SUB-PHVLUM 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 Cephalodéscus, has a 
U-shaped curvature and an anterior diverticulum (‘‘ notochord”). 
There are five coelomic cavities, and two collar-pores. There are no 
gill-slits, 
