71 THE EVOLUTION OF THE RADIO-MEDIAL AREA IN THE WINGS OF THE MUSCOIDEA ACALYPTRATA (DIPTERA). By Hakold F. Lower, Systematic Entomologist, Waite Agricultural Research Institute, University of Adelaide. (Thirty Text-figures.) [Read 27th June, 1951.] Synopsis. The writer attempts to homologize the venation of the Muscoidea Acalyptrata with that of the Nematocera and Orthorrhapha. As a basis for discussion of the changes involved, the wings of two generalized Nematocera are considered in some detail. The medial field is then traced through the higher Nematocera and Orthorrhapha to demonstrate that, in its essentials, this field has remained unaltered since its first appearance in the Dolichopodidae, and evidence in support of this view is presented. An essay is made to place the vena siniria and the vein in the wings of the Syrphoidea and Muscoidea, usually referred to as M^, in their correct relation to other parts of the venation, and to show that the vena svuria has exercised a profound influence, even in the wings of the most advanced Diptera. Finally, in a series of hypothetical figures, are set out the possible changes that have been necessary to evolve, from the wing of an asilid-bombyliid-like ancestor, the wing of the Muscoidea Acalyptrata. Introduction. During the past hundred years the venation of the dipterous wing has claimed the attention of many students. The need for a venational system early made itself felt in that period of entomology when descriptive work was practically its sole function. Through the efforts of Bates, Wallace, and others, great collections were being built up, and the rapid naming of hosts of newly discovered insects was of prime importance. In answer to this demand, the first venational systems were developed. Two of these appeared in 1862, Loew's system and Schiner's. Both had one feature in common: each was artificial, having as its object the supplying of a rapid and convenient method of notation for descriptive purposes. The first attempt at a study of wing venation, as contrasted with the mere giving of names or numbers to the veins, was made in 1886, when Josef Redtenbacher propounded his system of venational nomenclature. He realized that the six venational fields were a common inheritance in the wings of all insects. To the principal vein in each of these fields he gave the names accepted today, namely, Costa, Sub-costa, Radius, Media, Cubitus, and the Anal group, and further, he adopted Adolph's conception of the alternation of convex and concave veins, a suggestion which then fell into abeyance until its importance was again recognized by Lameere in 1922. Using Redtenbacher's ideas as a foundation, Comstock and Needham began their work in 1898, but it was not till 1918 that Comstock, in his book "The Wings of Insects", gave a complete account of the now well-known Comstock-Needham system. Based on morphology and homology, this system, modified as new evidence has become available, has been universally accepted as the only scientific one. Some of the more important modifications have resulted from the work of Tillyard, Alexander and, more recently, Vignon. Tillyard's researches have greatly clarified our ideas of the cubital and anal fields; our present conception of the radial field is the result of Alexander's work. Vignon has made a new study of the dipterous wing as a whole, and while all his conclusions are not yet accepted, there is much in his work that has real value. In Australia, considerable research on the dipterous wing has been done by several workers, but the outstanding contributions to our knowledge of the brachycerous venation have come from Hardy.
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