Campodeidae as a family may be briefly defined as Thysanura with the trophi buried in the head and with the body terminated by antenna-like processes. We shall consider some of the anatomical peculiarities of this interesting Insect after we have briefly reviewed some of the external characters of the other Thysanura.
The second family (Japygidae) consists of one genus Japyx, of which there are, no doubt, several different species in various parts of the world, such having already been detected in tropical Africa, in Malasia, and in Mexico, as well as in Madeira and Europe. The commoner species of the latter continent, Japyx solifugus, lives in moss or in shady places on the edges of woods. It possesses a great resemblance to a newly-hatched earwig, and the writer has found it in France under a stone in company with a number of the tiny creatures it was so much like. This species has been found as far north as Paris, but has not been met with in Britain. The family Japygidae is, like the Campodeidae, entotrophous, and is distinguished by the body being terminated behind by a pair of forceps instead of antennary organs.
The other two families of Thysanura, Machilidae and Lepismidae, are ectotrophous—that is, the parts of the mouth are not buried in the head, but are arranged in the fashion usual in mandibulate Insects.
Only one genus of Machilidae is known, but it is no doubt very numerous in species, and probably is distributed over most of the globe. Machilis maritima is common in some places on the coast of England. Another species (M. polypoda) occurs amongst dead leaves in the New Forest, and we have also observed a species of the genus under the loose stones that frequently form the tops of the "dykes" or piled walls in Scotland. In more southern Europe species of Machilis are commonly met with on the perpendicular faces of very large stones or rocks, over which they glide with wonderful facility. The scales on the bodies of these rock-inhabiting species form pretty patterns, but are detached with such facility that it is almost impossible to obtain specimens in satisfactory condition for examination.
In Machilidae the dorsal plates of the hind body are reflexed to the under surface so as to form an imbrication covering the sides of the ventral plates, and the eyes are largely developed; by which characters the family is distinguished from the Lepismidae. The pair of large compound eyes (Fig. 92, O) is a remarkable feature, being indeed unique in the Aptera. The structures (o, o′) that Oudemans considers to be simple eyes have, in external appearance, a resemblance to the fenestrae of the Blattidae; Grassi states, however, that not only are they eyes, but that they are of almost unique structure, being, in fact, intermediate between simple and compound eyes.
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.
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.
Fig. 93.—Lepisma cincta. (After Oudemans.) × 4. (The line indicates the natural length.)