LUMBRICUS. 97 



LUMBRICUS. (Earthworm.) 



Earthworms feed mostly at night. What reason is there 

 for this habit? You should look for earthworms with a lantern 

 some mild, calm summer evening when the ground is quite 

 moist. See if they leave their burrows entirely. How much 

 of the body is generally protruded? Can you determine what 

 the worms are doing? Are they disturbed by walking near 

 them? Are they ever disturbed by flashing the light suddenly 

 upon them? Of what service to them is the ability to distin- 

 guish light? Look for castings near the burrows. During day- 

 light look for castings and thus determine the relative abundance 

 of worms in lawns, gardens, etc. (As the worms come to the 

 surface only when it is moist, castings will be abundant only 

 at such times.) Do the castings indicate anything about the 

 feeding habits. 



Place a living specimen upon moist filter-paper and observe 

 the direction and method of movement. How can it reverse its 

 direction? Gently touch different parts of the body to see 

 which are the most sensitive. 



Observe the movement of the blood in the dorsal vessel. In 

 what direction does it move? Does the vessel change in shape? 



Place a preserved specimen in a dish with a little water and 

 notice : 



1. The difference in shape of the two ends of the body. The 

 mouth is at the anterior end, below the protruding lobe of the 

 prostomium. The anus is a vertical slit at the end of the last 

 somite. 



2. The dorsal and ventral sides. How do they differ? 



3. The right and left sides are symmetrical. Count the somites 

 of the body, compare with others, and record the result. 



4. On the anterior third of the body certain somites are 

 swollen and form the ctitellum. What somites are swollen? 

 The clitellum is not present in young individuals. It is used in 

 making egg-cases and providing food for developing embryos. 

 Understand how this is accomplished. 



5. Small swollen areas on the ventral side of the fifteenth 

 somite, where the vasa deferentia open. 



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