A Gcphyrean Worm. 51 



A GEPHYREAN WORM 



(Phascolosoma gouldit) . 



External Anatomy. The elongated body shows no 

 external traces of segmentation, and lateral appendages 

 are not present. The anterior end is often deeply with- 

 drawn, though in specimens killed with considerable care 

 the mouth will be found to occupy a terminal position, and 

 to be surrounded by a crown of tentacles. The anal open- 

 ing is not at the posterior end, but at the apex of a median 

 papilla, situated near the middle of the animal, and marking 

 the dorsal surface. 



Make a drawing of the animal as seen from the side. 



Internal Anatomy. With a pair of scissors open the 

 specimen along the median line a little to one side of the 

 anus and pin the body-walls so as to expose the internal 

 organs. Note the dorsal and the ventral pharyngeal retrac- 

 tors. They are large muscle bundles, longitudinally arranged, 

 and retract the anterior portion of the animal. 



The Digestive System. Locate the mouth and follow 

 the coiled stomach-intestine to the "posterior" end of the 

 body, thence back to its final opening on the dorsum. Do 

 you find mesenteries ? Are there dissepiments ? 



