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 csophagus 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 aseptum. 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 
