Permutations of Sex 



difficulties attached to a long series. To per- 

 suade the Osmia to nidify in a single tube long 

 enough to receive the whole of her laying and 

 at the same time narrow enough to leave her 

 only just the possibility of admittance appears 

 to me a project without the slightest chance 

 of success: the Bee would stubbornly refuse 

 such a dwelling or would content herself with 

 entrusting only a very small portion of her 

 eggs to it. On the other hand, with narrow 

 but short cavities, success, without being easy, 

 seems to me at least quite possible. Guided by 

 these considerations, I embarked upon the 

 most arduous part of my problem: to obtain 

 the complete or almost complete permutation 

 of one sex with the other; to produce a laying 

 consisting only of males by offering the 

 mother a series of lodgings suited only to 

 males. 



Let us in the first place consult the old nests 

 of the Mason-bee of the Shrubs. I have said 

 that these mortar spheroids, pierced all over 

 with little cylindrical cavities, are adopted 

 pretty eagerly by the Three-horned Osmia, 

 who colonizes them before my eyes with fe- 

 males in the deep cells and males in the shal- 

 low cells. That is how things go when the 



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