the Amazon regiment leave barracks, had followed them step by step and
placed her stones at intervals along the road covered. The Ants had
made their raid and were beginning to return along the track of tell-
tale pebbles. The distance to the nest was about a hundred paces,
which gave me time to make preparations for an experiment previously
contemplated.

I take a big broom and sweep the track for about a yard across. The
dusty particles on the surface are thus removed and replaced by
others. If they were tainted with any odorous effluvia, their absence
will throw the Ants off the track. I divide the road, in this way, at
four different points, a few feet a part.

The column arrives at the first section. The hesitation of the Ants is
evident. Some recede and then return, only to recede once more; others
wander along the edge of the cutting; others disperse sideways and
seem to be trying to skirt the unknown country. The head of the
column, at first closed up to a width of a foot or so, now scatters to
three or four yards. But fresh arrivals gather in their numbers before
the obstacle; they form a mighty array, an undecided horde. At last, a
few Ants venture into the swept zone and others follow, while a few
have meantime gone ahead and recovered the track by a circuitous
route. At the other cuttings, there are the same halts, the same
hesitations; nevertheless, they are crossed, either in a straight line
or by going round. In spite of my snares, the Ants manage to return to
the nest; and that by way of the little stones.

The result of the experiment seems to argue in favour of the sense of
smell. Four times over, there are manifest hesitations wherever the
road is swept. Though the return takes place, nevertheless, along the