124 STRUCTURE OF RADIATA, 
mals ; and it is only in a few that even these imperfect eyes 
can be discovered. In the inferior Radiata, not the slightest — 
Fig. 65.—SHELL oF STAR FisuH. 
traces of a nervous system have yet been discovered ; and 
it is very doubtful whether any such structure exists in 
: them. It is only among the higher 
Radiata that any locomotive power 
exists ; and this is usually so feeble 
that the animals remain in the same 
locality during the greater portion 
of their lives. Generally speaking, 
there is a period in the history of 
each species, in which there is a 
more active movement, that serves 
to prevent the accumulation of indi- 
Fig. 66.—Nervovus System Viduals in one spot ; but this move- 
om Pram Bran. ment is of a purely automatic 
character, rather resembling that of the “ zoospores” of plants, 
than the intentional change of place of the higher animals. 
