67 



ARTICULATA. 



ARTICULATED, or 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, 

 Witli spots of gold and purple, azure and green; 

 These, as a line, their long dimensions drew, 

 Streaking the ground with sinuous trace." — Miltom. 



The traveller who passes the line of demarcation which se- 

 parates two adjacent kingdoms, does not at once perceive any 

 obvious 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 been an observer 

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

 culated. The Leeches and Worms, among which^ie has come, 

 present very much the same aspect 

 as the vennifonn or worm-shaped 

 Echinodermata, from which he has 

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

 they be thus divided?" 



The question is best answered by 

 an examination of the internal struc- 

 ture. A ditfcrence in the nervous 



system is at once apparent. It is vf .flHlHL ^'^ 

 no longer arranged on the radiate 

 cype, but presents the brain in the 

 formof a ring surrounding the throat 

 {Fig. .36); a double nervous tliread 

 extends along the body at its lowest 

 Bide, united at certain distances by ^■"^- '"j; ciru'tV"''"^'' 



