. Class book of economic entomology. Insects, Injurious and beneficial. [from old catalog]; Insects; Insects. STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 15 May flies and the males of scale insects have their hind wings very much reduced or entirely wanting. In the flies {Diptera) the hind wings are converted into halteres (balancers). 2. Where the fore wings are either wholly or partially chitinized. Examples of such thickening of the wings occur among the grass- hoppers and crickets, the beetles and the heteropterous bugs. 3. Where the hind and fore wings are strongly reduced or completely at
. Class book of economic entomology. Insects, Injurious and beneficial. [from old catalog]; Insects; Insects. STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 15 May flies and the males of scale insects have their hind wings very much reduced or entirely wanting. In the flies {Diptera) the hind wings are converted into halteres (balancers). 2. Where the fore wings are either wholly or partially chitinized. Examples of such thickening of the wings occur among the grass- hoppers and crickets, the beetles and the heteropterous bugs. 3. Where the hind and fore wings are strongly reduced or completely atrophied, as in the fleas {Siphonaptera), bird-lice {Mallophaga) and sucking lice {Siphunculata). Venation.—It has been found that the system of veins in the different orders of insects is fundamentally ahke, being de- rived from the primitive type fairly well seen in some stone- flies and some cockroaches. This fact becomes evident only when a comparison is made of the wings of the more general- ized members of the different orders, as specialization has greatly modified their structure in most genera. Comstock and Needham have shown by a study of the developing wings of nymphs and pup^ that the /^^- 20.—Several stages in the de- . , , • T 1 • • velopment of the wmgs of a cabbage butter- prmcipal longitudmal vems m fly. {After Mercer.) the more generalized orders are formed about tracheae (Fig. 20). In the development of the wing these tracheae grow out into the wing-bud, and later the veins are formed about them. The cross veins, however, as a rule do not arise in this manner, as tracheae are apparently absent. In the course of development specialization has brought about changes in the venation, recognized, first, by the addition of veins through branching of the prin-. 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 resembl
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectinsects, bookyear1919
