THE EARTHWORM 111 



nephridia, or excretory organs. Look with a handlens for fine blood 

 vessels on these organs. Turning a part of the stomach-intestine to 

 one side, observe that these nephridial vessels are connected with the 

 median ventral vessel. Beneath the ventral vessel is a conspicuous 

 band, the nerve cord. Extend the cut through the body wall to the 

 posterior end and carefully separate the various organs to see them 

 more clearly. Which somites contain similar organs, and which ones 

 are differentiated? Make a full-page drawing of the region from the 

 prostomium to the beginning of the stomach-intestine to show all the 

 organs thus far identified, and locate them in the proper somites. 



(d) Lift up the esophagus wdth forceps, carefully cutting its attach- 

 ments to the septa. Cut it across near the pharynx and pull it gently 

 back, cutting the septa, but being careful not to remove any other 

 structures from the worm. Continue this as far back as the beginning 

 of the stomach-intestine, and lift up and remove the digestive tract in 

 one piece. Examine this removed portion under water and correct any 

 errors in your previous drawing. Find the calciferous glands, three 

 pairs of lateral pouches on the esophagus. 



Exercise 4. — The Ccelomic Fluid. 



(e) Draw out a drop of the ccelomic fluid from a living worm by 

 means of a capillary pipette. Place immediately upon a slide, adding 

 0.7% salt solution if necessary, and examine with the high-power 

 objective. Are cells present? What are their characteristics? What 

 organism do they resemble? Have they nuclei? Draw (3-5 X pro- 

 jected size) showing characteristic shapes. 



Exercise 5. — The Excretory System. 



(f) Using fine scissors, remove a part of a septum with a neph- 

 ridium attached and examine with a microscope under both low- and 

 high-power objectives. The nephridium is a convoluted tube, the walls 

 of which contain many blood vessels. What is the function of these 

 blood vessels? Look for the ciliated funnel, or nephrostome, and for 

 the bladderlike enlargement at the outer end of the tubule. Under- 

 stand the function and manner of action of the nephridium. If living 

 worms are available, remove one of the nephridia, and look with the 

 high-power objective for the flickering of the cilia within the tubule. 

 Draw the nephridium as observed. 



Exercise 6. — The Reproductive System. 



(g) Wash out the anterior region of the worm by gentle currents 

 from a pipette. Examine the posterior surface of the septum between 

 somites 12 and 13 with a handlens; the two ovaries can be seen lying 



