CHAPTER VI 



Subclass I. APTERYGOTA 

 Wingless Insects 



The members of this subclass are small wingless insects in which 

 the wingless condition is believed to be a primitive one, there being no 

 indication that they have descended from winged ancestors. The month- 

 parts vary. In some they are sucking, in others chewing. The meta- 

 morphosis is always slight and in some cases absent. 



This subclass contains but the three orders, Protura, Thysanura, 

 and Collembola. These insects are all primitive and usually general- 

 ized. They are all small and wingless and because of their usually 

 concealed habits are not as generally known as the winged forms. 

 They are widely distributed and about 1200 species are now known. 

 Probably many more remain to be discovered. A characteristic 

 feature of these primitive insects is the abdominal appendages, 

 especially the abdominal styli present in the Machilidae and in others 

 of the Thysanura. 



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