Wild Bees, Wasps and Ants Part 5

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 s.h.i.+eld; 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 _c.o.xa_ (_d_^1) and the _trochanter_ (_d_^2), are very short; then follows the _femur_ or thigh (_d_^3); then the _tibia_ or s.h.i.+n (_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 cus.h.i.+on; 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 s.p.a.ce between them, is the _post-costal nervure_ (2); these end in the _stigma_ (_s_), a dark in-cra.s.sation 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 s.p.a.ces 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 sh.e.l.l-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.