=Diagnostic or essential characters of Symphyla.=—_Head shaped as in Thysanura (Cinura), with the Y-shaped tergal suture, which occurs commonly in insects (Thysanura, Collembola, Dermaptera, Orthoptera, Platyptera, Neuroptera, etc.), but is wanting in Myriopoda (Diplopoda and Chilopoda); antennæ[8] unlike those of Myriopoda in being very long, slender, and moniliform. Clypeus distinct. Labrum emarginate, with six converging teeth. Mandibles 2–jointed, consisting of a vestigial stipes and distal or molar joint, the latter with eight teeth. First maxillæ with an outer and inner mala situated on a well-developed stipes; with a minute, 1–jointed palpus. Second pair of maxillæ: each forming two oblong flat pieces, median sutures distinct, with no palpi; these pieces are toothed in front, and appear to be homologous with the two median pieces of the gnathochilarium of Diplopoda. Hypopharynx? Epipharynx?_ _Trunk with from fifteen to sixteen dorsal, more or less free subequal scutes, the first the smallest. Pedigerous segments twelve; also twelve pairs of 5–jointed legs, which are of nearly equal length, the first pair 4–, the others 5–jointed, all ending in two claws, as in Synaptera and winged insects. A pair of 1–jointed anal cerci homologous with those of Thysanura and Orthoptera, into each of which opens a large abdominal silk-gland. Abdominal segments with movable styles or “pseudopods” (“Parapodia” of Latzel and of Schmidt), like those of Campodea and Machilis, and situated on the base of the coxal joint in front of the ventral sac. Within the body near the base of each abdominal style is an eversible coxal sac or blood-gill (Fig. 15, cg). The single genital opening is on the fourth trunk-segment in both sexes (Fig. 15, indicated by the arrow). The malpighian tubes (ur. t) are two in number, opening into the digestive canal at the anterior end of the hind intestine; they extend in front to the third or second segment from the head. They are broad and straight at their origin, becoming towards the end very slender and convoluted._ _The three divisions of the digestive tract are as in insects, the epithelium of the mid-gut being histologically as in Campodea and Japyx; rectal glands are present. A pair of very large salivary glands are situated in the first to the fourth trunk-segments, consisting of a glandular portion with its duct, which unite into a common duct opening on the under side of the head, probably in the labium._ _But a single pair of stigmata is present, and these are situated in the front of the head, beneath the insertion of the antennæ and within the stipes of the mandibles; the tracheæ are very fine, without spiral threads (tænidia), and mostly contained within the head, two fine branches extending on each side into the second trunk-segment._ _After birth the body increases in length by the addition of new segments at the growing point._