Lamellicorn beetle examined by these gentlemen. In the case of the set of earwigs we have mentioned, very little variation existed in the length of the forceps in the female sex. [Illustration: FIG. 109.—Forceps of the common earwig: A, of large male; B, of small male; C, of female.] In many earwigs—including _F. auricularia_—there may be seen on each side of the dorsal aspect of the true fourth, or of the fourth and neighbouring segments of the hind body a small elevation, called by systematists a plica or fold, and on examination the fold will be found to possess a small orifice on its posterior aspect. These folds are shown in Figs. 105 and 108; {210}they have been made use of for purposes of classification, though no functional importance was attached to them. Meinert, however, discovered[132] that there are foetid glands in this situation, and Vosseler has recently shown[133] that the folds are connected with scent-glands, from which proceed, in all probability, the peculiar odour that is sometimes given off by the earwig. The forms destitute of the folds, e.g. _Labidura_, are considered to have no scent glands. There is a very peculiar series of smooth marks in the earwigs on the dorsal aspect of the abdominal segments, and these are present in the glandless forms as well as in the others. The internal anatomy has been to some extent investigated by Dufour and Meinert. Dufour dissected _F. auricularia_ and _Labidura riparia_, and found[134] that salivary glands exist in the latter Insect (called by him _Forficula gigantea_), though he was unable to discover them in the common earwig. According to Meinert,[135] there are, however, salivary glands affixed to the stipes of the maxillae in _F. auricularia_, while (in addition?) _L. riparia_ possesses very elongate glands seated in the middle or posterior part of the breast. The alimentary canal is destitute of convolutions, but oesophagus, crop, and gizzard all exist, and the intestine behind the stomach consists of three divisions. The Malpighian tubes are numerous, 30 or 40, and elongate. The respiratory system is not highly developed. Earwigs—the European species at least—have, as already mentioned, very small powers of flight; the tracheal system is correspondingly small, and is destitute of the vesicular dilatations that are so remarkable in the migratory Locusts. [Illustration: FIG. 110.—_Labidura riparia_, male. Europe.] The three thoracic spiracles[136] are readily observed in living {211}individuals. There are seven pairs of abdominal spiracles, which, however, are very minute, and can only be found by distending the body as shown in Fig. 103. The ventral chain consists of nine ganglia (the sub-oesophageal centre is not alluded to by Dufour); the three thoracic are equidistant and rather small; the hindmost of the six abdominal ganglia is considerably larger than any one of the other five.