LINNEAN SOCIETY OF LONDON". \\ I 



.1 



0U> 



r--^HY 



Amonp;st the Orthoptera a stridulating-organ is "fcoitmionly 

 present, but in the male only. The grasshopper has long beayiOJS. 

 known to make its chirping sound by rubbing the file, on the*^-^ss: 

 inner surface of its posterior femora, against the elytra as they 

 lie by the sides of the abdomen, the insect standing on its two 

 anterior pairs of legs when performing. In Ci/sfocoelia immacu- 

 lafa the abdomen of the male is immensely distended with air, 

 and its second segment lias a curved ridge of eight teeth, the 

 curve having the femorous articulation as its centre ; the part 

 of the femur in contact Avith this ridge is provided with a 

 finely toothed process. In C. sexguttuta the abdominal file 

 resembles that on the chela of Ocypoda^ the lower portion having 

 the teeth from five to six times as close as the upper. 



In the crickets and their allies the stridulating-organ is found 

 on the overlapping portions of the elytra — the left having the file 

 on its under surface and at right angles to the axis of the body, 

 the right having a smooth ridge above in the axis of the body, 

 and with a tense resonating membrane on its outer and posterior 

 side ; the membrane is, in FseudopliyUus and Macrolyristes, partly 

 covered by a fold j^rojecting from its inner border, which, may 

 act like the sounding-board over a pulpit. 



Amongst the Hymenoptera certain ants in Central Africa were 

 heard by Dr. Livingstone to emit a sharp creaking sound ; a 

 special ridged surface on the two peduncular segments of the 

 abdomen has since been described. 



The most powerful and complex sound-producing organ in 

 insects is found in the Cicadidie ; it is of an entirely different type 

 to all previously considered. If we take as our example one in 

 which all parts are about equally developed, as, for ibstance, 

 Cicada australasice, we shall find on the upper and lateral surface 

 of the first abdominal segment a convex ridged membrane — the 

 drum ; to the middle of its inner surface is attached the short 

 and delicate tendon of a conical muscle that arises from the 

 sternites of the first and second segment ; the contraction of this 

 muscle pulls in the drum, the sudden recoil of the drum exciting 

 the sound-wave. The drum is coneealed and jjrotected by a 

 forward projection of the anterior border of the second segment, 

 named the cover. The ventral surface of the second segment, or 

 the membrane between it and the first, has a portion of the 

 cuticle exceedingly thin and tensely stretched ; this forms the 

 mirror ; it is often so thin as to decompose the light like a soap- 

 bubble ; it acts as a resonating organ in conjunction with the 

 general body of the insect. The mirror is jjrotected by a broad 

 plate-like prolongation of the metathorax called the operculum. 

 At the anterior border of the operculum is a strong spine, ' pes- 

 sellum,' projecting from the first joint, ' trochantin,' of the hind 

 leg ; it is thought that it checks undue depression of the oper- 

 culum. In Thoplia the chamber bounded by the cover is very 

 large, forming large pockets extending far backwards on either 

 side of the abdomen. In Dunduhia the operculum projects 



LLNN. SOC. PUOUEEDIXGS. — SESSION' 1592-93. C 



