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Organic Evolution in terms of the Implicate and Explicate Orders.

Part LXXI
Diptera (midges, mosquitoes, flies) (III)
The evolutionary diversification in the Order Diptera revisited.
Origin and Evolution of the Order Diptera

Derivation of the many dipterous wing-venations from the venational prototype of the Order Diptera, and a full exposition of the functional wing-types of the Order. (Sequel-2)
After having, in the preceding two documents, started and continued with the thematic treatment of the functional wing-types and subtypes of the Suborder Nematocera of the Order Diptera, and their derivation from the order-prototype, - in the present document we continue with those of the rest of the Order (Brachycera-orthorrapha and Brachycera_cyclorrapha), not already treated in earlier documents.
Traction-Lifting many-veined (tabanoid) type

Representatives of the type
Wings, built according to the traction-lifting many-veined (tabanoid) type, are possessed by representatives of various dipterous families, mainly belonging to the suborder Brachycera-Orthorrapha :  Rhagionidae, Tabanidae (horse flies), Erinnidae, Coenomyiidae, Solvidae, Therevidae, Apioceratidae, Acanthomeridae, Omphralidae, Nemestrinidae, Mydaidae, Asilidae (robber flies), Bombyliidae (bee flies), and some Cyrtidae. In addition, tabanoid wings are also possessed by certain recent-but-relict and fossil families of Nematocera, viz., Phryneidae (= Rhyphidae), Olbiogastridae, and Protorhyphidae.

Because we haven't systematically and biologically treated all these flies in earlier documents (except for the Rhyphidae, that were so treated together with the rest of the diptera-Nematocera), we will give here Figures of some of the representatives of the tabanoid functional wing-type (All Figures, After CHINERY, in Thieme, Nieuwe Insekten Gids, 1988) :

Rhyphus [= Phryne = Sylvicola] fenestralis  Scop. Rhyphidae [= Phryneidae].

Rhagio  scolopacea.  Rhagionidae.

Tabanus  bromius.  Tabanidae (Horse-flies).

Laphria  gilva.  Asilidae (Robber-flies).
For the study of the venation of the wings to come reference should be made to the dipterous venational order-prototype :

Venational Prototype of the Order Diptera
Let us now, then, depict wings belonging to the present functional wing-type, i.e. the tabanoid type.

  
From top to bottom :

Phryne  punctata  Fabr. ( Phryneidae )
Length 6 mm
(After ROHDENDORF, in ROHDENDORF, 1951)
Rhagio  scolopaceus  L. ( Rhagionidae )
Length 10.5 mm
(After ROHDENDORF, in ROHDENDORF, 1951)
Solva  ussuriensis  Pleske. ( Solvidae )
Length 11 mm
(After ROHDENDORF, in ROHDENDORF, 1951)
Tabanus  sp. ( Tabanidae )
Length about 15 mm.  y = phragm.
(After HENDEL, in ROHDENDORF, 1951)
Laphria  gilva  L. ( Asilidae )
Length 13 mm
(After ROHDENDORF in ROHDENDORF, 1951)
Figure 1 :  Recent traction-lifting many-veined wings of representatives of the phryneoid, ragionoid, erinnoid, tabanoid-proper, and asiloid subtypes.
Size of the wings
The absolute size of the wings is almost always large. Their length is, as a rule, not less than 10 mm, rarely less and surprisingly more often significantly larger, reaching up to 30 mm and more. The relative size of the wings is small, usually equal to the length of the body, often shorter, more rarely longer than it. Magnitude of the surface area of the wings is known only of representatives of the families Tabanidae (0.381-1.613 cm2 ), Rhagionidae (0.550 cm2 ), Asilidae (0.282-0.774 cm2 ), and Bombyliidae (0.485-0.671 cm2 ). These figures undoubtedly do not indicate the largest surface areas of wings characteristic of the largest forms of this type, for instance in the representatives of the families Mydaidae, Acanthomeridae, tropical and subtropical species of Asilidae and Bombyliidae. The weight of the wings is insignificant, reaching in Bombyliidae 1.47, in Asilidae only 0.55-0.98 percent of the weight of the whole insect. The load is investigated by me (Rohdendorf) in the above mentioned families, and in representatives of Tabanidae is equal to 0.050-0.215 gr/cm2, in Rhagionidae 0.061 gr/cm2, in Asilidae 0.063-0.307 gr/cm2, and in Bombyliidae 0.062-0.071 gr/cm2.
Shape of the wings
The wings always have a straight anterior edge with a well-differentiated apex and basiala, a convex hind margin, and a large well-developed anal lobe, usually a large alula and wing-, and sometimes also thoracic scales. Wings elongate, often fairly narrow, their length being 2-4 times their widths. The shape of the wings is variable. It differs in the representatives of the different subtypes.
Skeleton of the wing
The characteristic feature of this type is a rich venation, almost not having been subjected to reduction during the development of the processes of mechanical perfection of the wings. The Costal vein runs, as a rule, around the whole edge of the wing, rarely reduced at the hind margin. The Subcostal bein is long and strong, reaching up to the middle of the wing, sometimes significantly beyond it. The Radial veins (R and RS) well developed, almost always consisting of four branches (the Radius and the branches of its sector). More rarely there are additional branches (certain Nemestrinidae and Bombyliidae), positioned usually in the form of cross-veins. Very seldom there are only three Radial veins (Phryneidae). Medial veins usually as four branches, more rarely as three (anthracoid subtype). In very few cases the number of Medial branches decreases up to two (cyrtocioid subtype). Almost always there is a well-expressed intermedial (or so-called discoidal) cell, formed by branches of the Medial system of veins. The cross-veins rm and mcu strong. The Medio-Cubital vein (mcu) is sometimes positioned obliquely, changed into the basal section of the last Medial branch. The anal vein is strong and long. Costalization [= shift of a number of longitudinal veins toward the anterior(-proximal) wing-margin, or just the strengening of the veins of the anterior part of the wing] of the wing-blade shows itself [here in this type] as a marked thickening of the Costal vein (i.e. its part that is at the anterior wing-margin) and of the anterior branch of the Radius. The basiala, see Figure 7, Part LXIX  and next Figure, is clearly differentiated (from the rest of the wing) by its phragm and by the border between the anal lobe and the alula (winglet) [this border, more or less separating the basiala from the rest of the wing, then conceptually extends to the humeral cross-vein at the proximal anterior part of the wing].

