BEHAVIOR OF THE ANT-LION. 



293 



behavior of the body I could see that it was making vigorous 

 movements with its third pair of legs; but it made practically no 

 progress. 



Experiment 8. A layer of dirt equal in elevation to the greatest 

 height of the ant-lion was placed on a pasteboard rectangle. An 

 ant-lion was placed on this pile of dirt. Immediately it began 

 to burrow backward and continued to progress at a rapid rate. 



(In all of the experiments from 1-8 the same individual was 

 used. The series was repeated many times with different in- 





FIG. 10. A cluster of ant-lion pits (average cluster). 



dividuals; but, in each case, the same individual was put through 

 the eight experiments.) 



In experiments 7 and 8 the presence of the dirt makes it neces- 

 sary for more work to be performed in making progress backward. 

 Since the height of the pile is the same in each case, the amount of 

 work required is the same. Since the bristles are more numerous 

 on the sides of the body than on the ventral surface, the presence 

 of the dirt should give an added opportunity for them to function 

 in preventing forward slipping of the body; hence, if the progress 

 is due simply to a flexing and stretching of the body the ant-lion 

 should be able to move just as fast, if not faster, on a glass plate 

 with a layer of soil as on the naked glass. If, however, the hind 

 legs play an important role in dragging the body backward, then 

 the larva on the dirt-covered pasteboard should have a great 

 advantage over the one on the dirt-covered glass plate. These 



