290 



THIRD GREAT DIVISION OF THE ANIMAL 

 KINGDOM. 



ANIMALIA ARTICULATA. 



This third general form is as well characterised as that of the 

 Vertebrata; the skeleton is not internal as in the latter, neither is it 

 annihilated as in the Mollusca, the articulated rings which encir- 

 cle the body, and frequently the limbs, supply the place of it, and 

 as they are usually hard, they furnish to the powers of motion all 

 requisite points of support, so that here, as among the Vertebrata, 

 we find the walk, the run, the leap, natation and flight. Those fa- 

 milies only are restricted to reptation which are either deprived of 

 feet, or in which the articulations are membranous and soft. This 

 external position of the hard parts, and the internal one of the mus- 

 cles, reduce each articulation to the form of a sheath, and allow it 

 but two kinds of motion. When connected with the neighbouring 

 parts by a firm joint, as happens in the limbs, it is fixed there by two 

 points, and can only move by gynglymus, that is, in one single 

 plane, a disposition which requires a greater number of joints to 

 produce a same variety of motion. A greater loss of muscular 

 power is also the result, and consequently more general weakness 

 in each animal, in proportion to its size. 



But the parts which compose the body are not always articulated 

 in this way; most generally they are only united by flexible mem- 

 branes, or they fit into each other, and then their motions are more 

 various, but have not the same force. 



