254 THE WONDERS OF INSTINCT 



evitable. The female Osmiae, thongh nearly always 

 larger than the males, present marked differences among 

 one another: some are bigger, some are smaller. I had 

 to adjust the width of the narrow galleries to Bees of 

 average dimensions. It may happen therefore that a 

 gallery is too small to admit the large-sized mothers to 

 whom chance allots it. When the Osmia is unable to 

 enter the tube, obviously she will not colonize it. She 

 then closes the entrance to this space which she cannot 

 use and does her laying beyond it, in the wide tube. 

 Had I tried to avoid these useless apparatus by choosing 

 tubes of larger caliber, I should have encountered an- 

 other drawback : the medium-sized mothers, finding them- 

 selves almost comfortable, would have decided to lodge 

 females there. I had to be prepared for it: as each 

 mother selected her house at will and as I was unable to 

 interfere in her choice, a narrow tube would be colonized 

 or not, according as the Osmia who owned it was or was 

 not able to make her way inside. 



There remain some forty pairs of tubes with both 

 galleries colonized. In these there are two things to take 

 into consideration. The narrow rear tubes of 5 or 55^2 

 millimeters ^ — and these are the most numerous — con- 

 tain males and males only, but in short series, between 

 one and five. The mother is here so much hampered in 

 her work that they are rarely occupied from end to end ; 

 the Osmia seems in a hurry to leave them and to go and 

 colonize the front tube, whose ample space will leave her 

 the liberty of movement necessary for her operations. 



1 .195 to .214 inch. — Translator's Note. 



