the upper horns on the females would not have been thus obliterated.
[Fig. 23. Bledius taurus, magnified. Left-hand figure, male; right-hand
figure, female.]
The cases hitherto given refer to the Lamellicorns, but the males of
some few other beetles, belonging to two widely distinct groups,
namely, the Curculionidae and Staphylinidae, are furnished with
horns in the former on the lower surface of the body (66. Kirby and
Spence, Introduction to Entomology, vol. iii. p. 329.), in the latter
on the upper surface of the head and thorax. In the Staphylinidae, the
horns of the males are extraordinarily variable in the same species,
just as we have seen with the Lamellicorns. In Siagonium we have a case
of dimorphism, for the males can be divided into two sets, differing
greatly in the size of their bodies and in the development of their
horns, without intermediate gradations. In a species of Bledius (Fig.
23), also belonging to the Staphylinidae, Professor Westwood states
that, male specimens can be found in the same locality in which the
central horn of the thorax is very large, but the horns of the head
quite rudimental; and others, in which the thoracic horn is much
shorter, whilst the protuberances on the head are long. (67. Modern
Classification of Insects, vol. i. p. 172: Siagonium, p. 172. In the
British Museum I noticed one male specimen of Siagonium in an
intermediate condition, so that the dimorphism is not strict.) Here we
apparently have a case of compensation, which throws light on that just
given, of the supposed loss of the upper horns by the males of Onitis.
LAW OF BATTLE.
Some male beetles, which seem ill-fitted for fighting, nevertheless
engage in conflicts for the possession of the females. Mr. Wallace (68.
The Malay Archipelago, vol. ii. 1869, p. 276. Riley, Sixth Report on
Insects of Missouri, 1874, p. 115.) saw two males of Leptorhynchus
angustatus, a linear beetle with a much elongated rostrum, fighting
for a female, who stood close by busy at her boring. They pushed at
each other with their rostra, and clawed and thumped, apparently in the
greatest rage. The smaller male, however, soon ran away,
acknowledging himself vanquished. In some few cases male beetles are
well adapted for fighting, by possessing great toothed mandibles, much
larger than those of the females. This is the case with the common
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