Gruties.—On the Habits of the Trap-door Spider. 235 
This is, however, largely owing to the difficulty of transporting the raised 
ones, they get broken off so easily in carrying and packing them. Some 
also that are really flat, appear as if the whole mouth of the tube and the 
trap-door were raised above the ground, in consequence of the breaking 
away of the loose soil round about. Of the true raised trap-doors, Nos. 1, 
2, 5, 30, and 22, may be taken as fair specimens. Nos. 1 and 2 have 
this specialty, that the trap-doors are larger than the mouth of the nest, 
and overlap somewhat. No. 1 especially, overlaps very considerably. The 
mouth of the nest is only five lines in diameter, whilst the trap-door is eight 
lines, and the long way of the lidis from the hinge to the front. The cause 
of this is, that the nest itself, goes into the ground at an acute angle, and not 
straight down, and consequently the section of the cylindrical tube is elong- 
ated thus where the trap-door covers it. The spider has evidently calculated 
upon this, and so made its trap-door elongated in order to meet the require- 
ments of the sloped section. It is quite likely too, that these are instances 
where the spider intended to enlarge her nest, and like a prudent and wise 
builder, provide before hand against rain, and enemies getting in by the hole, 
whilst it was being enlarged, and so made her trap-door to extend over the 
area which she intended should ultimately form the mouth of her nest; 
but that like many other intentions with referencet o houses, it was never 
carried out. Hither this, or it is an instance of bungling workmanship, 
or over calculation on the part of the architect, of the length of a sloped 
section of a cylinder, and the Trap-door Spider is not the only architect or 
artificer that commits this sort of blunder. In any case, it is a 
variation from the general rule, and displays a remarkable capacity on the 
part of the spider, for estimation and foresight, and for adaptation to 
special circumstances as they arise. The second distinction, those that 
are flat, is more often accompanied by the beveled or cup-like form of 
the mouth of the tube, and the majority of clay or soil covered trap- 
doors are exactly coincident with the surface of the ground. Some 
(though only a few), are depressed, but this, I suspect, is an evidence of 
incomplete or bungling workmanship, and consequent weakness, more 
especially as in such cases, the excavated soil is always close by the mouth 
of the nest. 
Trap-doors, what made of. 
The trap-doors are made of several layers or plies of web, between 
which earth, grass, or other substances are woven to. thicken and stiffen 
them, * 
General remarks on mode of concealment. . 
We come now to what is by far the most wonderful thing about these 
Spiders, and that is the modes of concealment which they practise for the 
prevention of the discovery of their nests. This is accomplished in two 
