26 ANIMAL KINGDOM CLASSIFICATION". 



ANIMAL KINGDOM. 



CLASSIFICATION. 



SUB-KINGDOMS. In classifying animals they are first divided 

 into four large groups, called sub-kingdoms. These are : 



I. Sub-kingdom Yertebrata. 



II. Sub-kingdom Articulata. 



III. Sub-kingdom Mollusca. 



IV. Sub-kingdom Radiata. 



The first of these four great divisions is so named because all 

 the animals which compose it, without exception, possess an 

 internal skeleton ; that is, a bony framework covered with flesh, 

 like that of man, and consequently a vertebral column, i.e., a 

 column composed of vertebra). This is the origin of the name 

 of vertebrata, which is applied to this sub-kingdom. It com- 

 prises four classes : mammals, birds, reptiles, and fishes. The 

 sub-kingdom Articulata is composed of animals whose body is 

 formed of segments, or separate rings, arranged in a regular 

 series. Moreover, they have no internal skeleton, and, on the 

 contrary, the external parts are generally the hardest and 

 toughest, as in the crayfish and the centipede. Sometimes these 

 animals are only protected by a hard skin, like that of the earth- 

 worm, or the leech. The principal classes of this sub-kingdom 

 are insects, Crustacea, and worms. 



