318 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



has no chitinous extension covering the abdominal union. In the female 

 of this species, unlike Guttata, there is no trace of these organs. 



Of course, any sounds which might be produced by the organs thus 



described, must be occasioned by the flexion and extension of the two 



principal parts of the body; that is to say, by the drawing back 



°^ , and forward, within the socket, of the cartilaginous pedicle which 



are Made connects the thorax with the abdomen. But Mr. Campbell has 



also discovered an apparatus which he ventures to call stridu- 



lating, seated on the falces and palps in both sexes of Linyphia tene- 



brosus.i These are of a different structure from those 



heretofore described. On the outer side of the basal 



joint of each falx are about twenty parallel transverse 



chitinous bands, placed so that their inferior edges are 



free. (Fig. 301.) The effect, when viewed from the 



front, is that each falx has a distinctly serrated outer 



edge, which becomes more and more decided towards 



F,o.301. P.G.302. ^ijg ,^^gg_ 



Fig. 301. Right falx of Lin- . • ^i x <■ .i i i • • i 



yphia tenebricoia, male, 1 he opposiiig surtacc IS that ot the humcrai joint 



viewed obliquely from uie ^f g^ch palpus (Fig. 302), wliich is marked with a 



right side. Fig. 302. Hu- I i v to " 



merai joint of left palp, iiiore or Icss regular series of curved grooves deep 

 showing spines on the enough to givc the appearance of serration on its side 



inside alone, and at the ... 



top the horny plate. (Af- Under a two-tliird objective. On the under side of this 

 ter Campbell.) joiiit, closc to its basc, is a curvcd enlargement, and on 



the top a prominent, horny, somewhat triangular, knob like plate, with a 

 rounded apex. This differs in form, size, elevation, and position from the 

 chitinous prominences usually seen in connection with spines, of which 

 there is one near each side, but of which, in some individuals, it is inde- 

 pendent. 



The above described organs persist in all adult members of this species; 

 but those on the palps of females are not so highly developed, the chief 

 difference being the size of the enlargement at the base of the third joint. 

 When confined in a glass tube, Mr. Campbell observed that these spiders 

 often move their palps backward and forward, with a slight rotary motion, 

 in such a manner that the horny plate crosses the bands on the falces. 

 But he had been unable, even with the aid of the microphone, to detect 

 sounds in connection with these movements. 



Mr. Campbell adds the suggestion that the absence of specialized stridu- 

 lating organs in most Araneffi does not imply that they are mute. It is a 

 common practice with many to rub the falces against the maxilliE ; and 

 were the serrated edge of these latter found in another jiart of the body, 

 similarly opposed to a hard, toothed, chitinous surface, it is most likelj' 

 they would be pronounced stridulating organs.^ 



' Linyphia teriicola Blkw., or IJnypliia U'linuis lUUw. - Oj). cit., page 15.5. 



