Bramble-bees and Others 



the Mason-bee of the Walls, there is also a 

 difference in size, though less pronounced. 



The Three-pronged Osmia has not there- 

 fore to trouble about adjusting the dimensions 

 of the dwelling and the quantity of the food 

 to the sex of the egg which she is about to 

 lay: the measure is the same from one end of 

 the series to the other. It does not matter 

 if the sexes alternate without order: one and 

 all will find what they need, whatever their 

 position in the row. The two other Osmiae, 

 with their great disparity in size between the 

 two sexes, have to be careful about the two- 

 fold consideration of board and lodging. 

 And that, I think, is why they begin with 

 spacious cells and generous rations for the 

 homes of the females and end with narrow, 

 scantily-provisioned cells, the homes of the 

 males. With this sequence, sharply defined 

 for the two sexes, there is less fear of mis- 

 takes which might give to one what belongs 

 to another. If this is not the explanation of 

 the facts, I see no other. 



The more I thought about this curious 

 question, the more probable it appeared to 

 me that the irregular series of the Three- 

 pronged Osmia and the regular series of the 



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