CHAPTER III. 



SOME INTERESTING INSECTS, WITH NOTES ON THE CLASS. 



(Insecta.) 



NE of the great kingdoms in organic nature are the 

 Invertebrata, invertebrates being animals without a 

 vertebral column, and in this at least are distin- 

 guished from the Vertebrata, or vertebrated animals 



possessing a vertebral column or spine, it constituting in them 

 the median part of an osseous or cartilaginous skeleton. Ar- 

 rayed as one of the divisions of the Invertebrata, we find the 

 Arthropoda, joint-footed forms, including the Class Insecta (In- 

 sects), the largest one of all, as well as the Classes Arachnida, 

 Crustacea, and Myriopoda. 



As distinguished from a crustacean (crabs, lobsters, etc.), 

 from an arachnid (spiders, etc.), and from a myriopod (centipedes, 

 etc.), a true insect never has more than six legs; two antenna; 

 distinct head, thorax, and abdomen, with commonly two pairs of 

 wings, and certain peculiarities in the organs and function of 

 respiration. There are at least a million different species of in- 

 sects in the world, and they occur in every known part of it. Not 

 more than a quarter of a million of the earth's existing insect 

 fauna has as yet been described, however, and thousands of vol- 

 umes still remain to be written upon their biology. Fossil in- 

 sects occur as early as the Devonian, and from this they lead up 

 to the present era, becoming more and more like the groups now 

 in existence. Many species have been preserved in amber, which 

 is a fossil resin, as well as in gum copal; the former being usually 

 extinct types, while the latter agree as a rule with the species 

 still in existence. Some insects, such as certain ants and bees, 

 may have a duration of life extending over seven or eight years; 

 such species as the May-flies, on the other hand, have a duration 

 of life not exceeding twenty-four hours. The period of existence 

 in numerous species is greatly affected by the temperature; cold 

 increasing the duration and heat diminishing it. Many insects 

 are of vast economic importance to man; while in the economy 

 of nature, especially in the matter of the fertilization of plants, 

 they play no less an important role. 



M'Lachlan remarks that among "the varied relations of insects 



