Gitims.—On the Habits of the Trap-door Spider, 233 
whereas, the nests at the a and the one at the Stable, had, by far, 
the toughest and best lining, though the soil is such as to remain secure 
and solid without any protecting web. This leads me to think that the 
lining of the nest serves other, and more important, purposes in the house- 
hold economy of the inmate, than protection from the clay tumbling in. 
Probably prevention of damp, or exclusion of worms, ants, and other 
under-ground intruders, and the age of the nest, have all something to do 
withit. The lining is always more or less incorporated with the soil, so 
that it is difficult quite to separate them, and it is invariably neatly finished 
off, and fitted to the bevelled mouth (when it occurs), as seen in the speci- 
mens before you. The lining is continued up on one side forming the hinge, 
and widening out in a circular form into the trap-door. At the hinge, and 
for a short distance below it, the lining is often double, or thickened, but 
this is not the only, or principal cause of the spring which all the doors 
have, as indicated by some writers. 
Hinge of the Trap-door. 
That the trap-doors have always a decided spring causing them to fall 
quickly, and with force, into their position, and preventing them from 
tumbling back open, is beyond question, as any of you can test for your- 
selves, by lifting up any one of those now before you, with the edge of a 
pen-knife. But this is caused mainly, I feel sure, by the peculiar shape of the 
hinge, and not by its thickness. The hinge and trap-door is formed, as I 
have said, by the extension upwards of the silk lining of the nest, and by 
its being folded over at right angles to the tube. The mouth of the nest is, 
you will recollect, circular and the hinge is not simply a tag connecting the 
lining with the door, but extends along from a fourth to a sixth of the 
whole circumference of the mouth. It is therefore in reality an are of a 
circle of from 90° to 60° in length. If the circular lining of the nest were 
simply folded over, as I have said, it would cause a fold or loose crease at 
both sides of the hinge, though it would be tight in the centre. Now this 
is not the case, but the hinge is equally continuous and tight at all parts, it 
is, in fact, woven into a bend like the heel of a stocking, and not merely 
folded over. The consequence is, when the trap-door, which is stiff, is 
lifted, the outer edges of the hinge are opened further than the centre, and 
are strained tight, and when the door is let go, the elasticity of the material 
of the hinge brings down the door with a spring. It is almost impossible 
to turn the trap-doors right over backwards, without injury to theshinge, or 
to keep them open, without tying them back to something near. I feel 
sure you cannot but be struck with wonder at this i ingenious mechanical 
contrivance, so simple in construction, and yet so well adapted to the 
— and circumstances of the case, and so effective for all = purposes 
