THE EARTHWORM 12/ 



the fifteenth segment on the ventral side. They are the 

 openings of the vas deferens. Exactly in front of these on 

 the fourteenth segment are the two openings of the oviduct. 

 These are not very easily seen. 



DissECTJON OF THE EARTHWORM. — (i) Kill a large 

 worm by placing it in ether, chloroform, or alcohol. Ex- 

 tend the worm under water in the dissecting pan, dorsal 

 side up. Put a pin through the extreme anterior and poste- 

 rior ends. With a fine-pointed pair of scissors cut through 

 the body wall on dorsal side near the posterior end. Con- 

 tinue the cutting forward along the mid-dorsal line, being 

 careful not to cut deep enough to injure the organs below. 

 Pin back the body wall on both sides, slanting the pins so 

 that they will not interfere with dissecting. Notice a milky 

 hquid exuding from the cut. With a pipette put some of 

 this liquid on a slide and examine with the high power 

 lens. White blood corpuscles should be found moving 

 about in it. Draw. 



(2) Notice the dark-colored digestive tract extending 

 from mouth to anus. What gives it its color? Can you 

 now see clearly the dorsal blood vessel referred to above? 

 Trace it out. Notice the oval white bodies dorsal to the 

 digestive tract near the tenth segment. These are reproduc- 

 tive organs. Notice the muscular walls between the seg- 

 ments. These were partially cut through in laying back 

 the body wall. What is their relation to the digestive tract? 

 To the body wall? Compare these with the external seg- 

 ments. Note the relation. These portions are called septa. 

 These divide the body cavity, or coehim, into small cham- 

 bers. What is the shape of a septum? Represent by a 

 sketch. 



