CHAPTER IV. 



Order Thysanura (Thys-a-nu'ra). 



Bristle-tails, Spring-tails, Fish-moths^ and others. 



The members of this order are wingless insects which 

 undergo no metamorphosis, the larval form being retained by 

 the adult. The mandibles and maxillcs are retracted within 

 the cavity of the head, so that 07tly their tips are visible ; they 

 have, however, some freedom of motion, and can be used for 

 biting and chezving soft substances. True compound eyes are 

 rarely present ; but in some genera there is a group of shnple 

 eyes on each side of the head. The abdomen is sometimes 

 furnished with rudimentary legs. 



Under stones and decayed leaves and wood, in the chinks 



of bark, among moss, in damp 

 places, on snow or on pools, 

 or sometimes in houses, are 

 the members of this order to 

 be found. They are for the 

 most part very small insects, 

 but sometimes they are nu- 

 merous and lively enough to 

 make up for their lack in 

 size. They have no wings, 

 but they can either run very 



"^'^•J^^Tii^'X-^'b^^ ^^^t ^^ i^^P ^^'y ^^'' Their 



?o"'mUSyeTx?:mi^^^^^^^ mouth-parts are usually fit- 



labial palpus. ^^ j f^j. biting, but are very 



difficult to study, because they are reti-acted within the 



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