The Distribution of the Sexes 



The Horned Osmla gives us the following 

 average dimensions : 



2« = 15 mm./ 2b = g mm.' in the females; 

 2a = 12 mm.,^ 2b = "] mm.* in the males. 



Once again, the ratio between 15 X 9 X 

 9 = 1215 and 12 X 7 X 7 = 588 lies be- 

 tween 2 to I and 3 to I. 



Besides the Bees who arrange their laying 

 in a row, I have consulted others whose cells 

 are grouped in a way that makes it possible 

 to ascertain the relative order of the two 

 sexes, though not quite so precisely. One of 

 these is the Mason-bee of the Walls. I need 

 not describe again her dome-shaped nest, built 

 on a pebble, which is so well-known to us.^ 



Each mother chooses her stone and works 

 on it in solitude. She is an ungracious land- 

 owner and guards her site jealously, driving 

 away any Mason who even looks as though 

 she might alight on it. The inhabitants of 

 the same nest are therefore always brothers 

 and sisters; they are the family of one mother. 



^.585 inch. — Translator's Note. 

 2.351 inch. — Translator's Note. 

 8.468 mch.— Translator's Note. 

 <.273 inch. — Translator's Note. 

 ''Ci. The Mason-bees: chap. i. — Translator's Note. 



Ill 



