INSECTA 



531 



etc.) ; during the pupal stage no nourishment at all is taken, but the internal 

 organs undergo changes ; in some forms the rest is not absolute, as voluntary 

 local movements may take place (pupae of gnats). 



The insects are divided into numerous orders according to the form of the 

 mouth parts, the structure of the wings, as well as the manner of the development ; 

 with the exception of the lowest group (Apterygota), which is most nearly related to 

 the ancestors of the insects, and which has no wings and undergoes no metamorphosis, 

 all the remaining orders, which are termed Pterygota, have wings on the thorax, 

 though there are, of course, a few species and families of this group which have lost 

 their wings. 



The Pterygota include 



(1) Orthoptera. Biting mouth parts, anterior wings leathery, posterior wings 



thin, folded longitudinally ; metamorphosis incomplete (grasshoppers, 

 crickets, cockroaches). 



(2) Pseudoneuroptera. Biting mouth parts, wings of equal size, thin, not folded 



up (dragon-flies, hair and feather lice, termites). 



(3) Rhynchota or Hemiptera. Mouth parts formed for puncturing and sucking ; 



wings alike, or the anterior wings may be thickened, parchment-like at 

 their base (plant lice, cicadas, bugs and true lice). 



(4) Neuroptera. Biting mouth parts ; wings alike, thin ; metamorphosis 



complete (ant-lions, lace-wing flies, etc.). 



(5) Trichoptera. Licking mouth parts ; anterior wings narrow, posterior wings 



longitudinally folded, both ornamented with little hairs ; the larvae are 

 worm-like in form, live in water, and breathe through tracheal gills 

 (may flies, etc.). 



(6) Lepidoptera. Suctorial mouth parts ; wings covered with scales (butterflies). 



(7) Coleoptera. Biting mouth parts ; anterior wings thickened and differ in 



colour, appearance and function from the thin, folded posterior wings 

 (beetles). 



(8) Hymenoptera. Mouth parts for licking and biting ; the wings alike, 



membranous (ichneumon flies, ants, wasps, bees, humble bees). 



(9) Diptera. Mouth parts formed for puncturing, sucking or licking ; posterior 



wings degenerated (gnats, flies, gadflies, fleas). 



(10) Strepsiptera. Anterior wings shortened ; the female without wings and 



living parasitically (fan-wings). 



The parasites of man occur amongst the Rhynchota, Coleoptera, 

 and amongst the Diptera. 



[The most usual and recent classification of the Hexapoda is the following : 



(1) Aptera, Wingless insects ; scarcely any metamorphosis. 



(2) Neuroptera. Four membranous wings, frequently with much network ; 



the front pair not much, if at all, harder than the under pair ; the latter 

 with but little or no fan-like action in closing ; mandibulate ; meta- 

 morphosis variable, but rarely complete. 



(3) Orthoptera. Four wings ; front pair coriaceous or leather-like, usually 



smaller than the other pair, which are of more delicate texture and 

 contract in repose like a fan ; mandibulate ; metamorphosis complete. 



(4) Thysanoptera. Four very narrow fringed wings ; mouth imperfectly 



suctorial ; metamorphosis slight. 



(5) Hemiptera. Four wings ; the front pair either all transparent or with the 



basal half leathery; mouth suctorial; metamorphosis slight. 



