110 THE WONDERS OF INSTINCT 



They explore the metal receptacle for some time, seek- 

 ing an entrance. Finding naught that enables them to 

 reach the coveted morsel, they decide to lay their eggs 

 on the tin, just beside the aperture. Sometimes, when 

 the width of the passage allows of it, they insert the 

 ovipositor into the tin and lay the eggs inside, on the 

 very edge of the slit. Whether outside or in, the eggs 

 are dabbed down in a fairly regular and absolutely white 

 layer. 



We have seen the Bluebottle refusing to lay her eggs 

 on the paper bag, notwithstanding the carrion fumes of 

 the Linnet enclosed ; yet now, without hesitation, she lays 

 them on a sheet of metal. Can the nature of the floor 

 make any difference to her? I replace the tin lid by a 

 paper cover stretched and pasted over the orifice. With 

 the point of my knife I make a narrow slit in this new 

 lid. That is quite enough : the parent accepts the paper. 



What determined her, therefore, is not simply the 

 smell, which can easily be perceived even through the un- 

 cut paper, but, above all, the crevice, which will provide 

 an entrance for the vermin, hatched outside, near the 

 narrow passage. The maggots' mother has her own 

 logic, her prudent foresight. She knows How feeble her 

 wee grubs will be, how powerless to cut their way through 

 an obstacle of any resistance; and so, despite the tempta- 

 tion of the smell, she refrains from laying, so long as 

 she finds no entrance through which the new-born worms 

 can slip unaided. 



I wanted to know whether the color, the shininess, the 

 degree of hardness and other qualities of the obstacle 



