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Third Great Division of the Animal Kingdom. 



ANIMAL IÀ ARTICULATA. 



This division is well characterized by an external articu- 

 lated skeleton in the form of a sheath, adapted, according to 

 the different genera, for walking, running, swimming, or for 

 flight. This skeleton is either composed of hard articulated 

 rings or is membranous or soft. The mode of connection of 

 the articulations of the limbs is by two points, allowing only 

 a hinge-like motion ; but in the body the connection is by 

 flexible membranes or by parts fitting into each other. 



The Articulata resemble each other most in their nervous 

 system. The brain is situated upon the oesophagus, and 

 supplies the parts near the head with nerves. A double row 

 of ganglia extend along the abdomen, and are united together 

 and with the brain by nervous cords. Each of these supply 

 the place of additional brains, and send nerves to the neigh- 

 bouring parts. 



The kind of respiration, the organs of circulation, and even 

 the colour of the blood, exhibit so much difference, as to re- 

 quire separate notice in each class. 



The classes are four. The Annulata or red blooded 

 worms ; the Crustacea ; the Arachnides, and the Insecta. 



