280 ENTOMOLOGICAL NEWS. [November, 



After removing from live beetles all of those portions of the 

 elytra that could be reached by the pleural plates, it was found 

 that the insects could stridulate as loudly as before. 



Following out Riley's idea, the portion of the elytra that 

 could be rubbed by the pygidium was removed from several 

 live beetles and the same result was obtained as in the previous 

 experiment. 



As another experiment, melted paraffin was run in between 

 the edges of the abdomen and elytra. This on solidifying 

 effectually prevented any motion of the abdominal pleurities 

 or of the pygidium, but the beetles could still stridulate. 



Finally beetles from which both elytra had been entirely taken 

 away continued to produce the sound though but faintly. 



It was observed that with every raising of the abdomen there 

 was a simultaneous forward motion of the dorsal portion of the 

 fifth segment. Here, about half way from the center to each 

 lateral edge (see Fig. i, A) was found an ovate area about 

 4.5 mm. long by 2.5 mm. at its greatest breadth and with a 

 convex surface. This area, when magnified about 700 diame- 

 ters (Fig. 2), appeared as a regularly cross-lined surface not 

 unlike a rasp, but when examined in cross-section (Fig. 3), 

 was seen to be closely studded with erect stout spines, their 

 tips curving forward about .01 mm. in length at the center of 

 the area and shorter toward the boundaries. 



The only portion of the insect with which these areas could 

 come in contact to produce stridulation were not the elytra, 

 but the wings ; and so incisions were made near the base of 

 the elytra of live beetles and the wings removed through these 

 leaving the wing-covers still in place. When this had been 

 done the beetles were unable to produce any sound though 

 they continued to move their abdomens up and down in the 

 evident effort to stridulate. 



As a final experiment fresh beetles were taken and these areas 

 in turn were coated with paraffin and the result was silence. 



The wings were found to be more strongly chitinized at the 

 folds, and the portions of these that would come in contact 

 with the described areas of the abdomen were covered with 

 ridges running transversely to the axis of the body and with 

 short spines directed backward (Fig. 4). 



