With a grater, however, I scrape the outside of another nest so as to reduce the depth of the cavities to some ten millimetres.

(About two-fifths of an inch .-- Translator's Note.) This leaves in each cell just room for one cocoon, surmounted by the closing stopper.

Of the fourteen cavities in the nests, I leave two intact, measuring fifteen millimetres in depth.
(.585 inch .-- Translator's Note.) Nothing could be more striking than the result of this experiment, made in the first year of my home rearing.

The twelve cavities whose depth had been reduced all received males; the two cavities left untouched received females.
A year passes and I repeat the experiment with a nest of fifteen cells; but this time all the cells are reduced to the minimum depth with the grater.

Well, the fifteen cells, from first to last, are occupied by males.