234 THE WONDERS OF INSTINCT 



Distribution of the Sexes 



Does the insect which stores up provisions proportion- 

 ate to the needs of the egg which it is about to lay know 

 beforehand the sex of that egg? Or is the truth even 

 more paradoxical? What we have to do is to turn this 

 suspicion into a certainty demonstrated by experiment. 

 And first let us find out how the sexes are arranged. 



It is not possible to ascertain the chronological order 

 of a laying, except by going to suitably chosen species. 

 Fortunately there are a few species in which we do not 

 find this difficulty: these are the Bees who keep to one 

 gallery and build their cells in stories. Among the num- 

 ber are the different inhabitants of the bramble-stumps, 

 notably the Three-pronged Osmise, who form an excel- 

 lent subject for observation, partly because they are of 

 imposing size — bigger than any other bramble-dwellers 

 in my neighborhood — partly because they are so plen- 

 tiful. 



Let us briefly recall the Osmia's habits. Amid the 

 tangle of a hedge, a bramble-stalk is selected, still stand- 

 ing, but a mere withered stump. In this the insect digs 

 a more or less deep tunnel, an easy piece of work owing 

 to the abundance of soft pith. Provisions are heaped up 

 right at the bottom of the tunnel and an egg is laid on 

 the surface of the food : that is the first-born of the fam- 

 ily. At a height of some twelve millimeters, 1 a partition 

 is fixed. This gives a second story, which in its turn 

 receives provisions and an egg, the second in order of 



1 About half an inch. — Translator's Note. 



