ENEMIES AND THEIR INFLUENCE. 



415 



there would be an alternate opening and shutting of the nest until his 

 purpose was accomplished. 1 



It is the habit, according to Moggridge, Simon, and all observers who 

 have noted the point at all, for these animals to hang back downward 

 upon the inner surface of the door. In many nests which I have seen 

 there are holes along the outer or free edge of the door the part directly 

 opposite the hinge which mark the points at which, probably, the fangs 

 of the spider had been fixed, in order to give it a strong purchase against 

 intruders. These holes are usually three, and show with great distinct- 

 ness, even in the photograph from which Fig. 352 was drawn, which is 

 the upper part of the nest of our California Trapdoor spider, Cteniza cali- 

 fornica. 



XII. 



One of the most remarkable developments of industrial skill under 

 hostile influences is that described by Moggridge in the inner door of 

 Nemesia congener. 2 The general character 

 of the nest is that of a tube ten or twelve 

 inches long, drilled horizontally into the side 

 of a slope, and closed outside with a wafer 

 door. This horizontal burrow bends abrupt- 

 ly, and is continued perpendicularly down- 

 ward, with a short branch extending upwards 

 towards the surface. At the juncture or 

 bending is suspended a wedge shaped double 

 door, which tapers from below upwards to a 

 hinge. The door has two crowns, separated 

 from each other by the gusset like web of 

 silk that connects the door on either side with 

 the lining of the main tube. One of these 

 crowns fits into and closes the main tube, 

 while the other fits into the aperture of the 

 upward branch. This swinging door acts very 

 much in the fashion of a valve, dropping 

 down to close the entrance from the first to 

 the second tube, and swinging upward in such 

 a way as to protect the spider when it is 

 cowering within the upper branch of the per- 

 pendicular tube. The wedge like structure of this door is seen not only 

 in the adult spider's nest, but in even more exaggerated shape in the nests 

 of the younger ones. 



FIG. 354. 



FIG. 353. Cyclocosmia truncata. FIG. 

 354. Side view of same (After Hentz.) 



' Cuvier, Animal Kingdom, Lond. ed., Vol. XIII., Supplement, page 4C5. 

 - Trapdoor Spiders, Supplement, page 223 and pi. xvi. 



