380 
SEXUAL SELECTION. 
Part II- 
for tlie rasps are seated on the inferior surface of the 
elytra, near their apices, or along their outer margins, 
and the edges of the abdominal segments serve as the 
scrapers. In Pelobius he.rma.nni (one of Dytiscidse or 
water-beetles) a strong ridge runs parallel and near to 
the sutural margin of the elytra, and is crossed by ribs, 
coarse in the middle part, but becoming gradually finer 
at both ends, especially at the upper end ; when this 
insect is held under water or in the air, a stridulating 
noise is produced by scraping the extreme horny margin 
of the abdomen against the rasp. In a great number 
of long-homed beetles (Longicornia) the organs are alto- 
gether differently situated, the rasp being on the meso- 
thorax, which is rubbed against the pro-thorax ; Landois 
counted 238 very line ribs on the rasp of Ceraniby <C 
heron. 
Many Lamellicorns have the power of stridulating, 
and the organs differ greatly in position. Some species 
stridulate very loudly, so that when 
Mr. F. Smith caught a Trox sabu - 
losus, a gamekeeper who stood by 
thought that he had caught a 
mouse ; but I failed to discover the 
proper organs in this beetle. In 
Geotrupes and Typhous a narrow 
ridge runs obliquely across (r, fig- 
25) the coxa of each hind-leg, 
having in G. stercorarius 84 ribs, 
which are scraped by a specially 
projecting part of one of the abdo- 
Fig, 25. Hind-leg of Geotrupes . ^ . t i i «r 
stercorarius (from Landois). LHlHiil SGglUGIltS. Ill til 6 HCtU } 
r. Rasp, c. coxa. /. Femur, allied Copris lunar is, an excessively 
t. Tibia, tr. Tarsi. 7. , 
narrow tine rasp runs along 
sutural margin of the elytra, with another short rasp 
near the basal outer margin ; but in some other Coprin 1 
