598 



INVERTEBRATE MORPHOLOGY. 



are traversed, except towards the extremities of the lateral 

 tubes where the individuals occur, by a chitinous rod which 

 results from the chitiuizatiou of what was once the stem of the 

 various polyps. Each of these is stalked (Fig. 272), the stalk 

 (G) becoming continuous below with the chitinous rod, and 



E 



FIG. 272. INDIVIDUAL OF Rhabdopleura (slightly modified after LANKKSTER). 

 (N.B. The tentacles of one side of one arm only are represented.) 

 B anal papilla. G -- tentacle. 



C = stalk. Oa = arm. 



D = epistome. / = intestine. 



E = trunk region. K == sensory papilla. 



F collar region. N -- notochord. 



each consists of three well-marked regions. What may be 

 termed the anterior portion of the body is formed by a large 

 disklike epistome (D), beneath which on the ventral surface is 



