Very little information exists as to the life-history of the Aptera; as for their food, it is generally considered to consist of refuse vegetable or animal matter. It is usual to say that they are completely destitute of metamorphosis, but Templeton says of Lepisma niveo-fasciata that "the young differ so much from the mature Insect that I took them at first for a distinct species; the thoracic plates are proportionately less broad, and the first is devoid of the white marginal band." As regards the moults, it would appear that in this, as in so many other points, great diversity prevails, Grassi stating that in Campodea there is a single fragmentary casting of the skin; and Sommer informing us that in Macrotoma plumbea the moults are not only numerous, but continue, after the creature has attained its full growth, throughout life.
A very marked feature of the Aptera is their intolerance of a dry atmosphere. Although Campodea can exist under very diverse conditions, it dies very soon after being placed in a dry closed tube; and the same susceptibility appears to be shared by all the other members of the Order, though it is not so extreme in all; possibly it may be due to some peculiarity in the structure of the integument. So far as tolerance of heat and cold goes, the Aptera can apparently exist in any climate, for though some of the species extend to the Arctic regions, others are peculiar to the tropics.
Thysanura are recorded by Klebs and Scudder as occurring commonly in amber; the latter author has described a fossil, supposed to be a Lepisma, found in the Tertiary deposits at Florissant. Scudder has also described another fossil, likewise from Florissant, which he considers to form a special sub-order of Thysanura—Ballostoma—but it is extremely doubtful whether this anomalous creature should be assigned to the Order at all. A still older fossil, Dasyleptus lucasii Brongniart, from the Carboniferous strata in France, is considered to belong to the Order Aptera, but it must be admitted there is some doubt on this point.
The interest aroused in the minds of naturalists by the comparatively simple forms of these purely wingless and therefore anomalous Insects has been accompanied by much discussion as to their relations to other Insects, and as to whether they are really primitive forms, or whether they may perhaps be degenerate descendants from some less unusual states of Insect-life. Mayer and Brauer dissociated our Aptera entirely from other Insects, and proposed to consider the Hexapoda as being composed of two groups—(1) the Apterygogenea, consisting of the few species we have been specially considering; and (2) the Pterygogenea, including all the rest of the immense crowd of Insect forms. They were not, however, able to accompany their proposed division by any satisfactory characters of distinction, and the subsequent progress of knowledge has not supported their view, all the best investigators having found it necessary to recognise the extremely intimate relations of these Insects with the Orthoptera. Meinert thought that Lepisma must be included in the Orthoptera; Grassi proposes to consider the Thysanura as a distinct division of Orthoptera; and Oudemans recognises the close relations existing between Machilis and Orthoptera proper. Finot includes the Aptera in his Orthoptères de la France, and a species of Japyx has actually been described by a competent entomologist as an apterous earwig. At present, therefore, we must conclude that no good distinction has been found to justify the separation of the Aptera from all other Insects.
The taxonomy of the Collembola has not yet been adequately treated, and it is possible that more grounds will be found for separating them as a distinct Order from the Thysanura,—a course that was advocated by Lubbock,—than exist for dividing these latter from the Orthoptera proper. There are apparently no grounds for considering the Aptera to be degenerate Insects, and we may adopt the view of Grassi, that they are primitive, or rather little evolved forms. It must be admitted that there are not at present any sufficient reasons for considering these Insects to be "ancient" or "ancestral." The vague general resemblance of Campodea to many young Insects of very different kinds is clearly the correlative of its simple form, and is no more proof of actual ancestry to them than their resemblances inter se are proofs of ancestry to one another. But even if deprived of its claim to antiquity and to ancestral honours, it must be admitted that Campodea is an interesting creature. In its structure one of the most fragile of organisms, with a very feeble respiratory system, inadequate organs of sense, only one pair of ovarian tubes, very imperfect mouth-organs, and a simple alimentary canal, it nevertheless flourishes while highly-endowed Insects become extinct. In the suburban gardens of London, on the shores of the Mediterranean, on the summits of the higher Pyrenees, in North America even it is said in the caves of Kentucky, and in India, Campodea is at home, and will probably always be with us.
CHAPTER VIII
ORTHOPTERA—FORFICULIDAE, EARWIGS—HEMIMERIDAE
Order II.—Orthoptera.
Insects with the mouth parts conspicuous, formed for biting, the four palpi very distinct, the lower lip longitudinally divided in the middle. The tegmina (mesothoracic wings), of parchment-like consistence, in repose closed on the back of the Insect so as to protect it. The metathoracic wings, of more delicate consistence, ample, furnished with radiating or divergent nervures starting from the point of articulation, and with short cross nervules forming a sort of network; in repose collapsing like a fan, and more or less completely covered by the tegmina (except in certain Phasmidae, where, though the wings are ample, the tegmina are minute, so that the wings are uncovered). In a few forms (winged Forficulidae and some Blattidae) the metathoracic wings are, in addition to the longitudinal folding, contracted by means of one or two transverse folds. The mode of growth of each individual is a gradual increase of size, without any abrupt change of form, except that the wings are only fully developed in the final condition. There is no special pupal instar. Species in which the wings are absent or rudimentary are numerous.
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.