110 



PHYLUM ENTEROPNEUSTA. 



work, be placed in alliance with the Enteropneusta. It differs, 

 however, from the other members of the phylum by the absence 

 of pharyngeal apertures. 



It exists in the form of colonies, the zooids of which are con- 

 nected with one another 

 by living substance and 

 are contained in trans- 

 parent tubes of a chitin- 

 like material. The colo- 

 nies have the form of a 

 branching axis which lies 

 upon the substratum and 

 gives off at irregular 

 intervals the terminal 

 branches. These, for the 

 most part, after adhering 

 for a short distance to the 

 substratum, rise up and 

 project freely into the 

 water. At their free ends 

 are found the openings of 

 the tubes by which the 

 zooids come into relation 

 with the external world. 

 The zooids consist of a 

 body and a stalk (Fig. 81). 

 The body is small ('12 

 mm. in diameter) and 

 possesses at its anterior 

 end a preoral lobe the 

 buccal disc or proboscis, 

 a pair of tentaculiferous 

 arms arising laterally at 

 the level of the mouth 

 from the collar region (see 

 below), a mouth on the ventral side of the buccal disc (Fig. 82, 8} 

 and an anus (3) placed at about the same level as the mouth on 

 the dorsal side. The stalk is the narrow ventral end of the body 

 which passes down to join the common axis of the colony in the 

 creeping stolon. Its connexion with the body is somewhat an- 



Fitt. 80. Portion of a living colony of Rhabdopleura 

 normani (Allman), Lofoten Islands, x 16. a the 

 terminal branches with the zooids in different states 

 of protrusion ; c the proboscis (cephalic disc) ; d 

 the two tentacular arms ; / the stomach ; g the 

 intestine ; h the stalks of the zooids ; i the axial 

 rod in the creeping stolon. 



