468 THE INVERTEBRATA 



In another type, e.g. Locusta, a row of pegs on the hind limb is rubbed 

 against a thickened area of the fore wing. Where there are organs for 

 producing sound, there are also organs for perceiving it. These are 

 tympana^ chitinous ear drums, which can be set in vibration and then 

 affect special auditory sense organs. The auditory organs may be 

 found on the front tibiae or on the ist abdominal segment. The 

 posterior wings of the Saltatoria possess many parallel longitudinal 

 veins with a network developed between these by numerous cross 

 veins. They fold in a fan-like manner, a line of folding, the anal suture, 

 separating a prominent posterior "anal" area of the wing from the 

 main part of the wing in front. Besides the fully winged forms, like 

 locusts, there are found in the several families all stages of wing re- 

 duction to mere scales as in certain stick insects, or to their complete 

 absence as in Grylloblatta. 



Fig. 325. Forficula auricularia. Male. From Imms, after Chopard. 



Order DERMAPTERA 



Insects with biting mouth parts ; ligula two-lobed ; fore wings modi- 

 fied to form short leathery tegmina; cerci unjointed, always modified 

 into forceps; metamorphosis slight. 



The common earwig, Forficula auricularia (Fig. 325) is the best 

 example of this small but definite order. It comprises a number of 

 small, usually nocturnal insects, omnivorous in diet. The female 

 deposits the eggs in the soil, remains with them until they hatch, and 

 even protects them afterwards. The hind wings have a characteristic 

 venation and fold up along transverse as well as longitudinal furrows. 



