ii4 THE WONDERS OF INSTINCT 



From time to time the Bluebottle and the Flesh-fly 

 perch on the trellis-work, make a short investigation and 

 then decamp. Throughout the summer season, for three 

 whole months, the apparatus remains where it is, without 

 result: never a worm. What is the reason? Does the 

 stench of the meat not spread, coming from that depth? 

 Certainly it spreads : it is unmistakable to my dulled nos- 

 trils and still more so to the nostrils of my children, whom 

 I call to bear witness. Then why does the Flesh-fly, who 

 but now was dropping her grubs from a goodly height, 

 refuse to let them fall from the top of the column twice 

 as high ? Does she fear lest her worms should be bruised 

 by an excessive drop? There is nothing about her to 

 point to anxiety aroused by the length of the shaft. I 

 never see her explore the tube or take its size. She 

 stands on the trellised orifice ; and there the matter ends. 

 Can she be apprised of the depth of the chasm by the com- 

 parative faintness of the offensive odors that arise from 

 it? Can the sense of smell measure the distance and 

 judge whether it be acceptable or not ? Perhaps. 



The fact remains that, despite the attraction of the 

 scent, the Flesh-fly does not expose her worms to dis- 

 proportionate falls. Can she know beforehand that, 

 when the chrysalids break, her winged family, knocking 

 with a sudden flight against the sides of a tall chimney, 

 will be unable to get out? This foresight would be in 

 agreement with the rules which order maternal instinct 

 according to future needs. 



But, when the fall does not exceed a certain depth, 

 the budding worms of the Flesh-fly are dropped without 



