AN EARTHWORM 6i 



outer, very thin, longitudinal layer. Surrounding the muscle 

 layers and also forming a thick fold over the dorsal and lateral 

 intestinal surfaces are the pear-shaped chloragogue cells. Ob- 

 serve the dorsal and the ventral blood vessels, and also the com- 

 missural blood vessels, if any are in the section. Study carefully 

 the nervous system. Note the muscular sheath which surrounds 

 the nerve cord, and embedded in it the sections of three minute, 

 longitudinal blood vessels. Note the double nature of the nerve. 

 Note the large, pear-shaped nerve cells and the nerve fibers, 

 also the three large bodies in the dorsal portion of the ganglion. 

 These latter are called the giant fibers. Do lateral nerves join the 

 ganglion? If so, trace their fibers into it. Also trace their fibers 

 away from the ganglion and see where they go. Examine care- 

 fully the peritoneum. This is a layer of cells which lines the body 

 cavity and bounds all the organs in it. 



Exercise 8, Draw the cross section and carefully label all the organs. 



