largely upon the age and size of the spider.

[84] _Science_, 20th January 1893.

When the spider has decided upon a location, which is always in clay,
adobe or stiff soil, he excavates the shaft by means of the sharp
horns at the end of his mandibles, which are his pick and shovel and
mining tools. The earth is held between the mandibles and carried to
the surface. When the shaft is of the required size, the spider
smoothes and glazes the wall with a fluid which is secreted by itself.
Then the whole shaft is covered with a silken paper lining, spun from
the animal's spinnerets.

The door at the top of the shaft is made of several alternate layers
of silk and earth, and is supplied with an elastic and ingenious
hinge, and fits closely in a groove around the rim of the tube. This
door simulates the surface on which it lies, and is distinguishable
from it only by a careful scrutiny. The clever spider even glues earth
and bits of small plants on the upper side of his trap-door, thus
making it closely resemble the surrounding surface.

The spider generally stations itself at the bottom of the tube. When,
by tapping on the door, or by other means, a gentle vibration is
caused, the spider runs to the top of his nest, raises the lid, looks
out and reconnoitres. If a small creature is seen, it is seized and
devoured. If the invader is more formidable, the door is quickly
closed, seized and held down by the spider, so that much force is
required to lever it open. Then, with the intruder looking down upon
him, the spider drops to the bottom of his shaft.

It has been found by many experiments that when the door of his nest
is removed, the spider can renew it five times--never more than that.
Within these limitations, the door torn off in the evening was found
replaced by a new one in the morning. Each successive renewal showed,
however, a greater proportion of earth, and a smaller proportion of
silk, until finally the fifth door had barely enough silk to hold the
earth together. The sixth attempt, if made, was a failure, because the
spinnerets had exhausted their supply of the web fluid. When the poor
persecuted spider finds his domicile thus open and defenceless, he is
compelled to leave it, and wait until his stock of web fluid is
renewed.[85]

[85] The Trap-door Spiders of various parts of the world
have been carefully studied, and the gradual development of
their skill traced through various speci