256 THE WONDERS OF INSTINCT 



swarm starts with the converse of the normal order. 

 This inversion is continued, at no matter what period, 

 from the beginning to the end of the operations. The 

 series which, according to rule, would begin with females 

 now begins with males. Once the larger gallery is 

 reached, the laying is pursued in the usual order. 



We have advanced one step and that no small one: 

 we have seen that the Osmia, when circumstances re- 

 quire it, is capable of reversing the sequence of the sexes. 

 Would it be possible, provided that the tube were long 

 enough, to obtain a complete inversion, in which the 

 entire series of the males should occupy the narrow gal- 

 lery at the back and the entire series of the females the 

 roomy gallery in front ? I think not ; and I will tell you 

 why. 



Long and narrow cylinders are by no means to the 

 Osmia's taste, not because of their narrowness but be- 

 cause of their length. Observe that for each load of 

 honey brought the worker is obliged to move backwards 

 twice. She enters, head first, to begin by disgorging the 

 honey-syrup from her crop. Unable to turn in a passage 

 which she blocks entirely, she goes out backwards, crawl- 

 ing rather than walking, a laborious performance on the 

 polished surface of the glass and a performance which, 

 with any other surface, would still be very awkward, as 

 the wings are bound to rub against the wall with their 

 free end and are liable to get rumpled or bent. She goes 

 out backwards, reaches the outside, turns round and goes 

 in again, but this time the opposite way, so as to brush 

 off the load of pollen from her abdomen on to the heap. 



