The Cocoon 301 



fabric, using silk as cement. The upper surface 

 is built more slowly : the grains are carried up 

 one by one and fixed on with the silken putty. 



This first layer of sand as yet embraces only 

 the front half of the cocoon, the half that ends 

 at the mouth of the bag. Before turning round 

 to work at the back half, the grub renews its 

 supply of materials and takes certain precau- 

 tions so as not to be hindered in its mason's 

 work. The sand outside, heaped up in front of 

 the entrance, might slip inside and embarrass the 

 builder in so narrow a space. The grub foresees 

 this possibility : it glues a few grains together 

 and makes a rough curtain of sand, which stops 

 up the orifice very imperfectly, but sufficiently 

 to prevent an accident. Having taken these 

 precautions, the larva works at the back half 

 of the cocoon. From time to time it turns 

 round to fetch fresh supphes from outside, tear- 

 ing a corner of the curtain that protects it 

 against the outer sand and grabbing through 

 this window the materials which it requires. 



The cocoon is still incomplete, wide open at 

 the big end ; it wants the spherical cap that is 

 to close it. For this final labour the grub takes 

 a plentiful supply of sand, the last supply of all, 

 and then pushes away the heap outside the 

 entrance. At the opening it now weaves a 

 silken cap, which fits the mouth of the primitive 



