IN CONSTRUCTING EARTHWORKS. 249 
an inch in 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 capillary 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 little 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 
