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SüBPHYLüM III INSECTA \ ^ 795 



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Among the Orthopterons Insects of the British series of Carboniferl^us rocks are 

 a niim])ei' of forms allied to cockroaclies, and nodiiles of the same age contain wings of 

 Palaeodictyoi3terous and allied Insects, some of them showing colour bands (Brodjea). 

 At Comnientry (Allier), France, is found the riebest deposit of Carboniferous"' Insects 

 in the world, and this faiina has been ably investigated by Charles Brongniart 

 (1893) and later writers. Very numerous fossil remains are known from diiferent 

 Mesozoic and Cenozoic horizons. The Insects found in the English and German 

 Lias are for the most part small and insignificant, bat there are known a moderate- 

 sized dragonfly, and also a few Coleoptera. Various remains occur also in the Stones- 

 field Slate, Purbeck, Wealden, Bagshot Beds (Upper Eocene), and Bembridge Beds 

 (Oligocene) of England. Insects are well represented in the Lithographie Stone 

 (Kimmeridgian) of Bavaria ; in fresh water Oligocene deposits of Aix in Provence, 

 and especially in Baltic amber of the same age from East Prussia ; in the Miocene 

 brown coal of Rott near Bonn ; in the Miocene lacustrine deposits of Oeningen, 

 Baden, on Lake Constance ; and in similar deposits of Florissant, Colorado, also 

 of Miocene age. Many Insects also come from the Miocene deposits of Radoboj 

 in Croatia, and from the Indusial limestone of Lower Miocene age from Offenbach. 

 There is considerable reason to suppose that Insects were more numerous in species 

 during Tertiary times than they are at the present day. 



In the System here adopted the winged or wingless condition is made the basis 

 for dividing Insects into two classes, Pterygogenea and Äpterygogenea. The former 

 of these comprises forty Orders, thirteen of which are entirely extinct. The lowly 

 organised class of apterous Insects comprises four Orders, three of which have Tertiary 

 representatives as well as Recent, and the remaining order is without known fossil 

 representatives. 



If the opinion of Lankester and Börner,.that the primitive Insects have a special 

 afhnity with the Isopoda, be accepted, the discovery of Oxyuropoda in the Devonian 

 of County Kilkenny, Ireland, becomes of particular interest (see ante, p. 757). In 

 the view of G. H. Carpenter, a more general relationship between Insects and 

 Crustacea seems probable, so that this Devonian Isopod genus and the lowly organised 

 Pterygote order of Palaeodictyoptera must be regarded as having each advanced along 

 different lines of specialisation from their common ancestors. The common stock 

 from which both Crustacea and Insecta are descended must surely have been Arthro- 

 pods with undifferentiated trunk-segments, yet on the whole, resembling primitive 

 Crustaceans in structure, and possibly not very remote from Trilobites. 



Olass 1. PTERYGOGENEA Brauer. 



Insects normally winged in the adult, or secondarily wingless, with faceted eyes, and 

 ahdomen usually with nine or ten distinct Segments. 



t Order 1. PALAEODICTYOPTERA Goldenberg. 



Head moderately large, rounded, ivith siw/ple antennae, mouth parts adapted for 

 biting, and well-developed jaws. Two pairs of wings, suhequal in size, of similar form 

 and primitive venation, incapable of heing folded hacJcward over the ahdomen ; sometimes 

 a rudimentary third pair present on the first thoracic segment Ahdomen consisting of 

 ten nearly homonomous segments which often exhihit pleural lohes. Terminal segment 

 often with much elongated cerci. Thoracic legs similar. 



In this Order the wing structure is very primitive (Fig. 1531), corresponding 



t Tills sigu is iised tliroiigliout tlie following pages to indicate that the ßystematic group referred 

 to is extiuct. 



