28 THE INSECT WOELD. 



If, in addition to these characteristics, one considers that these 

 animals are not provided with interior skeletons that their 

 nervous system is formed of a double cord, swelling at intervals, 

 and placed along the underside of the body, with the exception of 

 the first swellings or ganglions which are under the head that they 

 are not provided with a complete circulating system that they 

 breathe by particular organs termed tracheae, extending parallel 

 to each other along each side of the body, and communicating 

 with the exterior air by lateral openings termed spiracles that 

 their sexes are distinct that they are reproduced from eggs and, 

 in conclusion, that the different parts we have mentioned are not 

 complete until the creature has passed through many successive 

 changes, called metamorphoses, a general idea may be formed of 

 what is meant in zoology by the word " insect." 



Insects, whose general organisation we have briefly traced, have 

 been classed by naturalists as follows : 



1. APTEKA (Fleas and Lice). 



2. DIPTERA (Gnats, Flies, etc.). 



3. HEMIPTERA (Bugs, etc.). 



4. LEPIDOPTERA (Butterflies and Moths). 



5. ORTHOPTERA (Grasshoppers, Crickets, etc.). 



6. HYMENOPTERA (Bees, Wasps, etc.). 



7. NEUROPTERA (Libellula, or Dragon-fly ; Ephemera, or May-fly ; 



Phryganea, or Alder- fly). 



8. *STREPSIPTERA, an anomalous order, the species composing which are 



parasitical on various Hymenoptera. 



9. COLEOPTERA (Cockchafers and Beetles). 



We shall commence the history of the various orders, by 

 examining the Aptera. 



* By some unaccountable oversight, this Order is omitted in the French Edition 

 Paris, 1867. ED. 



