=Baudelot, E.= Du mecanisme suivant lequel s’effectue chez les Coléoptères le retract des ailes inférieures sous les élytres au moment du passage a l’état de repos. (Bull. Soc. d. Scienc. nat., Strasbourg, 1 Année, 1868, pp. 137–138.) =Ris, Fr.= Die schweizerischen Libellen. Schaffhausen, 1885. (Beiheft der Mitteil. d. Schweiz. Ent. Ges., vii, pp. 35–84.) THE ABDOMEN AND ITS APPENDAGES [Illustration: FIG. 176.—Abdomen of _Termes flavipes_: 1–10, the ten tergites; 1–9, the nine urites; _c_, cercopod. ] [Illustration: FIG. 177.—End of abdomen of _Panorpa debilis_ drawn out, the chitinous pieces shaded: _L_, lateral, _D_, dorsal view; _c_, jointed cercopoda.—Gissler _del._ ] In the abdomen the segments are more equally developed than elsewhere, retaining the simple annular shape of embryonic life, and from their generalized nature their number can be readily distinguished (Fig. 176). The tergal and sternal pieces of each segment are of nearly the same size, the tergal often overlapping the sternal (though in the Coleoptera the sternites are larger than the tergites), while there are no pleural pieces, the lateral region being membranous when visible and bearing the stigmata (Fig. 177, _L_). In the terminal segments beyond the genital outlet, however, there is a reduction in and loss of segments, especially in the adults of the metabolous orders, notably the Panorpidæ (Fig. 177), Diptera, and aculeate Hymenoptera; in the Chrysididæ only three or four being usually visible, the distal segments being reduced and telescoped inward. The typical number of abdominal segments (uromeres), _i.e._ that occurring in each order of insects, is ten; and in certain families of Orthoptera, eleven. In the embryos, however, of the most generalized winged orders, Orthoptera (Fig. 199), Dermaptera, and Odonata, eleven can be seen, while Heymons has recently detected twelve in blattid and Forficula embryos, and he claims that in the nymphs of certain Odonata there are twelve segments, the twelfth being represented by the anal or lateral plates. It thus appears that even in the embryo condition of the more generalized winged insects, the number of uromeres is slightly variable. We have designated the abdomen as the _urosome_; the abdominal segments of insects and other Arthropods as _uromeres_, and the sternal sclerites as _urosternites_, farther condensed into _urites_. (See Third Report U. S. Entomological Commission, 1883, pp. 307, 324, 435, etc.) [Illustration: FIG. 178.—Nymph of the pear tree Psylla, with its glandular hairs.—After Slingerland. Bull. Div. Ent. U. S. Dep. Agr. ]