being almost
obsolete in the Poduridae, this being one of the most essential
characters of that family. Indeed, it is somewhat singular that these
and other important characteristics of this group have been almost
entirely passed over by authors, who have consequently separated these
insects from other groups on what appear to the writer as comparatively
slight and inconsiderable characters. The mouth-parts of the Lepismatidae
(especially the thermophilous Lepisma, which we now describe) are most
readily compared with those of the larva of Perla. The rather large,
stout mandibles are concealed at their tips, under the upper lip, which
moves freely up and down when the creature opens its mouth. The mandible
is about one-third as broad as long, armed with three sharp teeth on the
outer edge, and with a broad cutting edge within, and still further
inwards a lot of straggling spinules. In all these particulars, the
mandible of Lepisma is comparable with that of certain Coleoptera and
Neuroptera. So also are the maxillae and labium, though we are not aware
that any one has indicated how close the homology is. The accompanying
figure (152) of the maxilla of a beetle may serve as an example of the
maxilla of the Coleoptera, Orthoptera and Neuroptera. In these insects
it consists almost invariably of three lobes, the outer being the
palpus, the middle lobe the galea, and the innermost the lacinia; the
latter undergoing the greatest modifications, forming a comb composed of
spines and hairs varying greatly in relative size and length. How much
the palpi vary in these groups of insects is well known. The galea
sometimes forms a palpus-like appendage. Now these three lobes may be
easily distinguished in the maxilla of Lepisma. The palpus instead of
being directed forward, as in the insects mentioned above (in the pupa
of Ephemera the maxilla is much like that of Lepisma), is inserted
nearer the base than usual and thrown off at right angles to the
maxilla, so that it is stretched out like a leg, and in moving about the
insect uses its maxillae partly as supports for its head. They are very
long and large, and five or six-jointed. The galea, or middle division,
forms a simple lobe, while the lacinia has two large chitinous teeth on
the inner edge, and internally four or five hairs arising from a thin
edge.

[Illustration: 152. Maxilla.]

The labium is much as in that of Perla, being broad and short, with a
distinct median suture,