The Mother Decides the Sex 



each of whom had his own storey, his own 

 closed cell. 



When the accommodation consisted of no 

 more than a simple cylinder, with no state- 

 bedroom at the end of it, a bedroom always 

 reserved for a female, the contents varied 

 with the diameter of the cylinder. The series, 

 of which the longest were series of four, in- 

 cluded, with a wider diameter, first one or 

 two females, then one or two males. It also 

 happened, though rarely, that the series was 

 reversed, that is to say, It began with males 

 and ended with females. Lastly, there were 

 a good many isolated cocoons, of one sex or 

 the other. When the cocoon was alone and 

 occupied the Anthophora's cell. It invariably 

 belonged to a female. 



I have observed the same thing in the nests 

 of the Mason-bee of the Sheds, but not so 

 easily. The scries are shorter here, because 

 the Mason-bee does not bore galleries but 

 builds cell upon cell. The work of the whole 

 swarm thus forms a stratum of cells that 

 grows thicker from year to year. The cor- 

 ridors occupied by the Osmla are the holes 

 which the Mason-bee dug in order to reach 

 daylight from the deep layers. In these short 