Figure 2 :  Nemestrinus  capito  Loew (Nemestrinidae).  Basiala of right wing of a male, from above.
Length :  The whole wing 17.0 mm.  The basiala 4.5 mm.  (For the abbreviations see the aforementioned Figure).
(After ROHDENDORF, 1951)
The phragm is, as a rule, well-expressed as a strong and firm outgrowth, connecting the base of the Radial vein with the lower element of the basiala (the base of Cubital and First Anal vein). Seldom is the phragm in the form of a sclerotized and darkened fold (phryneoid, rhagionoid, and cyrtocioid subtypes). Chaetaria [characteristic patches of bristles on the basiala, see  Figure 7 ] present on the bases of the Radial and the Second Anal vein, but small and weakly expressed.
Coverings of the wing
The wing-blade is covered with dense, but very short, microtrichia (minute hairs), usually forming a compact covering. Rarely, certain parts of the wing-membrane (certain cells or their parts) are devoid of microtrichia. This heterogeneity of the covering with microtrichia is especially marked in various groups of the family of robber flies (Asilidae), but is not yet sufficiently studied, although being of definite interest for the clarification of aerodynamic features of the wing-beat. Bristles and macrotrichia are developed chiefly at the edge of the wing, whereby on the anterior edge, especially its proximal part, they attain their largest size. Sometimes bristles are present on the strongest veins in the anterior half of the wing. Still more rarely macrotrichia are present on the wing-membrane (Phryneidae). The hind-margin of the wing with a series of thin macrotrichia, longest at the apex and proximal side of the anal lobe, on the alula (winglet) and the wing-scale. Sometimes on the latter parts of the basiala the bristles are replaced by special elongate scales, essentially being flattened bristles (many species of Bombyliidae), or, by contrast, the wing-scales are covered with dense fluffy hairs. The nervous system of the wing is not investigated.
Functional features
The way of life of Diptera that possess wings of the traction-lifting many-veined (tabanoid) type, is unusually diverse. Of all is characteristic the great significance of the function of flight in their life-activities. With no exception all representatives of this type of wings do spend the greater part of their active life on the wing :  the blood-sucking horse flies, the robber flies, and the bee flies and Nemestrinidae which latter two feed on nectar of flowers. Only a few groups belonging to this functional wing-type fly relatively weak (such, for instance, Rhagionidae, Erinnidae, Coenomyiidae), but also with respect to these forms one cannot hold that flight has inferior significance.
Precise data on the characteristics of flight of the representatives of this type are almost non-existent. Known only is an indication as to the speed of flight of the horse fly (Tabanus sp.), reaching allegedly 15 m per second, and an indication as to the wing-beat frequency of a species of the genus Rhagio, reaching 122-126 (beats/sec). However, these random numbers do not at all, of course, give one an idea of the real properties of flight of these insects. General observations regarding the way of life indicate that the speed of flight is very high not only of the blood-sucking horse flies, but also of species of the families Bombyliidae and Nemestrinidae, visiting flowering plants. Moreover, the way of life of the robber flies, catching other insects, bears witness of the great power of flight which allows these flies to carry their prey which often is very big and heavy. Another sort of feature that witnesses a high quality of flight consists in the ability to suck nectar from flowers in flight by means of a long beak, hanging in the air at one point (many species of Nemestrinidae and Bombyliidae). Such a "motionless" flight is very peculiar and points, of course, to a high degree of perfection of the flying-apparatus.
In evaluating the features of the tabanoid type, one should first of all direct one's attention to the very high indexes (numerical values) of the load (weight of the insect per surface-unit of wing). In fact to this type do belong forms displaying the greatest load among all Diptera (such are species of robber flies of the genus Laphria, of which the load is up to 0.3 gr/cm2 ).  The high load is partly the result of great absolute size (and, consequently, weight) of the body, which size is very large in these insects. As already told, wings of this type are possessed by the largest gigantic forms of recent Diptera (Acanthomeridae, Mydaidae, Asilidae). Therefore the analysis and evaluation of features of the traction-lifting many-veined (tabanoid) type should be carried out while the size and weight of the body of the insect are contantly taken into account :  only in complying with this condition it is possible to uncover the functional significance of the features of the wings and the reasons of preservation or change of this or that structure of their skeleton (venation). As was stated already above, of this type a rich, little reduced venation is characteristic. Earlier I [Rohdendorf] even had called it "the most archaic", " having been preserved almost with certainty since jurassic times" (Rohdendorf, 1949, p.99-100). At that time the structure of the basiala of these flies was preliminary described by me, while I remarked that these diptera with their "weakly costalized wings  b y  c o n t r a s t  were provided with a complex basiala" (ibidem, p.103), and that these insects possess "the most primitive forms" of flight apparatus (p.150). It must now be said that, evidently, this analysis was insufficient, which analysis, as to the mechanics of the wing, only concerned the skeleton of the wing without taking into account the size of the body of these insects. As a result only the peculiarity of the structure of the wings was recorded, viz., the "ancientry" of the venation of the wing-blade, together with the high specialization of the basiala, while a clarification of this process was not attempted. The real reason-to-be of the features of tabanoid wings consisted in the perfection of the mechanical properties of the wings in diptera of large size. Increase of size of the insect inevitably brings with it an increase of load per unit surface of the wings. Therefore the processes of costalization, the strengthening of the anterior margin of the wing as an adaptation to an increase of wing-beat frequency (with a growth of the forces of traction and lifting), follows a different path, different from that of small (or in the process of becoming small) insects. Large insects cannot realize costalization of the wing by displacements and reduction of veins, because when this happens the strength of the blade of the wing as a whole will decrease, which is not allowed by the increase of the load. The strengthening of the anterior margin is realized by the thickening of the anterior veins (costal, radial, and subcostal) and [the mechanical features of the wing are further worked out] by the perfection of the mechanism of transition [of muscle force] of the wing, its basiala (formation of a phragm, strengthening of the cells of the basiala). The wing-venation [that is the venation of the wing-proper, the wing-blade] remaining rich, essentially not being reduced, turns out to be a very useful supporting skeletal element of a large wing. The veins of the wing only insignificantly changed their mutual position, guaranteeing a firmness of certain parts of the wing-blade and, probably, playing an important role in the creation of air-whirls during wing-beat. Consequently, the assertion of "primitiveness" of the tabanoid type of wings is not correct :  Only the plan of venation of the wing-blade is primitive, whereas the whole wing [and thus including its basiala] of the tabanoid type is not at all primitive, but represents a characteristic form of perfected flight-organs of large diptera. The rich venation on the wing-blade of these flies, although being a relict feature [i.e. a feature that has been preserved], nevertheless plays an important functional role.
History and transformations of the type
Wings of the traction-lifting many-veined (tabanoid) type are known beginning with the jurassic period. Wings of this type were possesed by various groups of diptera from Jurassic sediments of central Asia (Karatau [southern Kazachstan] and others), from the upper Jurassic limestone-layers of Solnhofen [Germany] and England. Already in the Jurassic fauna no less than six families were represented. See next four Figures (together with the venational order-prototype).

