XXI 



EXPERIMENTS 



Built on small pebbles which one can carry 

 whither one will, remove, or interchange, with- 

 out disturbing either the work of the constructor or 

 the quiet of the inhabitants of the cells, the nests 

 of Chalicodoma muraria lend themselves readily to 

 experiment — the only method capable of throwing a 

 little light on the nature of instinct. Profitably to 

 study the physical faculties of the animal it is not 

 enough to know how to turn to account such circum- 

 stances as a happy chance may offer to the observer : 

 one must be capable of originating others, and vary 

 them as much as possible and submit them to mutual 

 control ; in short, to give science a solid basis of fact 

 one must experiment. Then some day will vanish 

 before the evidence of exact documents the fantastic 

 legends which cumber our books, such as the Scara- 

 baeus inviting his comrades to help in dragging his 

 ball out of a rut, or a Sphex cutting up a fly to carry 

 it in spite of the wind, and much more which is mis- 

 used by those who desire to see in the animal world 

 that which is not there. Thus, too, will materials be 

 prepared which, used sooner or later by a learned 

 289 U 



