marily of six segments,
whereof the basal is large and usually fused with its fellow to form a
large coxal plate, the second is small and generally suppressed by
fusion with the third, the fourth and fifth are also small, while the
sixth is transformed into a great piercing fang, at the tip of which
opens the duct of a poison gland lodged within the appendage.

The tergal elements of the somites bearing the antennae, mandibles and
maxillae appear to be represented by the head-shield or cephalite. The
tergal element of the somite bearing the palpognath is usually
suppressed; that of the toxicognath is sometimes of large size as in
some Geophilomorpha (_Himantarium_), sometimes small as in
_Scutigera_, _Lithobius_, _Craterostigmus_, sometimes suppressed
probably by fusion with the tergum of the first leg-bearing somite as
in the Scolopendromorpha. The sternal plates of all the jaw-bearing
somites have disappeared, except in the case of the somite of the
toxicognath, where it may be vestigial. In the case of the somites
bearing the walking legs the tergal and sternal elements are preserved
without fusion with the corresponding plates of the preceding or
succeeding somites, so that great flexibility of the body is retained.
The only exception to this is presented by _Scutigera_, where the
terga corresponding to the somites bearing the fifteen pairs of legs
are reduced by fusion and suppression to seven. The walking legs are
articulated to the inferior portion of the pleural or lateral area of
the somites close to the external margins of the sterna, which widely
separate those of the left from those of the right side. Generally
speaking the legs resemble each other, although as a rule they
progressively increase in length towards the posterior end of the
body. They consist typically of six segments, of which the basal is
termed the coxa and the apical the tarsus. The tarsus is armed with a
single terminal claw, and, except in the Geophilomorpha and a few
genera of other orders, is divided by a mesial transverse joint into
two segments, as is the case in _Scolopendra_ and _Lithobius_ for
example. But in some of the longer-legged, swift-footed centipedes of
the order Lithobiomorpha (e.g. _Henicops_, _Cermalobius_) the tarsi
are further subdivided. The multiplication of sub-segments reaches its
maximum in _Scutigera_, where the tarsi are extremely long, slende