CLASSIFICATION 249 



CLASS I—APTERYGOTA 



These are primitively wingless and the abdomen bears appen- 

 dages of various sorts in addition to the external genitalia and 

 cerci. There are four orders : (i) the Diplura, (2) the Thysanura 

 or bristle tails, (3) the Collembola or springtails, and (4) the 

 Protura. The first, second, and third have biting mouth-parts, the 

 fourth piercing. The commonest example is the silverfish, Lepisma 

 saccharina, a thysanuran, which is a frequent inhabitant of 

 cupboards, bookcases and cracks in the floorboards of houses, 

 and the largest is the shore-living Petrobius 

 maritimus (Fig. 180), also a thysanuran. \ 



CLASS II—PTERYGOTA 



These are insects which possess wings, or, 

 if they do not, closely resemble in other 

 respects species which do. 



sub-class I — exopterygota 

 The winefs develop outside the body. There ^^^- ^^o.—Petrobtus 



c> ir J maritimus X i. — 



are several orders mostly with biting mouth- From Bandars, An 

 parts. There is no larva in the strict sense ex- ^pocket^''''^ ^""^ ^^' 

 cept in those orders which have aquatic naiads. 



Order 5. Orthoptera. This includes the cockroaches, crickets, 

 grasshoppers and stick insects, and its main features, such as 

 biting mouth-parts and hardened forewing, have been seen in 

 the previous chapter. Many of the jumping forms are notable 

 not only for their long legs but also for the way in which they 

 chirp or sing by rubbing wings or legs against some part of the 

 body, and for the presence of ears by which the noise made 

 by another individual is heard. The song is largely sexual in 

 character. 



Order 6. Dermaptera. These are the earwigs, which closely 

 resemble the Orthoptera but are always recognisable by the 

 gripping forceps, which is a modified pair of anal cerci, at the 

 posterior end of the body. The mouth-parts are biting. The 

 common earwig is Forficula auricular ia. 



Order 7. Isoptera. The termites or white ants of the tropics 

 are remarkable for their social organisation, which closely 

 M.z. — 9 



