The exotic genus _Rhipipteryx_ is allied to _Tridactylus_. It is widely distributed in South America, but the little Insects that {338}compose it are rare in collections, their saltatorial powers no doubt making it difficult to catch them; little is known as to their habits. In the undescribed Amazonian species we figure (Fig. 210), the wings, instead of being mere rudiments, as in _Tridactylus_, are elongate and project beyond the body; they are of a blue-black colour, and arranged so as to look as if they were the abdomen of the Insect; they, moreover, have a transverse pallid mark, giving rise to an appearance of division. It is difficult to form any surmise as to the nature of so curious a modification of the wings. The Tridactylides have no tympana on the legs, and their affinity with the Gryllidae is very doubtful. Dufour thought _T. variegatus_ to be more allied to the Acridiidae. He based this opinion chiefly on some points of the internal anatomy, but pointed out that _Tridactylus_ differs from the Acridiidae in having no air-sacs in the body. [Illustration: FIG. 210.—_Rhipipteryx_ sp., Amazon valley.] Not many of the Gryllidae are so peculiar as the forms we have mentioned. The family consists in larger part of Insects more or less similar to the common cricket, though exhibiting a great variety of external form. The common cricket of our houses, _Gryllus (Acheta) domesticus_ (Fig. 204), has a very wide distribution in the Old World, and is also found in North America. It is believed to have had its natural distribution extended by commerce, though really nothing is known as to its original habitat. The shrill chirping of this little Insect is frequently heard at night in houses, even in the most densely inhabited parts of great cities. Neither the female nor the young are musical, yet the chirping may be heard at all seasons of the year, as young and adults coexist independent of season. The predilection of _Gryllus domesticus_ for the habitations of man is very curious. The Insect is occasionally found out of doors in the neighbourhood of dwelling-houses in hot weather, but it does not appear that this species leads anywhere a truly wild life. It is fond of heat; though it rarely multiplies in dwelling-houses to any great extent, it is sometimes found in profusion in {339}bake-houses. Usually the wings in the cricket are elongate, and project backwards from under the tegmina like an additional pair of cerci; a variety, however, occurs in which these tails are absent, owing to abbreviation of the wings.