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,