. The Australian zoologist. Zoology; Zoology; Zoology. 132 A RECLASSIFICATION OF THE ORDER ODONATA. situated between costa and radius, somewhat before the apex, at the region of greatest impact of the wing on air during flight. Originally it appears to have covered only a single cell, , the sppce between two consecutive cross-nervures, but in some of the most heavily veined recent forms it may cover a space equivalent to a number of small cells. In a few forms (, the Pseudostigmatidae), (Fig. 20), it becomes hypertrophied or abnormal, while in others (males of some Agriidae) it is obso
. The Australian zoologist. Zoology; Zoology; Zoology. 132 A RECLASSIFICATION OF THE ORDER ODONATA. situated between costa and radius, somewhat before the apex, at the region of greatest impact of the wing on air during flight. Originally it appears to have covered only a single cell, , the sppce between two consecutive cross-nervures, but in some of the most heavily veined recent forms it may cover a space equivalent to a number of small cells. In a few forms (, the Pseudostigmatidae), (Fig. 20), it becomes hypertrophied or abnormal, while in others (males of some Agriidae) it is Fig. 4.—Typus permianus Sell. Forewing. The Arculus. The most important specializations in the wings of Odonata occur in the region of the arculus (Figs. 7, 9b). We have mentioned already that, in almost all Odonata, the original stem of MA has been lost, so that this vein becomes attached secondarily to Rs. The arculus m?.y be defined as the free basal portion of Rs H- MA alter it leaves the common stem with R, together with any supporting cross-vein beneath it. In recent forms (Fig. 23) the complete arculus consists of two parts, viz., the anterior arculus formed from the strongly bent basal portion of Rs + MA and the posterior arculus formed from a specialized cross-vein below it. The fossil record shows how this specialized form of complete arculus arose. There is, first of all, as in Kennedya (Fig. 9B) and Ditaxineuray only the oblique weakly specialized free basal portion of Rs + MA, without any sup- porting cross-vein below it; the cross-vein that comes nearest in position at this stage is the discoidal cross-vein, dv, (Fig. 9), whi^h is destined to play an entirely different part, as we shall see when considering the evolu- tion of the discoidal cell or quadrilateral. Consequently, in some primitive cross nervures which run from the Costa and Radius to meet at the same point on the Subcosta, and since the latter is concave to the Costa and Radius, the two halve
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1914
