THE MINERS 271 



sometimes excanvates its mies solitarily, on 

 sand-baks rencently laid bare n the middle 

 of the river, and closes the orifice before 

 going in search of prey. In these cases 

 the insect has to make a journey of at least 

 half a mile to procure the kind of fly, the 

 Motuca, with which it provisions its cell. 

 I often noticed it to take a few turns in 

 the air round the place before starting ; on 

 its return it made, without hesitation, 

 straight for the closed mouth of the mine. 

 I was convinced that the insects noted the 

 bearings of their nests, and the direction 

 they took in flying from them. The pro- 

 ceeding in this and similar cases seems to 

 be a mental act of the same nature as that 

 which takes place in ourselves when recog- 

 nising a locality. The senses, however, 

 must be immeasurably more keen, and the 

 mental operation much more certain, in 

 them than they are in man ; for to my eye 

 there was absolutely no landmark on the 

 even surface of sand which could serve as 



