er at some distance,
they place the animal in a bag which they twirl rapidly at the moment of
starting, thus preventing the animal from returning to the house which
it has quitted. Many others, besides Favier, described the same practice
to me. According to them, this twirling round in a bag was an infallible
expedient: the bewildered Cat never returned. I communicated what I
had learnt to England, I wrote to the sage of Down and told him how the
peasant had anticipated the researches of science. Charles Darwin was
amazed; so was I; and we both of us almost reckoned on a success.

These preliminaries took place in the winter; I had plenty of time to
prepare for the experiment which was to be made in the following May.

'Favier,' I said, one day, to my assistant, 'I shall want some of those
nests. Go and ask our next-door neighbour's leave and climb to the roof
of his shed, with some new tiles and some mortar, which you can fetch
from the builder's. Take a dozen tiles from the roof, those with the
biggest nests on them, and put the new ones in their place.'

Things were done accordingly. My neighbour assented with a good grace to
the exchange of tiles, for he himself is obliged, from time to time, to
demolish the work of the Mason-bee, unless he would risk seeing his roof
fall in sooner or later. I was merely forestalling a repair which became
more urgent every year. That same evening, I was in possession of twelve
magnificent rectangular blocks of nest, each lying on the convex surface
of a tile, that is to say, on the surface looking towards the inside of
the shed. I had the curiosity to weigh the largest: it turned the scale
at thirty-five pounds. Now the roof whence it came was covered with
similar masses, adjoining one another, over a stretch of some seventy
tiles. Reckoning only half the weight, so as to strike an average
between the largest and the smallest lumps, we find the total weight of
the Bee's masonry to amount to three-quarters of a ton. And, even so,
people tell me that they have seen this beaten elsewhere. Leave the
Mason-bee to her own devices, in the spot that suits her; allow the
work of many generations to accumulate; and, one fine day, the roof will
break down under the extra burden. Let the nests grow old; let them
fall to pieces when the damp gets into them; and you will have chunks
tumbling on your head big enough to crack your skull. There you see the
work of a very little-known insect. (The i