342 



THE DESCENT OF MAN". 



by their becoming confluent and straight, and at the 

 same time more prominent and smooth. A hard ridge 

 on an adjoining part of the body serves as the scraper 

 for the rasp, but this scraper in some cases has been spe- 

 cially modified for the purpose. It is rapidly moved across 

 the rasp, or conversely the rasp across the scraper. 



Fig. 35. Necrophorus (from Landois). r. The two rasps. Left-hand 

 figure, part of the rasp highly magnified. 



These organs are situated in widely different positions. 

 In the carrion - beetles (Necrophorus) two parallel rasps 

 (r, fig. 25) stand on the dorsal surface of the fifth abdomi- 

 nal segment, each rasp* consisting of 126 to 140 fine ribs. 

 These ribs are scraped against the posterior margins of the 

 elytra, a small portion of which projects beyond the gen- 

 eral outline. In many Crioceridae, and in Clythra 4-punc- 

 tat'a (one of the Chrysomelidaa), and in some Tenebrionidse, 

 etc.,f the rasp is seated on the dorsal apex of the abdomen, 

 on the pygidium or pro-pygidium, and is scraped in the 

 same manner by the elytra. In Heterocerus, which belongs 

 to another family, the rasps are placed on the sides of the 

 first abdominal segment and are scraped by ridges on the 



* Landois, " Zeitschrift fur wiss. Zoolog.," B. xvii, 1867, s. 127. 



f I am greatly indebted to Mr. G. R. Crotch for having sent me 

 many prepared specimens of various beetles belonging to these three 

 families and to others, as well as for valuable information. He be- 

 lieves that the power of stridulation in the Clythra has not been pre- 

 viously observed. I am also much indebted to Mr. E. W. Janson, 

 for information and specimens. I may add that my son, Mr. F. 

 Darwin, finds that Dermestes murimus stridulates, but he searched 

 in vain for the apparatus. Scolytus has lately been described by Dr. 

 Chapman as a stridulator, in the " Entomologist's Monthly Maga- 

 zine," vol. vi, p. 130. 



