. The Australian zoologist. Zoology; Zoology; Zoology. FRASER. 147 classification, this cell may be either open or closed basally, that is to say, the formation of the cell is reckoned not from the time that it becomes closed-in basally by the provision of an extra cross-vein to form its basal side, but from the time when, through the oblique alignment of the ori- ginal discoidal cross-vein (dv) with the basal free piece of Rs and MA above it, a complete arculus formation is provided connecting R with CuP. The discoidal ceil or quadrangle (q) is then defined as the space between the oblique ba
. The Australian zoologist. Zoology; Zoology; Zoology. FRASER. 147 classification, this cell may be either open or closed basally, that is to say, the formation of the cell is reckoned not from the time that it becomes closed-in basally by the provision of an extra cross-vein to form its basal side, but from the time when, through the oblique alignment of the ori- ginal discoidal cross-vein (dv) with the basal free piece of Rs and MA above it, a complete arculus formation is provided connecting R with CuP. The discoidal ceil or quadrangle (q) is then defined as the space between the oblique basal portion of MA above and the curving portion of CuP be- low; its distal side, dv, tends in the oldest types to extend the line of the basal portion of MA, but later on takes on greater individuality, when the discoidal cell becomes closed basally by an extra cross-vein. That this is the only logical way to consider the discoidal cell must be evident when we study primitive living forms as Hemiphlebia and Choris- magrion, in which the two stages of evolution of this cell are exhibited in a single insect. In the forewings of these two genera, the discoidal cell remains open and keeps the primitive form found in the Permian genus Permagrion Till., but in the hind wings, the same cell is closed and forms a typical quadrilateral. It should be noted that, as only a single wing of the Permian age is known, it cannot be stated definitely that this form possessed open dis- coidal cells in both fore and hind wings. It is indeed quite possible that this Permian wing represents a fore wing. At any rate, until more is known about it, the Permian genus cannot be given anything more than family rank within the Suborder Zygoptera. Amongst the immense number of genera belonging to the Zygoptera, the venational characters are so diverse that a definition of the Suborder must rest mainly on the structure of the discoidal cell, other characters taking only secondary place. The Suborder may then
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1914
