26o THE WONDERS OF INSTINCT 



deep cells and males in the shallow cells. That is how 

 things go when the old nest remains in its natural state. 

 With a grater, however, I scrape the outside of another 

 nest so as to reduce the depth of the cavities to some ten 

 millimeters.^ This leaves in each cell just room for one 

 cocoon, surmounted by the closing stopper. Of the four- 

 teen cavities in the nests, I leave two intact, measuring 

 fifteen millimeters^ in depth. 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. It must 

 be quite understood that, in each case, all the offspring 

 belonged to one mother, marked with her distinguishing 

 dot and kept in sight as long as her laying lasted. He 

 would indeed be difficult to please who refused to bow 

 before the results of these two experiments. If, how- 

 ever, he is not yet convinced, here is something to remove 

 his last doubts. 



The Three-horned Osmia often settles her family in 

 old shells, especially those of the Common Snail (Helix 

 aspersa), who is so common under the stone-heaps and 

 in the crevices of the little unmortared walls that support 

 our terraces. In this species the spiral is wide open, so 



1 About two-fifths of an inch. — Translator's Note. 



2 .585 inch. — Translator's Note. 



