highly remarkable, as the males are furnished with horns, of which the females are quite destitute. The horns spring from beneath the eyes, and curiously resemble those of a stag, being either branched or palmated. In one of the species they equal the whole body in length. They might be thought to be adapted for fighting, but as in one species they are of a beautiful pink color, edged with black, with a pale central stripe, and as these insects have altogether a very elegant appearance, it is perhaps more probable that they serve as ornaments. That the males of some Diptera fight together is certain; for Prof. Westwood" has several times seen this with the Tipulæ. The males of other Diptera apparently try to win the females by their music: H. Müller20 watched for some time two males of an Eristalis courting a female; they hovered above her, and flew from side to side, making a high humming noise at the same time. Gnats and mosquitoes (Culicidae) also seem to attract each other by humming; and Prof. Mayer has recently ascertained that the hairs on the antennæ of the male vibrate in unison with the notes of a tuning-fork, within the range of the sounds emitted by the female. The longer hairs vibrate sympathetically with the graver notes, and the shorter hairs with the higher ones. Landois also asserts that he has repeatedly drawn a whole swarm of gnats by uttering a particular note. It may be added that the mental faculties of the Diptera are probably higher than in most other insects, in accordance with their highly developed nervous system.

21

Order, Hemiptera (Field-Bugs).-Mr. J. W. Douglas, who has particularly attended to the British species, has kindly given me an account of their sexual differences. The males of some species are furnished with wings, while

19 Modern Classification of Insects," vol. ii., 1840, p. 526.

20 Anwendung, etc., "Verh. d. n. V. Jahrg.," xxix. p. 80. Mayer, in "American Naturalist," 1874, p. 236.

21 See Mr. B. T. Lowne's interesting work, "On the Anatomy of the Blowfly, Musca vomitora," 1870, p. 14. He remarks (p. 33) that "the captured flies utter a peculiar plaintive note, and that this sound causes other flies to disappear."

the females are wingless; the sexes differ in the form of their bodies, elytra, antennæ, and tarsi; but, as the signification of these differences are unknown, they may be here passed over. The females are generally larger and more robust than the males. With British, and, as far as Mr. Douglas knows, with exotic species, the sexes do not commonly differ much in color; but in about six British species the male is considerably darker than the female, and in about four other species the female is darker than the male. Both sexes of some species are beautifully colored; and as these insects emit an extremely nauseous odor, their conspicuous colors may serve as a signal that they are unpalatable to insectivorous animals. In some few cases their colors appear to be directly protective; thus Prof. Hoffmann informs me that he could hardly distinguish a small pink and green species from the buds on the trunks of lime-trees, which this insect frequents.

Some species of Reduvida make a stridulating noise; and, in the case of Pirates stridulus, this is said to be effected by the movement of the neck within the prothoracic cavity. According to Westring, Reduvius personatus also stridulates. But I have no reason to suppose that this is a sexual character, excepting that with non-social insects there seems to be no use for sound-producing organs, unless it be as a sexual call.

Order, Homoptera.-Every one who has wandered in a tropical forest must have been astonished at the din made by the male Cicada. The females are mute; as the Grecian poet Xenarchus says, "Happy the Cicadas live, since they all have voiceless wives." The noise thus made could be plainly heard on board the "Beagle," when anchored at a quarter of a mile from the shore of Brazil; and Captain Hancock says it can be heard at the distance of a mile. The Greeks formerly kept, and the Chinese now keep, these insects in cages for the sake of their song, so that it must be

*9 Westwood, "Modern Class. of Insects,” vol. ii. p. 473.

pleasing to the ears of some men." The Cicadide usually sing during the day, while the Fulgoridæ appear to be night-songsters. The sound, according to Landois," is produced by the vibration of the lips of the spiracles, which are set into motion by a current of air emitted from the tracheæ; but this view has lately been disputed. Dr. Powell appears to have proved" that it is produced by the vibration of a membrane, set into action by a special muscle. In the living insect, while stridulating, this membrane can be seen to vibrate; and in the dead insect the proper sound is heard, if the muscle, when a little dried and hardened, is pulled with the point of a pin. In the female the whole complex musical apparatus is present, but is much less developed than in the male, and is never used for producing sound.

