350 
NERVOUS SYSTEM OF RADIATA. 
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 
Glasses of Animals. 
434. In most of the Radiated 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 y 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 
other in function. Every one of 
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 
Fig. 180.— Nervous System of 
Star-fish. 
a , position of the mouth. 
