THE EARTHWORM. 145 



THE EARTHWORM. 



1. Can you distinguish a head and a tail? 



2. Has it a dorsal and a ventral surface? 



3. Has it a right and a left side? 



4. How many segments, or somites, can you 

 count? Are they all alike? 



5. Observe the cingulum, or girdle, near the 

 anterior part of the body. How many segments does 

 it cover? How many segments in front of it? 



6. If your earthworm is alive, watch it crawl. 

 Describe the action fully. Can it crawl backward? 



7. If your earthworm is alive, see the blood in the 

 dorsal blood vessel. Is there a corresponding ventral 

 blood vessel? 



8. Examine the first segment of the body. Note 

 the rounded lip in front, the prostomium. 



9. Find the mouth. 



10. Feel and see, on the ventral surface, little 

 bristle-like organs, the setse. How many on each 

 segment? Of what use can they be? 



11. Find a delicate outer membrane covering the 

 body — the cuticle. 



Internal Structure. 



1. Pin the body, back upward, under the water, 

 on weighted cork. Carefully cut through the body 

 wall from the tail to the head. Pin out the sides of 

 the cut. 



2. Find the septa, which divide the body cavity 

 into chambers. How many? 



3. Can you find the dorsal blood vessel? What 

 branches does it give off? 



4. Trace the alimentary canal. Distinguish the 

 following parts : the buccal sac, in the first three 

 segments ; the thick-walled portion, in segments 4-7 ; 

 the oesophagus, in segments 8-12 ; the crop, in seg- 