Venational Prototype of the Order Diptera

Figure 3 :  Traction-lifting many-veined (tabanoid) wings of fossil representatives of the rhagionoid and eostratiomyioid subtypes.
Upper image :  Rhagiophryne  bianalis  Rohd.  ( Rhagionidae ), Upper Jurassic of Karatau, southern Kazachstan.  Length 4.25 mm.
Lower image :  Eostratiomyia  avia  Rohd.  ( Eostratiomyiidae ), Upper Jurassic of Karatau, southern Kazachstan.  Length 7 mm, width 2.5 mm.
(After ROHDENDORF, 1951)

Figure 4 :  Traction-lifting many-veined (tabanoid) wings of fossil representatives of the palaeostratiomyioid and rhagionoid subtypes.
Upper image :  Palaeostratiomyia  pygmaea  Rohd.  ( Palaeostratiomyiidae ), Upper Jurassic of Karatau, southern Kazachstan.  Length 2.5 mm.
Middle image :  Rhagionempis  tabanicornis  Rohd.  ( Rhagionempididae ), Upper Jurassic of Karatau, southern Kazachstan.  Length 3.5 mm.
Bottom image :  Protorhagio  capitatus Rohd.  ( Rhagionidae ), Upper Jurassic of Karatau, southern Kazachstan.  Length 5 mm.
(After ROHDENDORF, 1938, in ROHDENDORF,1951)

Figure 5 :  Traction-lifting many-veined (tabanoid) wing of a fossil representative of the rhagionoid subtype.
Wing of  Protorhyphus  turanicus  Rohd.  ( Protorhyphidae ).  Liassic (lower Jurassic) of Issic-Kul.  Length of remains 2.7 mm. Length of the whole wing about 3.0 mm.  (After ROHDENDORF, 1962, in ROHDENDORF, 1964)

Figure 6 :  Traction-lifting many-veined (tabanoid) wing of a fossil representative of the rhagionoid subtype.
Wing of  Protorhyphus  stigmaticus  Handl.  ( Protorhyphidae ).  Upper Liassic (lower Jurassic) of Mecklenburg (northern Poland [formerly Germany] ).  (After HANDLIRSCH, 1938, in HENNIG, 1954)
These families were :  Protorhyphidae (suborder Nematocera) - ancestors of the recent Phryneidae (= Rhyphidae), and of the suborder Brachycera-orthorrapha :  Rhagionidae (preserved also in the recent fauna), Archisargidae, Palaeostratiomyiidae, Rhagionempididae and Eostratiomyiidae (the last four families are only known from the Jurassic). All these ancient mesozoic diptera were at the time already fairly diverse :  The Protorhyphidae (Nematocera) differed from the complex of Brachycera only by the fact that in them the anal and cubital veins were relatively far apart from each other. And all five brachycerous families also were not uniform as to the structure of the wings, the difference of which forces us to divide them into ten more subtypes (in addition to the phryneoid subtype) of the tabanoid type.
Let us now consider these  s u b t y p e s  one by one.
    1.   The wings of the Phryneidae [= Rhyphidae] (Nematocera) -- see  Figure 1, top image -- strongly differ from the other representatives of the tabanoid type by their small size and a smaller number of Radial branches of wich there are only three (including the Radius-proper). The Medial veins form a well-expressed intermedial cell (discoidal cell) and count four branches whereby the posterior branch [M4] is not the continuation of the cross-vein mcu [better written as m-cu], but being close to the common Medial trunk. The anal vein runs far away from the Cubitus. It does not coalesce with it nor coming near to it.

Figure 7 :  Basiala (schematically) of the wing of  Phryne sp.  ( Phryneidae ).
At the base of the Radius (R) and of the second anal vein (An2) we see the chaetaria, and from the Radius projecting downwards, we see the phragm (or that by which it is replaced).  (After ROHDENDORF, 1946)
In the basiala (generally) of this subtype, instead of a phragm there is only a well-visible fold.
In repose the wings are held obliquely backwards. The wings of such insects must be assigned to the special  phryneoid subtype,  which undoubtedly are derivatives of the rhagionoid subtype (see further below). The jurassic ancestors  ( Figure 5 and  Figure 6 )  of the recent Phryneidae possessed a fourth Radial branch, and their wings may certainly be united together with those of the Rhagionidae into the next subtype.
    2.   The jurassic Protorhagionidae (the genera  Protorhagio, Figure 4, bottom image ,  and  Rhagiophryne,  Figure 3, top image )  and their descendants, the caenozoic Rhagionidae,  Figure 1, second image ,  also living today, form the special  rhagionoid subtype,  characterized by the moderate size of the body, the weak development of the phragm (in the basiala), instead of which there is only a more or less expressed fold. However, in contrast to the previous subtype, the number of Radial branches is not reduced, having remained four [including the Radius-proper]. Moreover, an approach of the first anal vein and the Cubitus is evident, converging to the margin of the wing. The fork of the two last Radial branches is long and narrow. The posterior Medial branch is differentiated from the remaining system. Its base changes direction and becomes transverse. The hind-margin of the wing, as a rule, with the Costal vein [i.e. it is not reduced there]. In repose the wings are directed obliquely backwards. This subtyp is a derivative of not precisely known forms of the Tipuloid type, forms that have given rise to the Bibionoid and Fungivoroid types. In its turn, the rhagionoid subtype was the point of departure of a series of other forms of tabanoid wings, namely of the already above described phryneoid subtype, further of the tabanoid-proper, the erinnoid, and mydaoid subtypes (see below).
The next Figures provide some more examples (from the family Rhagionidae) of this subtype :

Figure 8 :
Left image (147) - Wing of  Lampromyia  pallida  Meig.  Rhagionidae. In all Rhagionidae the vein R3 [also written as  r 3] is missing. In this wing we can see where it originally was. Because of its slender form this wing might belong, not to the rhagionoid, but to the erinnoid subtype (see below).
Right image (148) - Wing of  Rhagio  scolopaceus  Lw.  Rhagionidae.
(After HENNIG, 1954)

