264 MINERALS AND GEOLOGY 



IV. 

 INSECTA. 



This large and important division of the Arthropoda is of compara- 

 tively little geological interest. In all insects, the head, thorax, and 

 abdomen are distinctly separated, the respiration is tracheal, and the 

 legs are always in three pairs. Hence the name of Hexapoda by 

 which the entire division is now often known. 



Some insects assume their perfect form at birth. These belong to 

 the Thysanura (or group Ametabola : e. g. Podura, Lepisma, &c.), and 

 are without fossil representatives except in amber. The recognized 

 forms, thus preserved, belong with one exception (Glessaria) to 

 existing genera. 



Other insects undergo an incomplete metamorphosis after birth. 

 They belong to the section Hemimetabola, and comprise the Hemip- 

 tera or Rhyncota (insects with rostral mouth : e. g. Aphides, Coccina, 

 Cicada, Nepa, &c.), and the Orthoptera, including with the latter the 

 so-called Pseudo-Neuroptera. Orthoptera comprise cockroaches, grass- 

 hoppers, locusts, &c., and the Pseudo-Neuroptera, the so-called " dra- 

 gon-flies " and related forms. Fossil examples occur in Devonian 

 strata (Platyphemera antiqua) ; in the Carboniferous formation (Blat- 

 tina } Termes, Euphemerites, Palingid), and more abundantly in 

 Mesozoic and Cainozoic deposits (Ephemera, Libellula, &c.). 



Other insects, again, undergo complete metamorphoses passing 

 through the three conditions of larva, pupa and imago. These form 

 the group or section Holomltabola and cromprise the Neuroptera 

 as now restricted ( e. g. " scorpion flies," " caddis worms," " ant-lions," 

 &c.); the Lepidoptera (butterflies and moths) ; Diptera (house-flies, 

 &c.) ; Hymenoptera (bees, wasps, ants) ; Strepsiptera (bee-parasites) ; 

 and Coleoptera (beetles). The parasitic Strepsiptera have no known 

 fossil representatives. Doubtful examples of Coleoptera have been 

 cited from Carboniferous strata, but the Order only dates with cer- 

 tainty from the Triassic period. Fossil Lepidoptera, Diptera and 

 Hymenoptera are Mesozoic and Cainozoic only. No examples of 

 fossil insects occur in the strata of Ontario and Quebec. This brief 

 summary, therefore, is all that need be given in the present work. 



