The Mother Decides the Sex 



set in the bottom of the old cocoon. This 

 double wrapper points very clearly to two gen- 

 erations, two separate years. I have even 

 found as many as three cocoons fitting one 

 into another at their bases. Consequently, 

 the nests of the Mason-bee of the Pebbles are 

 able to do duty for three years, if not more. 

 Eventually they become utter ruins, aban- 

 doned to the Spiders and to various smaller 

 Bees or Wasps, who take up their quarters 

 in the crumbling rooms. 



As we see, an old nest is hardly ever ca- 

 pable of containing the Mason-bee's entire lay- 

 ing, which calls for some fifteen apartments. 

 The number of rooms at her disposal is most 

 unequal, but always very small. It is say- 

 ing much when there are enough to receive 

 about half the laying. Four or five cells, 

 sometimes two or even one: that is what the 

 Mason usually finds In a nest that is not her 

 own work. This large reduction is explained 

 when we remember the numerous parasites 

 that live upon the unfortunate Bee. 



Now, how are the sexes distributed in those 

 layings which are necessarily broken up be- 

 tween one old nest and another? They are 

 distributed in such a way as utterly to upset 



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