The Descent of Man

transverse ridges on the furrowed border of the
abdominal segment do not, as far as I could
judge, come into play in scraping the rasps on
the elytra.), the parts are completely reversed in
position, for the 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
Hermanni (one of Dytiscidae or waterbeetles)
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
the extreme horny margin of the abdomen
being scraped against the rasps. In a great
number of long-horned beetles (Longicornia)
the organs are situated quite otherwise, the
rasp being on the meso-thorax, which is rubbed
against the pro-thorax; Landois counted 238
very fine ribs on the rasp of Cerambyx heros.