Figure 9 :
Left image (149) - Wing of  Atherix  ibis  Fabr.  Rhagionidae. The vein R2 [= r 2 = anterior branch of Radial Sector] ends up in R [= r 1].
Right image (150) - Wing of  Spaniopsis  clelandi  Ferg.  Rhagionidae.
(After HENNIG, 1954)
    3.   Special forms of tabanoid wings were shown in the specialized jurassic diptera, the Eostratiomyiidae  ( Figure 3, lower image ),  which form the peculiar  eostratiomyioid subtype. This family distinguishes itself by a relatively large wing-size, by the presence of four Radial branches, several interradial and radio-medial cross-veins, the absence of the Costal vein at the wing's hind-margin, and by a broad wing with a pointed and well-differentiated apex [differentiated, that is, from the rest of the wing]. This subtype is all-out idiosyncratic, being characterized by very ancient primitive features (cross-veins) together with a great mechanical perfection of the shape of the wing. Unfortunately the structure of the basiala could not be investigated in this fossil. Apparently, the phragm was not developed -- this assumption is based upon the nature of the venation of the wing-blade, which (venation) is relatively weak. The origin of the eostratiomyioid subtype is not clear, although, apparently, one may be convinced that there does not exist a direct affinity of this subtype with rhagionoid wings. The eostratiomyioid subtype is, probably, a derivative of certain not precisely known forms of that same original tipuloid type, namely of those forms in which there was still an abundance of cross-veins and an overall rich wing-venation in the absence of mechanical specializations in the structure of the basiala. This remarkable subtype probably was the point of departure of the development of two others :  the extinct palaeostratiomyioid and nemestrinoid subtypes, represented also in the recent fauna.
    4.   Special jurassic diptera, namely two representatives of the families Palaeostratiomyiidae  (  Figure 4, upper image )  and Rhagionempididae  (  Figure 4, middle image )  possess peculiar wings the structure of which may be derived from the previous subtype, and which form the special  palaeostratiomyioid subtype.  Of this subtype small sizes are characteristic, further (are characteristic) a marked development of costalization, appearing in the form of the thickening of the Costal and Radial (its two anterior branches, that is, the Radius-proper and a branch of the Radial Sector) veins, a broad costal field, the peculiar shape of the broad wings truncated at the apex, and the reduction of the Costa at the posterior wing-margin. Characteristic of one form, (Rhagionempis, Figure 4, middle image ),  is a perfection of mechanical qualities, expressed by the strong divergence of the two posterior Radial branches, reminding us of the analogous phenomenon in proper-tabanoid wings. The phragm (in the basiala) was absent and in its place there was merely a fold. The posterior Medial branch is situated in the original fashion, branching off from the main trunk of the Media. Cross-veins present only in the form of the basic r-m and m-cu [the presence of the latter seems to be assumed by Rohdendorf]. This subtype, only known as two fossils, undoubtedly shows a high degree of specialization, while the possibility is not excluded that it is further divided into two independent groups. The latter assumption is evoked by the marked differences in the structure of the wings of those two species. Being a derivative of the eostratiomyioid subtype, the present subtype, probably, is one of the sources of the stratiomidoid type [the next main type, being discussed later].
    5.   Several jurassic, tertiary, and recent diptera, belonging to the relict groups Erinnidae (Figure 10, left image), Solvidae  ( Figure 1, third image  and  Figure 10, right image ),  Vermileoninae, and certain Cyrtidae (the genera Cyrtus, Opsebius) possess peculiar wings of the tabanoid type, and as such form the special  erinnoid subtype.  The shape of the wings of this subtype is elongated. The phragm (in the basiala) is in the form of a fold, more rarely well developed (Cyrtidae). Especially characteristic is the form of the fork formed by the two posterior Radial branches, which (fork) is short and fairly wide. The hind-margin of the wing is often without Costal vein. The posterior medial branch [M4] is individualized with respect to the rest of the Medial system of veins [its basal section looks like a cross-vein]. How the wings are held in repose is not very well known to me [Rohdendorf]. This subtype is a derivative of rhagionoid wings, and in turn was the point of departure of the development of the cyrtocioid subtype and the stratiomidoid type. To the present subtype belong little studied insects, in their majority rare forms.
The next Figures present some more examples (from the family Erinnidae) of this subtype :

Figure 10 :
Left image (151) - Wing of  Erinna  atra  Meig.  Erinnidae.
Right image (157) - Wing of  Solva  marginata  Meig.  Solvidae.  The veins M3 and M4 [=  m 3 and  m 4] have a common ending at the posterior wing-margin, so also the veins CuA and A1 [=  Cu1b and 1a]. The vein M2 [=  m 2] has lost its end-part (i.e. it is retreating from the wing-margin).
(After HENNIG, 1954)

It might be that also the above mentioned  Lampromyia (Rhagionidae)  belongs to this subtype.
    6.   Another derivative of the rhagionoid subtype form the wings of horse flies (Tabanidae), pseudo-robberflies (Therevidae), Coenomyiidae, and, probably, the tropical Acanthomeridae not known to me [Rohdendorf] in nature. For this truly extensive and rich collection it is natural to let it represent the  tabanoid-proper subtype.  Examples :  Figure 1, fourth image ,  and next Figures.

Figure 11 :
Wing of  Coenomyia  ferruginea  Scop.  Erinnidae.  Here, the basal section of M4 is suppressed by CuA [=  Cu1b].
(After HENNIG, 1954)

Figure 12 :
Left image (167) - Wing of  Thereva  nobilitata  Fabr.  Therevidae.
Right image (168) - Wing of  Chrysanthemia  chrysanthemi  Fabr.  Therevidae.
(After HENNIG, 1954)

