3fi4 ZOOLOGY. 



wings ; three pairs of thoracic legs ; often a pair of jointed 

 abdominal appendages, besides the ovipositor or sting which 

 morphologically represents three pairs of legs. 



There are eight orders, forming two series : first, the 

 Heterometaiola, comprising the Tliysanura, Neuroptera, 

 Orthoptera, HemijJtera, and ColeopUra, in which the meta- 

 morphosis is either incomplete or complete ; the body 

 shows a tendency to become flattened ; the prothorax is 

 usually large and flattened ; the mouth-parts (excej)t in the 

 Hemiptera) adapted for biting. There are a number of 

 wingless forms. 



The second series of orders, or Metahola, comprising the 

 Diptera, Lepidoptera, and Hymmioptera, usually have a 

 cylindrical body, with the prothorax small, the mouth-parts 

 often adapted for sucking or lapping up liquid food ; with 

 a complete metamorphosis, the larva being worm-like, 

 cylindrical, very unlike the adult. 



Order 1. Tliysanura. — The spring-tails [Podura) and 

 bristle-tails {Lepisma) represent this group. They are 

 wingless, with some affinities to the Myriopods, and the 

 typical form Campodea (Fig. 334) is regarded as the ances- 

 tral form of the six-footed insects, as it is a 

 generalized type, and forms like it may have 

 been the earliest insects to appear. 



In Podura, the spring-tail, and also in 

 Smynthurtis {Sniyntlmrus quadrisignatus 

 Pack., Fig. 322), the characteristic organ is 

 a forked abdominal a^Dpendage or "spring," 

 held in place by a hook ; when released the 

 spring darts backward, sending the insect 

 high in the air. 



Our commonest Poduran is Tomocerus 

 plumieus Linn. (Fig. 323), found all over the northern 

 hemisphere in North America and Europe. The snow-flea, 

 Achorutes nivicola Pitch is blue-black, and is often seen 

 leaping about on the snow in forests. 



The Podurans belong to the suborder C'oUembola j the 

 higher forms, which bear a greater resemblance to the larvae 

 of Neuropterous insects and to the young cockroach, are 



