INSECT A. 509 



passage of air through the stigmata or through the mouth (Death's Head 

 Moth). 



The majority of Insecta are terrestrial, some are aquatic in the larval 

 and adult condition, or in one or the other. They feed on vegetable and 

 animal matters living or dead, and some few are parasitic {Siphonaptera, 

 Mallophaga, &c.). The oldest known fossil Insecta are genuine Orthoptera 

 (Blattidae, Phasmidae,Mantidae), genuine Neuroptera(Sialidae in Devonian 

 strata), and Rhynchota Homoptera (Fulgoridae\ which differ from living 

 forms only in genus or even, looking at generalised generic characters, 

 belong to genera still living (Brauer). A Blatta has been found in Silurian, 

 Coleoptera in Carboniferous strata ; Hymenoptera, a Lepidopteron, Heterop- 

 tera and Diptera occur in the Solenhofen Slates (Oolitic). 



The following classification is taken from Brauer (Systematisch Zool. Studien, 

 SB. Akad. Wien, xci. Abth. i, 1885). It is based upon recent advances in anatomy 

 and embryology. Italics, &c. have been employed, and the mode of numbering the 

 paragraphs altered. A small addition has also been introduced in Rhynchota 

 (B. 8), and a slight change made in C. * Oligonephria, section b, in order to make 

 it tally obviously with section a. The terms have been explained and used in the 

 foregoing text. 



I. INSECTA APTERYGOGENEA (= Collembola and Thysanura). 

 II. INSECTA PTERYGOGENEA. 



A. Meiiogiiatlia ametabola and liemimetabola. 



*POLYNEPHRIA. 



(a.) genital orifices of the male, or of both sexes double; or single 

 either by loss of one, or by the union of the two : ducts without 

 chitinoid lining. 



1. Ametabola. Wings very dissimilar ; fore wings short, corneous ; hind wings 

 folded longitudinally and transversely. Antennae filiform ; mouth-parts distinct. 

 Dermaptera (Earwigs). 



2. Hemimetabola. Larva aquatic ; imago with wings never folded ; hind 

 wings the smaller or lost ; antennae subulate; mouth-parts rudimentary. Ephemeridae 

 (May flies). 



(b.) genital orifice single ; vasa deferentia and oviducts united to a 

 common duct lined by chitin. 



3. Hemimetabola. Larva aquatic ; imago with sub-equal wings not folded, 

 reticulate ; antennae subulate ; male copulatory organs remote from sexual aperture ; 

 prothorax small. Odonata (Dragon flies). 



4. Hemimetabola or perennibranchiate. Larva aquatic; imago with hind 

 wings often folded ; longitudinal veins predominant ; antennae filiform ; prothorax 

 broad; wings sometimes wanting. Plecoptera (=-Perlariae or Orthoptera Amphi- 

 bioticd], 



5. Ametabola. Very generally winged ; hind wing dilated, folded longitu- 



