POLYGORDIUS 



47 



sphere produced into a conical projection at the lower pole. 

 Two parallel ciliated bands encircle the equator, and between 

 these the mouth opens on one side of the body. The mouth 

 leads into an oesophagus, which expands into a capacious 



M 



Fig. 10 



A. Dorsal view of Polygordius ap/>cndiculatus. ct, cephalic tentacles; /z, head; 

 an, anus. B. Trochosphere larva of Polygordius. e, eyespot ; rn, mouth; 

 an, anus. C. and D. Stages in the development of the trochosphere into the 

 worm. pnf>, pronephridium. E. Head and anterior segments of a polychaete, 

 Nereis rubicunda, showing the head, eyes, tentacles, and cirrhi, and parapodia. 

 (A to D after Fraipont, E after Ehk-rs.) 



stomach, from which a short and nearly straight intestine 

 proceeds, opening by an anus at the extremity of the conical 

 projection at the lower pole. There is a considerable space 

 between the walls of the gut and the body-wall ; this space is 

 filled with fluid, contains a few scattered stellate cells, and is 

 traversed by a few muscular fibres ; but it must not be con- 



