ARTICULATA. 



ARTICULATED, OB JOINTED ANIMALS. 



"Whatever creeps the ground, 

 Insect or worm ; those waved their limber fans 

 For wings, and smallest lineaments exact 

 In all the liveries deck'd of summer's pride, 

 With spots of gold and purple, azure and green ; 

 These, as a line, their long dimensions drew, 

 Streaking the ground with sinuous trace." MILTON. 



THE traveller who passes the line of demarcation which se- 

 parates two adjacent kingdoms, does not at once perceive any 

 ohvious change in their physical features or their natural pro- 

 ductions, nor see anything in the manners or customs of the 

 inhabitants to tell him that he has entered a new realm. 

 Such is the case with the naturalist who has heen an observer 

 of the radiate animals, and enters the dominions of the arti- 

 culated. The Leeches and Worms, among which he has come, 

 present very much the same aspect 

 as the vermiform or worm-shaped 

 Echinodermata, from which he has 

 parted. ' * Why, ' ' he asks, * < should 

 they he thus divided? " 



The question is best answered by 

 an examination of the internal struc- 

 ture. A difference in the nervous 

 system is at once apparent. It is 

 no longer arranged on the radiate 

 type, but presents the brain in the 

 form of a ring surrounding the throat 

 (Fig. 36) ; a double nervous thread 

 extends along the body at its lowest 



, . J ,. , , Fig. 36. XKRVOUS SYSTKM 



side, united at certain distances by OF CAUABUS. 



