PHASCOLOSOMA. lU 



Excretory System.— Find a pair of brown nephrldia, an 

 inch or more in length. Cut off a nephridium (from the fresh 

 worm) as close as possible to the body-wall, and examine it 

 under a microscope. Near the cut (the attached) end find the 

 ccelomic opening or nephrostome. Is it ciliated? 



Reproductive System.— The sexes are separate. Oogonia 

 and spermatogonia are detached from the ccelomic epithelium, 

 at the points where the ventral retractor muscles are attached 

 to the body-wall. These cells become detached and mature 

 while floating in the ccelomic fluid. They pass out through 

 the nephridia, which function as gonoduds. 



Nervous System.— Does the ventral nerve-core seem to be 

 double? Is it ganglionated? Does it give off lateral nerve 

 branches? Trace the drcum-esophageal connectives to the supra- 

 esophageal ganglion. The gangHon is small and situated behind 

 the crown of tentacles, to which sensory nerves extend. Does 

 any system of organs show segmentation? 



Make a drawing to show the internal anatomy, 



Gerould: The Development of Phascolosoma. Zool. Jahrb., 23, 1906 

 C. B. Wilson: Our North American Echiurids. Biol. BuL, 1, 1900. 



