302 



The Descent of Man. 



Part II. 



transition takes place 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 specially 

 modified for the purpose. It is rapidly moved across the rasp, 

 or conversely the rasp across tbe scraper. 



Fig. 25. Necrophorus (from Candois). 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 abdominal segment, each 

 rasp u 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 general outline. In many Crioeeridae, 

 and in Clylhra ^-punctata (one of the Chrysomelidse), and in some 

 Tenebrionidae, &c., 75 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 

 femora. 76 In certain Curculionidse and Carabiclse, 77 the parts 



74 Landois, ' Zcitschrift fur wiss. 

 Zoolog.' B. xvii. 1867, s. 127. 



75 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 believes 

 that the power of stridulation in 

 iheClythra has not been previously 

 observed. I am also much indebted 

 to Mr. E. W. Janson, for informa- 

 tion and specimens. I may add 

 that my son, Mr. F. Darwin, finds 

 that Dermestes murinus stridulates, 

 but he searched in vain for the 

 apparatus. Scolytus has lately 



been described by Dr. Chapman as 

 a stridulator, in the 'Entomolo- 

 gist's Monthly Magazine,' vol. vi. p. 

 130. 



76 Schiodte, translated in ' Annals 

 and Mag. of Nat. Hist.' vol. xx. 

 1867. p. 37. 



77 Westring has described (Kroyer, 

 ' Naturhist. Tidskrift,' B. ii. 1848- 

 49, p. 334) the stridulating organs 

 in these two, as well as in other 

 families. In the Carabidse I have 

 examined Elaphrus uliginosus and 

 Blethisa multipunctata, sent to me 

 by Mr. Crotch. In Blethisa the 

 transverse ridges on the furrowed 

 border of the abdominal segment do 



