A PolycJuetous Annelid. 



The mouth will be found as a transverse fold 

 integument of the antero-ventral surface of the peristomium. 



Make a drawing of the dorsal and of the ventral side of 

 peristomium. 



Observe the varying size of the lateral appendages, espe- 

 cially at the two ends of the animal. Carefully remove one 

 of the larger bundles of lateral appendages and examine 

 under a simple microscope. The bundle will divide itself 

 into a dorsal and into a ventral parapodium. The former 

 bears a large triangular blade, the gill. From the upper 

 edge of the gill projects a small movable cirrus. Do you 

 find ramifying blood-vessels in the gill? Do you find two 

 fleshy lobes immediately beneath the gill? The dorsal lobe 

 bears a large number of seta. 



The ventral parapodium is divided in much the same way 

 as the dorsal. Do you find a ventral cirrus ? Ventral setae ? 

 Closer examination will reveal the presence in each para- 

 podium of a supporting chitinous rod, aciculum. 



Draw, naming the parts. 



Examine the posterior end of the animal and note how 

 the lateral appendages become reduced. Which elements 

 are first lost? What is the point of attachment of the ter- 

 minal filaments? Does the anus open dorsally or ventrally? 



The external openings of the segmental organs will be found 

 on the ventral side of each body-segment, near the bases of 

 the parapodia. 1 



In a specimen that has been killed with extended probos- 

 cis note the large, laterally opening jaws. 



1 These openings are often difficult to find. They are placed at the 

 summit of the rounded elevation that lies just medially of each ventral 

 cirrus. The segmental organs themselves are often to be seen through 

 the transparent integument of smaller specimens. They are opaque 

 white in color, and lie just lateral to the longitudinal muscle bands. 



