so, in consequence of certain parts being of a white colour, as shown in our figure. If abstraction be made of the white parts, the form of the stalked abdomen of the ant is nicely reproduced. The specimens brought from the Soudan were wingless and destitute of ovipositor, and may be immature, but Brunner suggests that they may prove to be really mature, the ovipositor, tegmina, and wings being permanently absent. The existence of a long ovipositor would certainly detract greatly from the ant-like appearance of the Orthopteron. [Illustration: FIG. 199.—_Myrmecophana fallax._] It is certain that the plant-like appearance of some of the Locustidae renders them inconspicuous to the human eye in the situations they frequent. It is a matter of common observation that though the noise of their chirpings may be heard to such an extent as to make it certain that many individuals must be in the immediate neighbourhood, yet at the same time it may be most difficult to detect even a single individual. M. Boutan noticed this phenomenon in the case of _Ephippigera rugosicollis_, and tells us that the human eye can, with a little practice, acquire the art of detecting these concealed creatures. This consists {324}apparently in making use, not of a general inspection, but of a scrutiny of the outlines of the leaves and twigs of a tree. By this means, when the eye is accustomed to the task, the Insects can be detected with comparative ease; much in the same way, M. Boutan says, as a figure, placed in an engraving in such a way as to elude the eye, is appreciated with ease after the eye has once perceived it. Some of the Locustidae are provided with means of defence of a positive nature. The Algerian _Eugaster guyoni_ ejects two jets of a caustic orange-coloured fluid from two pores situate on the sides of the mesosternum, and covered by the anterior coxae. This species is carnivorous as well as herbivorous, and produces a sound more like humming than stridulation.[252] [Illustration: FIG. 200.—_Phasmodes ranatriformis_,female. Australia. (After Westwood.)]