The Spiders' Exodus 



formed of compact white satin, an insuperable 

 barrier. It opens into a round orifice wherein 

 is bedded a lid of the same material, through 

 which the feeble beasties would be incapable 

 of passing. It is not a porous felt, but a fab- 

 ric as tough as that of the sack. Then by 

 what mechanism is the delivery effected? 



Observe that the disk of the lid doubles 

 back into a short fold, which edges into the 

 orifice of the bag. In the same way, the lid of 

 a saucepan fits the mouth by means of a pro- 

 jecting 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 in- 

 serted, if, moreover, the birth of all the fam- 

 ily took place at the same time, we might 

 think that the door is forced open by the liv- 

 ing 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 



205 