Figure 13 :
Upper-Left image (153) - Wing of  Lycops  zoos  End.  Pantophthalmidae.
Upper-Right image (154) - Wing of  Pelecorrhynchus  personatus  Walk.  Tabanidae
Bottom-Left image (155) - Wing of  Pangonia  maculata  Rossi.  Tabanidae.
Bottom-Right image (156) - Wing of  Tabanus  bromius  L.  Tabanidae.
(153 after ENDERLEIN, 1931, in HENNIG, 1954.  154-156 After HENNIG, 1954)
This subtype is characterized by a number of features :  The phragm (in the basiala) well expressed in the form of a firm oblique outgrowth connecting the basal part of the Radial vein with the Cubital and the first Anal. In addition, the basiala in the representatives of this subtype is characterized by the development of a broadening of the base of the Costal vein, by the presence of well-developed wing and thoracic scales [i.e. a wing scale and a thoracic scale]. The two posterior Radial branches are strong, and sharply diverging, where the anterior one ends up at the anterior margin, while the posterior one ends up at the margin of the wing only after the latter's tip. There are four Medial branches, where the posterior branch usually is individualized, more rarely tigthtly unified into one common complex with the three other anterior branches (Coenomyiidae, see  Figure 11  [ There, the genus Coenomyiia is assigned to the famliy Erinnidae (by Hennig) ] ).  The veins at the posterior margin of the wing often form closed cells, or cells that are narrowed toward their end (for example the cubital cell, as a result of the coalescence of the terminal portions of Cu and An1 [= CuA and 1A, or CuA and 1a] ( Figure 13, 153-155-156 ),  the fifth Radial cell as a result of such a coalescence of M1 and R5 [= m1 and r5] ( Figure 13, 155 ),  the third Medial cell as a result of such a coalescence of M3 and M4 [= m3 and m4] ( Figure 13, 153 )).  The posterior margin of the wing is provided with a costal vein (C, Costa). The outline of the wing is fairly broad, with a well-differentiated apical part often with a pointed apex, a convex anal lobe, a large alula (winglet) and scales [the wing-scale and the thoracic scale]. This subtype is known only to have existed since the beginning of the Cenozoic (Teriary and Quarternary). In the Mezozoic fauna there is, until now, not found any form carrying tabanoid wings. The connections of this tabanoid-proper subtype are fairly clear :  Undoubtedly, from the base of tabanoid wings the asiloid and anthracoid wings have evolved.
    7.   One of the derivatives of the tabanoid-proper subtype of wings is expressed by representatives of the large family of robber flies (Asilidae). See  Figure 1, fifth image .  This  asiloid subtype  is characterized by the positioning of the wings in repose :  they are held folded over the abdomen, and by the development of an all-out firm phragm, looking like a strong outgrowth, unifying by means of a special kind of hinges the basal sections of the Radial and Cubital veins. Another characteristic feature consists of the sclerotization, thereby transformed into a firm surface, of the whole central cell of the basiala :  Essentially this cell is, qua firmness, the direct continuation of the phragm. The venation of the elongated wing-blade is characterized by the very long first Radial vein (R), which often unifies its end, not with the Costal vein, but with the next, second, Radial vein. The posterior branches of the Radial veins are variable. Usually they strongly diverge, more rarely they run parallel, and proceed in certain cases to the wing's hind-margin (Leptogastrinae), in other cases to the front-margin (several Asilinae, for example the genus Satanas). The Medial cells, as also in the previous subtype, often closed. The hind-margin[al area] of the wing is often attenuated. The Costal vein runs all around the whole wing, more rarely only reaches the Cubital vein. Sometimes the posterior margin is devoid of the Costal vein, whereby the venation of the posterior margin is also weakened. The in this way costalized wings are found in some Asilinae and Dasypogoninae. The anal lobe and the alula are well developed. Only in the Leptogastrinae the wings are narrow and almost without such structures. The thoracic scale is rudimentary. Of this subtype is, in addition, very characteristic the small size of the wings, which are shorter than the body. This subtype is known to exist only since Tertiary times, apparently already represented in the faunae by recent subfamilies and by almost exclusively recent genera. From Mesozoic faunae the asiloid subtype is not known. Transformation in this subtype consists of the development of a high degree of costalization, on the one hand, and of the formation of the narrow specialized wings of the Leptogastrinae, on the other. It is possible that these forms allow them to be individualized as separate subtypes. The next Figure provides some more examples of this subtype of wings.

Figure 14 :
Upper-Left image (179) - Wing of  Leptogaster  cylindrica  Deg.  Asilidae.
Upper-Right image (180) - Wing of  Promachus  leoninus  Lw.  Asilidae
Middle-Left image (181) - Wing of  Heteropogon  scoparius  Lw.  Asilidae.
Middle-Right image (182) - Wing of  Bathypogon  brachypterus  Macq.  Asilidae.
Bottom-Left image (183) - Wing of  Laphria  marginata  Lw.  Asilidae.
Bottom-Right image (184) - Wing of  Dasythrix  grisea  Herm.  Asilidae.
(After HENNIG, 1954)
In the next sections we will have to do with families such as Bombyliidae (bee-flies), Mydaidae, and Nemestrinidae. For good orientation we here give some Figures :

Bombilius  major.  8-12 mm. Bombyliidae.
(After SEVERA, in Thieme's insektengids voor West- en Midden-Europa)

Leptomydas  corsicanus.  Mydaidae.
(After CHINERY in Thieme Nieuwe Insektengids, 1988)

Fallenia  fasciata.  Nemestrinidae.
(After CHINERY in Elseviers Insektengids voor West-Europa, 1983)

    8.   Another sort of derivative of the tabanoid-proper wings we can see in many representatives of the extensive and diverse family of bee flies, Bombyliidae (especially of the group Anthracinae and some other groups). These characteristic forms of tabanoid wings constituting the special  anthracoid subtype, distinguish themselves by many features shared with the previous, asiloid, subtype. Similar is the development of a firm basiala, having a thickened Costal vein, a sclerotized central cell and a strong phragm. Also the anterior Radial branch (R) is significantly lengthened, and the wing-size has increased markedly. See next Figure (upper image).

Figure 15 :  Recent traction-lifting many-veined wings of the anthracoid, mydaoid, and nemestrinoid subtypes.
Upper image - Wing of  Exoprosopa  sp.  Bombyliidae.  Length about 20 mm. (After HENDEL).  y = phragm (see the "y" sign and the arrow added [by Rohdendorf] in the drawing of the wing).
Middle image - Wing of  Eremomydas  bek  Sem.  Mydaidae.  Length 14.5 mm. (After ROHDENDORF, 1951).
Bottom image - Wing of  Nemestrellus  abdominalis  Oliv.  Nemestinidae.  Length about 20 mm. (After SACK)
(In ROHDENDORF, 1951)
But totally differently structured is the venation of the wing-blade. The posterior Radial branches are, as a rule, peculiarly curved, unified one with the other by means of characteristic cross-veins (usually one in number, more rarely two). Of Medial veins there always are no more than three, whereby one of the middle branches is reduced. Features of costalization are only apparent by the strengthening of the marginal vein (Costa) and the base of the Radius. This subtype is, as is the previous one, known only from the beginning of the Tertiary. Study of Tertiary representatives of the Bombyliidae does not add much to our knowledge of the history of this subtype.
Anthracoid wings, as already noted above, are possessed by the majority of representatives of the family of bee flies. Some forms of these diptera show processes of specialization of the wings, which consist of reduction phenomena of the venation, while only partly showing the nature of costalization. These forms constitute a special subtype whereto we will turn after having added more examples of the present (and of some of the next) subtype.

