96 GENERAL BIOLOGY 



ing of two fleshy lobes. There is also a ventral cirrus. From 

 each blade a number of setae arise in bundles. In each 

 blade there is embedded a short -stiff rod, the aciculum, 

 which serves to support the appendage. Examine the last 

 body somite and note any differences from the other somites. 

 Make an enlarged drawing of a single parapodium. 



n. Internal Anatomy. 



Open the worm in the same manner as the earthworm. 

 Note the body wall, the ccelom, the septa, and observe any 

 differences from the conditions present in the other worm. 



The digestive system has a large muscular pharynx, in 

 which are the large jaws noted above, and also some small 

 teeth covering the walls. Can you account for the differences 

 in the pharynx of this worm and the earthworm? The 

 pharynx opens into a large crop, into which also empty 

 digestive glands. Was there anything corresponding to 

 the digestive glands in the earthworm? The rest of the 

 digestive tube is composed of the straight stomach-intestine. 



The pharynx is protrusible and there are protractor and 

 retractor muscles to operate the proboscis and the jaws. 



The circulatory and excretory systems are much like 

 those of the earthworm, though they are not so large nor 

 so easily worked out. 



In the sand worm the sexes are separate and the repro- 

 ductive organs are present only at the breeding season. 

 A portion of the tissue lining the ccelom produces sperms 

 or eggs at this time. When the reproductive products are 

 ripe the body wall is ruptured and the germ cells escape 

 into the water where the fertilization takes place.. Unless 

 the worms were obtained during the breeding season the 

 reproductive organs will not be found. 



