1612 THE STORY OF THE UNIVERSE 



retreat, settle down in it, and continue their dream 

 and their digestion till evening, when they again set 

 forth to prowl. 



The trap-door spiders of the south of Europe 

 construct burrows which have been studied with 

 great care and in much detail by Moggridge. He 

 found that there were four chief types of burrow. 

 The whole burrow as well as the door are lined with 

 silk, which also forms the hinge. The great art of 

 the trap-door spider lies in her skilful forming of 

 the door, which fits tightly, although it opens widely 

 when she emerges, and which she frequently holds 

 down when an intruder strives to enter, and in the 

 manner with which the presence of the door is con- 

 cealed, so as to harmonize with surrounding objects. 

 Perhaps in no case is the concealment more complete 

 than when dead leaves are employed to cover the 

 door. In some cases a single withered olive leaf is 

 selected, and it serves to cover the entrance; in other 

 cases several are woven together with bits of wood 

 or roots. 



The trap-door spider (Mybale henzii, Girard), 

 which is widely diffused in California, forms a sim- 

 ple shaft-like burrow, but, like the European trap- 

 door spider, it is very skilful in forming an entrance 

 and in concealing its presence. Its habits have 

 lately been described by D. Cleveland of San Diego. 

 In the adobe land hillocks are numerous; they are 

 about a foot in height, and some three or four feet 

 in diameter. These hillocks are selected by the 

 spiders apparently because they afford excellent 

 drainage, and can not be washed away by the winter 



