“That the males of some Diptera fight together is certain; for Professor Westwood has several times seen this with the Tipulæ. The males of other Diptera apparently try to win the females by their music: H. Müller 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 (Culicidæ) also seem to attract each other by humming; and Professor 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.” In the crickets, grasshoppers, and locusts, the males “are remarkable for their musical powers”; and it is generally assumed that the sounds serve to call or to excite the female. In these forms the noise is made by rubbing the wings over each other or the legs against the wing-covers. In some of these forms both sexes have stridulating organs, and in one case they differ to a certain extent from each other. “Hence we cannot suppose that they have been transferred from the male to the female, as appears to have been the case with the secondary sexual characters of many other animals. They must have been independently developed in the two sexes, which no doubt mutually call to each other during the season of love.” Some beetles also possess rasping organs in different parts of the body, but they cannot produce much noise by this means. “We thus see that in the different coleopterous families the stridulating organs are wonderfully diversified in position, but not much in structure. Within the same family some species are provided with these organs, and others are destitute of them. This diversity is intelligible, if we suppose that originally various beetles made a shuffling or hissing noise by the rubbing together of any hard and rough parts of their bodies, which happened to be in contact; and that from the noise thus produced being in some way useful, the rough surfaces were gradually developed into regular stridulating organs. Some beetles as they move, now produce, either intentionally or unintentionally, a shuffling noise, without possessing any proper organs for the purpose.” Darwin says that he expected from analogy to find in this group also differences in the sexes, but none such were found, although in some cases the males alone possess certain characters or have them more highly developed.