IN CONSTEUCTING EARTHWORKS. 249 



au inch iu depth. Over this moat I then placed a 

 paper bridge, one end of which rested on some fine 

 mould. I then put an ant to the honey, and soon a 

 little crowd was collected round it. I then removed 

 the paper bridge ; the ants could not cross the 

 glycerine ; they came to the edge and walked round and 

 round, but were unable to get across, nor did it occur 

 to them to make a bridge or bank across the glycerine 

 with the mould which I had placed so conveniently for 

 them. I was the more surprised at this on account of 

 the ingenuity with which they avail themselves of earth 

 for constructing their nests. For instance, wishing, if 

 possible, to avoid the trouble of frequently moistening 

 the earth in my nests, I supplied one of my communities 

 of Lasius flavus with a frame containing, instead of 

 earth, a piece of linen, one portion of which projected 

 beyond the frame and was immersed in water. The 

 linen then sucked up the water by capillaiy attraction, 

 and thus the air in the frame was kept moist. The 

 ants approved of this arrangement, and took up their 

 quarters in the frame. To minimize evaporation I 

 usually closed the frames all round, leaving only one or 

 two small openings for the ants, but in this case I left 

 the outer side of the frame open. The ants, however, 

 did not like being thus exposed ; they therefore brought 

 earth from some Httle distance, and built up a regular 

 wall along the open side, blocking up the space between 

 the upper and lower plates of glass, and leaving only 

 one or two small openings for themselves. This struck 



