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Figure 1 :  Gomphus  vulgatissimus.  Family Gomphidae, Suborder Anisoptera, Order Odonata (Dragonflies).  45-50 mm. Wing expanse 60-70 mm. Recent.  (After SEVERA, in Thieme's insektengids voor West- en Midden-Europa, 1977.)

Morphological features
A fairly neatly expressed homonomy of the wing-pairs is preserved. Homonomy of middle and hind thoracic segements also well expressed. The same is the case in the muscular apparatus, indicating a rigorously equated homonomous structure. The wings are distinctly elongate, with a straight anterior margin and well-expressed costalization. They are devoid of folds. The venation is very rich, with a large number of, not only longitudinal, but also cross-veins. Sometimes cross-veins are absent, and in their place an archedictyon is found [dense venational mesh work between the longitudinal veins]. Body of insect elongate, with a broadened head and thorax and a narrowed long abdomen. Size of the insects medium or large. Wings usually longer than abdomen, and about equal to the body. Body, although as a rule significantly elongate (such as in Aeschna), in a number of cases a little more stocky (as in Libellula and also in the fossil Palaeodictyoptera).

Functional features
Both pairs of wings take part in the flying movements in their role of supporting the body and creating traction. In this type we find synchronic movement in wing-beat as well as complete autonomy in both pairs. Features of flight are known only of some most specialized representatives of the type -- dragonflies (Order Odonata). Other, more primitive forms of the type are almost unstudied. Speed of flight may reach fairly high figures -- up to 10 m/sec in the dragonfly Libellula, -- normally much lower, about 4 m/sec. Wing-beat frequency is determined to be equal to 22 beats per second in the dragonfly Aeschna, and 28 in Libellula. Governability in flight is high, but not studied in more detail. Load exerted on a unit of wing-surface area varies between widely separated values -- from 0.0090 gr/cm² in the male damselfly Agria  virgo L.  up to 0.0450 gr/cm² in the dragonfly Libellula  depressa.
The biological significance of the flight-function in the representatives of this type is very high indeed. These insects spend the greater part of their active life in flight. Most characteristic this is of dragonflies, being active predators, catching prey and mate in flight, performing long-lasting and long-distance flights.

Long-wingedness, or dolichopterygia, is one of the most ancient types of specialization of the wings and originated as early as in upper Carboniferous times. The most ancient carboniferous insects known to us already possessed fully expressed features of dolichopterygia. Therefore we may assess things concerning the ways of formation of this type only on the basis of comparative morphology. In addition, in unravelling this problem, of great help is the observed genesis of other representatives of the type, the neuropterous Myrmeleonidae [ant-lions], having clearly originated from the  neuropterygia  of their nearest precursors. This legitimates us to assume that also the long-wingedness of the most ancient Palaeodictyoptera (See for example Figure 2 )  was formed out of the neuropterygia of their ancestors unknown to us. The singleness of the source of the formation of long-wingedness determined the relatively uniformity of this type [i.e. its containing only a few subtypes]. Long-wingedness turned out to be the simplest way to improve the aerodynamic qualities of the wings, being realized as a result of the increase of their surface area and their elongation without having to evolutionarily work out any auxiliary adaptations. The known instances of long-wingedness may be divided into three groups.

1.    Archidolichopterygia
The most ancient instances of long-wingedness (dolichopterygia) which are found in carboniferous insects are characterized by the weak development of the system of cross-veins, not yet having been formed out of the original meshwork (archedictyon), with the presence of already fully formed longitudinal veins in the elongated costalized wings, and [these most ancient instances together] make up the subtype of  archidolichopterygia  or, equivalently, ancient long-wingedness. The body of the representatives of this subtype is elongate, but not showing a distinct narrowing. Instances of archidolichopterygia may be found in some primitive families of the Order Palaeodictyoptera (for instance Dictyoneuridae). See next Figures.

Figure 2 :  Reconstruction of  Stenodictya,  Family Dictyoneuridae, Order Palaeodictyoptera, based on specimens in the Institut de Paléontologie, Paris, France. Upper Carboniferous of France. (After KUKALOVÁ, 1970.)

Figure 3 :
Top image :  Stenodictya  spinosa Brongniart,  Family Dictyoneuridae, Order Palaeodictyoptera. Specimen 22-2. Upper Carboniferous of France.  Archedictyon [see previous Figure] omitted in the drawing. Forewing length 61 mm, width 13 mm. Hindwing length 61 mm, width 15 mm.
Bottom image :  Stenodictya  laurentiauxi Kuk.  Upper Carboniferous of France.  Archedictyon omitted in the drawing. Forewing length 64 mm, width 17 mm. Hindwing length 64 mm, width 18 mm.
(After KUKALOVÁ, 1970.)

2.    Eudolichopterygia
The great majority of the representatives of dolichopterygia is characterized by a fully developed cross-vein venation, having already lost the traits of the original meshwork (archedictyon), and by a long thin abdomen. This is  true long-wingedness, or  eudolichopterygia. To this subtype do belong numerous families of the same ancient Palaeodictyoptera, for instance Homoiopteridae, Spilapteridae, and others) :

Figure 4 :  Homaloneura  bonnieri Brongniart.  Family Spilapteridae, Order Palaeodictyoptera.  Specimen 17-17 and 17-18. Upper Carboniferous of France.  Length of forewings 43-40.5 mm.  Width of forewings 12-11 mm. Length of hindwings 43-41 mm. Width of hindwings 15-14.5 mm.  Kukalova further mentions (p. 174) "Wing membrane very thin", and thus indicating that the wings are not coriaceous. (After KUKALOVÁ, 1969.)

