THE SANDWORM 53 



the brain. Remove the forward end of the nervous system from 

 the body, mount it in glycerine, and study it under a microscope. 

 Note the ganglionic enlargements and the double nature of the 

 nerve cord. Study the branches which pass off from the nerve 

 cord and from the brain. 



Exercise 7, Draw a diagram representing the opened body cavity in 

 a number of somites on a scale of from 5 to 10, showing all the above- 

 mentioned features which have been observed. 



The Reproductive System. There is no complicated repro- 

 ductive system in Nereis. The sexes are separate. The repro- 

 ductive glands make their appearance only during the periods of 

 sexual activity and then as swellings of the peritoneal lining of 

 the body cavity. The eggs or spermatozoa, as the case may be, 

 fall into the body cavity and find their way to the outside through 

 the nephridia or through ruptures in the body wall. 



Exercise 8. Draw a diagram representing an ideal cross section in the 

 region of the stomach intestine ; show the stomach intestine with 

 its mesenteries, the blood vessels, the nerves, and the muscles. 



