ENEMIES AND THEIR INFLUENCE. 



417 



Chapter XII., puge 355.) Mr. Simon also attribute,s this use ol' the; tube 

 to the ants of northern Africa, particularly to Dolichoscaptus vittatus, 

 which drives into the earth a horizontal burrow that is considerably con- 

 tracted and bent towards the end in the form of a little cul de sac, which 

 is full of the debris of insects upon which the spider has fed. In one 

 locality this insect debris consisted almost wholly of the remains of Atta 

 barbara, the well known harvesting ant of Palestine and the Mediterra- 

 nean shores.' I do not see that the two facts are at all contradictory. 

 The use of the silk lined burrow as a decoy for curious insects in no- 

 wise hinders it from being also useful as a defense against enemies of 

 various sorts. 



One of the most curious examples of relation of structure to enemies, 

 or perhaps of the reaction of hostile environment and agents upon struct- 

 ure is found in a Territelarian spider, Cyclocosmia trun- 

 cata.* 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. Tlje 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 trapdoor or lid. This conjecture, of course, 

 needs confirmation, though it seems not im- 

 probable; 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, pre- 

 sents notliing but a level surface where cer- 

 tainly a hole ought to have been! The dorsal 

 view of the spider is given at Fig. 353 ; the side 

 view at Fig. 354 ; and a diagramatic section 

 view of the creature is drawn at Fig. 355, as it 

 probably would appear when closing up the 

 opening to its burrow. 



Another mode in which enemies may infiuencc the formation of habit 

 in spiders has been suggested by observing the manner in which certain 

 Theridioids defend their cocoons. Theridium differens, a pretty little spi- 

 der inhabiting leaves and foliage (Fig. 357), which makes a Hossy round 

 cocoon somewhat larger than itself (about a (juarter of an inch in diameter), 

 will grasp her cocoon in her mouth when annoyed by one's finger or by 



' " lOtiulo sill- k's lOspocPs lie )ii I'mnillo dos Avicularidre," of North Africa. Actes de la 

 See. Linn, do liordoiiux, Vol. XLII., ISSS, i)a<;o 11. 



^ Mygalc truncaUi, Hentz, Spiders U. S., page IG, pi. i., Fig. 1. 



Flo. 356. 



Fia. 357. 



Pio. 356. Theridium differcn.s, much 

 enhirged, RiaspiiiK her cocoon when 

 annoyed. Fio. 357. Cocoon nest of 

 same. (Natural size.) 



