THIRD 
GREAT DIVISIO^J 
OF THE 
ANIMAL KINGDOM. 
ANIMALIA ARTICULATA. 
This third general form is as well characterised as that of the Verte- 
brata ; the skeleton is not internal as in the latter, neither is it anni 
hilated as in the Mollusca. The articulated rings which encircle 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, AVe find the walk, the 
run, the leap, natation and flight. Those families only are restricted 
to reptation Avhich are either deprived of feet, or in which the articu- 
lations are membranous and soft. This external position of the hard 
parts, and the internal one of the muscles, 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 gyn- 
glymus, 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 membranes, 
or they fit into each other, and then their motions are more various, 
but have not the same force. 
The system of organs in which the Articulata resemble each other 
the most, is that of the nerves. 
Their brain, which is placed on the esophagus, and furnishes nerves 
to the parts adhering to the head, is very small. Two cords which 
embrace the esophagus are extended along the abdomen, and united 
