THIRD GRAND DIVISION 



ANIMAL KINGDOM. 



THE ARTICULATED ANIMALS. 



This third general form is altogether as characteristic as 

 that of the vertebrated animals ; the skeleton is not interior, 

 as in the latter, but it is not reduced to a nullity, as in the mol- 

 lusca. The articulated rings which surround the body, and 

 frequently the limbs too, supply its place ; and as they are 

 almost always sufficiently hard, they can afford all the neces- 

 sary points of support for locomotion ; so that we find in this 

 division, as in the vertebrated, the different movements of 

 walking, running, leaping, swimming, and flying. It is only 

 the families destitute of feet, or whose feet have only soft and 

 membranaceous articulations, which are confined to the move- 

 ment of reptation. This external position of the hard parts, 

 and that of the muscles in their interior, reduce each articu- 

 lation to the form of a case, and allow it only two kinds of 

 motion. When it is attached to the neighbouring articulation 

 by a firm juncture, which happens in the limbs, it is fixed there 

 by two points, and can never move, only by gingiymus, that is 

 to say, on a single plane, which requires more numerous arti- 

 VOL. XIII. B 



