192 SYSTEMATIC ZOOLOGY. 



14. The nervous system consists of a brain and a pair 

 of ganglia in each somite. The oesophagus passes through 

 the nervous system between brain and ventral cord. 



15. The Annelida embrace the Chsetopoda and the 

 Hirudinei. 



16. The Chcctopoda have well-developed body-cavity, 

 and bristles on each segment, the bristles being frequently 

 supported by fleshy parapodia. 



17. The Hirudinei have reduced body-cavity and lack 

 setae and parapoclia. 



18. The MOLLUSCOIDEA were formerly regarded as mol- 

 luscs. They have a complete alimentary canal and a 

 circle of tentacles surrounding the mouth. 



19. The Molluscoidea are divided into Polyzoa and 

 Brachiopoda. 



20. The Polyzoa reproduce by eggs and by budding, 

 the result of the latter being to produce large colonies. 



21. The Brachiopoda have a bivalve shell, the two valves 

 being dorsal and ventral. They are attached by a ped- 

 uncle and reproduce solely by eggs. 



22. The few existing Brachiopoda are marine. In past 

 time they were far more numerous, and fossil brachio- 

 pods are abundant in the older rocks. 



