ENTOMOLOGY. 237 



Tribes of Insects. 



1. Coleoptera insects with sheathed wings, con- 

 sisting of beetles, &c. ; 4087 species. 



2. Strepsiptera of the genera xenos and sty lops. 



3. Dermaptera earwigs. 



4. Orthoptera cockroaches, locusts, grasshop- 

 pers, crickets, mantes, &c. 



5. Hemiptera half- winged insects, such as bugs, 

 water-scorpions, water-boatmen, leaf-lice, cochineal 

 insects, &c. ; 1427 species. 



6. Trichoptera consisting of flies produced by 

 various species of case-worms, phryganea, &c. 



7. Lepidoptera scaled wings, such as butterflies, 

 hawkmoths, and moths ; 2570 species. 



8. Neuroptera nerved wings, such as dragon- 

 flies, ant-lions, ephemerae, &c. ; 174 species. 



9. Hymenoptera membraneous wings, consisting 

 of bees, wasps, and other insects, armed with a sting, 

 or ovipositor, and its valves ; 1265 species. 



10. Diptera two-winged insects, such as flies, 

 gnats, &c. ; 692 species. 



11. Aphaniptera wings not apparent, as the flea 

 genus. 



12. Aptera without wings, such as mites, lice, 

 &c. ; 679 species. 



Thirty years ago, the recorded number of insects 

 amounted to about eleven thousand, but a great ad- 

 ditional number has since been discovered and .de- 

 scribed ; Humboldt says 44,000. 



Changes of Form. 



In general, insects undergo a material change in 

 their form at stated periods of their lives. There 

 are some, though few, such as the spider, &c. that 

 burst forth from the egg completely formed, but the 

 greater number exist in four different states, viz. 



The first is that of the egg, whence the larva or 



