214 ANIMAL INTELLIGENCE. 



angle with that tube, and terminates blindly just below 

 the surface of the soil. At its point of junction with or 

 departure from the main tube it is provided with a trap- 

 door resembling that which closes the orifice of the main 

 tube, and of such a size and arrangement that when closed 

 against the opening of the branch tube it just fills that 

 opening ; while when turned outwards, so as to uncork 

 this opening, it just fills the diameter of the main tube : 

 the latter, therefore, is in this species provided with two 

 trap-doors, one at the surface of the soil, and the other at 

 the fork of the branched tube. 



Each species of trap-door spider is very constant in 

 building a particular kind of trap-door ; but among the 

 different species there are four several kinds of trap- 

 doors to be distinguished. 1st. The single-door cork 

 nest, wherein the trap-door is a thick structure, and fits 

 into the tube like a cork into a bottle. 2nd. The single- 

 door wafer nest, wherein the trap-door is as thin as a 

 piece of paper. 3rd The double-door unbranched nest, 

 wherein there is a second trap-door situated a few inches 

 below the first one. And 4th, the double-door branched 

 nest already described. In all cases the trap-doors open 

 outwards, and when the nest is placed, as it usually is, on 

 a sloping bank, the trap-door opens upwards ; hence 

 there is no fear of its gaping, for gravity is on the side of 

 holding it shut. 



The object of the trap-door is to conceal the nest, and 

 for this purpose it is always made so closely to resemble 

 the general surface of the ground on which it occurs, that 

 even a practised eye finds it difficult to detect the struc- 

 ture when closed. In order to make the resemblance to 

 the surrounding objects as perfect as possible, the spider 

 either constructs the surface of its door of a portion of 

 leaf, or weaves inoss, grass, &c., into the texture. Mog- 

 gridge says, 1 



Thus, for example, in one case where I had cut out a little 

 clod of mossy earth, about two inches thick and three square 

 on the surface, containing the top of the tube and the moss- 

 covered cork door of N. ccementaria, I found, on revisiting the 



1 Harvesting Ants and Trap-door fyidcrs, p. 120. 



