310 THE BIOLOGY OF INSECTS 



paired limbs, the hindmost often elongate and many-jointed 

 cercopods (Fig. 52, b). 



Order 2. PROTURA 



These are very minute insects without feelers, wings, or 

 cercopods. The jaws are modified for piercing and sucking, 

 and the three hinder segments of the abdomen are not 

 developed until after hatching. 



Orders. COLLEMBOLA 



The Springtails have feelers with only four (rarely six) 

 segments ; there are no compound eyes. The abdomen 

 has only six segments, the first of which carries a ventral 

 tube, the third a catch, and the fourth a spring — all these 

 three structures being modified from paired appendages 

 (Figs. 66, 70) 



Sub-class II. EXOPTERYGOTA 



These are winged (or secondarily wingless) insects in 

 which the wing-rudiments appear outwardly at an early 

 stage on the second and third thoracic segments and increase 

 in size after each moult. They are generally active through- 

 out growth, but in some groups the wing-rudiments develop 

 beneath the unshed cuticle of a previous instar and there 

 may be a resting stage before the final moult. 



Order 4. DERMAPTERA 



The Earwigs and their allies have the wings (when 

 present) modified so that the forewings become shortened 

 horny pads beneath which the delicate membranous hind- 

 wings can be folded when not in use. The mandibles are 

 of the normal biting type, and there are fairly prominent 

 superlinguae (Fig. 6). The tail-appendages are usually 

 modified into a forceps, but in one family are jointed 

 cercopods. The genital ducts have no chitinous lining. 