Figure 5 :  The permian may-fly  Protereisma  permianum Sell.  Family Protereismatidae, Order Ephemeroptera [= Plectoptera = Agnatha].  Reconstruction by CARPENTER.  Lower Permian of Kansas (USA).
(After CARPENTER, in MARTYNOV, 1938.)

Figure 6 :  Wings of  Myrmeleon,  Family Myrmeleonidae, Order Neuroptera-Planipennia. A species from Katihar, former British India. Recent. (After COMSTOCK, 1918.)

Figure 7 :  Wings of  Acanthaclisis,  Family [prob.] Myrmeleonidae, Order Neuroptera-Planipennia. A species from the Seychelles Islands. Recent. (After COMSTOCK, 1918.)

Figure 8 :  Wings of  Ululodes  hyalina.  Family Ascalaphidae, Order Neuroptera-Planipennia.  Recent.  The Ascalaphidae are one of the few planipennian families of which the representatives are able flyers. They are not nocturnal, but fly at daytime.
(After COMSTOCK, 1918.)

Figure 8a :  Wings of  Climaciella  brunnea,  Family Mantispidae, Order Neuroptera-Planipennia. Recent.
(After COMSTOCK, 1918.)
Wing pairs homonomous, hindwing only a little shorter than forewing. Venation and shape similar in both wings.

Figure 9 :  A winged termite  ( Archotermopsis),  male. Order Isoptera.  Recent.
(After RICHARDS and DAVIES in Imms' General Textbook of Entomology, 1977.)

Figure 10 :  Fore- and hindwings of  Eutermes  sp.,  Order Isoptera.  Recent.
(After RICHARDS and DAVIES in Imms' General Textbook of Entomology, 1977.)

Not all termites have wings of the dolichopterygian type, for example Mastotermes  darwiniensis which belongs to the subtype neur-orthopterygia of the type  orthopterygia (straight-wingedness).

Yet another (albeit a remarkably small) wing (in addition to the ones figured higher above) of the Order Palaeodictyoptera is found (in permian strata) which gives a very clear example of eudolichopterygia :

Figure 11 :  Forewing of  Elmoboria  piperi Carp.  Family Elmoboriidae, Order Palaeodictyoptera.  Lower Permian of Kansas (USA).  Length of wing 15 mm.  Hindwing and body unknown. Because of the paleodictyopterous nature of this wing, we may safely assume that the hindwing was similar to the forewing (homonomy of wing-pairs) except for, perhaps, having a slightly broader anal area.
(After CARPENTER, 1976)

Figure 12 :  Wings of Panorpa, Mecoptera, Panorpidae.  Recent.
(After COMSTOCK, 1918, in IMMS' General Textbook of Entomology, 1977)

Figure 12a :  Paleuthygramma  acuta Carp.  Family Paleuthygrammidae, Order Caloneurodea.
Top - Forewing. Drawing based chiefly on holotype and specimen no. 4563.
Bottom - Hindwing. Drawing based chiefly on holotype and specimen no. 4554.
Forewing length (holotype) 18 mm, width 3 mm. Hindwing length (holotype) 17 mm, width 4 mm.
(After CARPENTER, 1943)

3.    Metadolichopterygia
Finally, the last, most specialized subtype of long-wingedness originated as a result of the working out by the wings of various mechanical adaptations increasing their elasticity while retaining a high degree of firmness involving the formation of special interruptions and nodes [nodi], and of the marked narrowing of the distal part of the body -- the abdomen. This kind of perfection of the wings took place together with a transformation of the muscular apparatus as a result of the development of pleural musculature at the expense of the reduction of other groups of muscles. The [in this way] achieved amazing distinction of the dragonflies perhaps justifies this subtype to be a type of its own.  Perfect long-wingedness or, equivalently, metadolichopterygia, is expressed in representatives of the Order Odonata, namely in the Suborders Permanisoptera (extinct), Protanisoptera (extinct), Anisozygoptera, and especially in Anisoptera, see  Figure 1,  and next Figures.

Figure 13 :  Wing of  Polytaxineura  stanleyi Till., Order Odonata-Anisoptera. Upper Permian (Warner's Bay) Australia.
(After TILLYARD, in MARTYNOV, 1938)

Figure 14 :  Wings [i.e. fore- and hindwing] of  Gomphus  descriptus.  Family Gomphidae, Order Odonata-Anisoptera. Recent.
Labelling and interpretation of veins and cells according to Comstock.
(After COMSTOCK, 1918)

Figure 15 :  Wings of  Anax  junius.  Family Aeschnidae, Order Odonata-Anisoptera. Recent.
Labelling and interpretation of veins and cells according to Comstock.
(After COMSTOCK, 1918)

Figure 16 :  Wings of  Orthemis  ferruginea.  Order Odonata-Anisoptera. Recent.
Labelling and interpretation of veins and cells according to Comstock.
(After COMSTOCK, 1918)

Figure 17 :  Relationships with other types and structure of long-wingedness (dolichopterygia).  (After ROHDENDORF, 1949)

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