Tlie Evidence from Sexual CJiaracters. 191 



acquire their perfect structure at the last moult, when 

 the insect is mature and ready to breed. 



Many beetles have rasp-like ridges with fine teeth on 

 certain parts of their bodies, for producing a stridulating 

 noise, by scraping against hard ridges or angles on the 

 adjoining parts. In most stridulating beetles they are 

 equally developed in both sexes: in some they are rudi- 

 mentary or entirely absent in the female. These or- 

 gans are situated on widely different parts of the body 

 in different beetles, even when they are very nearly re- 

 lated. In the carrion beetles there are two parallel rasps 

 with fine transverse ribs on the fifth abdominal segment, 

 and they are rubbed against the posterior edge of the 

 wing-cover. In other beetles the rasp is on the dorsal 

 apex of the abdomen. In others it is on the side of the 

 first abdominal segment, and is scraped by ridges on the 

 femur. . In others the rasps are on the lower sur- 

 faces of the wing-covers, and the edges of the abdominal 

 segments serve as scrapers. In others the horny tip of 

 the abdomen is scraped against a rasp on the wing-covers. 

 In a great number of species of long-horned beetles the 

 rasp is on the meso-thorax, and is rubbed against the 

 pro-thorax. In still other beetles there is a ribbed rasp 

 running obliquely across the coxa of each hin leg, and 

 this is scraped across a specially projecting ridge on one 

 of the abdominal segments. In still others the rasp is on 

 the pro-sternum, and the scraper on the meta-sternum. 



In the cases where the stridulating organs are con- 

 fined to the male, or where they are rudimentary and 

 functionless in the female, we have every reason to be- 

 lieve that the successive variations which have led to 

 their production have originated in males. 



In the cases where each sex has inherited them in full 

 perfection, there is, of course, no direct evidence to show 



