showing the gradual transfer and fusion of this segment with the thorax.) In the saw-flies the fusion is incomplete, as also in the Lepidoptera, while in the Diptera and all other orders the thorax consists of but three segments. (See also pp. 90–92.) [Illustration: FIG. 179.—Abdomen of _Machilis maritima_, ♀, seen from beneath: the left half of the 8th ventral plate removed; I-IX, abdominal segments; _c_, cercopoda; _cb_, coxal glands; _hs_, coxal stylets; _lr_, ovipositor.—After Oudemans, from Lang. ] =The cercopoda.=—We have applied this name to the pair of anal cerci appended to the tenth abdominal segment, and which are generally regarded as true abdominal legs. As is now well known, the embryos of insects of different orders have numerous temporary pairs of abdominal appendages which arise in the same manner, have the same embryonic structure, and are placed in a position homologous with those of the thorax. In the embryo of Œcanthus rudimentary legs appear, as shown by Ayers, on the first to tenth abdominal segment, the last or tenth pair becoming the cercopoda; and similar rudimentary appendages have been detected in the embryos of Coleoptera, Lepidoptera, and Hymenoptera (Apidæ). Cholodkowsky has observed eleven pairs of abdominal appendages in Phyllodromia. They are very long and multiarticulate in the Thysanura (Fig. 179). In the Dermaptera they are not jointed and are forcep-like. It should also be observed that in the larva or Sisyra (Fig. 181) there are seven pairs of 5–jointed abdominal appendages, though these may be secondary structures or tracheal gills. In the Perlidæ and the Plectoptera (Ephemeridæ), they are very long, sometimes over twice as long as the body, and composed of upward of 55 joints; they also occur in the Panorpidæ (Fig. 177). In the dragon-flies the cerci are large, but not articulated, and serve as claspers or are leaf-like[35] (Fig. 180). In a few Coleoptera, as the palm-weevil (_Rhynchophorus phœnicis_), Cerambyx, Drilus, etc., the so-called ovipositor ends in a hairy, 1–jointed, palpiform cercus. Short 25–jointed cercopoda are present in Termitidæ, and 2–jointed ones in Embiidæ. [Illustration: FIG. 180.—End of abdomen of _Æschna heros_, ♀: _ur_, urosternite; _or_, outer, _ir_, inner styles of the ovipositor; 11, 11th abdominal segment; _c_, cercopod. ] [Illustration: FIG. 181.—Larva of Sisyra, from beneath. _B_, an abdominal appendage.—After Westwood, from Sharp. ] [Illustration: FIG. 182.—Cercopoda (P) of Mantis.—After Lacaze-Duthiers. ]