82 CLASSIFICATION OF ARTICULATA. 



characterised by the division of the body into two distinct por- 

 tions, the cephalo-thorax (made up of the head united to the 

 thorax) and abdomen ; by the possession of four pairs of legs ; 

 by their want of antennae ; and by their aerial respiration. 



III. CRUSTACEA, or Crabs, Lobsters, &c. ; distinguished by 

 their aquatic respiration; and by the possession of horn Jive to 

 seven pairs of legs; the body sometimes divided nearly as in 

 Insects, sometimes even more concentrated than in the Arach- 

 nida, and sometimes formed on the plan of that of the Myriapoda. 



IV. MYRIAPODA, the Centipede tribe ; characterised by the 

 want of distinction between thorax and abdomen ; by the equality 

 of the segments of the body, the head, however, being very 

 distinct ; by the large number of legs, of which there are seldom 

 less than twenty-four pairs ; and by their aerial respiration. 



Intermediate in some respects between the two divisions of 

 this Sub-kingdom, we may rank the following remarkable 

 group : 



V. CIRRHOPODA, or the Barnacle tribe ; in these, there are no 

 locomotive members in the adult, although the young possesses 

 them; there are, however, a series of jointed tendril-like append- 

 ages, which probably serve both for respiration and for the 

 acquirement of food ; and the animals remain attached to one 

 spot, during all but the early period of their lives ; their respira- 

 tion is entirely aquatic. 



601. In the Second division of Articulata, characterised 

 by the absence of articulated members, we meet with but 

 three classes. 



VI. ANNELIDA, the Leech and Worm tribe ; characterised by 

 the extension of the body into numerous segments, which pre- 

 sent scarcely any differences from each other ; by the presence 

 of a distinct circulating system, and of respiratory organs; 

 and by the possession of a well- developed nervous system. 



VII. ENTOZOA, or Intestinal Worms, in which the Articulated 

 form is presented in (as it were) a still more degraded state ; 

 the segments being yet more completely repetitions of one 

 another, and often capable of existing separately ; special organs 

 of circulation and respiration being for the most part wanting ; 



