The Descent of Man

Fig.22. Onitis furcifer. Left-hand figure, male,
viewed laterally. Right-hand figure, female. a.
Rudiment of cephalic horn. b. Trace of thoracic
horn or crest.]
The males of Onitis furcifer (Fig. 21), and of
some other species of the genus, are furnished
with singular projections on their anterior femora,
and with a great fork or pair of horns on
the lower surface of the thorax. Judging from
other insects, these may aid the male in clinging
to the female. Although the males have not
even a trace of a horn on the upper surface of
the body, yet the females plainly exhibit a rudiment
of a single horn on the head (Fig. 22, a),
and of a crest (b) on the thorax. That the slight
thoracic crest in the female is a rudiment of a
projection proper to the male, though entirely
absent in the male of this particular species, is
clear: for the female of Bubas bison (a genus
which comes next to Onitis) has a similar slight
crest on the thorax, and the male bears a great