74 ZOOLOGY DIRECTIONS 



as the nephridiopore. The location of this nephridiopore is best 

 observed in the study of the cuticnla under Section IV, 



Note demonstration of stained nephridium. Draw three 

 somites showing arrangement of nephridia as seen under hand 

 lens. 



RESPIRATION 



In the earthworm there are no special organs for respiration. 

 The moist conditions under which the animal lives and the deli- 

 cate structure of the body wall make it possible for the entire 

 body surface to function in the process of respiration. 



NERVOUS SYSTEM 



1. The nerve cord lies against the body wall in the middle 

 of the ventral surface. It is conspicuous, thread-like struc- 

 ture, slightly enlarged in each somite. How many side branches 

 of this cord in each somite? Do these lateral branches follow 

 any definite plan of arrangement? 



2. Trace the nerve cord toward the anterior end of the 

 worm. 



3. Very carefully lift the posterior end of the pharynx and 

 tracing the nerve cord on forward locate the place where it di- 

 vides and passes around the pharynx. The nerve cord around 

 the pharynx is the circum-pharyngeal collar. 



4. The small, whitish, two-lobed mass on the dorsal sur- 

 face of the anterior end of the pharynx is the hrain. 



5. Make a diagram of the nervous system. 



BODY WALL 



With the hand lens examine the cut surface of the body 

 wall. Locate the muscle layers. Note the inner ends of the 

 setae protruding through the body wall. 



III. Study of Prepared Slides 



Under the microscope examine cross sections of the body 

 in the region of the intestine. 



