s.

The trip to the woods takes place on the 16th of May. The weather is
hot and hints at a coming storm. There is a perceptible breeze from
the south, but not enough to upset my travellers. Forty Mason-bees are
caught. To shorten the preparations, because of the distance, I do
not mark them while they are on the nests; I shall mark them at the
starting-point, as I release them. It is the old method, prolific of
stings; but I prefer it to-day, in order to save time. It takes me an
hour to reach the place. The distance, therefore, allowing for windings,
is about three miles.

The site selected must permit me to recognize the direction of the
insects' first flight. I choose a clearing in the middle of the copses.
All around is a great expanse of dense woods, shutting out the horizon
on every side; on the south, in the direction of the nests, a curtain
of hills rises to a height of some three hundred feet above the spot at
which I stand. The wind is not strong, but it is blowing in the opposite
direction to that which my insects will have to take in order to
reach their home. I turn my back on Serignan, so that, when leaving
my fingers, the Bees, to return to the nest, will be obliged to fly
sideways, to right and left of me; I mark the insects and release them
one by one. I begin operations at twenty minutes past ten.

One half of the Bees seem rather indolent, flutter about for a while,
drop to the ground, appear to recover their spirits and then start off.
The other half show greater decision. Although the insects have to fight
against the soft wind that is blowing from the south, they make straight
for the nest. All go south, after describing a few circles, a few loops,
around us. There is no exception in the case of any of those whose
departure we are able to follow. The fact is noted by myself and my
colleague beyond dispute or doubt. My Mason-bees head for the south as
though some compass told them which way the wind was blowing.

I am back at twelve o'clock. None of the strays is at the nest; but, a
few minutes later, I catch two. At two o'clock, the number has increased
to nine. But now the sky clouds over, the wind freshens and the storm is
approaching. We can no longer rely on any further arrivals. Total: nine
out of forty, or twenty-two per cent.

The proportion is smaller than in the former cases, when it varied
between thirty and forty per cent. Must we attribute this result to the
difficulties to be ove