_a_ Head. _a_^1 Antennae. _a_^2 Ocelli. _a_^3 Compound eyes.
_b_^1 Prothorax. _b_^2 Scutum of Mesothorax. _b_^3 Scutellum of
Mesothorax. _b_^4 Post-Scutellum of Metathorax. _b_^5 Propodeum.
_c_^1 _c_^2, etc., Segments of Abdomen.
Legs. _d_^1 Coxa. _d_^2 Trochanter. _d_^3 Femur. _d_^4 Tibia. _d_^5
Tarsi. _d_^6 Calcaria or Spurs. _d_^7 Unguiculi or claws. _d_^8
Pulvillus.
_e_ Front wing. 1 Costal nervure. 2 Post Costal nervure. 3 Median
nervure. 4 Posterior nervure. 5 Basal nervure. 6 Cubital nervure. 10
1st Recurrent nervure. 11 2nd Recurrent nervure.
_f._ Hind wing. 7 Anterior nervure. 8 Median nervure. 9 Posterior
nervure.
Cells. _A_ Marginal. _B_ Upper basal. _C_ Lower basal. _D_ 1st
Submarginal. _E_ 2nd Submarginal. _F_ 3rd Submarginal. _G_ 1st
Discoidal. _H_ 2nd Discoidal. _I_ 3rd Discoidal. _J_ 1st Apical. _K_
2nd Apical.
{134} The perfect insect when it emerges has therefore a head, a thorax of
four segments, and an abdomen of seven visible dorsal segments in the male,
and of six in the female. The [male] has six ventral segments exposed, and
often the apex of the eighth, which is frequently elongate, the seventh
being almost always short and hidden; the eighth dorsal segment can be
discovered hidden under the seventh, but it is very rarely exposed. The
head (_a_) bears numerous appendages; a pair of antennae (_a_^1), usually
of thirteen joints in the male and of twelve in the female; two compound
eyes (_a_^3), composed of many facets; three simple eyes (or ocelli)
(_a_^2), which are situated on its vertex; two _mandibles_; two _maxillae_,
bearing _palpi_ on each side, of a varying number of joints; and a
_labium_, or tongue, which also bears at its base two four-jointed palpi
(cf. fig. 20).
The thorax, as we are considering it, consists of four segments--the
_prothorax_ (_b_^1), which bears the two front legs; the _mesothorax_
(_b_^2), which bears the intermediate pair of legs and the anterior pair of
wings; and the _metathorax_ (_b_^3), which bears the posterior pair of
wings and the hind legs. The {135} propodeum has no appendages. The
mesothorax above has two parts, a larger portion in front called by some
the _scutum_ (_b_^2), and a smaller portion behind called the _scutellum_
(_b_^3). These are separated from each other by a transverse impression,
and the scutellum is often raised into a sort of little shield; behind this
is another little elevation called the _post-scutellum_ (_b_^4); this is
really the dorsal apex of the metathorax, and behind this lies the
_propodeum_ (_b_^5). Each leg is composed of various parts, and articulates
into a cavity of the thorax called the _acetabulum_. The first two joints
of the leg, the _coxa_ (_d_^1) and the _trochanter_ (_d_^2), are very
short; then follows the _femur_ or thigh (_d_^3); then the _tibia_ or shin
(_d_^4); and finally the _tarsi_ (_d_^5), which compose the foot. At the
apex of the _tibia_ are usually two spines called the _calcaria_ (_d_^6).
The _tarsi_ are five-jointed, the joints following each other in a linear
arrangement, and in the _Anthophila_ the basal joint is more or less
dilated; the apical joint bears two claws (_unguiculi_, _d_^7) which are
sometimes toothed, and between them, in some genera, there is what is
called a _pulvillus_ (_d_^8) or cushion; this is very large and dilated in
some of the fossors. {136}
The wing neuration is always rather troublesome, as various authors use
different names for the veins and cells. To begin with the anterior wing
(_e_), there are four nerves which start from the base and run
horizontally; the first of these, which forms the anterior margin of the
wing, is called the _costal nervure_ (1); immediately below this, and
running almost parallel to it with scarcely any space between them, is the
_post-costal nervure_ (2); these end in the _stigma_ (_s_), a dark
in-crassation towards the apex of the wing; from the stigma a nerve,
curving first downwards and then up to the anterior margin of the wing,
encloses the _marginal cell_ (_A_). Below the _post-costal_ nervure, and
situated about the centre of the wing, is the third longitudinal nervure
called the _median nervure_ (3); behind this again runs the _posterior
nervure_ (4), and behind that the actual margin of the wing which is not
provided with a protecting nervure, but is only folded back so as to
receive the hooks of the posterior wing. Across the wing at, roughly, about
a third of its length from the body runs the _basal nervure_ (5); this
extends in a somewhat zigzag line from the _post-costal_ to the _posterior
nervure_ crossing the _median_, and {137} thereby enclosing two cells, the
_upper basal cell_ (_B_) and the _lower basal cell_ (_C_). From the centre
of the apical nerve of each of these cells extends a longitudinal nervure;
the upper of these runs out nearly to the apical margin of the wing and is
called the _cubital nervure_ (6); this is united to the nervure of the
_marginal cell_ by one, two, or three cross nervures, enclosing thereby
one, two, or three cells called the first (_D_), second (_E_), and third
(_F_) _submarginal cells_. The nervure from the lower basal cell is a short
one, as it is met by a cross nervure called the first _recurrent nervure_
(10), which runs from the _cubital_ to the _posterior_, thereby enclosing
two cells, the first (_G_) and second (_H_) _discoidal_. The _second
recurrent_ (11) leaves the _cubital_ nearer the apex of the wing than the
first, meeting a nervure which, springing from the outer posterior angle of
the second discoidal, closes the third discoidal (_I_), and, curving
slightly upwards, nearly reaches the apical margin of the wing. Beyond the
second recurrent, and behind this last nervure which we have been talking
about, are two spaces not actually enclosed, but called the _first_ (_J_)
_and second_ (_K_) _apical cells_.
The posterior wings have very few cells. {138} Like the anterior pair they
have three longitudinal nervures; the _anterior_ (7), which runs close and
parallel to the anterior nerveless margin, and often touches it at about
half the length of the wing; the _median_ (8) and _posterior_ (9) run in
diverging lines from the base towards the exterior margin of the wing, the
anterior and median nervures being almost always joined by a cross nervure,
and the median usually united to the posterior by a cross or curved
nervure. The actual base of the anterior wing is covered by a little convex
somewhat shell-like cap, called the _tegula_ (_T_). The abdomen is composed
of a series of segments in linear arrangement (_c_^1 _c_^2, etc.). These
call for no special remark, beyond what has been said in the chapter on
males and females, but those who wish to investigate the very interesting
questions connected with the terminal segments of these creatures should
consult some more technical work.[3] The arrangements of the mouth parts
and of the apical segments of the Hymenoptera afford perhaps the most
important structural {139} characters of the order, but they involve an
amount of dissection and study which can only be undertaken by those who
are inclined to give themselves up to this subject as a speciality.
* * * * *
{141}