354 ARACHNIDA ARANEAE CHAP. 



of the body, but the operation is effected by a special apparatus. 

 These spiders are cribellate, and in front of the six ordinary 

 spinnerets there are a pair of perforated plates connected with a 

 large number of additional minute spinning glands (see Fig. 182, 

 p. 326). In conjunction with this, the female possesses on the last 

 joint but one of each hind leg a curious comb-like arrangement 

 of spines, the " calamistrum." The animal constructs a sort of 

 skeleton web by means of its ordinary spinnerets, and when this 

 is completed it combs out silk from the cribellum by means of 

 the calamistrum, using each hind leg alternately, and distributes 

 it with a curling motion upon the scaffolding prepared for it, 

 a nearly opaque web being the result. The silk from the 

 cribellum is of an adhesive nature, and renders escape from 

 the web very difficult. 



Spiders' Nests and Retreats. All Spiders construct some 

 description of nest, and often display great ingenuity in build- 

 ing them. Perhaps none are more curious than those of the 

 burrowing Aviculariidae, a family which includes the interesting 

 " Trap-door Spiders." They are nocturnal in their habits, about 

 which, consequently, little is known, but their nests have been 

 carefully studied, especially by Moggridge, who found them in 

 considerable abundance in various districts of the Riviera. 



The jaws of these spiders are especially adapted for digging, 

 and with them a hole is excavated in the ground to the depth 

 of several inches, and wide enough to allow the animal to turn. 

 This is carefully lined with silk which the spider throws against 

 the sides from its long and upturned posterior spinnerets. But 

 the chef d'ceuvre of the whole structure is a lid or door w r hich 

 protects the entrance to the tube. There are two types of door 

 which find favour with different species the wafer and the 

 cork type, as Moggridge has named them. The former consists 

 of a thin circular or oval sheet of silk which flaps down loosely 

 over the tube-entrance, with which it is connected by a hinge- 

 like attachment. A trap-door of the cork type is a more com- 

 plicated structure, being of considerable thickness and having a 

 bevelled edge, so that it fits into the tube like a plug. Like the 

 wafer door, it possesses a silken hinge. 



To form the wafer door, the spider covers the entrance to the 

 tube with a closely-woven layer of silk, which it afterwards bites 

 away at the edge, except at the point where the hinge is to be. 



