CLASSIFICATION 309 



moths, wasps and bees, in which the immature insect is a 

 larva, differing markedly in aspect from its parent, with the 

 wing- rudiments developing hidden in inpushed pouches, to 

 become visible only at the resting or pupal stage of the life- 

 history. These facts may be expressed in our classification 

 by dividing the v/inged insects (Pterygota) into two sub- 

 classes : (i) the Exopterygota whose members practise the 

 open type, and (2) the Endopterygota whose members show 

 the hidden type of wing-growth. This important systematic 

 distinction is due to D. Sharp (1898). Each of these sub- 

 classes comprises a number of orders, the distinction 

 between which depend upon the nature of the jaws, whether 

 for biting or sucking, upon the form, texture, and nervura- 

 tion of the wings, upon the presence or absence of tail- 

 processes (cerci), and upon details of the life-history such 

 as the typical form of the larva and pupa. For detailed 

 discussion of these subjects systematic treatises on ento- 

 mology should be consulted. Here it will suffice to give 

 such brief definitions of the orders as may serve for necessary 

 purposes of reference from the other chapters of this book. 



Class INSECTA (or Hexapoda) (see definition. Chap. I, 

 pp. 13-14) 



Sub-class I. APTERYGOTA 



These are wingless insects in which the wingless condition 

 seems to be primitive. When the jaws are typically de- 

 veloped the mandibles are of the crustacean type, and there 

 are paired superlinguae or paragnaths in front of the tongue 

 The abdomen carries a varying number of paired limbs. 



Order i. THYSANURA 



These are wingless insects known as Bristle-tails, with 

 elongate, many-jointed feelers, usually compound eyes, and 

 abdomen of ten segments, many of which usually carry 



