an extremely brilliant steel-blue, sometimes tinted with vivid green; the male being of a bright brassy color clothed with rich fulvous pubescence. As in this group the females are provided with excellent defensive weapons in their stings, it is not probable that they have come to differ in color from the males for the sake of protection.

He

Mutilla Europaea emits a stridulating noise; and according to Goureau" both sexes have this power. attributes the sound to the friction of the third and preceding abdominal segments; and I find that these surfaces are marked with very fine concentric ridges, but so is the projecting thoracic collar, on which the head articulates; and this collar, when scratched with the point of a needle, emits the proper sound. It is rather surprising that both sexes should have the power of stridulating, as the male is winged and the female wingless. It is notorious that Bees express certain emotions, as of anger, by the tone of their humming, as do some dipterous insects; but I have not referred to these sounds, as they are not known to be in any way connected with the act of courtship.

Order, Coleoptera (Beetles).—Many beetles are colored so as to resemble the surfaces which they habitually frequent. Other species are ornamented with gorgeous metallic tints-for instance, many Carabidae, which live on the ground and have the power of defending themselves by an intensely acrid secretion-the splendid diamond-beetles which are protected by an extremely hard covering-many species of Chrysomela, such as C. cerealis, a large species beautifully striped with various colors, and in Britain confined to the bare summit of Snowdon-and a host of other species. These splendid colors, which are often arranged in stripes, spots, crosses, and other elegant patterns, can hardly be beneficial, as a pro

57 Quoted by Westwood, 'Modern Class. of Insects,' vol. ii. p. 214.

tection, except in the case of some flower-feeding species; and we cannot believe that they are purposeless. Hence the suspicion arises that they serve as a sexual attraction; but we have no evidence on this head, for the sexes rarely differ in color. Blind beetles, which cannot of course behold each other's beauty, never exhibit, as I hear from Mr. Waterhouse, Jr., bright colors, though they often have polished coats: but the explanation of their obscurity may be that blind insects inhabit caves and other obscure stations.

Some Longicorns, however, especially certain Prionidæ, offer an exception to the common rule that the sexes of beetles do not differ in color. Most of these insects are large and splendidly colored. The males in the genus Pyrodes," as I saw in Mr. Bates's collection, are generally redder but rather duller than the females, the latter being colored of a more or less splendid golden green. On the other hand, in one species the male is golden green, the female being richly tinted with red and purple. In the genus Esmeralda the sexes differ so greatly in color that they have been ranked as distinct species: in one species both are of a beautiful shining green, but the male has a

* Pyrodes pulcherrimus, in which the sexes differ conspicuously, has been described by Mr. Bates in Transact. Ent. Soc.' 1869, p. 50. I will specify the few other cases in which I have heard of a difference in color between the sexes of beetles. Kirby and Spence (Introduct. to Entomology, vol. iii. p. 301) mention a Cantharis, Meloe, Rhagium, and the Leptura testacea; the male of the latter being testaceous, with a black thorax, and the female of a dull red all over. These two latter beetles belong to the Order of Longicorns. Messrs. R. Trimen and Waterhouse, Jr., inform me of two Lamellicorns, viz., a Peritrichia and Trichius, the male of the latter being more obscurely colored than the female. In Tillus elongatus the male is black, and the female always, as it is believed, of a dark-blue color with a red thorax. The male, also, of Orsodacna atra, as I hear from Mr. Walsh, is black, the female (the so-called 0. ruficollis) having a rufous thorax.

red thorax. On the whole, as far as I could judge, the females of those Prionidæ, in which the sexes differ, are colored more richly than the males; and this does not accord with the common rule in regard to color when acquired through sexual selection.

A most remarkable distinction between the sexes of many beetles is presented by the great horns which rise from the head, thorax, or clypeus of the males; and in some few cases from the under surface of the body. These horns, in the great family of the Lamellicorns, resemble those of various quadrupeds, such as stags, rhinoceroses, etc., and are wonderful both from their size and diversified shapes. Instead of describing them, I have given figures of the males and females of some of the more remarkable forms. (Figs. 15 to 19.) The females gen

erally exhibit rudiments of the horns in the form of small knobs or ridges; but some are destitute of even a rudiment. On the other hand, the horns are nearly as well developed in the female as in the male of Phanaus lancifer; and only a little less well developed in the females of some other species of the same genus and of Copris. In the several subdivisions of the family, the differences in structure of the horns do not run parallel, as I am informed by Mr. Bates, with their more important and characteristic differences; thus, within the same natural section of the genus Onthophagus, there are species which have either a single cephalic horn, or two distinct horns.

59

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 5 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. 19), 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 widelydifferent structure in closely-allied forms, indicate that they have been formed for some important 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 show marks of friction, as if used for any ordinary work. Some authors suppose 60 that as the males wander much more than the females, they require horns as a defence against their enemies; but in many cases the horns do not seem well adapted for defence, as they are not sharp. The most

59 Proc. Entomolog. Soc. of Philadelphia,' 1864, p. 228.
60 Kirby and Spence, 'Introduct. Entomolog.' vol. iii. p. 300.