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the Nest of Cteniza nidulans. 
about two-thirds of the whole length, is chiefly formed of two stout 
coats, each composed of numerous fine layers of webbing, but the 
entire thickness does not exceed that of strong cartridge paper. 
Those parts of its dwelling which would be liable to be injured 
by the effects of weather, pressure of the surrounding earth, or 
from the assaults of enemies, the insect forms particularly strong ; 
as the lid, the neck of the tube, and the convex upper surface of 
the curved portion at the bottom, while all the remainder is com- 
paratively very thin. The lid and the parietes of the neck for an 
inch from the aperture are at least an eighth of an inch in thick- 
ness, and have strata of the red dirt interposed between the layers 
of webbing, below which the latter becomes gradually thinner. 
It is remarkable that the strength bestowed upon the surface at 
the lower end, serves the important purpose of protecting the nest 
and its tenants from the downward pressure of the soil. 
Those parts of this ingeniously contrived fabric which more 
strikingly call for our particular admiration are, the licl, and a val- 
vular apparatus that is found inside, and immediately below the 
hinge. 
The Lid bears some analogy to the upper shell of the oyster, 
inasmuch that the upper surface of it is rough, laminated, thick 
and strong near the hinge, and becomes gradually thinner towards 
the surrounding edges. The elastic force with which the lid, upon 
being opened, closes of itself, is principally accomplished by a fold 
or duplicature of the webbing at each end or angle of the hinge, 
so that upon raising the lid, which cannot be done without vio- 
lence much beyond a right angle with the aperture, this fold is 
also opened, and the threads of the webbing are put upon the 
stretch in proportion to the extent to which the lid is elevated, 
and which, doubtless, in its proper use, by its lawful owner, never 
exceeds the insect’s requirements. 
The internal under-side of the lid is exceedingly firm and 
smooth, wdiich contributes, in connection with the prominent con- 
vex form, and highly polished surface, of the thorax of the spider, 
to diminish friction and resistance as much as possible, and thus 
to facilitate at all times the expeditious exit and entrance of the 
insect. 
Valvular apparatus . — About two months since I obtained a 
supply of four fresh nests, and, being tolerably well stocked be- 
fore, I could afford to open them longitudinally, in order to exa- 
mine their internal structure. One of them had no appearance 
whatever of any valves, but the other exhibited a beautiful in- 
stance of two regularly formed ones ; one placed immediately be- 
