794 



ARTHEOPODA phylüm vii 



/BüBPHYLUM C. Insecta (Hexapoda). In'sects.^ 



Tracheate, Arthropods with hodtj at maturity consisting of a distind head, thorax 

 and abdorrten. Head provided with 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 fheir dorsal surfaces 

 in the adult state. Abdomen composed of several (commonly ten) distinct segments, and 

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



No undovibted remains of Insecta are known from strata older than tlie 

 Cai'boniferoiis, but in the Goal Measiires and Perniian a considerable variety of 

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

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

 majority are referred by Handlirsch 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 depth, 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 wh'atever 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 appear 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 wmgs are replaced by a pair of horny sheaths that close together over the 

 back ot 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 night. In the Orthoptera the front wings also differ in consistence fmm the 



rnZriTi^T TJ^ . *^'^^^' in repose, and are called the tegmina." (Sharp, 

 Cambridge Natural History, vol. v.) b \ i^, 



lusL^l^TH''tlS£r''Z^ '" *'i V'7''S ™"^'^ -ell-known publications on fossil 

 1906-8. See IL nZd^Ch^. ^ Ta ^^•^- ^^''<^^i^'<^^ Die fossilen Insekten, Leipzig, 



•■'■'•• H..]in„ Brues Bufr ?W1 ll ^^^^tribuüons one shonld consult the writings of Agnns 



TlH- n„w, Z^^ S^'^lf^^'^' Ulmer, Wickham, and oth( 



lers. 



/^rj!/'.\'/7'/''' p"V'' \^'^ '"'"''* '''''"''' °^ Commentry are contained in the follow- 

 «tc. Saint- |.:t ienne, ' 1893 ^ ~-^Mry\'n-lr i^"" m """ ''T''' '' ^'^i^^^ire des insectes des temps primaires, 

 l-ilh.rde<^..n.ntry(Ailier).Tn;a^y,~:l;;^^^^^^^^^^^ '^^'^'^^ ^" '^''^'^ 



I 