With respect to the object of the music, Dr. Hartman, in speaking of the Cicada septemdecim of the United States, says, "the drums are now (June 6 and 7, 1851) heard in all directions. This I believe to be the marital summons from the males. Standing in thick chestnut sprouts about as high as my head, where hundreds were around me, I observed the females coming around the drumming males." He adds: "This season (August, 1868) a dwarf pear-tree in my garden produced about fifty larvæ of Cic. pruinosa; and I several times noticed the females to alight near a male while he was uttering his 'clanging notes.' Fritz Müller writes to me from South Brazil that he has often listened to a musical contest between two or three males of a species with a particularly loud voice, seated at a considerable distance from each other: as soon as one had finished his song, another immediately began, and then another. As there is so much rivalry between the males, it is probable that the females not only find them by their sounds, but that, like

99

23 These particulars are taken from Westwood's "Modern Class. of Insects, vol. ii., 1840, p. 422. See also, on the Fulgoridæ, Kirby and Spence, "Introduct., "vol. ii. p. 401.

24 "Zeitschrift für wissenschaft Zoolog.," B. xvii., 1867, s. 152-158. 25 Transact. New Zealand Institute," vol. v., 1873, p. 286.

96 I am indebted to Mr. Walsh for having sent me this extract from & "Journal of the Doings of Cicada septemdecim," by Dr. Hartman.

female birds, they are excited or allured by the male with the most attractive voice.

I have not heard of any well-marked cases of ornamental differences between the sexes of the Homoptera. Mr. Douglas informs me that there are three British species in which the male is black or marked with black bands, while the females are pale-colored or obscure.

28

Order, Orthoptera (Crickets and Grasshoppers).—The males in the three saltatorial families in this Order are remarkable for their musical powers, namely, the Achetidæ, or crickets, the Locustidæ, for which there is no equivalent English name, and the Acridiidæ, or grasshoppers. The stridulation produced by some of the Locustidæ is so loud that it can be heard during the night at the distance of a mile," and that made by certain species is not unmusical even to the human ear, so that the Indians on the Amazons keep them in wicker cages. All observers agree that the sounds serve either to call or excite the mute females. With respect to the migratory locusts of Russia, Körte has given an interesting case of selection by the female of a male. The males of this species (Pachytylus migratorius) while coupled with the female stridulate from anger or jealousy if approached by other males. The house-cricket when surprised at night uses its voice to warn its fellows.2o In North America the Katydid (Platyphyllum concavum, one of the Locustida) is described as mounting on the upper branches of a tree, and in the evening beginning "his noisy babble, while rival notes issue from the neighboring trees, and the groves resound with the call of Katy-did-shedid the livelong night." Mr. Bates, in speaking of the European field-cricket (one of the Achetida), says, "The male has been observed to place himself in the evening

27 Guilding, "Trans. Linn. Soc.," vol. xv. p. 154.

28 I state this on the authority of Köppen, "Ueber die Heuschrecken in Südrussland," 1866, p. 32, for I have in vain endeavored to procure Körte's work.

29 Gilbert White, "Nat. Hist. of Selborne," vol. ii., 1825, p. 262. 30 Harris, "Insects of New England," 1842, p. 128.

at the entrance of his burrow, and stridulate until a female

FIG. 11.-Gryllus campestris (from Landois). Right-hand figure, under side of part of a wing nervure, much magnified, showing the teeth, st. Left-hand figure, upper surface of wing-cover, with the projecting, smooth nervure, r, across which the teeth (st) are scraped.

sounds are differently produced. In the males of the Achetida both wing-covers have the same apparatus; and this in the field-cricket (Gryllus campestris, Fig. 11) consists, as described by Landois," of from 131 to 138 sharp, transverse ridges or teeth (st) on the under side. of one of the nervures of the wing-cover. This toothed nervure is rapidly scraped across a projecting, smooth, hard nervure (r) on the upper surface of the opposite wing. First one wing is rubbed over the other, and then the FIG. 12.-Teeth of movement is reversed. Both wings are raised nervure of Gryllus domesticus (from a little at the same time, so as to increase the Landois). resonance. In some species the wing-covers of the males are furnished at the base with a talc-like plate." I here give a drawing (Fig. 12) of the teeth on the under side

31 "The Naturalist on the Amazons," vol. i., 1863, p. 252. Mr. Bates gives a very interesting discussion on the gradations in the musical apparatus of the three families. See also Westwood, "Mod. Class.," vol. ii. pp. 445, 453. 32 Proc. Boston Soc. of Nat. Hist.," vol. xi., April, 1868.

33 "Nouveau Manuel d'Anat. Comp.," French translat., tom. i., 1850,

p. 567.

34 "Zeitschrift für Wissenschaft. Zoolog.," B. xvii., 1867, s. 117. 35 Westwood, "Modern Class. of Insects," vol. i. p. 440.