obvious conjecture is that they are used by the males for fighting together; but they 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, their size would probably have been increased through sexual selection, so as to have exceeded that of the female; but Mr. Bates, after comparing the two sexes in above a hundred species of the Copridæ, does not find in well-developed individuals any marked difference in this respect. There is, moreover, one beetle, belonging to the same great division of the Lamellicorns, namely, Lethrus, the males of which are known to fight, but they are not provided with horns, though their mandibles are much larger than those of the female.

The conclusion, which best agrees with the fact of the horns having been so immensely yet not fixedly developed as shown by their extreme variability in the same species and by their extreme diversity in closely-allied species-is that they have been acquired as ornaments.

This view will at first appear extremely improbable; but we shall hereafter find with many animals, standing much higher in the scale, namely, fishes, amphibians, reptiles, and birds, that various kinds of crests, knobs, horns, and combs, have been developed apparently for this sole purpose.

The males of Onitis furcifer (fig. 20) 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. This situation seems extremely ill-adapted for the display of these projections, and they may be of some real service;

It is a

but no use can at present be assigned to them. highly-remarkable fact, that although the males do not exhibit even a trace of horns on the upper surface of the body, yet in the females a rudiment of a single horn on the head (fig. 21, a), and of a crest (b) on the thorax, are plainly visible. That the slightest thoracic crest in the female

FIG. 21.-Left-hand figure, male of Onitis furcifer, viewed laterally. Right-hand figure, female. a. Rudiment of cephalic horn. b. Trace of thoracic horn or crest.

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 form which comes next to Onitis) has a similar slight crest on the thorax, and the male has in the same situation a great projection. So again there can be no doubt that the little point (a) on the head of the female Onitis furcifer, as well of the females of two or three allied species, is a rudimentary representative of the cephalic horn, which is common to the males of so many lamellicorn beetles, as in Phanæus, fig. 17. The males, indeed, of some unnamed beetles in the British Museum, which are believed actually to belong to the genus Onitis, are furnished with a similar horn. The remarkable nature of this case will be best perceived by an illustration: the Ruminant quadrupeds. run parallel with the lamellicorn beetles, in some females possessing horns as large as those of the male, in others having them much smaller, or existing as mere rudiments (though this is as rare with ruminants as it is common

with Lamellicorns), or in having none at all. Now, if a new species of deer or sheep were discovered with the female bearing distinct rudiments of horns, while the head of the male was absolutely smooth, we should have a case like that of Onitis furcifer.

In this case the old belief of rudiments having been created to complete the scheme of Nature is so far from holding good, that all ordinary rules are completely broken through. The view which seems the most probable is that some early progenitor of Onitis acquired, like other Lamellicorns, horns on the head and thorax, and then transferred them, in a rudimentary condition, as with so many existing species, to the female, by whom they have ever since been retained. The subsequent loss of the horns by the male may have resulted through the principle of compensation from the development of the projections on the lower surface, while the female has not been thus affected, as she is not furnished with these projections, and consequently has retained the rudiments of the horns on the upper surface. Although this view is supported by the case of Bledius immediately to be given, yet the projections on the lower surface differ greatly in structure and development in the males of the several species of Onitis, and are even rudimentary in some; nevertheless the upper surface in all these species is quite destitute of horns. As secondary sexual characters are so eminently variable, it is possible that the projections on the lower surface may have been first acquired by some progenitor of Onitis and produced their effect through com pensation, and then have been in certain cases almost completely lost.

All the cases hitherto given refer to the Lamellicorns, but the remains of some few other beetles, belonging to two widely-distinct groups, namely, the Curculionidæ and Staphylinidæ, are furnished with horns-in the former on

the lower surface of the body," in the latter on the upper surface of the head and thorax. In the Staphylinidæ the horns of the males in the same species are extraordinarily variable, just as we have seen with the Lamellicorns. In

FIG. 22.-Bledius taurus, magnified. Left-hand figure, male; right-hand figure, female.

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 any intermediate gradations. In a species of. Bledius (fig. 22); also belonging to the Staphylinidæ, male specimens can be found in the same locality, as Prof. Westwood states, "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, while the protuberances on the head are long." Here, then, we apparently have an instance of compensation of growth, which throws light on the curious case just given of the loss of the upper horns by the males of Onitis furcifer.

99 62

Law of Battle.-Some male beetles, which seem ill fitted for fighting, nevertheless engage in conflicts for the possession of the females. Mr. Wallace " saw two males of Leptorhynchus angustatus, a linear beetle with a much

61 Kirby and Spence, ibid. vol. iii. p. 329.

63

62 'Modern Classification of Insects,' vol. i. p. 172. On the same page there is an account of Siagonium. In the British Museum I noticed one male specimen of Siagonium in an intermediate condition, so that the dimorphism is not strict.

63 The Malay Archipelago,' vol. ii. 1869, p. 276.

MEDICAL LIBRAK

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 the males are well adapted for fighting, by possess. ing great toothed mandibles, much larger than those of the females. This is the case with the common stag-beetle (Lucanus cervus), the males of which emerge from the pupal state about a week before the other sex, so tha several may often be seen pursuing the same female. At this period they engage in fierce conflicts. When Mr. A. II. Davis** enclosed two males with one female in a box, the larger male severely pinched the smaller one, until he resigned his pretensions. A friend informs me that when a boy he often put the males together to see them fight, and he noticed that they were much bolder and fiercer than the females, as is well known to be the case with the higher animals. The males would seize hold of his finger, if held in front, but not so the females. With many of the Lucanida, as well as with the above-mentioned Leptorhynchus, the males are larger and more powerful insects than the females. The two sexes of Lethrus cephalotes (one of the Lamellicorns) inhabit the same burrow; and the male has larger mandibles than the female. If, during the breeding-season, a strange male attempts to enter the burrow, he is attacked; the female does not remain passive, but closes the mouth of the burrow, and en courages her mate by continually pushing him on from behind. The action does not cease until the aggressor is killed or runs away." The two sexes of another lamelli

64 Entomological Magazine,' vol. i. 1833, p. 82. See also, on the conflicts of this species, Kirby and Spence, ibid. vol. iii. p. 314; and Westwood, ibid. vol. i. p. 187.

Quoted from Fischer, in 'Dict. Class. d'Hist. Nat.' tom. x. p. 324.