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ANIMAL LIFE-HISTORIES 



tail out of the water, spreading her spinnerets, and entanghng 

 a small air-bubble between them. Diving down, she carries 

 the bubble to the stem selected as the site of the dwelling, and 

 leaves it clinging there. By successive additions the mass of 

 air becomes large enough for her purpose, and a web is then 

 spun over it to constitute the lining of the nest. Over this 



Fig. 895. — Trap-door Spiders [Cteniza ccemeninria) and Nests 



liquid silk is smeared, which soon hardens into an impervious 

 membrane. Mooring lines complete the structure. The spider 

 is, of course, able to introduce fresh air when necessary. 



The Trap-door Spiders (Ctenizidcz, fig. 895) construct homes 

 in many cases by digging a cylindrical hole in the ground, 

 smoothing its interior, and adding a silken lining. A neat lid 

 is then constructed of a mixture of earth and silk. It is smooth 

 on its under side, but rough e.xternally, so as to exactly match 

 its surroundings, and is provided with a silken hinge. In some 



