Larval Dimorphism 



To begin with, it is evident that the mother 

 cannot lodge her egg in the cell of the Mason- 

 bee, which has been long closed and barricaded 

 with a cement wall by the time that the An- 

 thrax makes her appearance. To penetrate it, 

 she would have to become an excavating-tool 

 once more and resume the cast-off rags which 

 she left behind in the exit-window; she would 

 have to retrace her steps, to be reborn a pupa; 

 and life knows none of these retrogressions. 

 The full-grown insect, if endowed with claws, 

 mandibles and plenty of perseverance, might 

 at a pinch force the mortar casket; but the 

 Fly is not so endowed. Her slender legs 

 would be strained and deformed by merely 

 sweeping away a little dust; her mouth is a 

 sucker for gathering the sugary exudations of 

 the flowers and not the solid pincers needed 

 for the crumbling of cement. There is no 

 auger either, no bore copied from that of the 

 Leucospis, no implement of any kind that can 

 work its way into the thickness of the wall and 

 dispatch the egg to its destination. In short, 

 the mother is absolutely incapable of settling 

 her eggs in the chamber of the Mason-bee. 



Can it be the grub that makes its own way 

 into the store-room, that same grub which we 

 have seen draining the Chalicodoma with its 



79 



