crossing is taking place.
Let us now see what will happen when the formic scent, if there really
be one on the trail, is replaced by another, much stronger odour, one
perceptible to our own sense of smell, which the first is not, at least
not under present conditions.

I wait for a third sortie and, at one point in the road taken by the
Ants, rub the ground with some handfuls of freshly gathered mint. I
cover the track, a little farther on, with the leaves of the same plant.
The Ants, on their return, cross the section over which the mint was
rubbed without apparently giving it a thought; they hesitate in front of
the section heaped up with leaves and then go straight on.

After these two experiments, first with the torrent of water which
washes away all traces of smell from the ground and then with the mint
which changes the smell, I think that we are no longer at liberty to
quote scent as the guide of the Ants that return to the nest by the road
which they took at starting. Further tests will tell us more about it.

Without interfering with the soil, I now lay across the track some large
sheets of paper, newspapers, keeping them in position with a few small
stones. In front of this carpet, which completely alters the appearance
of the road, without removing any sort of scent that it may possess, the
Ants hesitate even longer than before any of my other snares,
including the torrent. They are compelled to make manifold attempts,
reconnaissances to right and left, forward movements and repeated
retreats, before venturing altogether into the unknown zone. The paper
straits are crossed at last and the march resumed as usual.

Another ambush awaits the Amazons some distance farther on. I have
divided the track by a thin layer of yellow sand, the ground itself
being grey. This change of colour alone is enough for a moment to
disconcert the Ants, who again hesitate in the same way, though not
for so long, as they did before the paper. Eventually, this obstacle is
overcome like the others.

As neither the stretch of sand nor the stretch of paper got rid of any
scented effluvia with which the trail may have been impregnated, it
is patent that, as the Ants hesitated and stopped in the same way as
before, they find their way not by sense of smell, but really and truly
by sense of sight; for, every time that I alter the appearance of the
track in any way whatever--whether by my destructive broom, my streaming
water, my green