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 metamor pilosis, the larval form being retained by 

 the adult. The mandibles and maxilla are retracted within 

 the cavity of the head, so that only tJieir tips are visible ; they 

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

 biting and chewing soft substances. Trtie compound eyes are 

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

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

 furnished with rudimentary legs. 



Under stones and decayed leaves and wood, in the chinks 



of bark, amongmoss, 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 

 fast or jump very far. Their 

 mouth-parts are usually fit- 

 ted for biting, but are very 

 difficult to study, because they are retracted within the 



Fig. 8g. — Mouth-parts of a Spring-tail, Ento- 

 mobryidcB. (Drawn by J. M. Stedman, 

 under the author's direction.) 8, labrum; 

 10, mandible; u, maxilla; 12, labium; 12^, 

 labial palpus. 



