CLASSIFICATION OP ANIMALS. 



the variety to which it belongs, then the species of which this is 

 a variety, then the genus of the species, then the order of the 

 genus, then the class of the order, and, in fine, the great primary 

 division to which this class belongs. 



244. The four primary divisions above mentioned are resolved 

 into classes, as follows: The Vertebrata into four, the Annulate 

 into six, the Mollusca into five, and the Radiate into Jive, making 

 altogether twenty classes, as shown in the following table. 



CLASSIFATION OF ANIMALS. 



245. The Vertebrate division is characterised by an internal 

 skeleton and a cerebro- spinal nervous system. It takes its name 

 from the vertebral or spinal column, to which all the subordinate 

 parts of the skeleton are attached. 



The Annulata have no internal skeleton, but in its stead a tegu- 

 mentary covering, composed of movable rings, which gives them 

 their characteristic form. Their nervous system consists of two long 

 cords running longitudinally through the abdomen, twisted at inter- 

 vals into knots called ganglions. The tegumentary covering, which 

 is always annular, is sometimes hard and calcareous, as in the lobster 

 and shrimp, and sometimes soft, as in the earth-worm and leech. 



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