Figure 6 



The Annelida include a large subclass of marine worms, the Polychaeta, of 

 which the Sandworm {Nereis virens), here shown, is a well-known example. 

 The marine worms possess paired, muscular organs, the parapodia, which 

 function in locomotion and respiration. Nereis and many other related forms 

 are vigorous swimmers. Many species are found, however, which are tube 

 dwellers with degenerate or modified parapodia. The development of the 

 head region, particularly with regard to sensory structures, is also a note- 

 worthy feature of the Polychaets. 



83 



