NEREIS VIRENS SARS 101 



The funnel belongs to the segment preceding that of the ne- 

 phridiopore. Consequently, the canal perforates the septum. 



The nervous system consists of a chain of ganglia, one pair 

 of ganglia for each segment. The first pair is dorsal to the ali- 

 mentary canal and is situated in the head. It is the brain or 

 supracesophageal ganglion. It gives off four optic nerves to the 

 eyes, two palpal nerves to the palpi and two tentacular nerves to 

 the tentacles. The following ganglia are all ventral to the 

 alimentary canal. The first of these, the so-called subossophageal 

 ganglion is connected with the brain by commissures surrounding 

 the pharynx. Nerves supplying the peristomial tentacles arise 

 from small ganglia connected with the commissures. Each 

 abdominal ganglion sends off three pairs of nerves. Of these the 

 first pair supplies the muscles of the septum, the second passes 

 through the septum to the preceding segment, and the third 

 goes to the parapodia. A visceral nervous system is represented 

 by several dorsal and ventral ganglia on the pharynx; they are 

 connected with each other and with the brain. 



Reproductive system. The sexes are separate. The 

 gonads are developed from the peritoneum and the reproductive 

 cells, in the absence of special ducts, reach the outside through 

 the nephridiopores of the posterior region of the body. Fertili- 

 zation takes place in the water. Development is combined with 

 a metamorphosis. The larval stage is known as a Trochophora. 



Instructions 



i. Place a specimen with withdrawn proboscis into a dissecting 

 tray with water. Examine with the aid of the lens the anterior 

 end and make a drawing about three times natural size of the 

 dorsal surface of the first ten segments. Label head and body. 

 Label on the prostomium the eyes, tentacles and palpi, on the 

 peristomium the peristomial tentacles. Observe the length of 

 the two posterior dorsal tentacles and use this character to de- 

 termine the sex. Label the segments of the body and the para- 

 podia. 



