COLBOPTBRA. 301 



ring states that in Omaloplia brunnea the rasp is placed on the pro- 

 sternum, and the scraper on the meta-sternum, the parts thus oc- 

 cupying the under surface of the body, instead of the upper sur- 

 face as in the Longicorns. 



We thus see that in the different coleopterous families the 

 stridulating organs are wonderfully diversified in position, but not 

 much in structure. Within the same family some species are pro- 

 vided with these organs, and others are destitute of thqm. This 

 diversity is intelligible, if we suppose that originally various bee- 

 tles made a shuffling or hissing noise by the rubbing together of 

 any hard and rough parts of their bodies, which happened to be in 

 contact; and that from the noise thus produced being in some way 

 useful, the rough surfaces were gradually developed into regular 

 stridulating organs. Some beetles as they move, now produce, 

 either intentionally or unintentionally, a shuffling noise, without 

 possessing any proper organs for the purpose. Mr. Wallace in- 

 forms me that the Euchirus longimanus (a Lamellicorn, with the 

 anterior legs wonderfully elongated in the male) "makes, whilst 

 "moving, a low hissing sound by the protrusion and contraction of 

 "the abdomen; and when seized it produces a grating sound by 

 "rubbing its hind-legs against the edges of the elytra." The hiss- 

 ing sound is clearly due to a narrow rasp running along the sut- 

 ural margin of each elytron; and I could likewise make the grat- 

 ing sound by rubbing the shagreened surface of the femur against 

 the granulated margin of the corresponding elytron; but I could 

 not here detect any proper rasp; nor is it likely that I could have 

 overlooked it in so large an insect. After examining Cychrus, and 

 reading what Westring has written about this beetle, it seems very 

 doubtful whether it possesses any true rasp, though it has the 

 power of emitting a sound. 



From the analogy of the Orthoptera and Homoptera, I expected 

 to find the stridulating organs in the Coleoptera differing accord- 

 ing to sex; but Landois, who has carefully examined several 

 species, observed no such difference; nor did Westring; nor did 

 Mr. G. R. Crotch in preparing the many specimens which he had 

 the kindness to send me. Any difference in these organs, if slight, 

 would, however, be difficult to detect, on account of their great 

 variability. Thus, in the first pair of specimens of Necrophorus 

 humator and of Peloblus which I examined, the rasp was consider- 

 ably larger in the male than in the female; but not so with suc- 

 ceeding specimens. In Geotrupes stercorarius the rasp appeared 

 to me thicker, opaquer, and more prominent in three males than 

 in the same number of females; in order, therefore, to discover 

 whether the sexes differed in their power of stridulating, my son, 

 Mr. F. Darwin, collected fifty-seven living specimens, which he 

 separated Into two lots, according as they made a greater or lesser 

 noise, when held in the same manner. He then examined all 



