SECOND SUB-KINGDOM. 



ARTICULATES. (Lat. articulus, a joint.) 



SECTION I. 



IN leaving^ the Vertebrated Animals, we, in the descending 

 scale, first come to the class of ARTICULATES, (articulata.) These 

 rank first among the INVERTEBRATED Group, or those animals 

 that are destitute of a back bone. They are so named because 

 the different parts of their body are composed of movable 

 pieces articulated or jointed to each other. They deviate from 

 the Molluscous animals in generally possessing a skeleton ; but 

 the skeleton, unlike that of the Vertebrates, is exterior instead of 

 interior, being composed of a series of rings, protecting the in- 

 ternal parts, and serving as points of attachment for muscles. 

 Though exhibiting considerable diversity of character among 

 themselves, the Articulates are usually provided with a skin, 

 which is either soft, as in the leech and earth-worm, or horny 

 and crustaceous, as in the crab and craw-fish. Some families 

 are destitute of feet, but the greater portion possess these mem- 

 bers. When limbs are present, they are never fewer than six. 

 Articulated animals have the trunk of the body, for the most 

 part, long, cylindrical, and divided transversely into segments. 

 In the lowest of the series, where there are no appendages for 

 locomotion, and all the movements are effected by the body 

 itself, as in the common worm, the segments appear to be per- 

 fectly simple, but, as ascending in the scale, we observe that 

 gradually, the segments develop lateral organs, which are of 

 kinds quite various, according to the character of the animal. 



In many of the Annelidans, and in the Myriopoda or Centipede 

 tribe, especially, the articulated character of these animals is 

 conspicuous, the segments being numerous, and all of nearly 

 equal size, and each possessing a short pair of legs, which are 

 themselves also jointed. In the Crustaceans and the Arachnida 

 or Spiders, the divisions are reduced to eight or ten in number; 

 and in the Insects, to six. Where the design is to lighten the 



