52 



INSECT LIFE. 



The Classes of the Branch Arthropoda. 



In the study of the parts of a locust (see Lesson 

 VI) it was learned that the body of an insect is com- 

 posed of a series of more or less similar rings or seg- 

 ments joined together. This fact is also true of the 

 bodies of certain other animals that are not insects ; 

 thus, if the body of a scorpion, a centipede, or a lob- 

 ster be examined, it will be found to resemble that of 

 an insect in this respect. There is another charac- 

 teristic in which these animals resemble insects — 

 namely, some of the segments of the body bear 

 jointed legs. 



All the animals possessing these two character- 

 istics are classed together as the branch Arthropoda 

 {Ar-throp' o-dd) of the animal kingdom, the term 

 branch being applied to each of the principal divi- 

 sions of the animal kingdom. 



A similar segmented form of the body is char- 

 acteristic of worms, but these are distinguished from 

 the Arthropoda by the absence of legs. It should be 

 remembered that many animals commonly called 

 worms, as the tomato-worm, apple-worm, etc., are 

 not true worms, but are the larvee of insects. The 

 angleworm is the most familiar example of a true 

 worm. 



The principal divisions of a branch of the animal 

 kingdom are called classes. The more common rep- 

 resentatives of the branch Arthropoda are distributed 

 among four classes. These are the Crustacea, the 

 Arachnida, the Myriapoda, and the Hexapoda. The 

 last of these comprises the insects, the first three the 

 near relatives of insects. 



