CHAPTER II 



EXPERIMENTS 



AS THE nests of the Mason-bee of the 

 Walls are erected on small-sized peb- 

 bles, which can be easily carried wherever you 

 like and moved about from one place to an- 

 other, without disturbing either the work of 

 the builder or the repose of the occupants of 

 the cells, they lend themselves readily to prac- 

 tical experiment, the only method that can 

 throw a little light on the nature of Instinct. 

 To study the insect's mental faculties to any 

 purpose, it is not enough for the observer to 

 be able to profit by some happy combination 

 of circumstances: he must know how to pro- 

 duce other combinations, vary them as much 

 as possible and to test them by substitution 

 and interchange. Lastly, to provide science 

 with a solid basis of facts, he must experi- 

 ment. In this way, the evidence of formal 

 records will one day dispel the fantastic le- 

 gends with which our books are crowded : the 

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