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Abdomen consisting at the most of from ten to twelve segments. No functional abdominal legs except in the Thysanura, and in the larvæ of Lepidoptera. A pair of 1– or many-jointed cercopods on the tenth segment; and in certain forms a pair of styles on the ninth segment. In certain orders an ovipositor or sting formed of three pairs of styliform processes; in Collembola a single pair of processes forming the elater.

The genital openings opisthogoneate, usually single, but paired in Thysanura (Lepisma), Dermaptera, and Plectoptera (Ephemeridæ).

The digestive canal in the winged orders is highly differentiated, the fore-intestine being divided into an œsophagus and proventriculus, the hind-intestine into an ileum, colon, and rectum, with rectal glands.

The nervous system consists of a well-developed brain, in the more specialized orders highly complicated; no more than thirteen pairs of ganglia, which may be more or less fused in the more specialized orders. Three frontal ganglia, and a well-developed, sympathetic system present.