EARTHWORM 93 



4. Nerve Cord. What is the shape of the cord as seen in 

 section? If nerves are present notice the place and the 

 manner in which they emerge from the cord. The cord is 

 enclosed within a connective tissue sheath, scattered through 

 which are many muscle fibers. Are these circular or longi- 

 tudinal muscles? Also within this sheath are located three 

 longitudinal bloodvessels, ventrally the subneural, at the 

 sides the lateral-neural vessels. The pear-shaped cells in 

 the cord are the nerve cells, and the delicate fibers that seem 

 to be prolongations of the cells are the nerves. Are nuclei 

 present in the nerve cells? Are the nerve cells abundant? 

 Where are they located? At the dorsal side of the cord are 

 three areas that are called giant fibers. Filling up the bulk 

 of the cord are connective tissue fibers. 



Draw an enlarged section of the entire cord, showing the 

 points observed. 



IV. Physiology. 



Make the following study of the living worm. 



1. Movements. Place the worm on a damp, rough sur- 

 face, as filter paper, and observe the kinds of movements 

 and the way they are produced. By what means does the 

 worm move from place to place? Can it climb over ob- 

 structions? Place the worm on a moist, perfectly clean 

 glass. Explain the behavior observed. 



2. Sensitiveness. With a bristle or a blunt instrument, 

 touch the worm in different places. What regions are the 

 most sensitive? How is this indicated? Try the effect 

 of stimuli such as warmth of the breath, sunlight, vapor of 

 ammonia or chloroform, dilute acetic acid. Record the 

 results obtained. 



3. Circulation. If the body wall is not too thick, nor too 

 heavily pigmented, the pulsations of the dorsal bloodvessel 



