TRAP-DOOR SPIDERS. 
117 
attached to the surface. The mouth of the tube is 
commonly dilated a little, so as to form a slightly re- 
curved brim or lip ; and the lid is sometimes a little 
convex internally, so as to fall more accurately into 
the mouth and close it. The thickening of the hinge 
by additional layers is, I think, accidental only, as, 
out of many specimens that I have examined, only 
one or two had such a structure. In the neatest 
examples, the lid is of equal thickness throughout its 
extent, agreeing also with the walls for the first few 
inches of their depth. 
One of peculiar compactness now before me I have 
slit open longitudinally with a pair of scissors in the 
manner spoken of above. The thickness of the sub- 
stance is in no place greater than y^^th of an inch, 
which is very regularly maintained throughout the 
lid and upper parts. The appearance at the cut 
edge closely resembles that of millboard so divided; 
the layers of which it is composed being very nume- 
rous and compact, especially towards the interior side, 
where they can scarcely be distinguished even with a 
lens. In this specimen there is what I cannot find in 
any of the others that I have examined. A row of 
minute holes, such as might be made by a very fine 
needle, are pierced around the free edge of the lid, 
and a double row of similar ones just within the 
margin of the tube. There are about fifteen or six- 
teen punctures in each series; and they penetrate 
through the whole substance, the light being clearly 
seen through each hole. Now, what is the object of 
these orifices ? I do not think, as I have somewhere 
seen suggested, that they are intended to afibrd a 
