DEFENSES OF BURROWING SPIDERS. 



J 93 



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 (Cyclo- 

 cosmia truncata). This aranead, according to Hentz, dwells like 

 others of its kind in cylindrical cavities in the earth. Though 



many specimens were found, he nev- 

 er 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 con- 





Fig. 6. Cyclocosmia truncata. 



Fig. 7. Side View of same. 

 Hentz.) 



(After 







Fig. 8. Diagrammatic View of Truncata, clos- 

 ing her Burrow with her Abdomen. 



jecture, of course, needs confirmation, though it seems not improb- 

 able ; 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. 