 

 Figure 16 :  Wings of Bombyliidae. From left to right and from top to bottom :
211 - Wing of  Argyramoeba  oedipus  Fabr. 212 - Wing of  Exoprosopa  stupida  Rossi.
213 - Wing of  Ligyra  lugubris  Rond. 214 - Wing of  Henica  longirostris  Wied.
215 - Wing of  Hyperalonia  bombyliformis  Mac Leay. 216 - Wing of  Toxophora  maculata  Wied.
217 - Wing of  Thyridanthrax  afer  Fabr. 218 - Wing of  Callistoma  fascipennis  Macq.
219 - Wing of  Heterostylum  robustum  O.S. 220 - Wing of  Systropus  excisus  End.
221 - Wing of  Cyrtosia  meridionalis  Rond. 222 - Wing of  Glabellula  nobilis palaestinensis  Engel.
(After ENGEL, 1933)
(After HENNIG, 1954 (except 222))
Sometimes the venation of a representative of a given family can be the product of a transformation of the  f a m i l y-prototype such that the latter is hardly recognizable anymore even to the extent that the product-venation is almost identical to the typical venation of a non-aberrant representative of another suborder! The next Figure shows this for the venation of the bee fly  Empidideicus :

Figure 17 :  Convergence of wing-venation.
Left image - Wing of  Diadocidia  spec.  (Suborder Nematocera, Diadocidiidae).
Right image - Wing of  Empidideicus  spec.  (Suborder Brachycera-orthorrapha, Bombyliidae).
Both wings evidently do not belong to the tabanoid type, but probably to the ancient lifting venationally-attenuated (fungivoroid) wing type (discussed in Part LXIX ) (After EDWARDS, 1926, in HENNIG, 1954)
    9.   A number of forms of the family of bee flies (Bombyliidae), namely the genera  Usia,  Cyrtosia (221 of Figure 16),  Systropus (220 of Figure 16),  Apolysis,  Oligodranes,  Alloxytropus,  and species of the peculiar genus  Omphrale (Omphralidae) (next Figure),  show a characteristic reduction of the venation, its costalization. These wing-forms must be taken apart to constitute the special  cyrtosioid subtype.

Figure 18 :  Wing of  Omphrale  fenestralis  Lw.  Omphralidae.  Compare with  Cyrtosia  (Bombyliidae) ( Figure 16, 221 ).
(After HENNIG, 1954)
The basiala of the wings of this subtype is to a lesser extent strengthened than it is in the anthracoid subtype, lacking a phragm or only with a weak phragm or fold. The wing-venation of the wing-blade is markedly reduced. Of the Radial branches there are four, sometimes only three (Cyrtosia (Fig. 16-221). Of the Medial veins there are almost always only two branches, and only sometimes a third branch is seen (genera  Alloxytropus, Cyrtosia). Especially characteristic is the weakening of the hind-margin of the wing, lacking the Costal vein. This subtype is established exclusively on the basis of recent forms. There is no fossil material.
    10.   The chiefly tropical and subtropical diptera, the representatives of the families Mydaidae and Apioceratidae, possess wings that form a special transformation of the tabanoid type and which may be called the  mydaoid subtype.  These forms stand more closely to those of the asiloid subtype and distinguish themselves by the all-out peculiar structure of the venation of the apical part of the wing, and by the nature of its hind-margin. Mydaoid wings are, as to the structure of their basiala, similar to asiloid and tabanoid-proper  wings (see  Figure 7, Part LXXI ).  In them there is a well developed strong phragm, a large alula and wing-scale. The Subcostal (SC) and anterior Radial vein (R) are very long, where the latter, just as in many representatives of the asiloid subtype, ends up, not at the wing-margin, but unifies at its end with other Radial veins. See  Figure 15, middle image .  But most remarkable is the structure of the posterior Radial and all Medial veins, which do not end up at the wing-margin, but unify at their ends one with the other, forming peculiar closed cells, or, on the contrary, partly arch-wise curve to the wing-apex and end up at the Costal vein on the anterior wing-margin or even at the anterior Radial vein. The Costal vein only extends up to the wing-apex and no farther. The whole posterior margin[al area] of the wing is without veins, and only the apices of the Cubital vein, of the posterior, more rarely also of the middle (Apioceratidae) Medial veins, reach the wing-margin. Sometimes also these veins do not reach the margin. The wing of the representatives of this subtype is very peculiar indeed by its bow-like veins in the apical part of the wing, and by the free, lacking veins, membrane that fringes in the form of an edging the posterior wing-margin. This subtype is most elegantly expressed in the representatives of the family Mydaidae. The species of the family Apioceratidae are distinguished by the lesser degree of development of an attenuated hind-margin. The Mydaoid subtype stands closely to the asiloid subtype, but is its derivative only partly. The connections of these subtypes are undoubtedly more complex and consist in their origin from the rhagionoid subtype, whereby the asiloid wings branched off from a derivative of the latter, namely from the tabanoid-proper subtype (from wings of the type as they are seen in Therevidae ( Figure 12 )),  while mydaoid wings were formed not only from the tabanoid-proper subtype (also via Therevidae to Apioceratidae), but also directly from rhagionoid wings. There are practically no fossil documents that could throw light on the history of mydaoid wings, if we do not count the single finding of not-determined forms of Mydaidae from miocene deposits of North America.
The next Figures provide some more examples of wings of the mydaoid subtype (Apioceratidae, Mydaidae).

Figure 19 :  Apioceratidae (= Apioceridae).
171 - Wing of  Apiocera  maritima  Hardy.  (After CAZIER, 1941).
172 - Wing of  Apiocera  bigoti  Macq.  (After HENNIG, 1954).
173 - Wing of  Megascelus  nigricornis  Phil.  (After CAZIER, 1941).
174 - Wing of  Neorhaphiomidas  hardyi  Norr.  (After CAZIER, 1941).
(In HENNIG, 1954)

