. Entomology for medical officers. Insect pests; Insects as carriers of disease. 38 ENTOMOLOGY FOR MEDICAL OFFICERS large in flies whose movements are particularly sudden and quick. The posterior (metathoracic) wings are represented by a pair of small club-shaped organs known as halteres, or balancers (aXr^/oej = weights held in the hand to give impetus in jumping), the use of which is supposed to be either for maintaining equilibrium or for stridulating. They are very constant, and are even, as a rule, present in wingless flies. The venation of the wings is comparatively simple, but the gener
. Entomology for medical officers. Insect pests; Insects as carriers of disease. 38 ENTOMOLOGY FOR MEDICAL OFFICERS large in flies whose movements are particularly sudden and quick. The posterior (metathoracic) wings are represented by a pair of small club-shaped organs known as halteres, or balancers (aXr^/oej = weights held in the hand to give impetus in jumping), the use of which is supposed to be either for maintaining equilibrium or for stridulating. They are very constant, and are even, as a rule, present in wingless flies. The venation of the wings is comparatively simple, but the general plan varies a good deal in detail throughout the order. It is enough for our purpose to compare the wing- venation of a house-fly, a mosquito, and a gadfly as standards. In the house-fly (Fig. 5) a veinâthe costalâruns along the front margin (the wing is supposed to be extended at .^ itcilm CO ^ Fig. 5.âWing of House-fly. â """TMialoii. mn/ right angles with the body) from the root of the wing almost to the tip. A second veinâthe subcostal, or auxiliaryâ-runs parallel with the costal for a short distance and then curves into the latter. Behind the subcostal, three veinsâ\^^ first, second, and third longitudinalâarising from a common stem, radiate, in the anterior half of the wing, to successive points in the costal vein. Three longitudinal veins in the posterior half of the wing complete the series; two of them the fourth and fifth longitudinalâa^nse together, and diverge to the margin of the wing; the remaining oneâthe sixth longitudinalâarises more or less independently and runs. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Alcock, A. (Alfred), 1859-1933. London, Gurney & Jackson
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