66 A GUIDE FOR THE STUDY OF ANIMALS 



pine, cork, peat, paraffin), preferably under water, and pin 

 out the walls so that you can see into the interior. 



Identify the structures defined above, as well as the 

 dorsal and ventral blood vessels and the " hearts." 



The nephridia are not easily distinguished, though they 

 are very numerous. They are long, slender, coiled tubes, 

 two in each somite, lying in the body cavity, one on each 

 side of the ahmentary canal. If possible, identify them. 



Notice that most of the internal organs are free from 

 the body wall, lying free in the body cavity. 



Questions. 



1 . What is the extent of the body cavity, anteriorly and 

 posteriorly } What is its shape } 



2. What, in general, is the shape of the food canal .'' 

 How many external openings has it .' 



3. Into what regions is the food canal differentiated 1 

 Suggest one advantage of having these specialized regions. 



4. How is the alimentary canal of the worm kept away 

 from the body walls } Why have it thus supported .-' 



5. What is a septum.? How many septa are there.' 

 What vessels and tubes pass through a septum .■' 



6. Locate the nerve cord. How long is it? How fre- 

 quently do the ganglia occur on it.' Which end of the 

 living worm is the more sensitive. Suggest the connection 

 between this fact and the location of ganglia. 



Suggested drawings. 



a. Earthworm, showing structures mentioned in this 



study. 



Details of Structure — Microscopic Anatomy 



Materials. 



Sections of earthworms, preferably both cross sections 



and dorso-ventral, longitudinal ones. 



