THE CLASS AND ORDERS OF INSECTS 179 



in the adult, and there is only slight difference in texture 

 between the fore- and hind wings. 



These insects develop from aquatic nymphs which live 

 submerged in streams and breathe by means of tufted thoracic 

 gills. In some stone-flies these gills persist in a reduced 

 condition in the winged adult. 



Order 7. Isoptera 



The Isoptera (including termites or " white ants ") have 

 jaws like those of the Orthoptera, but the fore- and hindwings 

 are very closely alike and the cerci very short. The vast 

 majority of these insects are wingless (" workers ' and 

 " soldiers "). The form of the individual insect within the 

 same species may vary to such a degree as to call for some 

 considerable change of form during growth. 



Order 8. Corrodentia 



The Corrodentia (booklice and allies) have elongate feelers, 

 biting mandibles, maxillae with the lacinia narrow and elongate 

 forming a characteristic " pick," wings (when present) delicate, 

 the forewings longer and broader than the hindwings, and the 

 abdomen without cerci. 



Young booklice resemble their parents in general form, but 

 during the growth of the winged insects, the prothorax becomes 

 relatively reduced. 



Order 9. Thysanoptera 



The Thysanoptera (Thrips) have short feelers, slender 

 piercing mandibles, and maxillae in which a piercing lacinia 

 is present on the left side only. Both maxillae and labium 

 bear palps. The insects feed by suction. Wings, when 

 present, are very narrow, relatively long, and fringed with 

 fine bristles. The abdomen is narrow and elongate and the 

 female has a well-developed ovipositor. Cerci are absent. 



Young Thrips resemble the adult in general form, but the 

 last nymphal stage, with prominent wing-rudiments, is 

 quiescent (so-called " pupa "). 



