THE BRITISH SNAKE-FLIES (RAPHIDIA). 83
The imagines are soft-bodied insects with the mouth parts
formed for biting; the head is comparatively large, widest in
front, and the posterior reduced to what looks like a neck.
The mandibles are sharp-pointed, sickle-shaped organs with two
teeth on their inner surface. The antennae are of medium
length, composed of many bead-like segments, of which the
first and second are larger than the others. The con-
spicuous compound eyes are placed on the sides of the head
just behind the antenna?. The prothorax is developed into a
long cylinder, much narrower than the head, giving the insect
what appears to be a long neck. Theoretically each segment
of an insect is composed of a number of chitinous plates joined
together by an elastic membrane, there being two dorsal, two
ventral, and two pairs of lateral plates. In the Snake-flies it
seems to me that the dorsal plates have joined to form a tube,
leaving only a triangular opening on the posterior ventral
surface, into which the other plates have been forced, so that
the first pair of legs, when held in the natural position, force
the prothorax into a nearly vertical position. The meso- and
meta-thorax are short, but much wider than the pro-
thorax. The legs are of medium length, the third joint of
the tarsi is dilated and cleft, partly concealing the fourth joint.
The Snake-flies possess four membranous, nearly equal, wings,
the nervation being very similar in both pairs; when at rest
the wings are deflexed. The abdomen of the female is furnished
with a long flexible ovipositor, composed of two transversely
striated tubes, with a valve at the apex of each. In the
male the genitalia are upon the penultimate segment,
the last segment being hollowed out on the ventral surface
so as to fold over the genitalia.
The larvae of Raphidiae live in or under the bark of trees, and
are long and flat in form; they have a squarish head with
mouth-parts similar to those of the adult; the antennae are
composed of three segments. The prothorax is large and
parallel-sided, the meso- and meta-thorax small, the legs also
small. The abdomen is gradually attenuated to each end and
is clothed with fine hairs.
The pupa is very similar to the imago, the limbs being free,
like those of a beetle-pupa. In the female the ovipositor does
not project backwards in line with the body, but is folded back