THE EARTHWORM. 41 



seize the worm near the posterior end and drag it back- 

 ward ; is there resistance ? Repeat, and listen attentively. 

 Lay the worm over the tip of the forefinger, and drag it 

 backward and forward. Look for fine spines; how are 

 they arranged, and in what direction do they point? Note 

 the mouth opening at one end, and the anus at the other. 

 Draw as seen from above (dorsal view). 



DISSECTION OF THE EARTHWORM. 



Use the dissecting pan as for the crayfish. Half fill the 

 can with water, and renew if it becomes muddy during 

 dissection. Have in readiness two dozen pins. 



Kill a large earthworm by putting it into a tumbler and 

 covering it with ether or alcohol. 



1. Lay the specimen lengthwise in the middle of the dis- 

 secting pan, stretch it, and pin it firmly at each end. 

 With sharp, fine-pointed scissors cut through the skin 

 of the back, near the posterior end, continuing the cut 

 forward a little to one side of the middle line. Stretch 

 the edges of the skin out to the sides, and pin down, 

 slanting the pins so they will be out of the way. 



2. If a milky liquid be found, place a drop of it on a 

 slide, cover it with a cover-slip, and examine with a 

 high power of the microscope. White blood cor- 

 puscles should be seen. 



3. As soon as the edges of the cut are separated, the 

 intestine, usually of a dark color, from its contents, 

 is seen. 



4. Along the top of the intestine runs the dorsal vessel. 

 This is perhaps not a true "blood-vessel," for many 

 regard the milky liquid, above noted, as the real 

 blood. 



