794 ARTHEOPODA phylum vii 



SuBPHYLUM C. Insecta (Hexapoda). Insects.^ 



Trarheate Arthropods loitli body at maturity consisting of a distinct head, thorax 

 and abdomen. Head provided loith one pair of antennae, one of mandibles, and two of 

 maxillae. Thorax composed of three segments, each supplied with a pair of legs, and the 

 second and third segments also usually carrying a pair of wings on their dorsal surfaces 

 in the adult stcde. Abdom.en composed of several {commonly ten) distinct segments, and 

 usually without leg-like appendages. Development usually throthgh metamorphic stages. 



No undoubted remains of Insecta are known from strata older than the 

 Carboniferous, but in the Coal ]\Ieasures and Permian a considerable variety of 

 winged forms has been detected, in Ijoth Europe and North America. These earlier 

 Insects appear to be more generalised than are the post- Paleozoic forms, and the 

 majority are referred by Handlirscli to orders distinct from those occurring in Mesozoic 

 and later formations. But one order, the Blattoidea, seems to have survived from 

 Paleozoic times onward to our own day. The primitive extinct order Palaeodictyop- 

 tera is regarded as the ancestral stock which gave rise to the other Paleozoic orders, 

 and from the latter in turn have originated the modern Insect groups. 



Although it is clear that strangely differentiated forms occurred among the 

 different Insect groups as early as the Carboniferous, yet it has been conclusively 

 shown that this differentiation had little dej^th, and that it is only through Mesozoic 

 and later descendants that we have any clue to a wide separation of the original 

 Paleozoic forms. Among the latter, the neuration of the wings, though diversified, 

 had yet a far greater homogeneity than is found now, or than existed during Mesozoic 

 time, from the Trias onward. The fore wings of whatever type were as diaphanous as 

 the hind, and could never (as in most of their descendants) properly be called tegmina. 

 The wings of the Protodonata of Brongniart had indeed a superficial resemblance 

 to those of living Odonata in shape, reticulation, and sweep of the veins. But in 

 fundamental neuration they were altogether different, and no trace is to be discovered 

 of those characteristic features of the Odonata, such as the nodus, triangle and 

 pterostigma, which apj^ear fully elaborated in the Mesozoic species. 



" The wings, broadly speaking, may be said to be three-margined. The margin 

 that is anterior when the wings are extended is called the costa, and the edge tliat is 

 then most distant from the body is the outer margin, while the limit that lies along 

 the body when the wings are closed is the inner margin. 



"The only great order of insects provided with a single pair of wings is the Diptera, 

 and in these the metathorax possesses, instead of wings, a pair of little capitate 

 bodies called halteres or poisers. In the great order Coleoptera, or beetles, the 

 anterior wings are rejilaced by a jiair of horny sheaths that close together over the 

 back of the insect, concealing the hind wings, so that the beetle looks like a wingless 

 insect ; in other four-winged insects it is usually the front wings that are most useful, 

 in flight. In the Orthoptera the front wings also differ in consistence from the 

 other pair over which they lie in repose, and are called the tegmina." (Sharp, 

 Cambridge Natural History, vol. v.) 



^ The most complete bililiograpliies are to be found in various well-known publications on fossil 

 Insects by S. H. Scudder, and in the work by A. Handlirsch, Die fossileu Insekten, Leipzig, 

 1906-8. See also Handlirscli s Revision of American Paleozoic Insects, in Proc. U. S. Nat. Mus. , 

 1906, vol. xxix. For important recent contributions one should consult the writings of Agnus, 

 Bode, Bolton, Brnes, Burr, Cockerell, Dainpf, Enderlein, Leriche, Melandrr, Meunier, Olfers, 

 Pruvost, Reis, Rohwer, Schlechtendal, Sellards, Shelford, Ulnier, Wickham, and others. 



The most elal)orate descriptions of the insect faiuia of Commeutry are contained in the follow- 

 ing memoirs : — Brongniart, C, Recherches pour servir a I'histoire des insectes des temps primaires, 

 etc. Saint-Etienne, 1893. — Meunier, F., Nouvelles recherches sur quelques insectes dii terrain 

 houiller de Commentry (AUier). Annales de Paleont. , vols, iv., vi., 1906-12. 



