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 connec ts 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. 1 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 

 the base. 



The opposing surface is that of the humeral joint 



m\ n 



FIG. 301. FIG. 302. 



FIG. 301. Right falx of Lin- 

 yphia tenebricola, male, 



viewed obliquely from the o f eacn p a i pus (Fig. 302), which is marked with a 



right side. FIG. 302. Hu- 

 meral joint of left palp, more or less regular series of curved grooves deep 

 showing spines on the enoug h to give the appearance of serration on its side 



inside alone, and at the 



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

 ter campbeii.) joint, close to its base, is a curved enlargement, and on 



the top a prominent, horny, somewhat triangular, knob like plate, witli 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 Aranea3 does not imply that they are mute. It is a 

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

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

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

 they would be pronounced stridulating organs. 2 



1 Linyphia terricola Blkw., or Linyphia tennuis Blkw. 2 Op. cit., page 155. 