Figure 20 :  Mydaidae.
175 - Wing of  Rhopalia  paulseni  Phil.
176 - Wing of  Dolichogaster  nigricornis  Phil.
177 - Wing of  Mitrodetus  dentitarsis  Macq.
(After HENNIG, 1954)
    11.   The wings of the most peculiar diptera,  Nemestrinidae  (  Figure 15, bottom image ),  together make up a special subtype of tabanoid wings, which might be called the  nemestrinoid subtype  (see also the  Figures below ).  This subtype may be best characterized by the almost constant presence of "supplementary veins" (in reality undoubtedly remnants of an ancient rich venation!), chiefly in the form of many cross-veins, positioned between the branches of the Radial and Medial systems. Another characteristic feature of this subtype is the development of a special so-called diagonal vein, made up by sections of radial and medial veins, and positioned obliquely across the wing from the basal part of the anterior margin down to the middle of the termen (see  Figure 15, bottom image ).  This complex additional structure delimits the apex from behind [i.e. forms the posterior-proximal border of the apical region of the wing), and probably has a certain mechanical function or significance. Nemestrinoid wings are, in addition, characterized by the bend of all Radial and anterior Medial veins to the apex of the wing. These branches run parallel to the hind margin and end up at the anterior margin of the wing-apex (see Figure 21, below ).  This similarity with the mydaoid wings is supplemented by a certain attenuation of the whole hind-margin[al area] of the wing, which sometimes lacks the Costal vein, and has a free membraneous zone (for instance in the genera  Atriadops,  Fallenia [193 in  Fig. 21] )  [This, is, by the way, also seen in many hymenopterous wings.]. Very characteristic of this subtype is the great enlargement of the basiala, reaching a large size indeed, sometimes up to more than one fourth of the length of the whole wing. The phragm is almost always very strong [forming a structure that is analogous with the Radio-Medial T-vein in many Hymenoptera-Apocrita] in the form of an oblique firm vein between the base of the radial and cubito-anal veins (see  Figure 2, above ).  Anal lobe, as a rule, well developed, seldom narrow (in the genera  Nycterimorpha [197 in  Fig. 22],  Cyclopsidea [196 in Fig. 22] ). Alula almost always large, seldom being absent (in the genera  Cyclopsidea, Nycterimopha), or rudimentary  (in the genera  Fallenia [193 in next Figure],  Symmictoides [187 in next Figure],  Symmictus). The wing-scale is rudimentary.
The next two Figures depict wings of a number of Nemestrinidae.

Figure 21 :  Nemestrinidae.
185 - Wing of  Hirmoneura  bellula  Phil.
 186 - Wing of  Hirmoneura  obscura  Meig.
187 - Wing of  Symmictoides  simplex  Lw.
 188 - Wing of  Rhynchocephalus  fasciatus  Macq.
189 - Wing of  Nemestrinus  aegyptianus  Wied.
 190 - Wing of  Neorhynchocephalus  tauscheri  Fisch.
191 - Wing of  Trichophthalma  barbarossa  Big.
 192 - Wing of  Stenopteromyia  bolivari  Strobl.
193 - Wing of  Fallenia  fasciata  Fabr.
 194 - Wing of  Prohirmoneura  jurassica  Handl.,
from the upper Jurassic (Malm) of Bavaria, Germany.
(After HANDLIRSCH, 1908)
All, except 194, are recent Nemestrinidae.
(After HENNIG, 1954 (except 194))

