98 (1848),* considered that the nature of metamorphosis was the first-order character, with wings, mouthparts, etc. of secondary importance. If nothing else, the use of metamorphosis as a separating character drew further attention to the heterogeneity of the neuropteroid group, which contained both hemi- and holometabolous forms. Indeed, in his classification von Siebold adopted Erichson's (1839)* arrangement in which the termites, psocids, embi-ids, mayflies, dragonflies, and damselflies were removed from the Neuroptera and placed together as the suborder Pseudoneuroptera in the order Orthoptera.

The foundations of modern systems of classification were laid by Brauer (1885),* who appears to have been greatly influenced by the principles of comparative anatomy and paleontology established by the French zoologist Cuvier, and by the work of Darwin. Brauer divided the Insecta into two subclasses, the Apterygogenea, containing the primitively wingless Thysanura and Collembola, the latter having been given ordinal status by Lubbock (1873),* and the Pterygogenea, containing 16 orders, in which he placed the winged and secondarily wingless forms. Three major divisions were established in the Pterygogenea: (1) Menognatha ametabola and hemimetabola (insects with biting mouthparts in both juvenile and adult stages, or mouthparts atrophied in the adult and with no or partial metamorphosis) containing the orders Dermaptera, Ephemerida, Odonata, Plecoptera, Or-thoptera (including Embioptera), Corrodentia (which included the termites, psocids, and lice), and Thysanoptera; (2) Menorhyncha (insects with sucking mouthparts in both the juvenile and adult stages), containing the order Rhynchota (= Hemiptera); and (3) Menognatha metabola and Metagnatha metabola (insects having a complete metamorphosis, and with biting mouthparts in the juvenile stage and biting, sucking, or atrophied mouthparts in the adult), containing the neuropteroid insects, and the orders Panorpatae (= Mecoptera), Tri-choptera, Lepidoptera, Diptera, Siphonaptera, Coleoptera, and Hymenoptera. Thus, Brauer appreciated the heterogeneity of the "Neuroptera" and correctly separated the Plecoptera, Odonata, and Ephemerida from the neuropteroids, Mecoptera, and Trichoptera. He failed, however, to recognize the heterogeneity of the orders Orthoptera and Corrodentia.

Between 1885 and 1900, a number of modifications to Brauer's system were suggested. Most of these were concerned solely with the subdivision or aggregation of orders according to the author's views on the affinity of the groups. There were, however, two proposals that have a more direct bearing on modern systems. In 1888 Lang* proposed that the terms Apterygota and Pterygota be substituted for Apterygogenea and Pterygogenea, respectively. Sharp (1899) refocused attention on the importance of metamorphosis, but, claiming that the terms Ametabola, Hemimetabola, and Holometabola were not sufficiently definite for taxonomic purposes, proposed new terms describing whether the wings developed internally or externally. His arrangement was as follows: Apterygota (primitively wingless forms); Anapterygota (secondarily wingless forms); Exopterygota (forms in which the wings develop externally); Endopterygota (forms in which the wings develop internally). Sharp was criticized for grouping together the secondarily wingless orders (Mallophaga, Anoplura, Siphonaptera), as these contained both hemi- and holometabolous forms, and the term Anapterygota was discarded. The terms Exopterygota and Endopterygota were widely accepted, however, and became synonymous with Hemimetabola and Holometabola, respectively. It was not until the work of Crampton and Martynov in the 1920s (see below) that it was realized that these terms had no phylogenetic significance but were merely descriptive, indicating "grades of organization." Sharp recognized 21 orders of insects. His system improved on Brauer's mainly in the splitting of the Corrodentia and Orthoptera, thereby giving ordinal status to the Isoptera, Embioptera, Psocoptera, Mallophaga, and Siphunculata.

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