NEREIS 65 



ventral artery. In . this vessel the blood flows toward the hinder 

 end of the body. 



Exercise 7. Draw a view of the opened animal on a scale of 5, 

 showing the organs above described. Label all the organs 

 carefully. 



Sever the alimentary tract at the oesophagus and remove the 

 stomach-intestine from the body. Observe the muscle bands in 

 the body-wall ; note the difference in direction and size of the 

 different bands. Observe the muscles at the base of the acicula. 



The excretory system. The kidneys of the animal consist of a 

 pair of glandular organs called nephridia, which lie in the body- 

 cavity against the ventral body-wall in each somite except 

 the last two or three. Each nephridium opens through the 

 body -wall to the exterior in a minute pore on the ventral sur- 

 face of each somite near the base of the parapodium. The 

 anterior end of the nephridium passes through the septum 

 which forms the anterior wall of the somite in which that organ 

 lies, and opens into the body-cavity. The opening, which is 

 ciliated, is called the nephrostome ; it lies, as will be seen, against 

 the anterior surface of a septum. Study the nephridia carefully 

 in several parts . of the body under a dissecting microscope ; 

 some of them may have been torn in removing the intestine. 

 Examine a portion of the worm in which that organ is still 

 in the body and note the relation of the nephridia to it and 

 to the septa. 



Exercise 8. Draw a diagram representing the opened body- 

 cavity in a number of somites and the position of the 

 nephridia and the muscles. 



The nervous system. Observe in the mid-ventral line of the 

 body-cavity the nerve cord. Trace it forward to the brain. 

 Note the connectives which encircle the pharynx and connect 

 it with the brain. Remove the forward end of the nervous 



