[Footnote 66: Since writing the above I have learned, thanks to a better method which I have recently adopted for preserving the nests for examination, that sometimes the lower door, instead of being free within the tube and only attached to the lining by the hinge, is surrounded on either side by a delicate silk web, which extends from either edge of its lower surface to the silk walls of the tube below and forms a sort of double gusset. This admits of the movement of the lower door in the way described above, but perhaps serves, together with the solid appendage at the extremity of the free end of the door (that away from the hinge), to prevent the door from being driven too far in an upward direction and thus becoming so tightly jammed as to make the spider a prisoner in her own nest. I think it possible that the lower door is always attached to the tube in this way, but, as it parts readily from the silk on either side when the earth which supports the tube is removed, it very frequently appears to be free, as I have represented it in Plates IX., X., and XI.] When digging out these nests, after carefully removing the upper portion, I have frequently seen the lower door move across and block up the main tube in a mysterious manner, it being in reality pushed by the spider from below, and she may sometimes be captured at her post with her back set against the door. More frequently, when the spider finds that resistance is hopeless and sees the earth crumbling in, she drops to the bottom of her nest and lies there helpless, with her legs folded against her body like an embryonic creature; some, however, more savage than their neighbours, fly out and strike at the intruder with their fangs. [Illustration: _Plate X._] What then, it may be asked, is the use of the branch? I do not think that we can draw any safe conclusion from what takes place when we dig out a spider, as to what would occur if she were besieged by one of her natural enemies, such as ichneumons, sand-wasps, centipedes (_Scolopendra_), small lizards &c.[67] [Footnote 67: For some account of the principal enemies of spiders generally, see p. 134.] Let us suppose, however, that one of these creatures has found its way into the nest and is crawling down the tube. What will probably happen? Why, in the first place, the spider will slam the second door in the face of the intruder, and then, if worsted in the pushing match which follows, quickly draw this door back again and run up into the safety branch, when the enemy, after descending precipitately to the bottom of the main tube, will look in vain for the spider as it searches on its way up for the secret passage now closed by its trap-door. This is but a purely imaginary case, and it may be that the branch has some wholly different purpose.