On the under surface of the abdomen of the earwig the full number of 10 plates cannot be superficially distinguished; but it is found by dissection that in the female the short eighth and ninth dorsal rings are joined on the ventral aspect by a delicate membrane, while the tenth ventral is of a less delicate {205}nature, and forms a triangular plate at the base of each half of the forceps. Between the branches of the forceps there is a perpendicular plate, the pygidium of Orthopterists, possibly the unpaired terminal portion of the body seen in some embryos, and called the telson. The pygidium is a separate sclerite, though it looks as if it were only a portion of the large tenth dorsal plate bent downwards, and in some descriptive works is erroneously described as being such. [Illustration: FIG. 105.—_Chelidura dilatata_, male. Pyrenees.] [Illustration: FIG. 106.—Tegmina and wings (visible in part or invisible) of apterous earwigs. 1, _Chelidura_ sp.; 2, _Chelidura dilatata_; 3, _Anisolabis moesta_; 4. _A. maritima_. _a_, First thoracic segment; _b_, second; _c_, third; _d_, basal portion of abdomen.] A very large number of species of Forficulidae have the organs of flight undeveloped. Fig. 105 represents _Chelidura dilatata_, an apterous form that is very common in the Eastern Pyrenees. The condition of the meso- and meta-nota—the parts from which the tegmina and wings are developed, and to which they are attached when present—is very remarkable in these forms, and exhibits much variety. In Fig. 106 we represent the conditions of these parts in a few apterous forms. The tegmina or the segment from which they are developed (_b_), are seen in the shape of a plate which may extend all across the middle and be undivided (No. 4); in which case the appearance indicates entire absence of the tegmina; these are, on the contrary, evidently present in the form of slips grafted one to each side of the second thoracic segment in _Anisolabis_ (No. 3); or they may look like short broad slips extending all across the body, and marking off a piece frequently called a scutellum, but which is really the mesonotum (some species of _Chelidura_, as No. 2); or, again, they may be nearly free tegmina, somewhat similar to those of the winged forms; this is the case with some species of _Chelidura_, as represented by No. 1. This last figure is taken from a species from the Sierra Nevada, apparently undescribed, allied to _C. bolivari_.