It has been found in several species that there are eight pairs of abdominal spiracles, making, with the two thoracic, ten pairs in all. The first of the abdominal spiracles is larger than the others, and in the winged species may be easily detected by raising the tegmina and wings, it being more dorsal in position than those following, which are in some species exposed on the ventral surface owing to the cutting away of the hind angles of the ventral plates; but the terminal spiracles are in all cases difficult to detect, and it is possible that the number may not be the same in all the species of the family. The cerci exhibit a great deal of variety. In the species with elongate tegmina and wings the cerci are elongate, and are like antennae in structure; in many of the purely apterous forms the cerci appear to be entirely absent (cf. Fig. 130, _Gromphadorhina_), but on examination may be found to exist in the form of a small plate, or papilla scarcely protuberant. In the males of _Heterogamia_ they are, on the {225}contrary, very like little antennae; in the unwinged females of this genus they are concealed in a chink existing on the under-surface of the apex of the body. The alar organs of Blattidae are of considerable interest from several points of view. They exist in various conditions as regards size and development, and in some forms are very large; each tegmen in some species of the genus _Blabera_ (Fig. 132) may attain a length of nearly three inches; in other cases wings and tegmina are entirely absent, and various intermediate conditions are found. In Fig. 121 we give a diagram of the tegmen or front wing, A, and the hind wing, B, to explain the principal nervures and areas. The former are four in number, and, adopting Brunner's nomenclature[149] for them, are named proceeding from before backwards mediastinal, _a_; radial, _b_; infra-median (or ulnar), _c_; and dividens, _d_. An adventitious vein, vena spuria, existing in the hind wings of certain genera is marked _sp_ in B. [Illustration: FIG. 121.—Diagram of tegmen, A, and wing, B, in Blattidae. Nervures: _a_, mediastinal; _b_, radial; _c_, ulnar or infra-median; _d_, dividens; _sp_, spuria. Areas: 1, mediastinal or marginal; 2, scapular or radial; 3, median; 4, anal or axillary.]