CHAPTER XXI 

 PHYLUM ARTHROPOD A (CONT'D) 



CLASS INSECTA 



(By Vasco M. Tanner, Brigham Young University) 



Insects are the most abundant creatures on the earth today. There 

 is said to be over 650,000 living species, many of which have never 

 been seen by the great majority of mankind. This, no doubt, is 

 because insects exist in every type of habitat known. They are 

 found in sea water along the shore; in fresh water that ranges in 

 temperature from 50° C. to ice cold; in the soil; in dry desert con- 

 ditions; on the vegetation of plain and swamp; from the tundra 

 of the north to the tropical pampas; in trees; on and in animals, 

 as well as man, many of which are carriers of disease. They ravage 

 our crops and damage our stored foods. In short, we may say that 

 insects are omnipresent. One noted entomologist has said that this 

 is an age of insects, and to this we may add that every man's farm 

 is "no man's land" and that the contending forces are insects and 

 man. 



This great class Insecta has been upon the earth from the Penn- 

 slyvanian times, of the late Paleozoic era, to the present. This means 

 that for probably one hundred million years these arthropods have 

 been adjusting to a changing environmental complex, and the suc- 

 cess with which they have met the challenge is quite evident today. 

 Various explanations have been advanced to account for the great 

 adaptability^ of insects in filling practically every niche in nature. 

 The Russian biologist, S. S. Chetverikov, argues that the chitinous 

 exoskeleton has been of great value in the evolution of this group, 

 in that it has permitted them to develop strong appendages, un- 

 limited external features, and a small size which has opened up an 

 entirely new place in the world of living animals. Dr. C. H. Ken- 

 nedy, however, has pointed out that there are advantages as well 

 as disadvantages to the possession of an exoskeleton. He says: 



300 



