68 A GUIDE FOR THE STUDY OF ANIMALS 



What is the effect of this indentation upon the amount of 

 surface in the alimentary canal ? 



5. Study the cells of the nerve cord. How do they 

 compare in size and shape with the muscle cells ? 



Suggested drawings. 



a. A diagram of a cross section, showing the relation of 

 the organs. 



6. A diagram of a longitudinal section, at least 

 through the body wall, to show the arrangement of muscle 

 fibers. 



c. A drawing of a portion of the body wall, to show 

 details. 



Summary of Important Points in Study of the Earthworm 



1. Compared with a hydra, how many cells has an earth- 

 worm ? 



2. Compared with a hydra, how much are the cells of an 

 earthworm differentiated ? 



3. How are these differentiated cells usually arranged 

 with respect to one another ? What advantage is there in 

 this arrangement .■' 



4. Recall .the kinds of work done by paramecium, 

 sponge, hydra, and worm, and at the same time consider 

 also the efficiency of each. Can earthworms do any more 

 kinds of work than any of the others ? Can they do any 

 more work .-' Can they do any of it better .'' Give the 

 probable reasons for this .■■ 



Comparative Study of Worms 



Materials. 



As many different kinds of worms as you can get, living 

 or dead. 



