section of the genus Onthophagus, there are species which have a single
horn, and others which have two.
In almost all cases, the horns are remarkable from their excessive
variability; so that a graduated series can be formed, from the most
highly developed males to others so degenerate that they can barely be
distinguished from the females. Mr. Walsh (64. Proceedings of the
Entomological Society of Philadephia, 1864, p. 228.) found that in
Phanaeus carnifex the horns were thrice as long in some males as in
others. Mr. Bates, after examining above a hundred males of Onthophagus
rangifer (Fig. 20), thought that he had at last discovered a species in
which the horns did not vary; but further research proved the contrary.
The extraordinary size of the horns, and their widely different
structure in closely-allied forms, indicate that they have been formed
for some purpose; but their excessive variability in the males of the
same species leads to the inference that this purpose cannot be of a
definite nature. The horns do not shew marks of friction, as if used
for any ordinary work. Some authors suppose (65. Kirby and Spence,
Introduction to Entomology, vol. iii. p. 300.) that as the males
wander about much more than the females, they require horns as a
defence against their enemies; but as the horns are often blunt, they
do not seem well adapted for defence. The most obvious conjecture is
that they are used by the males for fighting together; but the males
have never been observed to fight; nor could Mr. Bates, after a careful
examination of numerous species, find any sufficient evidence, in their
mutilated or broken condition, of their having been thus used. If the
males had been habitual fighters, the size of their bodies would
probably have been increased through sexual selection, so as to have
exceeded that of the females; but Mr. Bates, after comparing the two
sexes in above a hundred species of the Copridae, did not find any
marked difference in this respect amongst well-developed individuals.
In Lethrus, moreover, a beetle belonging to the same great division of
the Lamellicorns, the males are known to fight, but are not provided
with horns, though their mandibles are much larger than those of the
female.
The conclusion that the horns have been acquired as ornaments is that
which best agrees with the fact of their having been so immensely, yet
not fixedly, developed, as shewn by their extreme variability in the
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