THE BLUEBOTTLE 117 



thick. The jar has a wide mouth and is left quite open. 

 Let whoso come that will, attracted by the smell. The 

 Bluebottles are not long in inspecting what I have pre- 

 pared for them : they enter the jar, go out and come back 

 again, inquiring into the invisible thing revealed by its 

 fragrance. A diligent watch enables me to see them 

 fussing about, exploring the sandy expanse, tapping it 

 with their feet, sounding it with their proboscis. I leave 

 the visitors undisturbed for a fortnight or three weeks. 

 None of them lays any eggs. 



This is a repetition of what the paper bag, with its 

 dead bird, showed me. The Flies refuse to lay on the 

 sand, apparently for the same reasons. The paper was 

 considered an obstacle which the frail vermin would not 

 be able to overcome. With sand, the case is worse. 

 Its grittiness would hurt the new-born weaklings, its dry- 

 ness would absorb the moisture indispensable to their 

 movements. Later, when preparing for the metamor- 

 phosis, when their strength has come to them, the grubs 

 will dig the earth quite well and be able to descend ; but, 

 at the start, that would be very dangerous for them. 

 Knowing these difficulties, the mothers, however greatly 

 tempted by the smell, abstain from breeding. As a 

 matter of fact, after long waiting, fearing lest some 

 packets of eggs may have escaped my attention, I inspect 

 the contents of the jar from top to bottom. Meat and 

 sand contain neither larvae nor pupae : the whole is abso- 

 lutely deserted. 



The layer of sand being only a finger's-breadth thick, 

 this experiment requires certain precautions. The meat 



