214 
ANIMAL INTELLIGENCE. 
angle with that tube, and terminates blindly just below 
the surface of the soil. At its point of junction with oi 
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 Lube : 
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 moss, 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 AT. ccementaria , I found, on revisiting the 
1 Harvesting Ants and Trap-door Spiders , p. 120 
