The high number of abdominal segments found in the Cockroach (ten or eleven) is characteristic of the lower orders of Insecta. It is never exceeded; though in the more specialised orders, such as Lepidoptera and Diptera, it may be reduced to nine, eight, or even seven. The sessile abdomen of the Cockroach is primitive with respect to the pedunculate abdomen found in such insects as Hymenoptera, where the constricted and flexible waist stands in obvious relation to the operations of stinging and boring, or to peculiar modes of oviposition. The first abdominal segment, which is especially liable to dislocation and alteration in Insects, occupies its theoretical position in the Cockroach, though both tergum and sternum are reduced in size. The sternum is often altogether wanting, while the tergum may unite with the metathorax. The externally visible appendages of the abdomen are the cerci and the styles of the male Cockroach. The cerci are found in both sexes; they are composed of sixteen rings each, and project beneath the edge of the tenth tergum. They are capable of erection by special muscles, and are supplied by large nerves.[81] The sub-anal styles are peculiar in their insertion, being carried upon the sternum of their segment (the ninth). [81] Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera); in the Earwig they become modified and form the forceps. The “caudal filaments” of _Apus_ are curiously like cerci. The cerci are concealed in the American _Cryptocercus_, Scudd. (Fam. _Panesthidæ_). [Illustration: Fig. 33.--Profile of Male and Female Cockroach. × 4.] The abdominal segments are never furnished with functional legs in adult Insects, but representatives of the lost appendages are often met with in larvæ. According to Bütschli,[82] all the abdominal segments are provided with appendages in the embryo of the Bee, though they disappear completely before hatching. Some Hymenopterous larvæ have as many as eight pairs of abdominal appendages, Lepidopterous larvæ at most five (3–6; 10).[83] [82] Entw. der Biene. Zeits. f. wiss. Zool. Bd. XX. Or, see Balfour’s Embryology, Vol. I., p. 338. [83] From more recent observations it is probable that abdominal appendages are usually present in the embryos of Orthoptera, Coleoptera, Lepidoptera, and possibly Hymenoptera. The subject is rapidly advancing, and more will be known very shortly. CHAPTER V. THE MUSCLES; THE FAT-BODY AND CŒLOM. _SPECIAL REFERENCES._ VIALLANES. Histologie et Développement des Insectes. Ann. Sci. Nat., Zool., Tom. XIV. (1882). KÜHNE in Stricker’s Histology, Vol. I., chap. v. PLATEAU. Various Memoirs in Bull. Acad. Roy. de Belgique (1865, 1866, 1883, 1884). [Relative and Absolute Muscular Force.] LEYDIG. Zum feineren Bau der Arthropoden. Müller’s Archiv., 1855. WEISMANN. Ueber zwei Typen contractilen Gewebes, &c. Zeits. für ration. Medicin. Bd. XV. (1862).