The Spiders' Exodus 173 



of passing. It is not a porous felt, but a fabric 

 as tough as that of the sack. Then by what 

 mechanism is the deUvery effected ? 



Observe that the disk of the hd doubles back 

 into a short fold, which edges into the orifice 

 of the bag. In the same way, the lid of a sauce- 

 pan fits the mouth by means of a projecting rim, 

 with this difference, that the rim is not attached 

 to the saucepan, whereas, in the Epeira's work, 

 it is soldered to the bag or nest. Well, at the 

 time of the hatching, this disk becomes unstuck, 

 lifts and allows the new-born Spiders to pass 

 through. 



If the rim were movable and simply inserted, 

 if, moreover, the birth of all the family took 

 place at the same time, we might think that the 

 door is forced open by the living wave of inmates, 

 who would set their backs to it with a common 

 effort. We should find an approximate image 

 in the case of the saucepan, whose lid is raised 

 by the boiling of its contents. But the fabric 

 of the cover is one with the fabric of the 

 bag, the two are closely welded; besides, the 

 hatching is effected in small batches, incapable 

 of the least exertion. There must, therefore. 



