Stridulatiiig-organ in an Egyptian Beetle. 



153 



Microscopical examination at once showed the position and 

 structure of the organ that causes the sound. It consists, on 

 the one hand, of two finely toothed or serrated ridges on each 

 side of the body, one running along the admedian edge of 

 the lateral inturned area of the elytron, the other along the 

 adjacent edges of the sterna of the abdominal somites 

 (figs. A, B, str.) ; and, on the other hand, of a smooth 

 angular crest traversing the postaxial side of the femur of the 

 third leg, and lying in a general way parallel to the long 

 axis of this segment (see fig. C, cr.). This crest is not a 



Stridulatiug-organ of Graphvpterus variecjatus (Fabr.). 



Ventral surface of right half of abdomen and of posterior somites 

 of thorax, f'^,/^ femora of second and third legs ; el, inturned 

 edge of right elytron ; sir., serrated stridulating-crests on eljtron 

 and adjacent margins of abdominal sterna. 



Piece of the right elytron (el.) and of one of the abdominal sterna {v), 

 ■with adjacent serrated stridulating-crests {str.). 



Fostaxial side of femur of third leg, showing the smooth crest {cr.). 



sharply defined upstanding ridge, but resembles rather an 

 angular elevation, such as would be produced by pinching up 

 the horny integument of the femoral segment. A similar 



