"The wings are traversed by a system of _Veins_--tubular structures which
serve at once as extensions of the tracheal system, and to form a stiff
framework for the support of the wing. In the normal type of _Lepidoptera_
the fore-wings possess three free veins towards the dorsum, termed 1_a_,
1_b_, and 1_c_; a central cell, out of which rise ten veins, numbered 2 to
11, the sides of the cell being known as the upper median, lower median,
and transverse veins respectively; and a free subcostal vein, numbered 12;
whilst the hind-wings differ from the fore-wings in having only six veins
rising from the central cell, numbered 2 to 7, so that the free subcostal
vein is numbered 8 (see Plate I., figs. 3 and 4, assumed type of neuration
of a Lepidopterous insect). In some forms a forked parting-vein traverses
the middle of the cell longitudinally, and a second parting-vein traverses
the upper portion, so as to form a secondary cell; but these are more
frequently absent or represented only by folds in the membrane. In a few
forms there is a tendency to the production of several false veins, termed
_pseudoneuria_, appearing as short branches from the subcostal vein of the
hind-wings to the costa; these are thickenings of the membrane, and are
commonly very irregular and variable, often uneven in thickness or
incomplete. Sometimes one of these near the base is better developed and
more permanent in character; it is then termed the _præcostal spur_ (see
Plate I., figs. 8^9 and 27^9). Modifications in the general arrangement of
the veins may arise through any of the following processes, viz.: (1)
_obsolescence_, when a vein loses its normal tubular structure, becoming
attenuated and reduced in substance, until it appears a mere fold of the
membrane (Plate II., fig. 60, vein 5 in hind-wings of _Selidosema_); (2)
_stalking_, when the two veins are fused together for a portion of their
length from their base, so as to appear to rise on a common stalk (Plate
II., fig. 34, veins 6 and 7 in hind-wing of _Hydriomena_); (3)
_coincidence_, when two veins are fused together for the whole of their
length, so that one appears entirely absent, an extreme form of stalking;
(4) _anastomosis_, when two veins rise separate, meet, and are fused
together for a certain distance, and then separate again (Plate II., fig.
23, veins 7 and 8 in the hind-wings of the [F] of _Tatosoma_); (5)
_concurrence_, when a vein rises separate, runs into another, and does not
separate again, an extreme form of anastomosis; (6) _connection_, when two
veins are connected by a short transverse bar passing from one to the
other, a special form of anastomosis, evolved from the ordinary form under
the influence of a tendency to lateral extension (Plate II., fig. 28, veins
7 and 8 in hind-wing of _Paradetis_). Vein 1_b_ in both wings is often
furcate at the base.
{xiii}"The type of veins in the _Micropterygina_ differs from that
described above in two essential particulars, viz.: (1) there may be three
additional veins in the fore-wings, rising out of vein 11 or 12; and (2)
the veins of the hind-wings are practically identical in number and
structure with those of the fore-wings, being thus much more numerous than
in the ordinary type. There is also often a system of cross-bars between
the veins near the base of the wing (Plate I., figs. 22 and 23, neuration
of _Hepialus_).
"The structure of the veins can be best observed on the under surface of
the wing, where they are more prominent. The student should begin by
completely denuding of scales a few wings of common species: the wing
should be cut off and laid on a moistened piece of glass, to which it will
adhere; the scales should then be removed, first from one surface and then
from the other, with a fine, moist camel's-hair brush--an operation
requiring a little patience and delicacy of touch; the veins will thus be
rendered conspicuous.[2] When, however, the student has familiarised
himself with the general subject, it will not be found necessary in
practice to resort to this process; most details will be easily observed
without denudation[3]; where this is not the case (as where the veins are
closely crowded or otherwise obscured), the scales can be removed with the
brush on the under surface in the locality of the difficulty only, without
cutting off the wing or otherwise damaging the specimen, which remains in
the collection available for all purposes as before; with proper practice,
even the smallest species are amenable to this treatment, which does not
require more skill than the actual setting of the specimen. Some workers
prefer to put a drop of benzine on the spot, which renders it temporarily
transparent; the effect is short-lived, as the benzine evaporates rapidly,
and the cilia (if long) are liable to be damaged by this method."
The _Legs_ consist of the following joints (see Plate I., fig. 21): (1)
_coxa_, (2) _trochanter_, (3) _femur_, (4) _tibia_, (5) _tarsus_, (6)
_claw_. The tarsus normally consists of five joints, but is more or less
aborted when the leg is not employed for walking. The spines (SS) on the
tibiæ of the several legs vary considerably in size and number. They are
often useful to the systematist for purposes of classification.