The Descent of Man

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 infe-