Figure 22 :  Nemestrinidae.
195 - Wing of  Nycterimyia  horni  Lichtw. (after the type in Deutsches Entomologisches Institut)
196 - Wing of  Cyclopsidea  spec.  (After HARDY, 1946)
197 - Wing of  Nycterimorpha  speiseri  Lichtw. (after the type in Deutsches Entomologisches Institut)
198 - Wing of  Atriadops  spec. (After HARDY, 1946)
199 - Wing of  Trichopsidea  spec. (After HARDY, 1946)
(After HENNIG, 1954 (except 196, 198, 199))
Of fossil documents on the history of the nemestrinoid subtype there are only a few. The sole mesozoic representative of the family Nemestrinidae is found in the upper Jurassic deposits (Malm) of Bavaria (Germany) and was described by Handlirsch under the name of  Prohirmoneura  jurassica  Handl. (see 194 in  Figure 21 ).  This form is very insufficiently studied, and to judge about its features from the existing description and drawing of Handlirsch is not possible. Only its being close to the family Nemestrinidae is clear :  the absence of a long snout [in the complete fossil] was evidence for the author to assume it to be close to the genus Hirmoneura, which has little basis. The venation of the wings is not described and not drawn in an exact way. Other fossil nemestrinids are known only from the cenozoic. Such are a few species of recent genera from the Miocene of North America and from the upper Oligocene of France. All fossil material, as to the history of the nemestrinoid subtype, does throw almost no light on the way of its formation.
(End of description of the eleven subtypes of the tabanoid type of wings)
General considerations concerning the tabanoid type
The considered content of the tabanoid type indicates its extreme diversity and broad differentiation. Having first appeared already in jurassic times, this type was closely connected with the evolution of the Suborder Brachycera-orthorrapha. The large majority of its [this type's] forms characterize the basic groups of the mentioned Suborder. As was already stated above, the characteristic traits of the tabanoid type were detemined by the general direction of the evolution of the Brachycera-orthorrapha in which usually has taken place an increase in absolute body-size. Clarification and analysis of this process in the evolution of the Brachycera-orthorrapha does not belong to the aims of the present investigation. Here it suffices to just indicate the directions of the historical development of the different forms of this type.
The chief factor, having determined the formation of the type, the process of increase of size, did, in the evolution of the different groups of Brachycera-orthorrapha, by far not have a uniform significance and distribution. Living or developing in conditions of abundancy of high-caloric food contributed to the increase of size. Such, for instance, are the plant-eating [as larva] and predatory Asilidae, Mydaidae, many horse flies (Tabanidae), some bee flies (Bombyliidae) (for instance the genera  Spongostylum, Exoprosopa, and others). On the other hand, developing in narrow environments, for instance parasitizing in the body or provisions of arthropods (as do Bombyliidae), or living in the tissues of small plants (for instance grasses -- many Asilinae), did not contribute to an increase of body-size. Such concise and insufficiently reasoned assertions of mine [=  Rohdendorf] are given only to provide an indication of the diversity in the paths of evolution of these diptera. More strictly they will be developed at another place. On the other hand, the way of life of the Brachycera-orthorrapha, especially the features of feeding -- active predation, blood-sucking, feeding on nectar of plants, and, finally, aphagia [= not at all taking food] -- all this determined the great differences in the demands on the organs of locomotion, especially the wings. Not developing any further this analysis of factors having determined the definite development of the wings (about which will be spoken below), here we need only note that the tabanoid type developed along two chief directions :  On the one hand the wings became elongate and strong whereby the basiala developed a particularly strong phragm, while, on the other hand, wings increased the strength of their anterior margin simultaneously with the weakening (attenuation) of the posterior margin -- costalization developed. Both these evolutionary directions of the tabanoid type were by far not realized uniformly in different cases.
The nemestrinoid, anthracoid, and in a lesser degree mydaoid, subtypes clearly illustrate the lengthening of the wings which morphologically expressed itself by a change of the structure of the venation in the apical part of the wing [This can also be seen in Tipulidae]. The change of the position of the veins of the apical wing-part bear witness of a [as a result] stiffer construction of the wing-blade, and especially of the reduction of veins in the hind-marginal area, the part of the wing that swings [relative to the rest of the wing] during the wing-beat, which part is always supported by the posterior-radial and medial veins in the majority of the other diptera (and generally in many other insects for that matter). Such a structure of the wing of these large diptera indicates that the perfection of their flight was determined by the increase of the length of the wings, and, consequently, the increase of their surface area and the decrease of load [amount of weight of the insect per unit of wing-surface area]. Increase of wing-beat frequency did not take place or was insignificant. These subtypes with elongated wings include representatives of groups of which the winged forms are exclusively vegetarian, or, more rarely, do not take food at all. The flight of these insects is distinguished by speed and ease. Many of them are able to feed in flight, holding themselves almost motionless in the air in front of the flower.
The other direction of change taken by tabanoid wings consists of the development of the phenomenon of costalization, sometimes appearing only as a broadening of the posterior part of the wings, without reduction of the number, or change of position, of the veins of the hind-margin. Such a path of specialization of the wings is taken by the tabanoid-proper, cyrtocioid, erinnoid, rhagionoid subtypes, and by the extinct eostratiomyioid and palaeostratiomyioid subtypes. This process of the broadening and attenuation of the hind-part of the wings we also observe in some representatives of the "elongated-wing" subtypes -- in the nemestrinoid subtype (for instance in the genus  Atriadops  [ 198 in   Figure 22 ],  and especially in the anthracoid subtype (in a number of genera, for instance  Cytherea,  Legnotomyia,  some  Bombylius,  and many others).
The biological features of these insects, with "broadened" tabanoid wings are peculiar :  Here do belong the blood-sucking horse flies (Tabanidae), the predatory Rhagionidae and Therevidae, and also certain vegetarian bee flies (Bombyliidae) and Nemestrinidae. Broadening of the wings bears witness first of all of a high wing-beat frequency, and of the great significance of the swinging posterior part of the wing during wing-beat for the mechanics of wing-beat. Such kind of flight is characterized by a great navigability, by the ability to execute sharp turns in low absolute speeds of movement of the insect. The possibility to reach high speeds is, of course, not excluded in the presence of sufficiently long wings and a powerful muscle apparatus (as we see it in horese flies). But the very presence of broadenings of the posterior parts of the wing first of all guarantees a better control during wing-beat. In addition, the development of costalization bears witness also of the increase of load-lifting capacity of the flight-apparatus as a result of that same increase of wing-beat frequency. However, in the present case this feature has subordinate importance judging from the way of life of these diptera, not needing a large store of power of their flight-apparatus. Only the blood-sucking horse flies and the predatory Rhagionidae and Therevidae may significantly change their weight as a result of having absorbed food or of the carrying of the prey, and for them the "store of power" is necessary.
A very special evolutionary direction of tabanoid wings is evident in the asiloid subtype, containing representatives of the family of robber flies (Asilidae), being active predators, attacking a variety of other insects, often significantly more massive than themselves (for instance grasshoppers).
Wings of the asiloid subtype are characterized by a decrease of size (they often are significantly shorter than their body!), and by a very firm and at the same time elastic basiala provided with an articulated phragm and strong veins of the [its] anterior margin. The shape of the wings is peculiar :  They have a pointed apex and a broadened anal lobe. Reductions and displacements of veins are usually little expressed :  Only in a few forms, referred to earlier, the hind-margin[al area] of the wing has transformed into a membrane devoid of veins. Such features of the asiloid wings (first of all their small relative size) bear witness of a high wing-beat frequency. The life habits of these insects make this trait of their flight-apparatus clear :  Robber flies need a high "stock of power" as a consequence of the need to transport its seized prey, which often is quite heavy. A high degree of flight-control is also very important for these active predators, catching usually winged insects.
In concluding this list of directions of development of the type we must look into the character of the first, phryneoid, subtype to which some representatives of the rhagionoid subtype stand close. Perhaps the wings of these subtypes must be reckoned as being the point of departure of the whole tabanoid type. Although the global relatively broad shape of the wing seemingly points to features of the wings of the tabanoid-proper subtype, these wings sharply distinguish themselves by their little strengthened basiala, by their low degree of costalization, and their large relative size with small absolute size of the insect. The flight of phryneoids is weak and has a subordinate significance in the life-habits of the insect, it is not, as it seems, strongly connected with the realization of feeding.
The origin of the tabanoid type is very obscure. Paleontological documents connecting this type with the original tipuloid type are still unknown. Purely comparative-anatomical data point to a connection of tabanoid wings with the most primitive forms of wings of diptera, in which many interradial and intermedial cross-veins were still preserved. Such fossil forms are not yet found. The formation of the tabanoid type was determined first of all by the increase of flight-capabilities, increase of wing-beat frequency stimulating the formation of a differentiated [from the rest of the wing] basiala, the appearence of the alula. This process was accompanied by the increase of absolute size of the insect, which delayed reduction of the venation of the wing-blade, that is, especially [delayed] a higher degree of costalization. The formation of the tabanoid type apparently was realized along two ways. On the one hand, the rhagionoid subtype branched off from original forms. This subtype characterizes itself by the weak, but already clear, development of the phragm in the form of a fold in the basiala, and by an already reduced number of cross-veins with an absence of costalization and small absolute size. On the other hand, from ancestral forms there developed the wings of the eostratiomyioid subtype. Of them is characteristic a rudimentary costalization, large relative size [of the wings with respect to the body], and the preservation of many cross-veins. The latter subtype served as a point of departure of two others :  the extinct palaeostratiomyioid subtype and nemestrinoid subtype. The rhagionoid subtype turned out to be the point of departure of all the remaining diversity of the type. The connections of the tabanoid type with other types are more or less clear. First of all, on the basis of the palaeostratiomyioid, erinnoid, and cyrtocioid subtypes various forms of the stratiomidoid type originated. On the basis of cyrtocioid wings, in addition, the wings of the empidoid type were formed.
We have now concluded the description of the tabanoid functional wing-type and its subtypes.
In the next document we will look to the formal aspect of the venation of these wings, that is, we will investigate the formal derivational relationships they have to the dipterous prototype and to each other.
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