The Orthoptera are Insects of comparatively large size. The Order, indeed, includes the largest of existing Insects, while none are so minute as many of the members of the other Orders are; three millimetres is the least length known for an Orthopterous Insect, and there are very few so small, though this is ten times the length of the smallest beetle. The Order includes earwigs, cockroaches, soothsayers or praying-insects, stick- and leaf-insects, grasshoppers, locusts, green grasshoppers, and crickets. {199}The changes of form that accompany the growth of the individual are much less abrupt and conspicuous than they are in most other Insects. The metamorphosis is therefore called Paurometabolous. It has been supposed by some naturalists that Orthoptera go through a larger portion of their development in the egg than other Insects do. This does not clearly appear to be the case, though it seems that there are distinctions of a general character in the embryology; the period of development in the egg is prolonged, and the yolk is said by Wheeler[126] to be more than usually abundant in comparison with the size of the young embryo. The embryonic development may in tropical countries be accomplished in three weeks (see Mantidae), but in countries where winter supervenes, the period may in some species be extended over seven or eight months. The external features of the post-embryonic development—a term that is more convenient in connexion with Orthoptera than metamorphosis—are as follows: the wings are never present when the Insect is first hatched, but appear subsequently, and increase in size at the moults; the form and proportions of the segments of the body—especially of the thorax—undergo much change; an alteration of colour occurs at some of the moults, and the integument becomes harder in the adult condition. Neither the development of the internal organs, nor the physiological processes by which the changes of external form are effected, appear to have been studied to any great extent. Many of the Orthoptera do not possess wings fit for flight, and some species even in the adult state have no trace whatever of such organs. Flight, indeed, appears to be of minor importance in the Order; in many cases where the wings exist they are purely musical organs, and are not of any use for flight. The apterous and the flightless conditions are not confined to one division of the Order, but are found in all the families and in many of their subdivisions. As the front pair of wings in Orthoptera do not really carry out the function of flight, and as they differ in several particulars from the hinder pair, or true wings, it is usual to call them tegmina. The musical powers of the Orthoptera are confined to the saltatorial group of families. {200}[Illustration: FIG. 101.—_Poecilimon affinis_ ♂. Bulgaria. Alar organs serving only as musical organs. The ear on front tibia and aural orifice of prothorax are well shown.]