xi] THERAPHOSID SPIDERS 97 



tunnel at a depth of some three inches, and reaching 

 the surface perhaps two inches away from the trap- 

 door, so that the whole excavation is Y-shaped. This 

 branch tube is permanently closed by a thin sheet 

 of silk and earth, which, however, it would not be 

 difficult to break through if it were urgent for the 

 spider to escape while the enemy was exploring the 

 main tunnel. 



But a more interesting case is the occurrence of 

 another trap-door some way down the tube. If the 

 tube is tmbranched, this forms merely a second 

 line of defence if the outer door is forced, but in the 

 case of a branched tube the additional door hangs at 

 the fork of the Y, and is so shaped as to form a 

 perfect valve, so that the spider, by holding it against 

 one or the other side of the tunnel, can connect the 

 bottom limb of the Y with either fork at will, leaving 

 to the intruder a beautifully smooth-lined tube to 

 explore, with no hint of the possibility of escape in 

 other directions. 



There are sometimes other complications in the 

 ramification of the tube, but these need not detain 

 us. Each species of spider adheres to its own 

 particular type of architecture, and may safely in 

 a given neighbourhood be identified by its nest. 



As with the Lycosidae, the burrowing is all done 

 by the mandibles, but here the first joint the handle 

 of the penknife is of more importance than the 



w. s. 7 



