ANNULATA 



223 



Does the animal respond equally to contact (with pencil or 

 toothpick) at anterior, posterior, and middle parts of the body ? 

 Devise a method of determining whether it is sensitive to light. 

 Record results. 



Place moist soil and dry soil side by side on a board; place 

 the worm in various positions to test his preference. Record 

 results. Place a piece of filter paper which has been dipped in 

 acetic acid in the path of a worm. How does it react? Try 

 similarly a sugar solution; a salt solution; a decoction of decay- 

 ing leaves. Will an earthworm pass into water ? Do your ex- 

 periments bear in any way on the habits of the earthworm in 

 nature? Can you secure any evidence as to the food of the 

 earthworm ? How ? Record your results. 



3. Special External Structures. Locate the mouth, the pre- 

 oral lobe, clitellum (a series of swollen segments), anus. Com- 

 pare preoral lobe with other segments. With a lens and by 

 drawing the worm backward between the fingers discover the 

 setae or bristles. Are they found on all segments? Number 

 and position of the groups of setae in each segment ? What is 

 the function of the setae ? Proofs ? 



4. Internal Anatomy. Pin out a large specimen, which has been hardened in 

 alcohol, on dissecting board or pan, and carefully remove the dorsal wall from the 

 anterior half of the body by making lateral incisions with sharp-pointed scissors, 

 or make a single incision along the back a little to one side of the middle line. 

 After noting the cross membranes (dissepiments}, their relation to the rings on the 

 outside, and their attachments, cut them so the body wall may be folded back and 

 pinned. The dissection should proceed under fluid, 50 per cent, alcohol, for 

 example. Make all the outline drawings necessary to show all your discoveries. 

 Notice the coelom. It is completely divided by the dissepiments? Are the cham- 

 bers of equal size? 



(a) Digestive organs: Beginning at the anterior end, note the following re- 

 gions: 



Pharynx, a pear-shaped enlargement: how held in place? In what seg- 

 ments is it situated ? 



Esophagus, a narrow tube; crop; gizzard; intestine. 



Determine the segments in which each region occurs. Does the digestive 

 tract show any signs of segmentation, i.e., in correspondence with the 

 external rings? 



(6) Circulatory system: A living or newly killed specimen is somewhat better 

 for this. Discover, if possible: 



Dorsal vessel (just dorsal to the digestive tract). 

 Ventral vessel (just ventral to the digestive tract). 



