CHAPTER XIII. 



OF THE VERMIFORM CLASSES. 



902. We are now arrived at the lower division of the Arti- 

 culated Sub-kingdom, in which there is an absence of articulated 

 members, and a general inferiority in the structure of the animals 

 composing it ; so that, as we descend, we lose one after another 

 of those characters, by which this group is distinguished. 

 Nevertheless, the lateral symmetry ( 47) of the body is almost 

 uniformly preserved ; and it is only in the very lowest that we 

 meet with any approach to the circular arrangement of the parts 

 of the body, which is characteristic of the Radiata. The Ner- 

 vous System cannot be traced in the simplest animals of this 

 division ; but wherever it can be detected, it presents the same 

 essential characters as in the higher classes, consisting of a 

 double cord running along the ventral surface from one extremity 

 of the body to the other, and studded with ganglia at intervals. 

 These ganglia are smaller, in proportion as they are more nume- 

 rous ; and their size diminishes, too, with the diminution of the 

 locomotive powers of the animal. The cephalic ganglia, or those 

 which are placed at the anterior extremity of the body, above the 

 oesophagus, are usually larger than the rest ; especially when 

 they are connected with organs of special sense, such as eyes and 

 antennas. But as we descend through this series, we find the 

 eyes disappearing, and then the antennae ; so that the head is 

 only marked by its being the situation of the mouth ; and the 

 cephalic ganglia are then scarcely to be distinguished from the 

 rest. 



903. "!The body of these animals is generally long, slender, 

 and more or less cylindrical ; it is frequently divided into dis- 

 tinct segments ; but these are only marked externally by a 

 folding or wrinkling of the integuments ; and there does not 



