Scudder has informed us[114] that not only were Insects abundant in the Tertiaries, but that their remains indicate conditions of existence very similar to what we find around us. "Certain peculiarities of secondary sexual dimorphism accompanying special forms of communistic life, such as the neuters and workers in Hymenoptera and the soldiers among the Termitina, are also found, as would be expected, among the fossils, at least through the whole series of the Tertiaries. The same may be said of other sexual characteristics, such as the stridulating organs of the Orthoptera, and of peculiarities of oviposition, as seen in the huge egg-capsules of an extinct Sialid of the early Tertiaries. The viviparity of the ancient Aphides is suggested, according to Buckton, by the appearance of one of the specimens from the Oligocene of Florissant, while some of the more extraordinary forms of parasitism are indicated at a time equally remote by the occurrence in amber of the triungulin larva of _Meloe_, already alluded to, and of a characteristic strepsipterous Insect; not only, too, are the present tribes of gall-making Insects abundant in the Tertiaries, but their galls as well have been found." {180}CHAPTER VII THE ORDER APTERA–DEFINITION–CHIEF CHARACTERISTICS–THYSANURA–CAMPODEA– JAPYX–MACHILIS–LEPISMA–DIVERSITY OF INTERNAL STRUCTURE IN THYSANURA– ECTOTROPHI AND ENTOTROPHI–COLLEMBOLA–LIPURIDAE–PODURIDAE–SMYNTHURIDAE– THE SPRING–THE VENTRAL TUBE–ABDOMINAL APPENDAGES–PROSTEMMATIC ORGAN– TRACHEAL SYSTEM–ANURIDA MARITIMA–COLLEMBOLA ON SNOW–LIFE-HISTORIES OF COLLEMBOLA–FOSSIL APTERA–APTERYGOGENEA–ANTIQUITY AND DISTRIBUTION OF CAMPODEA. ORDER I. APTERA. _Small Insects with weak outer skin, destitute throughout life of wings or their rudiments, but with three pairs of legs; antennae large or moderate in size._ The above definition is the only one that can at present be framed to apply to all the Insects included in our Aptera. Unfortunately it is far from diagnostic, for it does not enable us to distinguish the Aptera from the larvae or young individuals of many Insects of other Orders. There are, however, certain characters existing in many species of Aptera that enable their possessors to be recognised with ease, though, as they are quite wanting in other members, they cannot correctly be included in a definition applying to the whole of the Order. We are thus brought in view of two of the most important generalisations connected with the Aptera, viz. that these Insects in their external form remain throughout their life in a condition resembling the larval state of other Insects, and that they nevertheless exhibit extreme variety in structural characters.