The Mother Decides the Sex 



fourth tube, which she abandons, probably 

 because of its excessive width, after laying one 

 female in it. Lastly, from the 26th to the 

 30th of May, a fifth tube, which she colon- 

 izes with two females and three males. 

 Total: twenty-five Osmias, including seven- 

 teen females and eight males. And it will 

 not be superfluous to observe that these un- 

 finished series do not in any way correspond 

 with periods separated by intervals of rest. 

 The laying is continuous, in so far as the 

 variable condition of the atmosphere allows. 

 As soon as one tube is full and closed, an- 

 other Is occupied by the Osmia without delay. 



The tubes reduced to the exact length of 

 two cells fulfilled my expectation in the great 

 majority of cases: the lower cell was occupied 

 by a female and the upper by a male. There 

 were a few exceptions. More discerning than 

 I in her estimate of what was strictly neces- 

 sary, better-versed in the economy of space, 

 the Osmia had found a way of lodging two 

 females where I had only seen room for one 

 female and a male. 



This experiment speaks volumes. When 

 confronted with tubes too small to receive all 

 her family, she is in the same plight as the 



135 



