354 ZOOLOGY 



2. Head end, dorsal view, x 5. 



3. Tail end, dorsal view, x 5. 



4. Two adjacent middle segments, dorsal view, x 5. 



5. Posterior aspect of a single middle segment, showing parapodia. 

 x 8. 



QUESTIONS ON EXTERNAL ANATOMY 



1. Which segments are most specialized? 



2. Does the number of segments increase during life? Compare 

 several worms. 



3. Which segments are last formed in the individual's development ? 



OBSERVATIONS ON THE LIVING ANIMAL 



(Two persons may work together upon a single Nereis.} Each stu- 

 dent should be provided with the following: (1) hand lens; (2) 

 needle ; (3, 4) vials containing 5% sugar solution and 5% acetic acid ; 

 (5) pipette. 



1. How is locomotion accomplished by Nereis? Analyze the move- 

 ments involved in locomotion. Relation of phases of writhe to 

 phases of stroke and recovery of fin. Form of fin at various phases 

 of its movement. Indicate by diagrams the relations which you 

 discover. 



2. Touch the head with a needle; what movements? The tail; 

 what movements? What faculty in Nereis is indicated by the 

 changes of movement after contact ? 



3. Drop quietly, by means of a pipette, sea-water upon the head end 

 and the middle of Nereis; repeat with acetic acid; with sugar solu- 

 tion. What difference in the movements? What faculty in Nereis is 

 indicated by these differences in movement? 



TOPICS FOR FURTHER STUDY 



1. Habitat and food of Nereis. 2. Its distribution. 3. Its allies : 

 Autolytus, Lepidonotus, Amphitrite, Serpula, etc. 4. The round 

 worms and flat worms. 



XL SLUG (Limax) 



Slugs may be found during the winter in greenhouses and during 

 the spring and autumn in gardens and orchards, under boards and 

 stones. They may be kept for considerable periods in a box whose 



