INSECTS. 225 



CHAPTER XXII. 



INSECTS. 



379. THE sub-kingdom which we have already consid 

 ered is the Vertebrate. The other three sub-kingdoms 

 are said to be Invertebrate, the prefix in being here used 

 as meaning the same as the very common negative prefix 

 un. Of these sub-kingdoms I will notice the Articulata 

 first. The two chief characteristics of it were stated in 

 Chapter I. These, however, and other characteristics, 

 require a more particular notice here, before I enter on 

 the consideration of Insects, the special subject of this 

 chapter. 



380. The kingdom of the Articulates includes a wide 

 range of animals of great variety Insects, Worms, the 

 Spider and Scorpion tribe, and the Crab tribe. But they 

 all agree in one thing in having a covering which an- 

 swers the purpose of the internal skeleton of the Verte- 

 brates. This covering, or jointed armor, gives firmness 

 to the body, and furnishes points of attachment to the 

 muscles. 



381. This skeleton coat of mail is very commonly ar- 

 ranged on the bodies of these animals in segments in the 

 form of rings. This arrangement is seen most perfectly 

 carried out in the Centipede, Fig. 178 (p. 226). You can 

 also see it plainly in the bodies of most insects, as, for ex- 

 ample, in the common Fly. This arrangement mostly 

 disappears in the Crab tribe, where, for the sake of firm- 

 ness, the skeleton covering the body of the animal is in 

 one piece. So, also, on the other hand, it nearly disap- 

 pears in such soft Articulates as the Leech and Earth- 

 worm, because there the rings would not allow the requi- 

 site limberness. 



