oup of Poduras are remarkably constant, a description of one
genus will suffice for all. The labrum, or upper lip, is separated by a
deep suture from the clypeus, and is trapezoidal in form. The mandibles
and maxillae are long and slender, and buried in the head, with the tips
capable of being extended out from the ring surrounding the mouth for a
very short distance. The mandibles (_md_, Fig. 159) are like those of
the Neuroptera, Orthoptera and Coleoptera in their general form, the tip
ending in from three to six teeth (three on one mandible and six on the
other), while below, is a rough, denticulated molar surface, where the
food seized by the terminal teeth is triturated and prepared to be
swallowed. Just behind the mandibles are the maxillae, which are
trilobate at the end, as in the three orders of insects above named. The
outer lobe, or palpus, is a minute membranous tubercle ending in a hair
(Fig. 161, _mp_), while the middle lobe, or galea, is nearly obsolete,
though I think I have seen it in Smynthurus, where it forms a lobe on
the outside of the lacinia. The lacinia, or inner lobe (Fig. 161, _lc_;
162, the same enlarged), in Tomocerus consists of two bundles of
spinules, one broad like a ruffle, and the other slender, pencil-like,
ending in an inner row of spines, like the spinules on the lacinia of
the Japyx and Campodea and, more remotely, the laciniae of the three
sub-orders of insects above referred to. There is also a horny,
prominent, three-toothed portion (Fig. 161, _g_). These homologies have
never been made before, so far as the writer is aware, but they seem
natural, and suggested by a careful examination and comparison with the
above-mentioned mandibulate insects.

[Illustration: 159. 161. 160. 162.

Tomocerus plumbeus and mouth-parts, greatly enlarged.]

The spring consists of a pair of three-jointed appendages, with the
basal joints soldered together early in embryonic life, while the other
two joints are free, forming a fork. It is longest in Smynthurus and
Degeeria, and shortest in Achorutes (Fig. 172, _b_), where it forms a
simple, forked tubercle; and is obsolete in Lipura and Anura, its place
being indicated by an oval scar. The third joint varies in form, being
hairy, serrate and knife-like in form, as in Tomocerus (Fig. 159, _a_),
or minute, with a supplementary tooth, as in Achorutes (Fig. 172,
_c_). This spring is in part homologous with the ovipositor of the
higher insects, which orig