178 INSECT TRANSFORMATION 



insects). Most Exopterygota are active and take food in all 

 stages of the life-history. 



Eleven living orders of insects are included in this 

 sub-class. 



Order 4. Dermaptera 



The Dermaptera have biting mandibles, fairly prominent 

 maxillulae, typical maxillae and a labium of which the parts 

 of the component appendages are distinctly recognizable. 

 The forewings are modified into short, firm covers beneath 

 which the delicate membranous hindwings can be folded when 

 at rest. Many Demaptera are wingless. The tenth abdo- 

 minal segment carries a pair of limbs which are usually strong 

 and un jointed forming a forceps (Forficulidae or earwigs). 

 In the wingless, parasitic Hemimeridae these limbs are jointed 

 cerci. The genital ducts (either paired, or single through the 

 suppression of one) are entirely mesodermal in origin. 



Young members of this order resemble their parents very 

 closely, but in some earwigs, the tail-appendages of the newly- 

 hatched insect are jointed, becoming transformed into forceps 

 after the first moult. 



Order 5. Orthoptera 



The Orthoptera (cockroaches, stick and leaf insects, 

 grasshoppers, crickets, etc.) have biting mandibles and 

 reduced maxillulae ; maxillae and labium are as in the Dermap- 

 tera. The forewings are elongate, relatively narrow and firm 

 in texture, the more delicate and ampler hindwings being 

 folded beneath them when at rest. The abdomen has jointed 

 cerci on the tenth segment. The outer genital ducts, as in 

 the vast majority of insects, are unpaired and ectodermal in 

 origin, lined with chitin. The female's ovipositor is well and 

 typically developed. 



Young Orthoptera resemble their parents very closely except 

 for the absence of wings. 



Order 6. Plecoptera 



The Plecoptera (stone-flies) have the same general characters 

 as the Orthoptera, but the mandibles are often much reduced 



