220 THE EYE IN EVOLUTION 



into two, depending on whether their wings are developed externally (Exoptery- 

 gota) or internally (Endopterygota) ; in the latter the wings become evident 

 only in the adult (imago) stage. 



(a) EXOPTERYGOTA, insects which undergo a series of moults marked by 

 the gradual development of wings. The more important orders are : — • 



ORTHOPTERA — cockroaches, locusts, grasshoppers, crickets, stick- 

 insects, praying mantis. 



DERMAPTERA — earwigs. 



PLECOPTERA — stone-flies, a small and little known order, the aquatic 

 larvte being found beneath the stones of mountain streams, and the 

 slow-flying adults having a very short life. 



ISOPTERA — termites living under grovmd without eyes. 



EMBIOPTERA — a few species of insignificant tropical insects. 



ZORAPTERA — a few species of minute insects resembling termites. 



psocoPTERA — small plump, book-lice (winged or wingless). 



ANOPLURA — biting or sucking lice, wingless, parasitic on man and 

 animals and frequently disease-producing {Pediculus, Phthirus, etc.). 



EPHEMEROPTERA — mayflies, the aquatic larva3 living up to 3 years, the 

 delicate adult a few hours. 



ODONATA — brilliantly colovired dragonflies and demoiselle flies with 

 aquatic larvae, the former unusually active, swift-flying and 

 voracious, the latter more delicate. 



THYSANOPTERA — the minute thrips, vegetarian in habit, living on 

 flowers, leaves and decayed vegetation. 



HEMiPTERA — bugs with a specially developed proboscis (rostrum) 

 adapted for piercing and sucking, many of them beautiful and slender 

 despite their name : land bugs including the bed-bug, water bugs 

 varying from the giant flsh-killer or the water-scorpion to the water 

 boatman (Notonecta), the cicadas, the frog-hoppers, tree-hoppers, 

 leaf-hoppers, the aphids (or green-flies) and the scale-insects. 



(b) ENDOPTERYGOTA, winged insects which have a complete metamorphosis 

 (egg, larva, pupa, adult) with a resting pupa (or chrysalis). 



NEUROPTERA — lace-wings, alder-flies, scorpion-flies. 



TRiCHOPTERA — caddis-flies, with aquatic larvae and moth-like adults 

 with hair-covered bodies and wings. 



LEPIDOPTERA — butterflies and moths. 



COLEOPTERA — beetles, including over 200,000 known species, both 

 terrestrial and water-beetles. 



STREPSiPTERA — Stylops, miuvitc insects, parasitic on other insects, 

 particularly wasps and bees. 



HYMENOPTERA — gall-flies, saw-flies, ichneumon-flies, bees, wasps, ants. 



DIPTERA — two-winged flies, midges, gnats, mosquitoes and frviit-flies. 



APHANiPTERA — the secondarily wingless fleas (jiggers, etc.), blood- 

 sucking in habit and parasitic on birds and mammals. 



Ill the larval form all insects possess simple lateral eyes (stemmata; 

 ardixixy., a garland). The adult also frequently possesses simple eyes 

 (DOES.\f. ocelli), although they are absent or vestigial in many species, 

 as in rt.ost beetles and mosquitoes, some families of flies, and noctuid 

 moths nt in addition it is provided with multifaceted compound 

 EYES. his generalization there are some exceptions in degenerative 



