114 ANNELIDA 



1. The cuticle will probably be absent in most sections, 

 in which case the outer covering will be the cellular hypo- 

 dermis or skin. How many cells thick is this layer? Look 

 for the gland cells that keep the living worm moist. Do you 

 know how the cuticle is formed? 



2. Beneath the hypodermis is the circular muscle layer, 

 which is followed by the longitudinal muscle layer. The 

 fibers of the latter are arranged in conspicuous bundles. 

 Lining the body wall is the thin peritoneal layer. Do you 

 understand the function of each of these layers? How is the 

 body elongated? 



3. Find the setae and determine where they are placed, 

 how many are in each group, how many groups there are, 

 how they pierce the body wall, and what muscles are at- 

 tached to them. Why are setae not in every section? 



4. The alimentary canal consists of a lining epithelium, 

 followed by connective tissue and muscle, and, on its outer 

 wall, peritoneal cells, which in the region of the stomach-in- 

 testine are large, very numerous, and are known as the 

 chlorogogue cells. 



5. Lying in the midventral line, beneath the alimentary 

 canal and close to the body wall, is the ventral nerve cord. 

 Examine its structure. See if any of the sections show nerves 



leaving it. 



6. Dorsal to the alimentary canal is the dorsal blood ves- 

 sel, on its ventral side is the ventral blood vessel, and ventral 

 to the nerve cord the subneural vessel. 



7. Find sections of the nephridia. Where are they placed? 

 How do the sections appear? Why? 



Other organs will appear in most of the sections. See if 

 you can identify them. 



Draw an enlarged cross section. 



Darwin: The Formation of Vegetable Mold through the Action of 



Worms. Appleton and Co., 1888. 

 Harrington: The Calciferous Glands of the Earthworm, with Appendix 



on the Circulation. Jour. Morph., 15, 1899. 



