INSECTS. PHYLUM ARTHROPODA 



body and hair by disinfectants, and from clothes by very moderate 

 temperatures (53.5° C. for five minutes kills both insects and eggs). 

 Persons who wash, and change their clothes with some frequency, 

 are never likely to become more than temporarily and lightly 



infected. , ^-^ . n • . 



Order 16. Thysanoptera. These are the thrips, small msects 



with sucking mouth-parts, mostly feeding on plants, of some 

 economic importance. 



SUB-CLASS II— ENDOPTERYGOTA 



The wings develop in sacs which are pushed inward from the 

 surface of the body. There is a true larva, and at metamorphosis, 

 which is restricted in time, the wings are everted. Some orders 

 have biting mouth-parts, but the majority have specialised 

 mouth-parts of various kinds. 



Order 17. Neuroptera. This is the rump of a much larger 

 Linnaan order, and as now defined it includes insects with biting 

 mouth-parts and a characteristic ladder-Uke venation on the 

 fore edge of the wings. The alderfly, Sialis lutaria, has an aquatic 

 larva with long tracheal gills, and biting mouth-parts, and the 

 lacewings, Chrysopa, have terrestrial larvae with pecuhar sucking 

 mouth-parts. All neuropteran larvae are carnivorous and cam- 

 podeiform (p. 247). 



Order 18. Mecoptera. This is a small order with biting mouth- 

 parts, eruciform larvae (p. 247) and external male genitaUa which 

 superficially resemble the tail of a scorpion. An example is Panorpa 

 communis, the scorpion fly. 



Order 19. Trichoptera. The caddis flies are well known for 

 their aquatic caterpillars which build themselves cases of sticks 

 or stones from which only the head and thorax protrude. The 

 mouth-parts of the larvae are biting, but in the adults the 

 mandibles are vestigial, and if they eat anything it can only 

 be liquid. The bodies are covered with hair-like processes. The 

 larvee have tracheal gills. 



Order 20. Lepidoptera. The butterflies and moths have larvae 

 which are caterpillars and have biting mouth-parts, and adults 

 with characteristic sucking mouth-parts which have been 

 described on p. 244. The body and wings are covered with scales. 

 The pupa is often enclosed in a cocoon spun of silk secreted by the 

 larva through spinnerets on the head. A diagram of a typical 



