ANNULATA. 2 17 



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 de- 

 caying leaves. Will an earthworm pass into water? Do your 

 experiments bear in any way on the habits of the earthworm 

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

 earthworm ? 



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

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

 Compare 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 ? Num- 

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

 is the function of the setse? Proofs? 



4. Internal Anatomy. Pin out a worm, 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 out- 

 line drawings necessary to show all your discoveries. Notice the coelom. 

 Is it completely divided by the dissepiments? Are the chambers of equal 

 size? 



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

 regions : 



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



segments 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, *. e., in corre- 

 spondence with the external rings? 



