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Page:Popular Science Monthly Volume 38.djvu/205

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shutting of the nest until his purpose was accomplished. 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.

One of the most curious examples of relation of structure to enemies, or perhaps of the reaction of hostile environment and agents upon structure, is found in a territelarian spider (Cyclocosmia truncata). This aranead, according to Hentz, dwells like others of its kind in cylindrical cavities in the earth. Though many specimens were found, he never saw any lid or closure to the aperture of its dwelling. The very singular formation of its abdomen, which is as hard as leather behind, and is truncated to form a perfect circle, induced Hentz to believe that when in danger it closes its dwelling with that part of its body instead of with a trap-door or lid. This conjecture,

PSM V38 D205 Cyclocosmia truncata.png
Fig. 6.Cyclocosmia truncata.
Fig. 7.—Side View of same. (After Hentz.) Fig. 8.—Diagrammatic View of Truncata, closing her Burrow with her Abdomen.

of course, needs confirmation, though it seems not improbable; and one may imagine the intellectual confusion of a pursuing enemy which finds its prey suddenly disappearing within a hole in the ground, but which, when investigated, presents nothing but a level surface where certainly a hole ought to have been! The dorsal view of the spider is given at Fig. 6, the side view at Fig. 7; and a diagrammatic section view of the creature is drawn at Fig. 8, as it probably would appear when closing up the opening to its burrow.