The mode of development of the compound eyes of _Machilis_ is of considerable interest, but unfortunately very little is known about it, even the period at which the eyes appear being uncertain. Judging from analogy with the Orthoptera, we should suppose them to be present when the Insect leaves the egg, and Oudemans apparently considers this to be the case, but Bolivar states[118] that in the early stages of _Machilis_ the eyes are only simple eyes; these being replaced by compound eyes in the later life. The writer has observed very young individuals of _Machilis polypoda_, and found the eyes to be evidently compound. [Illustration: FIG. 92.—Head of _Machilis maritima_ (after Oudemans): _A_, base of antenna; _C_, clypeus; _F_, vertex; _P_, fold; _O_, eye; _o_, _o′_, supposed simple eye; _M_, mandible; _m_, maxilla; _L_, upper lip; _l_, lower lip; _T_, portion of maxillary palp; _t_, of labial palp. × 20.] [Illustration: FIG. 93.—_Lepisma cincta._ (After Oudemans.) × 4. (The line indicates the natural length.)] The remaining family of Thysanura, the Lepismidae, is in certain respects the most highly developed of the Order. The covering of scales found on the body is very remarkable in some of the species, especially in the genus _Lepisma_ (Fig. 93, _L. cincta_); the thoracic segments are different from one another {186}and from those of the abdomen, and the tracheal system is more highly developed than it is in the Machilidae. Several genera are known, but only two members of the family have yet been detected in Britain. One of them (_Lepisma saccharina_), occurs only in houses, and is sometimes called the silver fish; it is, when full grown, less than half an inch long, and is covered with scales that give it a feebly metallic lustre. Like the other Thysanura, its movements are very perfect. It is said that it is occasionally injurious by nibbling paper, but the writer's observations lead him to doubt this; its usual food is doubtless farinaceous or saccharine matter. _Thermobia furnorum_, our other British Lepismid, has only recently been discovered; it is found in bakehouses at Cambridge and elsewhere. The bakers call these Insects fire-brats, apparently considering them to be fond of heat.