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 
