The Mother Decides the Sex 



entrance-halls. Lastly, the deeper cavities on 

 the circumference are allotted to females and 

 the shallower to males. 



I will add that a single mother peoples 

 each nest and also that she proceeds from cell 

 to cell without troubling to ascertain the 

 depth. She goes from the centre to the edges, 

 from the edges to the centre, from a deep 

 cavity to a shallow cavity and vice versa, 

 which she would not do if the sexes were to 

 follow upon each other in a settled order. 

 For greater certainty, I numbered the cells of 

 one nest as each of them was closed. On open- 

 ing them later, I was able to see that the 

 sexes were not subjected to a chronological 

 arrangement. Females were succeeded by 

 males and these by females without its being 

 possible for me to make out any regular se- 

 quence. Only — and this is the essential point 

 — the deep cavities were allotted to the fe- 

 males and the shallow ones to the males. 



We know that the Three-horned Osmia 

 prefers to haunt the habitations of the Bees 

 who nidify in populous colonies, such as the 

 Mason-bee of the Sheds and the Hairy- 

 footed Anthophora. Exercising the very 

 greatest care, I broke up some great lumps 



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