350 NERVOUS SYSTEM OP BADIATA. 



ideas ; keeping in check the passions and emotions, or, on the 

 other hand, promoting their healthful activity by directing the 

 attention to the objects of them ; and determining the move- 

 ments which the reason prompts : and the acquirement and 

 right direction of such regulating power is the highest object 

 of all Education. 



433. It will be recollected that every form of Nervous 

 System essentially consists of two kinds of nervous tissue, 

 the tubular or fibrous, whose functions seem to be purely 

 conductive ( 60, 62), and the vesicular or ganglionic, which 

 seems to be the seat of all the changes to which this apparatus 

 ministers, and the source of all its peculiar powers ( 61, 63). 

 The principal forms under which this apparatus presents 

 itself in the several divisions of the Animal Kingdom, and 

 the general nature of the functions to which it is subservient 

 in each, will now be successively described in the ascending 

 series, from Zoophytes up to Man. 



Structure and Actions of the Nervous System in the principal 

 Classes of Animals. 



434. In most of the EADIATED classes, it is difficult to dis- 

 cover any distinct traces of a Nervous System ; the general 

 softness of their tissues being such, that it cannot be certainly 

 distinguished amongst them. It clearly exists, however, in 

 the highest group, the ECHINODERMATA ; and it presents an 



extremely simple form, which par- 

 takes of the general arrangement of 

 parts in these animals. In the 

 Star-fish, for instance, it forms a 

 ring which surrounds the opening 

 into the stomach (fig. 180) ; this 

 ring consists of a nervous cord that 

 forms communications between five 

 ganglia, one of which is placed at 

 the base of each ray. These ganglia 

 appear to be all similar to each 



Fig. ISO.- 



position of the mouth. them sends a large trunk along its 

 own ray ; and two small branches 

 to the organs in the central disk. The rays being all similar 

 to each other in structure, it would appear that no one of these 



