CLASSIFICATION AND CREATION. 61 



again, form only an order in the class of Gas- 

 teropoda, as Brachiopods form an order in the 

 class of Acephala. 



In the third division of the Animal Kingdom, 

 the Articulates, we have again three classes: 

 Worms, Crustacea, and Insects. The lowest of 

 these three classes, the Worms, presents the 

 typical structure of that branch in the most 

 uniform manner, with little individualization of 

 parts. The body is a long cylinder divided 

 through its whole length by movable joints, 

 while the head is indicated only by a difference 

 in the front joints. There is here no concentra- 

 tion of vitality in special parts of the structure, 

 as in the higher animals, but the nervous force is 

 scattered through the whole body, every ring 

 having, on its lower side, either two nervous 

 swellings, one on the right, the other on the left 

 side, connected by nervous threads with those 

 that precede and those that follow them, or these 

 swellings are united in the median line. It is to 

 this equal distribution of nervous force through 

 the whole system that these animals owe their 

 extraordinary power of repairing any injured 

 part, so that, if cut in two, the front part may 

 even reconstruct a tail for itself, while the hind 

 part produces a new head, and both continue to 

 live as distinct animals. This facility of self- 

 repair, after a separation of the parts, which is 



